tcp_input.c revision 974c12360dfe6ab01201fe9e708e7755c413f8b6
1/* 2 * INET An implementation of the TCP/IP protocol suite for the LINUX 3 * operating system. INET is implemented using the BSD Socket 4 * interface as the means of communication with the user level. 5 * 6 * Implementation of the Transmission Control Protocol(TCP). 7 * 8 * Authors: Ross Biro 9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 10 * Mark Evans, <evansmp@uhura.aston.ac.uk> 11 * Corey Minyard <wf-rch!minyard@relay.EU.net> 12 * Florian La Roche, <flla@stud.uni-sb.de> 13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 14 * Linus Torvalds, <torvalds@cs.helsinki.fi> 15 * Alan Cox, <gw4pts@gw4pts.ampr.org> 16 * Matthew Dillon, <dillon@apollo.west.oic.com> 17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 18 * Jorge Cwik, <jorge@laser.satlink.net> 19 */ 20 21/* 22 * Changes: 23 * Pedro Roque : Fast Retransmit/Recovery. 24 * Two receive queues. 25 * Retransmit queue handled by TCP. 26 * Better retransmit timer handling. 27 * New congestion avoidance. 28 * Header prediction. 29 * Variable renaming. 30 * 31 * Eric : Fast Retransmit. 32 * Randy Scott : MSS option defines. 33 * Eric Schenk : Fixes to slow start algorithm. 34 * Eric Schenk : Yet another double ACK bug. 35 * Eric Schenk : Delayed ACK bug fixes. 36 * Eric Schenk : Floyd style fast retrans war avoidance. 37 * David S. Miller : Don't allow zero congestion window. 38 * Eric Schenk : Fix retransmitter so that it sends 39 * next packet on ack of previous packet. 40 * Andi Kleen : Moved open_request checking here 41 * and process RSTs for open_requests. 42 * Andi Kleen : Better prune_queue, and other fixes. 43 * Andrey Savochkin: Fix RTT measurements in the presence of 44 * timestamps. 45 * Andrey Savochkin: Check sequence numbers correctly when 46 * removing SACKs due to in sequence incoming 47 * data segments. 48 * Andi Kleen: Make sure we never ack data there is not 49 * enough room for. Also make this condition 50 * a fatal error if it might still happen. 51 * Andi Kleen: Add tcp_measure_rcv_mss to make 52 * connections with MSS<min(MTU,ann. MSS) 53 * work without delayed acks. 54 * Andi Kleen: Process packets with PSH set in the 55 * fast path. 56 * J Hadi Salim: ECN support 57 * Andrei Gurtov, 58 * Pasi Sarolahti, 59 * Panu Kuhlberg: Experimental audit of TCP (re)transmission 60 * engine. Lots of bugs are found. 61 * Pasi Sarolahti: F-RTO for dealing with spurious RTOs 62 */ 63 64#include <linux/mm.h> 65#include <linux/slab.h> 66#include <linux/module.h> 67#include <linux/sysctl.h> 68#include <linux/kernel.h> 69#include <net/dst.h> 70#include <net/tcp.h> 71#include <net/inet_common.h> 72#include <linux/ipsec.h> 73#include <asm/unaligned.h> 74#include <net/netdma.h> 75 76int sysctl_tcp_timestamps __read_mostly = 1; 77int sysctl_tcp_window_scaling __read_mostly = 1; 78int sysctl_tcp_sack __read_mostly = 1; 79int sysctl_tcp_fack __read_mostly = 1; 80int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH; 81EXPORT_SYMBOL(sysctl_tcp_reordering); 82int sysctl_tcp_ecn __read_mostly = 2; 83EXPORT_SYMBOL(sysctl_tcp_ecn); 84int sysctl_tcp_dsack __read_mostly = 1; 85int sysctl_tcp_app_win __read_mostly = 31; 86int sysctl_tcp_adv_win_scale __read_mostly = 2; 87EXPORT_SYMBOL(sysctl_tcp_adv_win_scale); 88 89int sysctl_tcp_stdurg __read_mostly; 90int sysctl_tcp_rfc1337 __read_mostly; 91int sysctl_tcp_max_orphans __read_mostly = NR_FILE; 92int sysctl_tcp_frto __read_mostly = 2; 93int sysctl_tcp_frto_response __read_mostly; 94int sysctl_tcp_nometrics_save __read_mostly; 95 96int sysctl_tcp_thin_dupack __read_mostly; 97 98int sysctl_tcp_moderate_rcvbuf __read_mostly = 1; 99int sysctl_tcp_abc __read_mostly; 100 101#define FLAG_DATA 0x01 /* Incoming frame contained data. */ 102#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */ 103#define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */ 104#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */ 105#define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */ 106#define FLAG_DATA_SACKED 0x20 /* New SACK. */ 107#define FLAG_ECE 0x40 /* ECE in this ACK */ 108#define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/ 109#define FLAG_ONLY_ORIG_SACKED 0x200 /* SACKs only non-rexmit sent before RTO */ 110#define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */ 111#define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */ 112#define FLAG_NONHEAD_RETRANS_ACKED 0x1000 /* Non-head rexmitted data was ACKed */ 113#define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */ 114 115#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED) 116#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED) 117#define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE) 118#define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED) 119#define FLAG_ANY_PROGRESS (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED) 120 121#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH) 122#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH)) 123 124/* Adapt the MSS value used to make delayed ack decision to the 125 * real world. 126 */ 127static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb) 128{ 129 struct inet_connection_sock *icsk = inet_csk(sk); 130 const unsigned int lss = icsk->icsk_ack.last_seg_size; 131 unsigned int len; 132 133 icsk->icsk_ack.last_seg_size = 0; 134 135 /* skb->len may jitter because of SACKs, even if peer 136 * sends good full-sized frames. 137 */ 138 len = skb_shinfo(skb)->gso_size ? : skb->len; 139 if (len >= icsk->icsk_ack.rcv_mss) { 140 icsk->icsk_ack.rcv_mss = len; 141 } else { 142 /* Otherwise, we make more careful check taking into account, 143 * that SACKs block is variable. 144 * 145 * "len" is invariant segment length, including TCP header. 146 */ 147 len += skb->data - skb_transport_header(skb); 148 if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) || 149 /* If PSH is not set, packet should be 150 * full sized, provided peer TCP is not badly broken. 151 * This observation (if it is correct 8)) allows 152 * to handle super-low mtu links fairly. 153 */ 154 (len >= TCP_MIN_MSS + sizeof(struct tcphdr) && 155 !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) { 156 /* Subtract also invariant (if peer is RFC compliant), 157 * tcp header plus fixed timestamp option length. 158 * Resulting "len" is MSS free of SACK jitter. 159 */ 160 len -= tcp_sk(sk)->tcp_header_len; 161 icsk->icsk_ack.last_seg_size = len; 162 if (len == lss) { 163 icsk->icsk_ack.rcv_mss = len; 164 return; 165 } 166 } 167 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED) 168 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2; 169 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED; 170 } 171} 172 173static void tcp_incr_quickack(struct sock *sk) 174{ 175 struct inet_connection_sock *icsk = inet_csk(sk); 176 unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss); 177 178 if (quickacks == 0) 179 quickacks = 2; 180 if (quickacks > icsk->icsk_ack.quick) 181 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS); 182} 183 184static void tcp_enter_quickack_mode(struct sock *sk) 185{ 186 struct inet_connection_sock *icsk = inet_csk(sk); 187 tcp_incr_quickack(sk); 188 icsk->icsk_ack.pingpong = 0; 189 icsk->icsk_ack.ato = TCP_ATO_MIN; 190} 191 192/* Send ACKs quickly, if "quick" count is not exhausted 193 * and the session is not interactive. 194 */ 195 196static inline int tcp_in_quickack_mode(const struct sock *sk) 197{ 198 const struct inet_connection_sock *icsk = inet_csk(sk); 199 return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong; 200} 201 202static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp) 203{ 204 if (tp->ecn_flags & TCP_ECN_OK) 205 tp->ecn_flags |= TCP_ECN_QUEUE_CWR; 206} 207 208static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb) 209{ 210 if (tcp_hdr(skb)->cwr) 211 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR; 212} 213 214static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp) 215{ 216 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR; 217} 218 219static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *skb) 220{ 221 if (!(tp->ecn_flags & TCP_ECN_OK)) 222 return; 223 224 switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) { 225 case INET_ECN_NOT_ECT: 226 /* Funny extension: if ECT is not set on a segment, 227 * and we already seen ECT on a previous segment, 228 * it is probably a retransmit. 229 */ 230 if (tp->ecn_flags & TCP_ECN_SEEN) 231 tcp_enter_quickack_mode((struct sock *)tp); 232 break; 233 case INET_ECN_CE: 234 tp->ecn_flags |= TCP_ECN_DEMAND_CWR; 235 /* fallinto */ 236 default: 237 tp->ecn_flags |= TCP_ECN_SEEN; 238 } 239} 240 241static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th) 242{ 243 if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr)) 244 tp->ecn_flags &= ~TCP_ECN_OK; 245} 246 247static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th) 248{ 249 if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr)) 250 tp->ecn_flags &= ~TCP_ECN_OK; 251} 252 253static inline int TCP_ECN_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th) 254{ 255 if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK)) 256 return 1; 257 return 0; 258} 259 260/* Buffer size and advertised window tuning. 261 * 262 * 1. Tuning sk->sk_sndbuf, when connection enters established state. 263 */ 264 265static void tcp_fixup_sndbuf(struct sock *sk) 266{ 267 int sndmem = SKB_TRUESIZE(tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER); 268 269 sndmem *= TCP_INIT_CWND; 270 if (sk->sk_sndbuf < sndmem) 271 sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]); 272} 273 274/* 2. Tuning advertised window (window_clamp, rcv_ssthresh) 275 * 276 * All tcp_full_space() is split to two parts: "network" buffer, allocated 277 * forward and advertised in receiver window (tp->rcv_wnd) and 278 * "application buffer", required to isolate scheduling/application 279 * latencies from network. 280 * window_clamp is maximal advertised window. It can be less than 281 * tcp_full_space(), in this case tcp_full_space() - window_clamp 282 * is reserved for "application" buffer. The less window_clamp is 283 * the smoother our behaviour from viewpoint of network, but the lower 284 * throughput and the higher sensitivity of the connection to losses. 8) 285 * 286 * rcv_ssthresh is more strict window_clamp used at "slow start" 287 * phase to predict further behaviour of this connection. 288 * It is used for two goals: 289 * - to enforce header prediction at sender, even when application 290 * requires some significant "application buffer". It is check #1. 291 * - to prevent pruning of receive queue because of misprediction 292 * of receiver window. Check #2. 293 * 294 * The scheme does not work when sender sends good segments opening 295 * window and then starts to feed us spaghetti. But it should work 296 * in common situations. Otherwise, we have to rely on queue collapsing. 297 */ 298 299/* Slow part of check#2. */ 300static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb) 301{ 302 struct tcp_sock *tp = tcp_sk(sk); 303 /* Optimize this! */ 304 int truesize = tcp_win_from_space(skb->truesize) >> 1; 305 int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1; 306 307 while (tp->rcv_ssthresh <= window) { 308 if (truesize <= skb->len) 309 return 2 * inet_csk(sk)->icsk_ack.rcv_mss; 310 311 truesize >>= 1; 312 window >>= 1; 313 } 314 return 0; 315} 316 317static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb) 318{ 319 struct tcp_sock *tp = tcp_sk(sk); 320 321 /* Check #1 */ 322 if (tp->rcv_ssthresh < tp->window_clamp && 323 (int)tp->rcv_ssthresh < tcp_space(sk) && 324 !sk_under_memory_pressure(sk)) { 325 int incr; 326 327 /* Check #2. Increase window, if skb with such overhead 328 * will fit to rcvbuf in future. 329 */ 330 if (tcp_win_from_space(skb->truesize) <= skb->len) 331 incr = 2 * tp->advmss; 332 else 333 incr = __tcp_grow_window(sk, skb); 334 335 if (incr) { 336 tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, 337 tp->window_clamp); 338 inet_csk(sk)->icsk_ack.quick |= 1; 339 } 340 } 341} 342 343/* 3. Tuning rcvbuf, when connection enters established state. */ 344 345static void tcp_fixup_rcvbuf(struct sock *sk) 346{ 347 u32 mss = tcp_sk(sk)->advmss; 348 u32 icwnd = TCP_DEFAULT_INIT_RCVWND; 349 int rcvmem; 350 351 /* Limit to 10 segments if mss <= 1460, 352 * or 14600/mss segments, with a minimum of two segments. 353 */ 354 if (mss > 1460) 355 icwnd = max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2); 356 357 rcvmem = SKB_TRUESIZE(mss + MAX_TCP_HEADER); 358 while (tcp_win_from_space(rcvmem) < mss) 359 rcvmem += 128; 360 361 rcvmem *= icwnd; 362 363 if (sk->sk_rcvbuf < rcvmem) 364 sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]); 365} 366 367/* 4. Try to fixup all. It is made immediately after connection enters 368 * established state. 369 */ 370static void tcp_init_buffer_space(struct sock *sk) 371{ 372 struct tcp_sock *tp = tcp_sk(sk); 373 int maxwin; 374 375 if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) 376 tcp_fixup_rcvbuf(sk); 377 if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) 378 tcp_fixup_sndbuf(sk); 379 380 tp->rcvq_space.space = tp->rcv_wnd; 381 382 maxwin = tcp_full_space(sk); 383 384 if (tp->window_clamp >= maxwin) { 385 tp->window_clamp = maxwin; 386 387 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss) 388 tp->window_clamp = max(maxwin - 389 (maxwin >> sysctl_tcp_app_win), 390 4 * tp->advmss); 391 } 392 393 /* Force reservation of one segment. */ 394 if (sysctl_tcp_app_win && 395 tp->window_clamp > 2 * tp->advmss && 396 tp->window_clamp + tp->advmss > maxwin) 397 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss); 398 399 tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp); 400 tp->snd_cwnd_stamp = tcp_time_stamp; 401} 402 403/* 5. Recalculate window clamp after socket hit its memory bounds. */ 404static void tcp_clamp_window(struct sock *sk) 405{ 406 struct tcp_sock *tp = tcp_sk(sk); 407 struct inet_connection_sock *icsk = inet_csk(sk); 408 409 icsk->icsk_ack.quick = 0; 410 411 if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] && 412 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) && 413 !sk_under_memory_pressure(sk) && 414 sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) { 415 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc), 416 sysctl_tcp_rmem[2]); 417 } 418 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) 419 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss); 420} 421 422/* Initialize RCV_MSS value. 423 * RCV_MSS is an our guess about MSS used by the peer. 424 * We haven't any direct information about the MSS. 425 * It's better to underestimate the RCV_MSS rather than overestimate. 426 * Overestimations make us ACKing less frequently than needed. 427 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss(). 428 */ 429void tcp_initialize_rcv_mss(struct sock *sk) 430{ 431 const struct tcp_sock *tp = tcp_sk(sk); 432 unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache); 433 434 hint = min(hint, tp->rcv_wnd / 2); 435 hint = min(hint, TCP_MSS_DEFAULT); 436 hint = max(hint, TCP_MIN_MSS); 437 438 inet_csk(sk)->icsk_ack.rcv_mss = hint; 439} 440EXPORT_SYMBOL(tcp_initialize_rcv_mss); 441 442/* Receiver "autotuning" code. 443 * 444 * The algorithm for RTT estimation w/o timestamps is based on 445 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL. 446 * <http://public.lanl.gov/radiant/pubs.html#DRS> 447 * 448 * More detail on this code can be found at 449 * <http://staff.psc.edu/jheffner/>, 450 * though this reference is out of date. A new paper 451 * is pending. 452 */ 453static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep) 454{ 455 u32 new_sample = tp->rcv_rtt_est.rtt; 456 long m = sample; 457 458 if (m == 0) 459 m = 1; 460 461 if (new_sample != 0) { 462 /* If we sample in larger samples in the non-timestamp 463 * case, we could grossly overestimate the RTT especially 464 * with chatty applications or bulk transfer apps which 465 * are stalled on filesystem I/O. 466 * 467 * Also, since we are only going for a minimum in the 468 * non-timestamp case, we do not smooth things out 469 * else with timestamps disabled convergence takes too 470 * long. 471 */ 472 if (!win_dep) { 473 m -= (new_sample >> 3); 474 new_sample += m; 475 } else if (m < new_sample) 476 new_sample = m << 3; 477 } else { 478 /* No previous measure. */ 479 new_sample = m << 3; 480 } 481 482 if (tp->rcv_rtt_est.rtt != new_sample) 483 tp->rcv_rtt_est.rtt = new_sample; 484} 485 486static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp) 487{ 488 if (tp->rcv_rtt_est.time == 0) 489 goto new_measure; 490 if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq)) 491 return; 492 tcp_rcv_rtt_update(tp, jiffies - tp->rcv_rtt_est.time, 1); 493 494new_measure: 495 tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd; 496 tp->rcv_rtt_est.time = tcp_time_stamp; 497} 498 499static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, 500 const struct sk_buff *skb) 501{ 502 struct tcp_sock *tp = tcp_sk(sk); 503 if (tp->rx_opt.rcv_tsecr && 504 (TCP_SKB_CB(skb)->end_seq - 505 TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss)) 506 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0); 507} 508 509/* 510 * This function should be called every time data is copied to user space. 511 * It calculates the appropriate TCP receive buffer space. 512 */ 513void tcp_rcv_space_adjust(struct sock *sk) 514{ 515 struct tcp_sock *tp = tcp_sk(sk); 516 int time; 517 int space; 518 519 if (tp->rcvq_space.time == 0) 520 goto new_measure; 521 522 time = tcp_time_stamp - tp->rcvq_space.time; 523 if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0) 524 return; 525 526 space = 2 * (tp->copied_seq - tp->rcvq_space.seq); 527 528 space = max(tp->rcvq_space.space, space); 529 530 if (tp->rcvq_space.space != space) { 531 int rcvmem; 532 533 tp->rcvq_space.space = space; 534 535 if (sysctl_tcp_moderate_rcvbuf && 536 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) { 537 int new_clamp = space; 538 539 /* Receive space grows, normalize in order to 540 * take into account packet headers and sk_buff 541 * structure overhead. 542 */ 543 space /= tp->advmss; 544 if (!space) 545 space = 1; 546 rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER); 547 while (tcp_win_from_space(rcvmem) < tp->advmss) 548 rcvmem += 128; 549 space *= rcvmem; 550 space = min(space, sysctl_tcp_rmem[2]); 551 if (space > sk->sk_rcvbuf) { 552 sk->sk_rcvbuf = space; 553 554 /* Make the window clamp follow along. */ 555 tp->window_clamp = new_clamp; 556 } 557 } 558 } 559 560new_measure: 561 tp->rcvq_space.seq = tp->copied_seq; 562 tp->rcvq_space.time = tcp_time_stamp; 563} 564 565/* There is something which you must keep in mind when you analyze the 566 * behavior of the tp->ato delayed ack timeout interval. When a 567 * connection starts up, we want to ack as quickly as possible. The 568 * problem is that "good" TCP's do slow start at the beginning of data 569 * transmission. The means that until we send the first few ACK's the 570 * sender will sit on his end and only queue most of his data, because 571 * he can only send snd_cwnd unacked packets at any given time. For 572 * each ACK we send, he increments snd_cwnd and transmits more of his 573 * queue. -DaveM 574 */ 575static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb) 576{ 577 struct tcp_sock *tp = tcp_sk(sk); 578 struct inet_connection_sock *icsk = inet_csk(sk); 579 u32 now; 580 581 inet_csk_schedule_ack(sk); 582 583 tcp_measure_rcv_mss(sk, skb); 584 585 tcp_rcv_rtt_measure(tp); 586 587 now = tcp_time_stamp; 588 589 if (!icsk->icsk_ack.ato) { 590 /* The _first_ data packet received, initialize 591 * delayed ACK engine. 592 */ 593 tcp_incr_quickack(sk); 594 icsk->icsk_ack.ato = TCP_ATO_MIN; 595 } else { 596 int m = now - icsk->icsk_ack.lrcvtime; 597 598 if (m <= TCP_ATO_MIN / 2) { 599 /* The fastest case is the first. */ 600 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2; 601 } else if (m < icsk->icsk_ack.ato) { 602 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m; 603 if (icsk->icsk_ack.ato > icsk->icsk_rto) 604 icsk->icsk_ack.ato = icsk->icsk_rto; 605 } else if (m > icsk->icsk_rto) { 606 /* Too long gap. Apparently sender failed to 607 * restart window, so that we send ACKs quickly. 608 */ 609 tcp_incr_quickack(sk); 610 sk_mem_reclaim(sk); 611 } 612 } 613 icsk->icsk_ack.lrcvtime = now; 614 615 TCP_ECN_check_ce(tp, skb); 616 617 if (skb->len >= 128) 618 tcp_grow_window(sk, skb); 619} 620 621/* Called to compute a smoothed rtt estimate. The data fed to this 622 * routine either comes from timestamps, or from segments that were 623 * known _not_ to have been retransmitted [see Karn/Partridge 624 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88 625 * piece by Van Jacobson. 626 * NOTE: the next three routines used to be one big routine. 627 * To save cycles in the RFC 1323 implementation it was better to break 628 * it up into three procedures. -- erics 629 */ 630static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt) 631{ 632 struct tcp_sock *tp = tcp_sk(sk); 633 long m = mrtt; /* RTT */ 634 635 /* The following amusing code comes from Jacobson's 636 * article in SIGCOMM '88. Note that rtt and mdev 637 * are scaled versions of rtt and mean deviation. 638 * This is designed to be as fast as possible 639 * m stands for "measurement". 640 * 641 * On a 1990 paper the rto value is changed to: 642 * RTO = rtt + 4 * mdev 643 * 644 * Funny. This algorithm seems to be very broken. 645 * These formulae increase RTO, when it should be decreased, increase 646 * too slowly, when it should be increased quickly, decrease too quickly 647 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely 648 * does not matter how to _calculate_ it. Seems, it was trap 649 * that VJ failed to avoid. 8) 650 */ 651 if (m == 0) 652 m = 1; 653 if (tp->srtt != 0) { 654 m -= (tp->srtt >> 3); /* m is now error in rtt est */ 655 tp->srtt += m; /* rtt = 7/8 rtt + 1/8 new */ 656 if (m < 0) { 657 m = -m; /* m is now abs(error) */ 658 m -= (tp->mdev >> 2); /* similar update on mdev */ 659 /* This is similar to one of Eifel findings. 660 * Eifel blocks mdev updates when rtt decreases. 661 * This solution is a bit different: we use finer gain 662 * for mdev in this case (alpha*beta). 663 * Like Eifel it also prevents growth of rto, 664 * but also it limits too fast rto decreases, 665 * happening in pure Eifel. 666 */ 667 if (m > 0) 668 m >>= 3; 669 } else { 670 m -= (tp->mdev >> 2); /* similar update on mdev */ 671 } 672 tp->mdev += m; /* mdev = 3/4 mdev + 1/4 new */ 673 if (tp->mdev > tp->mdev_max) { 674 tp->mdev_max = tp->mdev; 675 if (tp->mdev_max > tp->rttvar) 676 tp->rttvar = tp->mdev_max; 677 } 678 if (after(tp->snd_una, tp->rtt_seq)) { 679 if (tp->mdev_max < tp->rttvar) 680 tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2; 681 tp->rtt_seq = tp->snd_nxt; 682 tp->mdev_max = tcp_rto_min(sk); 683 } 684 } else { 685 /* no previous measure. */ 686 tp->srtt = m << 3; /* take the measured time to be rtt */ 687 tp->mdev = m << 1; /* make sure rto = 3*rtt */ 688 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk)); 689 tp->rtt_seq = tp->snd_nxt; 690 } 691} 692 693/* Calculate rto without backoff. This is the second half of Van Jacobson's 694 * routine referred to above. 695 */ 696static inline void tcp_set_rto(struct sock *sk) 697{ 698 const struct tcp_sock *tp = tcp_sk(sk); 699 /* Old crap is replaced with new one. 8) 700 * 701 * More seriously: 702 * 1. If rtt variance happened to be less 50msec, it is hallucination. 703 * It cannot be less due to utterly erratic ACK generation made 704 * at least by solaris and freebsd. "Erratic ACKs" has _nothing_ 705 * to do with delayed acks, because at cwnd>2 true delack timeout 706 * is invisible. Actually, Linux-2.4 also generates erratic 707 * ACKs in some circumstances. 708 */ 709 inet_csk(sk)->icsk_rto = __tcp_set_rto(tp); 710 711 /* 2. Fixups made earlier cannot be right. 712 * If we do not estimate RTO correctly without them, 713 * all the algo is pure shit and should be replaced 714 * with correct one. It is exactly, which we pretend to do. 715 */ 716 717 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo 718 * guarantees that rto is higher. 719 */ 720 tcp_bound_rto(sk); 721} 722 723/* Save metrics learned by this TCP session. 724 This function is called only, when TCP finishes successfully 725 i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE. 726 */ 727void tcp_update_metrics(struct sock *sk) 728{ 729 struct tcp_sock *tp = tcp_sk(sk); 730 struct dst_entry *dst = __sk_dst_get(sk); 731 732 if (sysctl_tcp_nometrics_save) 733 return; 734 735 dst_confirm(dst); 736 737 if (dst && (dst->flags & DST_HOST)) { 738 const struct inet_connection_sock *icsk = inet_csk(sk); 739 int m; 740 unsigned long rtt; 741 742 if (icsk->icsk_backoff || !tp->srtt) { 743 /* This session failed to estimate rtt. Why? 744 * Probably, no packets returned in time. 745 * Reset our results. 746 */ 747 if (!(dst_metric_locked(dst, RTAX_RTT))) 748 dst_metric_set(dst, RTAX_RTT, 0); 749 return; 750 } 751 752 rtt = dst_metric_rtt(dst, RTAX_RTT); 753 m = rtt - tp->srtt; 754 755 /* If newly calculated rtt larger than stored one, 756 * store new one. Otherwise, use EWMA. Remember, 757 * rtt overestimation is always better than underestimation. 758 */ 759 if (!(dst_metric_locked(dst, RTAX_RTT))) { 760 if (m <= 0) 761 set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt); 762 else 763 set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3)); 764 } 765 766 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) { 767 unsigned long var; 768 if (m < 0) 769 m = -m; 770 771 /* Scale deviation to rttvar fixed point */ 772 m >>= 1; 773 if (m < tp->mdev) 774 m = tp->mdev; 775 776 var = dst_metric_rtt(dst, RTAX_RTTVAR); 777 if (m >= var) 778 var = m; 779 else 780 var -= (var - m) >> 2; 781 782 set_dst_metric_rtt(dst, RTAX_RTTVAR, var); 783 } 784 785 if (tcp_in_initial_slowstart(tp)) { 786 /* Slow start still did not finish. */ 787 if (dst_metric(dst, RTAX_SSTHRESH) && 788 !dst_metric_locked(dst, RTAX_SSTHRESH) && 789 (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH)) 790 dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_cwnd >> 1); 791 if (!dst_metric_locked(dst, RTAX_CWND) && 792 tp->snd_cwnd > dst_metric(dst, RTAX_CWND)) 793 dst_metric_set(dst, RTAX_CWND, tp->snd_cwnd); 794 } else if (tp->snd_cwnd > tp->snd_ssthresh && 795 icsk->icsk_ca_state == TCP_CA_Open) { 796 /* Cong. avoidance phase, cwnd is reliable. */ 797 if (!dst_metric_locked(dst, RTAX_SSTHRESH)) 798 dst_metric_set(dst, RTAX_SSTHRESH, 799 max(tp->snd_cwnd >> 1, tp->snd_ssthresh)); 800 if (!dst_metric_locked(dst, RTAX_CWND)) 801 dst_metric_set(dst, RTAX_CWND, 802 (dst_metric(dst, RTAX_CWND) + 803 tp->snd_cwnd) >> 1); 804 } else { 805 /* Else slow start did not finish, cwnd is non-sense, 806 ssthresh may be also invalid. 807 */ 808 if (!dst_metric_locked(dst, RTAX_CWND)) 809 dst_metric_set(dst, RTAX_CWND, 810 (dst_metric(dst, RTAX_CWND) + 811 tp->snd_ssthresh) >> 1); 812 if (dst_metric(dst, RTAX_SSTHRESH) && 813 !dst_metric_locked(dst, RTAX_SSTHRESH) && 814 tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH)) 815 dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_ssthresh); 816 } 817 818 if (!dst_metric_locked(dst, RTAX_REORDERING)) { 819 if (dst_metric(dst, RTAX_REORDERING) < tp->reordering && 820 tp->reordering != sysctl_tcp_reordering) 821 dst_metric_set(dst, RTAX_REORDERING, tp->reordering); 822 } 823 } 824} 825 826__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst) 827{ 828 __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0); 829 830 if (!cwnd) 831 cwnd = TCP_INIT_CWND; 832 return min_t(__u32, cwnd, tp->snd_cwnd_clamp); 833} 834 835/* Set slow start threshold and cwnd not falling to slow start */ 836void tcp_enter_cwr(struct sock *sk, const int set_ssthresh) 837{ 838 struct tcp_sock *tp = tcp_sk(sk); 839 const struct inet_connection_sock *icsk = inet_csk(sk); 840 841 tp->prior_ssthresh = 0; 842 tp->bytes_acked = 0; 843 if (icsk->icsk_ca_state < TCP_CA_CWR) { 844 tp->undo_marker = 0; 845 if (set_ssthresh) 846 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); 847 tp->snd_cwnd = min(tp->snd_cwnd, 848 tcp_packets_in_flight(tp) + 1U); 849 tp->snd_cwnd_cnt = 0; 850 tp->high_seq = tp->snd_nxt; 851 tp->snd_cwnd_stamp = tcp_time_stamp; 852 TCP_ECN_queue_cwr(tp); 853 854 tcp_set_ca_state(sk, TCP_CA_CWR); 855 } 856} 857 858/* 859 * Packet counting of FACK is based on in-order assumptions, therefore TCP 860 * disables it when reordering is detected 861 */ 862static void tcp_disable_fack(struct tcp_sock *tp) 863{ 864 /* RFC3517 uses different metric in lost marker => reset on change */ 865 if (tcp_is_fack(tp)) 866 tp->lost_skb_hint = NULL; 867 tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED; 868} 869 870/* Take a notice that peer is sending D-SACKs */ 871static void tcp_dsack_seen(struct tcp_sock *tp) 872{ 873 tp->rx_opt.sack_ok |= TCP_DSACK_SEEN; 874} 875 876/* Initialize metrics on socket. */ 877 878static void tcp_init_metrics(struct sock *sk) 879{ 880 struct tcp_sock *tp = tcp_sk(sk); 881 struct dst_entry *dst = __sk_dst_get(sk); 882 883 if (dst == NULL) 884 goto reset; 885 886 dst_confirm(dst); 887 888 if (dst_metric_locked(dst, RTAX_CWND)) 889 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND); 890 if (dst_metric(dst, RTAX_SSTHRESH)) { 891 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH); 892 if (tp->snd_ssthresh > tp->snd_cwnd_clamp) 893 tp->snd_ssthresh = tp->snd_cwnd_clamp; 894 } else { 895 /* ssthresh may have been reduced unnecessarily during. 896 * 3WHS. Restore it back to its initial default. 897 */ 898 tp->snd_ssthresh = TCP_INFINITE_SSTHRESH; 899 } 900 if (dst_metric(dst, RTAX_REORDERING) && 901 tp->reordering != dst_metric(dst, RTAX_REORDERING)) { 902 tcp_disable_fack(tp); 903 tp->reordering = dst_metric(dst, RTAX_REORDERING); 904 } 905 906 if (dst_metric(dst, RTAX_RTT) == 0 || tp->srtt == 0) 907 goto reset; 908 909 /* Initial rtt is determined from SYN,SYN-ACK. 910 * The segment is small and rtt may appear much 911 * less than real one. Use per-dst memory 912 * to make it more realistic. 913 * 914 * A bit of theory. RTT is time passed after "normal" sized packet 915 * is sent until it is ACKed. In normal circumstances sending small 916 * packets force peer to delay ACKs and calculation is correct too. 917 * The algorithm is adaptive and, provided we follow specs, it 918 * NEVER underestimate RTT. BUT! If peer tries to make some clever 919 * tricks sort of "quick acks" for time long enough to decrease RTT 920 * to low value, and then abruptly stops to do it and starts to delay 921 * ACKs, wait for troubles. 922 */ 923 if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) { 924 tp->srtt = dst_metric_rtt(dst, RTAX_RTT); 925 tp->rtt_seq = tp->snd_nxt; 926 } 927 if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) { 928 tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR); 929 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk)); 930 } 931 tcp_set_rto(sk); 932reset: 933 if (tp->srtt == 0) { 934 /* RFC2988bis: We've failed to get a valid RTT sample from 935 * 3WHS. This is most likely due to retransmission, 936 * including spurious one. Reset the RTO back to 3secs 937 * from the more aggressive 1sec to avoid more spurious 938 * retransmission. 939 */ 940 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_FALLBACK; 941 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_FALLBACK; 942 } 943 /* Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been 944 * retransmitted. In light of RFC2988bis' more aggressive 1sec 945 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK 946 * retransmission has occurred. 947 */ 948 if (tp->total_retrans > 1) 949 tp->snd_cwnd = 1; 950 else 951 tp->snd_cwnd = tcp_init_cwnd(tp, dst); 952 tp->snd_cwnd_stamp = tcp_time_stamp; 953} 954 955static void tcp_update_reordering(struct sock *sk, const int metric, 956 const int ts) 957{ 958 struct tcp_sock *tp = tcp_sk(sk); 959 if (metric > tp->reordering) { 960 int mib_idx; 961 962 tp->reordering = min(TCP_MAX_REORDERING, metric); 963 964 /* This exciting event is worth to be remembered. 8) */ 965 if (ts) 966 mib_idx = LINUX_MIB_TCPTSREORDER; 967 else if (tcp_is_reno(tp)) 968 mib_idx = LINUX_MIB_TCPRENOREORDER; 969 else if (tcp_is_fack(tp)) 970 mib_idx = LINUX_MIB_TCPFACKREORDER; 971 else 972 mib_idx = LINUX_MIB_TCPSACKREORDER; 973 974 NET_INC_STATS_BH(sock_net(sk), mib_idx); 975#if FASTRETRANS_DEBUG > 1 976 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n", 977 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state, 978 tp->reordering, 979 tp->fackets_out, 980 tp->sacked_out, 981 tp->undo_marker ? tp->undo_retrans : 0); 982#endif 983 tcp_disable_fack(tp); 984 } 985} 986 987/* This must be called before lost_out is incremented */ 988static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb) 989{ 990 if ((tp->retransmit_skb_hint == NULL) || 991 before(TCP_SKB_CB(skb)->seq, 992 TCP_SKB_CB(tp->retransmit_skb_hint)->seq)) 993 tp->retransmit_skb_hint = skb; 994 995 if (!tp->lost_out || 996 after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high)) 997 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq; 998} 999 1000static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb) 1001{ 1002 if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) { 1003 tcp_verify_retransmit_hint(tp, skb); 1004 1005 tp->lost_out += tcp_skb_pcount(skb); 1006 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 1007 } 1008} 1009 1010static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, 1011 struct sk_buff *skb) 1012{ 1013 tcp_verify_retransmit_hint(tp, skb); 1014 1015 if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) { 1016 tp->lost_out += tcp_skb_pcount(skb); 1017 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 1018 } 1019} 1020 1021/* This procedure tags the retransmission queue when SACKs arrive. 1022 * 1023 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L). 1024 * Packets in queue with these bits set are counted in variables 1025 * sacked_out, retrans_out and lost_out, correspondingly. 1026 * 1027 * Valid combinations are: 1028 * Tag InFlight Description 1029 * 0 1 - orig segment is in flight. 1030 * S 0 - nothing flies, orig reached receiver. 1031 * L 0 - nothing flies, orig lost by net. 1032 * R 2 - both orig and retransmit are in flight. 1033 * L|R 1 - orig is lost, retransmit is in flight. 1034 * S|R 1 - orig reached receiver, retrans is still in flight. 1035 * (L|S|R is logically valid, it could occur when L|R is sacked, 1036 * but it is equivalent to plain S and code short-curcuits it to S. 1037 * L|S is logically invalid, it would mean -1 packet in flight 8)) 1038 * 1039 * These 6 states form finite state machine, controlled by the following events: 1040 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue()) 1041 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue()) 1042 * 3. Loss detection event of two flavors: 1043 * A. Scoreboard estimator decided the packet is lost. 1044 * A'. Reno "three dupacks" marks head of queue lost. 1045 * A''. Its FACK modification, head until snd.fack is lost. 1046 * B. SACK arrives sacking SND.NXT at the moment, when the 1047 * segment was retransmitted. 1048 * 4. D-SACK added new rule: D-SACK changes any tag to S. 1049 * 1050 * It is pleasant to note, that state diagram turns out to be commutative, 1051 * so that we are allowed not to be bothered by order of our actions, 1052 * when multiple events arrive simultaneously. (see the function below). 1053 * 1054 * Reordering detection. 1055 * -------------------- 1056 * Reordering metric is maximal distance, which a packet can be displaced 1057 * in packet stream. With SACKs we can estimate it: 1058 * 1059 * 1. SACK fills old hole and the corresponding segment was not 1060 * ever retransmitted -> reordering. Alas, we cannot use it 1061 * when segment was retransmitted. 1062 * 2. The last flaw is solved with D-SACK. D-SACK arrives 1063 * for retransmitted and already SACKed segment -> reordering.. 1064 * Both of these heuristics are not used in Loss state, when we cannot 1065 * account for retransmits accurately. 1066 * 1067 * SACK block validation. 1068 * ---------------------- 1069 * 1070 * SACK block range validation checks that the received SACK block fits to 1071 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT. 1072 * Note that SND.UNA is not included to the range though being valid because 1073 * it means that the receiver is rather inconsistent with itself reporting 1074 * SACK reneging when it should advance SND.UNA. Such SACK block this is 1075 * perfectly valid, however, in light of RFC2018 which explicitly states 1076 * that "SACK block MUST reflect the newest segment. Even if the newest 1077 * segment is going to be discarded ...", not that it looks very clever 1078 * in case of head skb. Due to potentional receiver driven attacks, we 1079 * choose to avoid immediate execution of a walk in write queue due to 1080 * reneging and defer head skb's loss recovery to standard loss recovery 1081 * procedure that will eventually trigger (nothing forbids us doing this). 1082 * 1083 * Implements also blockage to start_seq wrap-around. Problem lies in the 1084 * fact that though start_seq (s) is before end_seq (i.e., not reversed), 1085 * there's no guarantee that it will be before snd_nxt (n). The problem 1086 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt 1087 * wrap (s_w): 1088 * 1089 * <- outs wnd -> <- wrapzone -> 1090 * u e n u_w e_w s n_w 1091 * | | | | | | | 1092 * |<------------+------+----- TCP seqno space --------------+---------->| 1093 * ...-- <2^31 ->| |<--------... 1094 * ...---- >2^31 ------>| |<--------... 1095 * 1096 * Current code wouldn't be vulnerable but it's better still to discard such 1097 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat 1098 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in 1099 * snd_nxt wrap -> snd_una region will then become "well defined", i.e., 1100 * equal to the ideal case (infinite seqno space without wrap caused issues). 1101 * 1102 * With D-SACK the lower bound is extended to cover sequence space below 1103 * SND.UNA down to undo_marker, which is the last point of interest. Yet 1104 * again, D-SACK block must not to go across snd_una (for the same reason as 1105 * for the normal SACK blocks, explained above). But there all simplicity 1106 * ends, TCP might receive valid D-SACKs below that. As long as they reside 1107 * fully below undo_marker they do not affect behavior in anyway and can 1108 * therefore be safely ignored. In rare cases (which are more or less 1109 * theoretical ones), the D-SACK will nicely cross that boundary due to skb 1110 * fragmentation and packet reordering past skb's retransmission. To consider 1111 * them correctly, the acceptable range must be extended even more though 1112 * the exact amount is rather hard to quantify. However, tp->max_window can 1113 * be used as an exaggerated estimate. 1114 */ 1115static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack, 1116 u32 start_seq, u32 end_seq) 1117{ 1118 /* Too far in future, or reversed (interpretation is ambiguous) */ 1119 if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq)) 1120 return 0; 1121 1122 /* Nasty start_seq wrap-around check (see comments above) */ 1123 if (!before(start_seq, tp->snd_nxt)) 1124 return 0; 1125 1126 /* In outstanding window? ...This is valid exit for D-SACKs too. 1127 * start_seq == snd_una is non-sensical (see comments above) 1128 */ 1129 if (after(start_seq, tp->snd_una)) 1130 return 1; 1131 1132 if (!is_dsack || !tp->undo_marker) 1133 return 0; 1134 1135 /* ...Then it's D-SACK, and must reside below snd_una completely */ 1136 if (after(end_seq, tp->snd_una)) 1137 return 0; 1138 1139 if (!before(start_seq, tp->undo_marker)) 1140 return 1; 1141 1142 /* Too old */ 1143 if (!after(end_seq, tp->undo_marker)) 1144 return 0; 1145 1146 /* Undo_marker boundary crossing (overestimates a lot). Known already: 1147 * start_seq < undo_marker and end_seq >= undo_marker. 1148 */ 1149 return !before(start_seq, end_seq - tp->max_window); 1150} 1151 1152/* Check for lost retransmit. This superb idea is borrowed from "ratehalving". 1153 * Event "B". Later note: FACK people cheated me again 8), we have to account 1154 * for reordering! Ugly, but should help. 1155 * 1156 * Search retransmitted skbs from write_queue that were sent when snd_nxt was 1157 * less than what is now known to be received by the other end (derived from 1158 * highest SACK block). Also calculate the lowest snd_nxt among the remaining 1159 * retransmitted skbs to avoid some costly processing per ACKs. 1160 */ 1161static void tcp_mark_lost_retrans(struct sock *sk) 1162{ 1163 const struct inet_connection_sock *icsk = inet_csk(sk); 1164 struct tcp_sock *tp = tcp_sk(sk); 1165 struct sk_buff *skb; 1166 int cnt = 0; 1167 u32 new_low_seq = tp->snd_nxt; 1168 u32 received_upto = tcp_highest_sack_seq(tp); 1169 1170 if (!tcp_is_fack(tp) || !tp->retrans_out || 1171 !after(received_upto, tp->lost_retrans_low) || 1172 icsk->icsk_ca_state != TCP_CA_Recovery) 1173 return; 1174 1175 tcp_for_write_queue(skb, sk) { 1176 u32 ack_seq = TCP_SKB_CB(skb)->ack_seq; 1177 1178 if (skb == tcp_send_head(sk)) 1179 break; 1180 if (cnt == tp->retrans_out) 1181 break; 1182 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) 1183 continue; 1184 1185 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)) 1186 continue; 1187 1188 /* TODO: We would like to get rid of tcp_is_fack(tp) only 1189 * constraint here (see above) but figuring out that at 1190 * least tp->reordering SACK blocks reside between ack_seq 1191 * and received_upto is not easy task to do cheaply with 1192 * the available datastructures. 1193 * 1194 * Whether FACK should check here for tp->reordering segs 1195 * in-between one could argue for either way (it would be 1196 * rather simple to implement as we could count fack_count 1197 * during the walk and do tp->fackets_out - fack_count). 1198 */ 1199 if (after(received_upto, ack_seq)) { 1200 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; 1201 tp->retrans_out -= tcp_skb_pcount(skb); 1202 1203 tcp_skb_mark_lost_uncond_verify(tp, skb); 1204 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT); 1205 } else { 1206 if (before(ack_seq, new_low_seq)) 1207 new_low_seq = ack_seq; 1208 cnt += tcp_skb_pcount(skb); 1209 } 1210 } 1211 1212 if (tp->retrans_out) 1213 tp->lost_retrans_low = new_low_seq; 1214} 1215 1216static int tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb, 1217 struct tcp_sack_block_wire *sp, int num_sacks, 1218 u32 prior_snd_una) 1219{ 1220 struct tcp_sock *tp = tcp_sk(sk); 1221 u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq); 1222 u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq); 1223 int dup_sack = 0; 1224 1225 if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) { 1226 dup_sack = 1; 1227 tcp_dsack_seen(tp); 1228 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV); 1229 } else if (num_sacks > 1) { 1230 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq); 1231 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq); 1232 1233 if (!after(end_seq_0, end_seq_1) && 1234 !before(start_seq_0, start_seq_1)) { 1235 dup_sack = 1; 1236 tcp_dsack_seen(tp); 1237 NET_INC_STATS_BH(sock_net(sk), 1238 LINUX_MIB_TCPDSACKOFORECV); 1239 } 1240 } 1241 1242 /* D-SACK for already forgotten data... Do dumb counting. */ 1243 if (dup_sack && tp->undo_marker && tp->undo_retrans && 1244 !after(end_seq_0, prior_snd_una) && 1245 after(end_seq_0, tp->undo_marker)) 1246 tp->undo_retrans--; 1247 1248 return dup_sack; 1249} 1250 1251struct tcp_sacktag_state { 1252 int reord; 1253 int fack_count; 1254 int flag; 1255}; 1256 1257/* Check if skb is fully within the SACK block. In presence of GSO skbs, 1258 * the incoming SACK may not exactly match but we can find smaller MSS 1259 * aligned portion of it that matches. Therefore we might need to fragment 1260 * which may fail and creates some hassle (caller must handle error case 1261 * returns). 1262 * 1263 * FIXME: this could be merged to shift decision code 1264 */ 1265static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb, 1266 u32 start_seq, u32 end_seq) 1267{ 1268 int in_sack, err; 1269 unsigned int pkt_len; 1270 unsigned int mss; 1271 1272 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && 1273 !before(end_seq, TCP_SKB_CB(skb)->end_seq); 1274 1275 if (tcp_skb_pcount(skb) > 1 && !in_sack && 1276 after(TCP_SKB_CB(skb)->end_seq, start_seq)) { 1277 mss = tcp_skb_mss(skb); 1278 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq); 1279 1280 if (!in_sack) { 1281 pkt_len = start_seq - TCP_SKB_CB(skb)->seq; 1282 if (pkt_len < mss) 1283 pkt_len = mss; 1284 } else { 1285 pkt_len = end_seq - TCP_SKB_CB(skb)->seq; 1286 if (pkt_len < mss) 1287 return -EINVAL; 1288 } 1289 1290 /* Round if necessary so that SACKs cover only full MSSes 1291 * and/or the remaining small portion (if present) 1292 */ 1293 if (pkt_len > mss) { 1294 unsigned int new_len = (pkt_len / mss) * mss; 1295 if (!in_sack && new_len < pkt_len) { 1296 new_len += mss; 1297 if (new_len > skb->len) 1298 return 0; 1299 } 1300 pkt_len = new_len; 1301 } 1302 err = tcp_fragment(sk, skb, pkt_len, mss); 1303 if (err < 0) 1304 return err; 1305 } 1306 1307 return in_sack; 1308} 1309 1310static u8 tcp_sacktag_one(const struct sk_buff *skb, struct sock *sk, 1311 struct tcp_sacktag_state *state, 1312 int dup_sack, int pcount) 1313{ 1314 struct tcp_sock *tp = tcp_sk(sk); 1315 u8 sacked = TCP_SKB_CB(skb)->sacked; 1316 int fack_count = state->fack_count; 1317 1318 /* Account D-SACK for retransmitted packet. */ 1319 if (dup_sack && (sacked & TCPCB_RETRANS)) { 1320 if (tp->undo_marker && tp->undo_retrans && 1321 after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker)) 1322 tp->undo_retrans--; 1323 if (sacked & TCPCB_SACKED_ACKED) 1324 state->reord = min(fack_count, state->reord); 1325 } 1326 1327 /* Nothing to do; acked frame is about to be dropped (was ACKed). */ 1328 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) 1329 return sacked; 1330 1331 if (!(sacked & TCPCB_SACKED_ACKED)) { 1332 if (sacked & TCPCB_SACKED_RETRANS) { 1333 /* If the segment is not tagged as lost, 1334 * we do not clear RETRANS, believing 1335 * that retransmission is still in flight. 1336 */ 1337 if (sacked & TCPCB_LOST) { 1338 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS); 1339 tp->lost_out -= pcount; 1340 tp->retrans_out -= pcount; 1341 } 1342 } else { 1343 if (!(sacked & TCPCB_RETRANS)) { 1344 /* New sack for not retransmitted frame, 1345 * which was in hole. It is reordering. 1346 */ 1347 if (before(TCP_SKB_CB(skb)->seq, 1348 tcp_highest_sack_seq(tp))) 1349 state->reord = min(fack_count, 1350 state->reord); 1351 1352 /* SACK enhanced F-RTO (RFC4138; Appendix B) */ 1353 if (!after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark)) 1354 state->flag |= FLAG_ONLY_ORIG_SACKED; 1355 } 1356 1357 if (sacked & TCPCB_LOST) { 1358 sacked &= ~TCPCB_LOST; 1359 tp->lost_out -= pcount; 1360 } 1361 } 1362 1363 sacked |= TCPCB_SACKED_ACKED; 1364 state->flag |= FLAG_DATA_SACKED; 1365 tp->sacked_out += pcount; 1366 1367 fack_count += pcount; 1368 1369 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */ 1370 if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) && 1371 before(TCP_SKB_CB(skb)->seq, 1372 TCP_SKB_CB(tp->lost_skb_hint)->seq)) 1373 tp->lost_cnt_hint += pcount; 1374 1375 if (fack_count > tp->fackets_out) 1376 tp->fackets_out = fack_count; 1377 } 1378 1379 /* D-SACK. We can detect redundant retransmission in S|R and plain R 1380 * frames and clear it. undo_retrans is decreased above, L|R frames 1381 * are accounted above as well. 1382 */ 1383 if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) { 1384 sacked &= ~TCPCB_SACKED_RETRANS; 1385 tp->retrans_out -= pcount; 1386 } 1387 1388 return sacked; 1389} 1390 1391static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb, 1392 struct tcp_sacktag_state *state, 1393 unsigned int pcount, int shifted, int mss, 1394 int dup_sack) 1395{ 1396 struct tcp_sock *tp = tcp_sk(sk); 1397 struct sk_buff *prev = tcp_write_queue_prev(sk, skb); 1398 1399 BUG_ON(!pcount); 1400 1401 if (skb == tp->lost_skb_hint) 1402 tp->lost_cnt_hint += pcount; 1403 1404 TCP_SKB_CB(prev)->end_seq += shifted; 1405 TCP_SKB_CB(skb)->seq += shifted; 1406 1407 skb_shinfo(prev)->gso_segs += pcount; 1408 BUG_ON(skb_shinfo(skb)->gso_segs < pcount); 1409 skb_shinfo(skb)->gso_segs -= pcount; 1410 1411 /* When we're adding to gso_segs == 1, gso_size will be zero, 1412 * in theory this shouldn't be necessary but as long as DSACK 1413 * code can come after this skb later on it's better to keep 1414 * setting gso_size to something. 1415 */ 1416 if (!skb_shinfo(prev)->gso_size) { 1417 skb_shinfo(prev)->gso_size = mss; 1418 skb_shinfo(prev)->gso_type = sk->sk_gso_type; 1419 } 1420 1421 /* CHECKME: To clear or not to clear? Mimics normal skb currently */ 1422 if (skb_shinfo(skb)->gso_segs <= 1) { 1423 skb_shinfo(skb)->gso_size = 0; 1424 skb_shinfo(skb)->gso_type = 0; 1425 } 1426 1427 /* We discard results */ 1428 tcp_sacktag_one(skb, sk, state, dup_sack, pcount); 1429 1430 /* Difference in this won't matter, both ACKed by the same cumul. ACK */ 1431 TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS); 1432 1433 if (skb->len > 0) { 1434 BUG_ON(!tcp_skb_pcount(skb)); 1435 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED); 1436 return 0; 1437 } 1438 1439 /* Whole SKB was eaten :-) */ 1440 1441 if (skb == tp->retransmit_skb_hint) 1442 tp->retransmit_skb_hint = prev; 1443 if (skb == tp->scoreboard_skb_hint) 1444 tp->scoreboard_skb_hint = prev; 1445 if (skb == tp->lost_skb_hint) { 1446 tp->lost_skb_hint = prev; 1447 tp->lost_cnt_hint -= tcp_skb_pcount(prev); 1448 } 1449 1450 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(prev)->tcp_flags; 1451 if (skb == tcp_highest_sack(sk)) 1452 tcp_advance_highest_sack(sk, skb); 1453 1454 tcp_unlink_write_queue(skb, sk); 1455 sk_wmem_free_skb(sk, skb); 1456 1457 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED); 1458 1459 return 1; 1460} 1461 1462/* I wish gso_size would have a bit more sane initialization than 1463 * something-or-zero which complicates things 1464 */ 1465static int tcp_skb_seglen(const struct sk_buff *skb) 1466{ 1467 return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb); 1468} 1469 1470/* Shifting pages past head area doesn't work */ 1471static int skb_can_shift(const struct sk_buff *skb) 1472{ 1473 return !skb_headlen(skb) && skb_is_nonlinear(skb); 1474} 1475 1476/* Try collapsing SACK blocks spanning across multiple skbs to a single 1477 * skb. 1478 */ 1479static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb, 1480 struct tcp_sacktag_state *state, 1481 u32 start_seq, u32 end_seq, 1482 int dup_sack) 1483{ 1484 struct tcp_sock *tp = tcp_sk(sk); 1485 struct sk_buff *prev; 1486 int mss; 1487 int pcount = 0; 1488 int len; 1489 int in_sack; 1490 1491 if (!sk_can_gso(sk)) 1492 goto fallback; 1493 1494 /* Normally R but no L won't result in plain S */ 1495 if (!dup_sack && 1496 (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS) 1497 goto fallback; 1498 if (!skb_can_shift(skb)) 1499 goto fallback; 1500 /* This frame is about to be dropped (was ACKed). */ 1501 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) 1502 goto fallback; 1503 1504 /* Can only happen with delayed DSACK + discard craziness */ 1505 if (unlikely(skb == tcp_write_queue_head(sk))) 1506 goto fallback; 1507 prev = tcp_write_queue_prev(sk, skb); 1508 1509 if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) 1510 goto fallback; 1511 1512 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && 1513 !before(end_seq, TCP_SKB_CB(skb)->end_seq); 1514 1515 if (in_sack) { 1516 len = skb->len; 1517 pcount = tcp_skb_pcount(skb); 1518 mss = tcp_skb_seglen(skb); 1519 1520 /* TODO: Fix DSACKs to not fragment already SACKed and we can 1521 * drop this restriction as unnecessary 1522 */ 1523 if (mss != tcp_skb_seglen(prev)) 1524 goto fallback; 1525 } else { 1526 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq)) 1527 goto noop; 1528 /* CHECKME: This is non-MSS split case only?, this will 1529 * cause skipped skbs due to advancing loop btw, original 1530 * has that feature too 1531 */ 1532 if (tcp_skb_pcount(skb) <= 1) 1533 goto noop; 1534 1535 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq); 1536 if (!in_sack) { 1537 /* TODO: head merge to next could be attempted here 1538 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)), 1539 * though it might not be worth of the additional hassle 1540 * 1541 * ...we can probably just fallback to what was done 1542 * previously. We could try merging non-SACKed ones 1543 * as well but it probably isn't going to buy off 1544 * because later SACKs might again split them, and 1545 * it would make skb timestamp tracking considerably 1546 * harder problem. 1547 */ 1548 goto fallback; 1549 } 1550 1551 len = end_seq - TCP_SKB_CB(skb)->seq; 1552 BUG_ON(len < 0); 1553 BUG_ON(len > skb->len); 1554 1555 /* MSS boundaries should be honoured or else pcount will 1556 * severely break even though it makes things bit trickier. 1557 * Optimize common case to avoid most of the divides 1558 */ 1559 mss = tcp_skb_mss(skb); 1560 1561 /* TODO: Fix DSACKs to not fragment already SACKed and we can 1562 * drop this restriction as unnecessary 1563 */ 1564 if (mss != tcp_skb_seglen(prev)) 1565 goto fallback; 1566 1567 if (len == mss) { 1568 pcount = 1; 1569 } else if (len < mss) { 1570 goto noop; 1571 } else { 1572 pcount = len / mss; 1573 len = pcount * mss; 1574 } 1575 } 1576 1577 if (!skb_shift(prev, skb, len)) 1578 goto fallback; 1579 if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack)) 1580 goto out; 1581 1582 /* Hole filled allows collapsing with the next as well, this is very 1583 * useful when hole on every nth skb pattern happens 1584 */ 1585 if (prev == tcp_write_queue_tail(sk)) 1586 goto out; 1587 skb = tcp_write_queue_next(sk, prev); 1588 1589 if (!skb_can_shift(skb) || 1590 (skb == tcp_send_head(sk)) || 1591 ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) || 1592 (mss != tcp_skb_seglen(skb))) 1593 goto out; 1594 1595 len = skb->len; 1596 if (skb_shift(prev, skb, len)) { 1597 pcount += tcp_skb_pcount(skb); 1598 tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0); 1599 } 1600 1601out: 1602 state->fack_count += pcount; 1603 return prev; 1604 1605noop: 1606 return skb; 1607 1608fallback: 1609 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK); 1610 return NULL; 1611} 1612 1613static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk, 1614 struct tcp_sack_block *next_dup, 1615 struct tcp_sacktag_state *state, 1616 u32 start_seq, u32 end_seq, 1617 int dup_sack_in) 1618{ 1619 struct tcp_sock *tp = tcp_sk(sk); 1620 struct sk_buff *tmp; 1621 1622 tcp_for_write_queue_from(skb, sk) { 1623 int in_sack = 0; 1624 int dup_sack = dup_sack_in; 1625 1626 if (skb == tcp_send_head(sk)) 1627 break; 1628 1629 /* queue is in-order => we can short-circuit the walk early */ 1630 if (!before(TCP_SKB_CB(skb)->seq, end_seq)) 1631 break; 1632 1633 if ((next_dup != NULL) && 1634 before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) { 1635 in_sack = tcp_match_skb_to_sack(sk, skb, 1636 next_dup->start_seq, 1637 next_dup->end_seq); 1638 if (in_sack > 0) 1639 dup_sack = 1; 1640 } 1641 1642 /* skb reference here is a bit tricky to get right, since 1643 * shifting can eat and free both this skb and the next, 1644 * so not even _safe variant of the loop is enough. 1645 */ 1646 if (in_sack <= 0) { 1647 tmp = tcp_shift_skb_data(sk, skb, state, 1648 start_seq, end_seq, dup_sack); 1649 if (tmp != NULL) { 1650 if (tmp != skb) { 1651 skb = tmp; 1652 continue; 1653 } 1654 1655 in_sack = 0; 1656 } else { 1657 in_sack = tcp_match_skb_to_sack(sk, skb, 1658 start_seq, 1659 end_seq); 1660 } 1661 } 1662 1663 if (unlikely(in_sack < 0)) 1664 break; 1665 1666 if (in_sack) { 1667 TCP_SKB_CB(skb)->sacked = tcp_sacktag_one(skb, sk, 1668 state, 1669 dup_sack, 1670 tcp_skb_pcount(skb)); 1671 1672 if (!before(TCP_SKB_CB(skb)->seq, 1673 tcp_highest_sack_seq(tp))) 1674 tcp_advance_highest_sack(sk, skb); 1675 } 1676 1677 state->fack_count += tcp_skb_pcount(skb); 1678 } 1679 return skb; 1680} 1681 1682/* Avoid all extra work that is being done by sacktag while walking in 1683 * a normal way 1684 */ 1685static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk, 1686 struct tcp_sacktag_state *state, 1687 u32 skip_to_seq) 1688{ 1689 tcp_for_write_queue_from(skb, sk) { 1690 if (skb == tcp_send_head(sk)) 1691 break; 1692 1693 if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq)) 1694 break; 1695 1696 state->fack_count += tcp_skb_pcount(skb); 1697 } 1698 return skb; 1699} 1700 1701static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb, 1702 struct sock *sk, 1703 struct tcp_sack_block *next_dup, 1704 struct tcp_sacktag_state *state, 1705 u32 skip_to_seq) 1706{ 1707 if (next_dup == NULL) 1708 return skb; 1709 1710 if (before(next_dup->start_seq, skip_to_seq)) { 1711 skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq); 1712 skb = tcp_sacktag_walk(skb, sk, NULL, state, 1713 next_dup->start_seq, next_dup->end_seq, 1714 1); 1715 } 1716 1717 return skb; 1718} 1719 1720static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache) 1721{ 1722 return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache); 1723} 1724 1725static int 1726tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb, 1727 u32 prior_snd_una) 1728{ 1729 const struct inet_connection_sock *icsk = inet_csk(sk); 1730 struct tcp_sock *tp = tcp_sk(sk); 1731 const unsigned char *ptr = (skb_transport_header(ack_skb) + 1732 TCP_SKB_CB(ack_skb)->sacked); 1733 struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2); 1734 struct tcp_sack_block sp[TCP_NUM_SACKS]; 1735 struct tcp_sack_block *cache; 1736 struct tcp_sacktag_state state; 1737 struct sk_buff *skb; 1738 int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3); 1739 int used_sacks; 1740 int found_dup_sack = 0; 1741 int i, j; 1742 int first_sack_index; 1743 1744 state.flag = 0; 1745 state.reord = tp->packets_out; 1746 1747 if (!tp->sacked_out) { 1748 if (WARN_ON(tp->fackets_out)) 1749 tp->fackets_out = 0; 1750 tcp_highest_sack_reset(sk); 1751 } 1752 1753 found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire, 1754 num_sacks, prior_snd_una); 1755 if (found_dup_sack) 1756 state.flag |= FLAG_DSACKING_ACK; 1757 1758 /* Eliminate too old ACKs, but take into 1759 * account more or less fresh ones, they can 1760 * contain valid SACK info. 1761 */ 1762 if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window)) 1763 return 0; 1764 1765 if (!tp->packets_out) 1766 goto out; 1767 1768 used_sacks = 0; 1769 first_sack_index = 0; 1770 for (i = 0; i < num_sacks; i++) { 1771 int dup_sack = !i && found_dup_sack; 1772 1773 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq); 1774 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq); 1775 1776 if (!tcp_is_sackblock_valid(tp, dup_sack, 1777 sp[used_sacks].start_seq, 1778 sp[used_sacks].end_seq)) { 1779 int mib_idx; 1780 1781 if (dup_sack) { 1782 if (!tp->undo_marker) 1783 mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO; 1784 else 1785 mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD; 1786 } else { 1787 /* Don't count olds caused by ACK reordering */ 1788 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) && 1789 !after(sp[used_sacks].end_seq, tp->snd_una)) 1790 continue; 1791 mib_idx = LINUX_MIB_TCPSACKDISCARD; 1792 } 1793 1794 NET_INC_STATS_BH(sock_net(sk), mib_idx); 1795 if (i == 0) 1796 first_sack_index = -1; 1797 continue; 1798 } 1799 1800 /* Ignore very old stuff early */ 1801 if (!after(sp[used_sacks].end_seq, prior_snd_una)) 1802 continue; 1803 1804 used_sacks++; 1805 } 1806 1807 /* order SACK blocks to allow in order walk of the retrans queue */ 1808 for (i = used_sacks - 1; i > 0; i--) { 1809 for (j = 0; j < i; j++) { 1810 if (after(sp[j].start_seq, sp[j + 1].start_seq)) { 1811 swap(sp[j], sp[j + 1]); 1812 1813 /* Track where the first SACK block goes to */ 1814 if (j == first_sack_index) 1815 first_sack_index = j + 1; 1816 } 1817 } 1818 } 1819 1820 skb = tcp_write_queue_head(sk); 1821 state.fack_count = 0; 1822 i = 0; 1823 1824 if (!tp->sacked_out) { 1825 /* It's already past, so skip checking against it */ 1826 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache); 1827 } else { 1828 cache = tp->recv_sack_cache; 1829 /* Skip empty blocks in at head of the cache */ 1830 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq && 1831 !cache->end_seq) 1832 cache++; 1833 } 1834 1835 while (i < used_sacks) { 1836 u32 start_seq = sp[i].start_seq; 1837 u32 end_seq = sp[i].end_seq; 1838 int dup_sack = (found_dup_sack && (i == first_sack_index)); 1839 struct tcp_sack_block *next_dup = NULL; 1840 1841 if (found_dup_sack && ((i + 1) == first_sack_index)) 1842 next_dup = &sp[i + 1]; 1843 1844 /* Skip too early cached blocks */ 1845 while (tcp_sack_cache_ok(tp, cache) && 1846 !before(start_seq, cache->end_seq)) 1847 cache++; 1848 1849 /* Can skip some work by looking recv_sack_cache? */ 1850 if (tcp_sack_cache_ok(tp, cache) && !dup_sack && 1851 after(end_seq, cache->start_seq)) { 1852 1853 /* Head todo? */ 1854 if (before(start_seq, cache->start_seq)) { 1855 skb = tcp_sacktag_skip(skb, sk, &state, 1856 start_seq); 1857 skb = tcp_sacktag_walk(skb, sk, next_dup, 1858 &state, 1859 start_seq, 1860 cache->start_seq, 1861 dup_sack); 1862 } 1863 1864 /* Rest of the block already fully processed? */ 1865 if (!after(end_seq, cache->end_seq)) 1866 goto advance_sp; 1867 1868 skb = tcp_maybe_skipping_dsack(skb, sk, next_dup, 1869 &state, 1870 cache->end_seq); 1871 1872 /* ...tail remains todo... */ 1873 if (tcp_highest_sack_seq(tp) == cache->end_seq) { 1874 /* ...but better entrypoint exists! */ 1875 skb = tcp_highest_sack(sk); 1876 if (skb == NULL) 1877 break; 1878 state.fack_count = tp->fackets_out; 1879 cache++; 1880 goto walk; 1881 } 1882 1883 skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq); 1884 /* Check overlap against next cached too (past this one already) */ 1885 cache++; 1886 continue; 1887 } 1888 1889 if (!before(start_seq, tcp_highest_sack_seq(tp))) { 1890 skb = tcp_highest_sack(sk); 1891 if (skb == NULL) 1892 break; 1893 state.fack_count = tp->fackets_out; 1894 } 1895 skb = tcp_sacktag_skip(skb, sk, &state, start_seq); 1896 1897walk: 1898 skb = tcp_sacktag_walk(skb, sk, next_dup, &state, 1899 start_seq, end_seq, dup_sack); 1900 1901advance_sp: 1902 /* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct 1903 * due to in-order walk 1904 */ 1905 if (after(end_seq, tp->frto_highmark)) 1906 state.flag &= ~FLAG_ONLY_ORIG_SACKED; 1907 1908 i++; 1909 } 1910 1911 /* Clear the head of the cache sack blocks so we can skip it next time */ 1912 for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) { 1913 tp->recv_sack_cache[i].start_seq = 0; 1914 tp->recv_sack_cache[i].end_seq = 0; 1915 } 1916 for (j = 0; j < used_sacks; j++) 1917 tp->recv_sack_cache[i++] = sp[j]; 1918 1919 tcp_mark_lost_retrans(sk); 1920 1921 tcp_verify_left_out(tp); 1922 1923 if ((state.reord < tp->fackets_out) && 1924 ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) && 1925 (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark))) 1926 tcp_update_reordering(sk, tp->fackets_out - state.reord, 0); 1927 1928out: 1929 1930#if FASTRETRANS_DEBUG > 0 1931 WARN_ON((int)tp->sacked_out < 0); 1932 WARN_ON((int)tp->lost_out < 0); 1933 WARN_ON((int)tp->retrans_out < 0); 1934 WARN_ON((int)tcp_packets_in_flight(tp) < 0); 1935#endif 1936 return state.flag; 1937} 1938 1939/* Limits sacked_out so that sum with lost_out isn't ever larger than 1940 * packets_out. Returns zero if sacked_out adjustement wasn't necessary. 1941 */ 1942static int tcp_limit_reno_sacked(struct tcp_sock *tp) 1943{ 1944 u32 holes; 1945 1946 holes = max(tp->lost_out, 1U); 1947 holes = min(holes, tp->packets_out); 1948 1949 if ((tp->sacked_out + holes) > tp->packets_out) { 1950 tp->sacked_out = tp->packets_out - holes; 1951 return 1; 1952 } 1953 return 0; 1954} 1955 1956/* If we receive more dupacks than we expected counting segments 1957 * in assumption of absent reordering, interpret this as reordering. 1958 * The only another reason could be bug in receiver TCP. 1959 */ 1960static void tcp_check_reno_reordering(struct sock *sk, const int addend) 1961{ 1962 struct tcp_sock *tp = tcp_sk(sk); 1963 if (tcp_limit_reno_sacked(tp)) 1964 tcp_update_reordering(sk, tp->packets_out + addend, 0); 1965} 1966 1967/* Emulate SACKs for SACKless connection: account for a new dupack. */ 1968 1969static void tcp_add_reno_sack(struct sock *sk) 1970{ 1971 struct tcp_sock *tp = tcp_sk(sk); 1972 tp->sacked_out++; 1973 tcp_check_reno_reordering(sk, 0); 1974 tcp_verify_left_out(tp); 1975} 1976 1977/* Account for ACK, ACKing some data in Reno Recovery phase. */ 1978 1979static void tcp_remove_reno_sacks(struct sock *sk, int acked) 1980{ 1981 struct tcp_sock *tp = tcp_sk(sk); 1982 1983 if (acked > 0) { 1984 /* One ACK acked hole. The rest eat duplicate ACKs. */ 1985 if (acked - 1 >= tp->sacked_out) 1986 tp->sacked_out = 0; 1987 else 1988 tp->sacked_out -= acked - 1; 1989 } 1990 tcp_check_reno_reordering(sk, acked); 1991 tcp_verify_left_out(tp); 1992} 1993 1994static inline void tcp_reset_reno_sack(struct tcp_sock *tp) 1995{ 1996 tp->sacked_out = 0; 1997} 1998 1999static int tcp_is_sackfrto(const struct tcp_sock *tp) 2000{ 2001 return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp); 2002} 2003 2004/* F-RTO can only be used if TCP has never retransmitted anything other than 2005 * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here) 2006 */ 2007int tcp_use_frto(struct sock *sk) 2008{ 2009 const struct tcp_sock *tp = tcp_sk(sk); 2010 const struct inet_connection_sock *icsk = inet_csk(sk); 2011 struct sk_buff *skb; 2012 2013 if (!sysctl_tcp_frto) 2014 return 0; 2015 2016 /* MTU probe and F-RTO won't really play nicely along currently */ 2017 if (icsk->icsk_mtup.probe_size) 2018 return 0; 2019 2020 if (tcp_is_sackfrto(tp)) 2021 return 1; 2022 2023 /* Avoid expensive walking of rexmit queue if possible */ 2024 if (tp->retrans_out > 1) 2025 return 0; 2026 2027 skb = tcp_write_queue_head(sk); 2028 if (tcp_skb_is_last(sk, skb)) 2029 return 1; 2030 skb = tcp_write_queue_next(sk, skb); /* Skips head */ 2031 tcp_for_write_queue_from(skb, sk) { 2032 if (skb == tcp_send_head(sk)) 2033 break; 2034 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) 2035 return 0; 2036 /* Short-circuit when first non-SACKed skb has been checked */ 2037 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) 2038 break; 2039 } 2040 return 1; 2041} 2042 2043/* RTO occurred, but do not yet enter Loss state. Instead, defer RTO 2044 * recovery a bit and use heuristics in tcp_process_frto() to detect if 2045 * the RTO was spurious. Only clear SACKED_RETRANS of the head here to 2046 * keep retrans_out counting accurate (with SACK F-RTO, other than head 2047 * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS 2048 * bits are handled if the Loss state is really to be entered (in 2049 * tcp_enter_frto_loss). 2050 * 2051 * Do like tcp_enter_loss() would; when RTO expires the second time it 2052 * does: 2053 * "Reduce ssthresh if it has not yet been made inside this window." 2054 */ 2055void tcp_enter_frto(struct sock *sk) 2056{ 2057 const struct inet_connection_sock *icsk = inet_csk(sk); 2058 struct tcp_sock *tp = tcp_sk(sk); 2059 struct sk_buff *skb; 2060 2061 if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) || 2062 tp->snd_una == tp->high_seq || 2063 ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) && 2064 !icsk->icsk_retransmits)) { 2065 tp->prior_ssthresh = tcp_current_ssthresh(sk); 2066 /* Our state is too optimistic in ssthresh() call because cwnd 2067 * is not reduced until tcp_enter_frto_loss() when previous F-RTO 2068 * recovery has not yet completed. Pattern would be this: RTO, 2069 * Cumulative ACK, RTO (2xRTO for the same segment does not end 2070 * up here twice). 2071 * RFC4138 should be more specific on what to do, even though 2072 * RTO is quite unlikely to occur after the first Cumulative ACK 2073 * due to back-off and complexity of triggering events ... 2074 */ 2075 if (tp->frto_counter) { 2076 u32 stored_cwnd; 2077 stored_cwnd = tp->snd_cwnd; 2078 tp->snd_cwnd = 2; 2079 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); 2080 tp->snd_cwnd = stored_cwnd; 2081 } else { 2082 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); 2083 } 2084 /* ... in theory, cong.control module could do "any tricks" in 2085 * ssthresh(), which means that ca_state, lost bits and lost_out 2086 * counter would have to be faked before the call occurs. We 2087 * consider that too expensive, unlikely and hacky, so modules 2088 * using these in ssthresh() must deal these incompatibility 2089 * issues if they receives CA_EVENT_FRTO and frto_counter != 0 2090 */ 2091 tcp_ca_event(sk, CA_EVENT_FRTO); 2092 } 2093 2094 tp->undo_marker = tp->snd_una; 2095 tp->undo_retrans = 0; 2096 2097 skb = tcp_write_queue_head(sk); 2098 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) 2099 tp->undo_marker = 0; 2100 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) { 2101 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; 2102 tp->retrans_out -= tcp_skb_pcount(skb); 2103 } 2104 tcp_verify_left_out(tp); 2105 2106 /* Too bad if TCP was application limited */ 2107 tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1); 2108 2109 /* Earlier loss recovery underway (see RFC4138; Appendix B). 2110 * The last condition is necessary at least in tp->frto_counter case. 2111 */ 2112 if (tcp_is_sackfrto(tp) && (tp->frto_counter || 2113 ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) && 2114 after(tp->high_seq, tp->snd_una)) { 2115 tp->frto_highmark = tp->high_seq; 2116 } else { 2117 tp->frto_highmark = tp->snd_nxt; 2118 } 2119 tcp_set_ca_state(sk, TCP_CA_Disorder); 2120 tp->high_seq = tp->snd_nxt; 2121 tp->frto_counter = 1; 2122} 2123 2124/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO, 2125 * which indicates that we should follow the traditional RTO recovery, 2126 * i.e. mark everything lost and do go-back-N retransmission. 2127 */ 2128static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag) 2129{ 2130 struct tcp_sock *tp = tcp_sk(sk); 2131 struct sk_buff *skb; 2132 2133 tp->lost_out = 0; 2134 tp->retrans_out = 0; 2135 if (tcp_is_reno(tp)) 2136 tcp_reset_reno_sack(tp); 2137 2138 tcp_for_write_queue(skb, sk) { 2139 if (skb == tcp_send_head(sk)) 2140 break; 2141 2142 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; 2143 /* 2144 * Count the retransmission made on RTO correctly (only when 2145 * waiting for the first ACK and did not get it)... 2146 */ 2147 if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) { 2148 /* For some reason this R-bit might get cleared? */ 2149 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) 2150 tp->retrans_out += tcp_skb_pcount(skb); 2151 /* ...enter this if branch just for the first segment */ 2152 flag |= FLAG_DATA_ACKED; 2153 } else { 2154 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) 2155 tp->undo_marker = 0; 2156 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; 2157 } 2158 2159 /* Marking forward transmissions that were made after RTO lost 2160 * can cause unnecessary retransmissions in some scenarios, 2161 * SACK blocks will mitigate that in some but not in all cases. 2162 * We used to not mark them but it was causing break-ups with 2163 * receivers that do only in-order receival. 2164 * 2165 * TODO: we could detect presence of such receiver and select 2166 * different behavior per flow. 2167 */ 2168 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) { 2169 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 2170 tp->lost_out += tcp_skb_pcount(skb); 2171 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq; 2172 } 2173 } 2174 tcp_verify_left_out(tp); 2175 2176 tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments; 2177 tp->snd_cwnd_cnt = 0; 2178 tp->snd_cwnd_stamp = tcp_time_stamp; 2179 tp->frto_counter = 0; 2180 tp->bytes_acked = 0; 2181 2182 tp->reordering = min_t(unsigned int, tp->reordering, 2183 sysctl_tcp_reordering); 2184 tcp_set_ca_state(sk, TCP_CA_Loss); 2185 tp->high_seq = tp->snd_nxt; 2186 TCP_ECN_queue_cwr(tp); 2187 2188 tcp_clear_all_retrans_hints(tp); 2189} 2190 2191static void tcp_clear_retrans_partial(struct tcp_sock *tp) 2192{ 2193 tp->retrans_out = 0; 2194 tp->lost_out = 0; 2195 2196 tp->undo_marker = 0; 2197 tp->undo_retrans = 0; 2198} 2199 2200void tcp_clear_retrans(struct tcp_sock *tp) 2201{ 2202 tcp_clear_retrans_partial(tp); 2203 2204 tp->fackets_out = 0; 2205 tp->sacked_out = 0; 2206} 2207 2208/* Enter Loss state. If "how" is not zero, forget all SACK information 2209 * and reset tags completely, otherwise preserve SACKs. If receiver 2210 * dropped its ofo queue, we will know this due to reneging detection. 2211 */ 2212void tcp_enter_loss(struct sock *sk, int how) 2213{ 2214 const struct inet_connection_sock *icsk = inet_csk(sk); 2215 struct tcp_sock *tp = tcp_sk(sk); 2216 struct sk_buff *skb; 2217 2218 /* Reduce ssthresh if it has not yet been made inside this window. */ 2219 if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq || 2220 (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) { 2221 tp->prior_ssthresh = tcp_current_ssthresh(sk); 2222 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); 2223 tcp_ca_event(sk, CA_EVENT_LOSS); 2224 } 2225 tp->snd_cwnd = 1; 2226 tp->snd_cwnd_cnt = 0; 2227 tp->snd_cwnd_stamp = tcp_time_stamp; 2228 2229 tp->bytes_acked = 0; 2230 tcp_clear_retrans_partial(tp); 2231 2232 if (tcp_is_reno(tp)) 2233 tcp_reset_reno_sack(tp); 2234 2235 if (!how) { 2236 /* Push undo marker, if it was plain RTO and nothing 2237 * was retransmitted. */ 2238 tp->undo_marker = tp->snd_una; 2239 } else { 2240 tp->sacked_out = 0; 2241 tp->fackets_out = 0; 2242 } 2243 tcp_clear_all_retrans_hints(tp); 2244 2245 tcp_for_write_queue(skb, sk) { 2246 if (skb == tcp_send_head(sk)) 2247 break; 2248 2249 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) 2250 tp->undo_marker = 0; 2251 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED; 2252 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) { 2253 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED; 2254 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 2255 tp->lost_out += tcp_skb_pcount(skb); 2256 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq; 2257 } 2258 } 2259 tcp_verify_left_out(tp); 2260 2261 tp->reordering = min_t(unsigned int, tp->reordering, 2262 sysctl_tcp_reordering); 2263 tcp_set_ca_state(sk, TCP_CA_Loss); 2264 tp->high_seq = tp->snd_nxt; 2265 TCP_ECN_queue_cwr(tp); 2266 /* Abort F-RTO algorithm if one is in progress */ 2267 tp->frto_counter = 0; 2268} 2269 2270/* If ACK arrived pointing to a remembered SACK, it means that our 2271 * remembered SACKs do not reflect real state of receiver i.e. 2272 * receiver _host_ is heavily congested (or buggy). 2273 * 2274 * Do processing similar to RTO timeout. 2275 */ 2276static int tcp_check_sack_reneging(struct sock *sk, int flag) 2277{ 2278 if (flag & FLAG_SACK_RENEGING) { 2279 struct inet_connection_sock *icsk = inet_csk(sk); 2280 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING); 2281 2282 tcp_enter_loss(sk, 1); 2283 icsk->icsk_retransmits++; 2284 tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); 2285 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 2286 icsk->icsk_rto, TCP_RTO_MAX); 2287 return 1; 2288 } 2289 return 0; 2290} 2291 2292static inline int tcp_fackets_out(const struct tcp_sock *tp) 2293{ 2294 return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out; 2295} 2296 2297/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs 2298 * counter when SACK is enabled (without SACK, sacked_out is used for 2299 * that purpose). 2300 * 2301 * Instead, with FACK TCP uses fackets_out that includes both SACKed 2302 * segments up to the highest received SACK block so far and holes in 2303 * between them. 2304 * 2305 * With reordering, holes may still be in flight, so RFC3517 recovery 2306 * uses pure sacked_out (total number of SACKed segments) even though 2307 * it violates the RFC that uses duplicate ACKs, often these are equal 2308 * but when e.g. out-of-window ACKs or packet duplication occurs, 2309 * they differ. Since neither occurs due to loss, TCP should really 2310 * ignore them. 2311 */ 2312static inline int tcp_dupack_heuristics(const struct tcp_sock *tp) 2313{ 2314 return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1; 2315} 2316 2317static inline int tcp_skb_timedout(const struct sock *sk, 2318 const struct sk_buff *skb) 2319{ 2320 return tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto; 2321} 2322 2323static inline int tcp_head_timedout(const struct sock *sk) 2324{ 2325 const struct tcp_sock *tp = tcp_sk(sk); 2326 2327 return tp->packets_out && 2328 tcp_skb_timedout(sk, tcp_write_queue_head(sk)); 2329} 2330 2331/* Linux NewReno/SACK/FACK/ECN state machine. 2332 * -------------------------------------- 2333 * 2334 * "Open" Normal state, no dubious events, fast path. 2335 * "Disorder" In all the respects it is "Open", 2336 * but requires a bit more attention. It is entered when 2337 * we see some SACKs or dupacks. It is split of "Open" 2338 * mainly to move some processing from fast path to slow one. 2339 * "CWR" CWND was reduced due to some Congestion Notification event. 2340 * It can be ECN, ICMP source quench, local device congestion. 2341 * "Recovery" CWND was reduced, we are fast-retransmitting. 2342 * "Loss" CWND was reduced due to RTO timeout or SACK reneging. 2343 * 2344 * tcp_fastretrans_alert() is entered: 2345 * - each incoming ACK, if state is not "Open" 2346 * - when arrived ACK is unusual, namely: 2347 * * SACK 2348 * * Duplicate ACK. 2349 * * ECN ECE. 2350 * 2351 * Counting packets in flight is pretty simple. 2352 * 2353 * in_flight = packets_out - left_out + retrans_out 2354 * 2355 * packets_out is SND.NXT-SND.UNA counted in packets. 2356 * 2357 * retrans_out is number of retransmitted segments. 2358 * 2359 * left_out is number of segments left network, but not ACKed yet. 2360 * 2361 * left_out = sacked_out + lost_out 2362 * 2363 * sacked_out: Packets, which arrived to receiver out of order 2364 * and hence not ACKed. With SACKs this number is simply 2365 * amount of SACKed data. Even without SACKs 2366 * it is easy to give pretty reliable estimate of this number, 2367 * counting duplicate ACKs. 2368 * 2369 * lost_out: Packets lost by network. TCP has no explicit 2370 * "loss notification" feedback from network (for now). 2371 * It means that this number can be only _guessed_. 2372 * Actually, it is the heuristics to predict lossage that 2373 * distinguishes different algorithms. 2374 * 2375 * F.e. after RTO, when all the queue is considered as lost, 2376 * lost_out = packets_out and in_flight = retrans_out. 2377 * 2378 * Essentially, we have now two algorithms counting 2379 * lost packets. 2380 * 2381 * FACK: It is the simplest heuristics. As soon as we decided 2382 * that something is lost, we decide that _all_ not SACKed 2383 * packets until the most forward SACK are lost. I.e. 2384 * lost_out = fackets_out - sacked_out and left_out = fackets_out. 2385 * It is absolutely correct estimate, if network does not reorder 2386 * packets. And it loses any connection to reality when reordering 2387 * takes place. We use FACK by default until reordering 2388 * is suspected on the path to this destination. 2389 * 2390 * NewReno: when Recovery is entered, we assume that one segment 2391 * is lost (classic Reno). While we are in Recovery and 2392 * a partial ACK arrives, we assume that one more packet 2393 * is lost (NewReno). This heuristics are the same in NewReno 2394 * and SACK. 2395 * 2396 * Imagine, that's all! Forget about all this shamanism about CWND inflation 2397 * deflation etc. CWND is real congestion window, never inflated, changes 2398 * only according to classic VJ rules. 2399 * 2400 * Really tricky (and requiring careful tuning) part of algorithm 2401 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue(). 2402 * The first determines the moment _when_ we should reduce CWND and, 2403 * hence, slow down forward transmission. In fact, it determines the moment 2404 * when we decide that hole is caused by loss, rather than by a reorder. 2405 * 2406 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill 2407 * holes, caused by lost packets. 2408 * 2409 * And the most logically complicated part of algorithm is undo 2410 * heuristics. We detect false retransmits due to both too early 2411 * fast retransmit (reordering) and underestimated RTO, analyzing 2412 * timestamps and D-SACKs. When we detect that some segments were 2413 * retransmitted by mistake and CWND reduction was wrong, we undo 2414 * window reduction and abort recovery phase. This logic is hidden 2415 * inside several functions named tcp_try_undo_<something>. 2416 */ 2417 2418/* This function decides, when we should leave Disordered state 2419 * and enter Recovery phase, reducing congestion window. 2420 * 2421 * Main question: may we further continue forward transmission 2422 * with the same cwnd? 2423 */ 2424static int tcp_time_to_recover(struct sock *sk) 2425{ 2426 struct tcp_sock *tp = tcp_sk(sk); 2427 __u32 packets_out; 2428 2429 /* Do not perform any recovery during F-RTO algorithm */ 2430 if (tp->frto_counter) 2431 return 0; 2432 2433 /* Trick#1: The loss is proven. */ 2434 if (tp->lost_out) 2435 return 1; 2436 2437 /* Not-A-Trick#2 : Classic rule... */ 2438 if (tcp_dupack_heuristics(tp) > tp->reordering) 2439 return 1; 2440 2441 /* Trick#3 : when we use RFC2988 timer restart, fast 2442 * retransmit can be triggered by timeout of queue head. 2443 */ 2444 if (tcp_is_fack(tp) && tcp_head_timedout(sk)) 2445 return 1; 2446 2447 /* Trick#4: It is still not OK... But will it be useful to delay 2448 * recovery more? 2449 */ 2450 packets_out = tp->packets_out; 2451 if (packets_out <= tp->reordering && 2452 tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) && 2453 !tcp_may_send_now(sk)) { 2454 /* We have nothing to send. This connection is limited 2455 * either by receiver window or by application. 2456 */ 2457 return 1; 2458 } 2459 2460 /* If a thin stream is detected, retransmit after first 2461 * received dupack. Employ only if SACK is supported in order 2462 * to avoid possible corner-case series of spurious retransmissions 2463 * Use only if there are no unsent data. 2464 */ 2465 if ((tp->thin_dupack || sysctl_tcp_thin_dupack) && 2466 tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 && 2467 tcp_is_sack(tp) && !tcp_send_head(sk)) 2468 return 1; 2469 2470 return 0; 2471} 2472 2473/* New heuristics: it is possible only after we switched to restart timer 2474 * each time when something is ACKed. Hence, we can detect timed out packets 2475 * during fast retransmit without falling to slow start. 2476 * 2477 * Usefulness of this as is very questionable, since we should know which of 2478 * the segments is the next to timeout which is relatively expensive to find 2479 * in general case unless we add some data structure just for that. The 2480 * current approach certainly won't find the right one too often and when it 2481 * finally does find _something_ it usually marks large part of the window 2482 * right away (because a retransmission with a larger timestamp blocks the 2483 * loop from advancing). -ij 2484 */ 2485static void tcp_timeout_skbs(struct sock *sk) 2486{ 2487 struct tcp_sock *tp = tcp_sk(sk); 2488 struct sk_buff *skb; 2489 2490 if (!tcp_is_fack(tp) || !tcp_head_timedout(sk)) 2491 return; 2492 2493 skb = tp->scoreboard_skb_hint; 2494 if (tp->scoreboard_skb_hint == NULL) 2495 skb = tcp_write_queue_head(sk); 2496 2497 tcp_for_write_queue_from(skb, sk) { 2498 if (skb == tcp_send_head(sk)) 2499 break; 2500 if (!tcp_skb_timedout(sk, skb)) 2501 break; 2502 2503 tcp_skb_mark_lost(tp, skb); 2504 } 2505 2506 tp->scoreboard_skb_hint = skb; 2507 2508 tcp_verify_left_out(tp); 2509} 2510 2511/* Detect loss in event "A" above by marking head of queue up as lost. 2512 * For FACK or non-SACK(Reno) senders, the first "packets" number of segments 2513 * are considered lost. For RFC3517 SACK, a segment is considered lost if it 2514 * has at least tp->reordering SACKed seqments above it; "packets" refers to 2515 * the maximum SACKed segments to pass before reaching this limit. 2516 */ 2517static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head) 2518{ 2519 struct tcp_sock *tp = tcp_sk(sk); 2520 struct sk_buff *skb; 2521 int cnt, oldcnt; 2522 int err; 2523 unsigned int mss; 2524 /* Use SACK to deduce losses of new sequences sent during recovery */ 2525 const u32 loss_high = tcp_is_sack(tp) ? tp->snd_nxt : tp->high_seq; 2526 2527 WARN_ON(packets > tp->packets_out); 2528 if (tp->lost_skb_hint) { 2529 skb = tp->lost_skb_hint; 2530 cnt = tp->lost_cnt_hint; 2531 /* Head already handled? */ 2532 if (mark_head && skb != tcp_write_queue_head(sk)) 2533 return; 2534 } else { 2535 skb = tcp_write_queue_head(sk); 2536 cnt = 0; 2537 } 2538 2539 tcp_for_write_queue_from(skb, sk) { 2540 if (skb == tcp_send_head(sk)) 2541 break; 2542 /* TODO: do this better */ 2543 /* this is not the most efficient way to do this... */ 2544 tp->lost_skb_hint = skb; 2545 tp->lost_cnt_hint = cnt; 2546 2547 if (after(TCP_SKB_CB(skb)->end_seq, loss_high)) 2548 break; 2549 2550 oldcnt = cnt; 2551 if (tcp_is_fack(tp) || tcp_is_reno(tp) || 2552 (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) 2553 cnt += tcp_skb_pcount(skb); 2554 2555 if (cnt > packets) { 2556 if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) || 2557 (oldcnt >= packets)) 2558 break; 2559 2560 mss = skb_shinfo(skb)->gso_size; 2561 err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss); 2562 if (err < 0) 2563 break; 2564 cnt = packets; 2565 } 2566 2567 tcp_skb_mark_lost(tp, skb); 2568 2569 if (mark_head) 2570 break; 2571 } 2572 tcp_verify_left_out(tp); 2573} 2574 2575/* Account newly detected lost packet(s) */ 2576 2577static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit) 2578{ 2579 struct tcp_sock *tp = tcp_sk(sk); 2580 2581 if (tcp_is_reno(tp)) { 2582 tcp_mark_head_lost(sk, 1, 1); 2583 } else if (tcp_is_fack(tp)) { 2584 int lost = tp->fackets_out - tp->reordering; 2585 if (lost <= 0) 2586 lost = 1; 2587 tcp_mark_head_lost(sk, lost, 0); 2588 } else { 2589 int sacked_upto = tp->sacked_out - tp->reordering; 2590 if (sacked_upto >= 0) 2591 tcp_mark_head_lost(sk, sacked_upto, 0); 2592 else if (fast_rexmit) 2593 tcp_mark_head_lost(sk, 1, 1); 2594 } 2595 2596 tcp_timeout_skbs(sk); 2597} 2598 2599/* CWND moderation, preventing bursts due to too big ACKs 2600 * in dubious situations. 2601 */ 2602static inline void tcp_moderate_cwnd(struct tcp_sock *tp) 2603{ 2604 tp->snd_cwnd = min(tp->snd_cwnd, 2605 tcp_packets_in_flight(tp) + tcp_max_burst(tp)); 2606 tp->snd_cwnd_stamp = tcp_time_stamp; 2607} 2608 2609/* Lower bound on congestion window is slow start threshold 2610 * unless congestion avoidance choice decides to overide it. 2611 */ 2612static inline u32 tcp_cwnd_min(const struct sock *sk) 2613{ 2614 const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops; 2615 2616 return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh; 2617} 2618 2619/* Decrease cwnd each second ack. */ 2620static void tcp_cwnd_down(struct sock *sk, int flag) 2621{ 2622 struct tcp_sock *tp = tcp_sk(sk); 2623 int decr = tp->snd_cwnd_cnt + 1; 2624 2625 if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) || 2626 (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) { 2627 tp->snd_cwnd_cnt = decr & 1; 2628 decr >>= 1; 2629 2630 if (decr && tp->snd_cwnd > tcp_cwnd_min(sk)) 2631 tp->snd_cwnd -= decr; 2632 2633 tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1); 2634 tp->snd_cwnd_stamp = tcp_time_stamp; 2635 } 2636} 2637 2638/* Nothing was retransmitted or returned timestamp is less 2639 * than timestamp of the first retransmission. 2640 */ 2641static inline int tcp_packet_delayed(const struct tcp_sock *tp) 2642{ 2643 return !tp->retrans_stamp || 2644 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && 2645 before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp)); 2646} 2647 2648/* Undo procedures. */ 2649 2650#if FASTRETRANS_DEBUG > 1 2651static void DBGUNDO(struct sock *sk, const char *msg) 2652{ 2653 struct tcp_sock *tp = tcp_sk(sk); 2654 struct inet_sock *inet = inet_sk(sk); 2655 2656 if (sk->sk_family == AF_INET) { 2657 printk(KERN_DEBUG "Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n", 2658 msg, 2659 &inet->inet_daddr, ntohs(inet->inet_dport), 2660 tp->snd_cwnd, tcp_left_out(tp), 2661 tp->snd_ssthresh, tp->prior_ssthresh, 2662 tp->packets_out); 2663 } 2664#if IS_ENABLED(CONFIG_IPV6) 2665 else if (sk->sk_family == AF_INET6) { 2666 struct ipv6_pinfo *np = inet6_sk(sk); 2667 printk(KERN_DEBUG "Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n", 2668 msg, 2669 &np->daddr, ntohs(inet->inet_dport), 2670 tp->snd_cwnd, tcp_left_out(tp), 2671 tp->snd_ssthresh, tp->prior_ssthresh, 2672 tp->packets_out); 2673 } 2674#endif 2675} 2676#else 2677#define DBGUNDO(x...) do { } while (0) 2678#endif 2679 2680static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh) 2681{ 2682 struct tcp_sock *tp = tcp_sk(sk); 2683 2684 if (tp->prior_ssthresh) { 2685 const struct inet_connection_sock *icsk = inet_csk(sk); 2686 2687 if (icsk->icsk_ca_ops->undo_cwnd) 2688 tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk); 2689 else 2690 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1); 2691 2692 if (undo_ssthresh && tp->prior_ssthresh > tp->snd_ssthresh) { 2693 tp->snd_ssthresh = tp->prior_ssthresh; 2694 TCP_ECN_withdraw_cwr(tp); 2695 } 2696 } else { 2697 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh); 2698 } 2699 tp->snd_cwnd_stamp = tcp_time_stamp; 2700} 2701 2702static inline int tcp_may_undo(const struct tcp_sock *tp) 2703{ 2704 return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp)); 2705} 2706 2707/* People celebrate: "We love our President!" */ 2708static int tcp_try_undo_recovery(struct sock *sk) 2709{ 2710 struct tcp_sock *tp = tcp_sk(sk); 2711 2712 if (tcp_may_undo(tp)) { 2713 int mib_idx; 2714 2715 /* Happy end! We did not retransmit anything 2716 * or our original transmission succeeded. 2717 */ 2718 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans"); 2719 tcp_undo_cwr(sk, true); 2720 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss) 2721 mib_idx = LINUX_MIB_TCPLOSSUNDO; 2722 else 2723 mib_idx = LINUX_MIB_TCPFULLUNDO; 2724 2725 NET_INC_STATS_BH(sock_net(sk), mib_idx); 2726 tp->undo_marker = 0; 2727 } 2728 if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) { 2729 /* Hold old state until something *above* high_seq 2730 * is ACKed. For Reno it is MUST to prevent false 2731 * fast retransmits (RFC2582). SACK TCP is safe. */ 2732 tcp_moderate_cwnd(tp); 2733 return 1; 2734 } 2735 tcp_set_ca_state(sk, TCP_CA_Open); 2736 return 0; 2737} 2738 2739/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */ 2740static void tcp_try_undo_dsack(struct sock *sk) 2741{ 2742 struct tcp_sock *tp = tcp_sk(sk); 2743 2744 if (tp->undo_marker && !tp->undo_retrans) { 2745 DBGUNDO(sk, "D-SACK"); 2746 tcp_undo_cwr(sk, true); 2747 tp->undo_marker = 0; 2748 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO); 2749 } 2750} 2751 2752/* We can clear retrans_stamp when there are no retransmissions in the 2753 * window. It would seem that it is trivially available for us in 2754 * tp->retrans_out, however, that kind of assumptions doesn't consider 2755 * what will happen if errors occur when sending retransmission for the 2756 * second time. ...It could the that such segment has only 2757 * TCPCB_EVER_RETRANS set at the present time. It seems that checking 2758 * the head skb is enough except for some reneging corner cases that 2759 * are not worth the effort. 2760 * 2761 * Main reason for all this complexity is the fact that connection dying 2762 * time now depends on the validity of the retrans_stamp, in particular, 2763 * that successive retransmissions of a segment must not advance 2764 * retrans_stamp under any conditions. 2765 */ 2766static int tcp_any_retrans_done(const struct sock *sk) 2767{ 2768 const struct tcp_sock *tp = tcp_sk(sk); 2769 struct sk_buff *skb; 2770 2771 if (tp->retrans_out) 2772 return 1; 2773 2774 skb = tcp_write_queue_head(sk); 2775 if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS)) 2776 return 1; 2777 2778 return 0; 2779} 2780 2781/* Undo during fast recovery after partial ACK. */ 2782 2783static int tcp_try_undo_partial(struct sock *sk, int acked) 2784{ 2785 struct tcp_sock *tp = tcp_sk(sk); 2786 /* Partial ACK arrived. Force Hoe's retransmit. */ 2787 int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering); 2788 2789 if (tcp_may_undo(tp)) { 2790 /* Plain luck! Hole if filled with delayed 2791 * packet, rather than with a retransmit. 2792 */ 2793 if (!tcp_any_retrans_done(sk)) 2794 tp->retrans_stamp = 0; 2795 2796 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1); 2797 2798 DBGUNDO(sk, "Hoe"); 2799 tcp_undo_cwr(sk, false); 2800 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO); 2801 2802 /* So... Do not make Hoe's retransmit yet. 2803 * If the first packet was delayed, the rest 2804 * ones are most probably delayed as well. 2805 */ 2806 failed = 0; 2807 } 2808 return failed; 2809} 2810 2811/* Undo during loss recovery after partial ACK. */ 2812static int tcp_try_undo_loss(struct sock *sk) 2813{ 2814 struct tcp_sock *tp = tcp_sk(sk); 2815 2816 if (tcp_may_undo(tp)) { 2817 struct sk_buff *skb; 2818 tcp_for_write_queue(skb, sk) { 2819 if (skb == tcp_send_head(sk)) 2820 break; 2821 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; 2822 } 2823 2824 tcp_clear_all_retrans_hints(tp); 2825 2826 DBGUNDO(sk, "partial loss"); 2827 tp->lost_out = 0; 2828 tcp_undo_cwr(sk, true); 2829 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO); 2830 inet_csk(sk)->icsk_retransmits = 0; 2831 tp->undo_marker = 0; 2832 if (tcp_is_sack(tp)) 2833 tcp_set_ca_state(sk, TCP_CA_Open); 2834 return 1; 2835 } 2836 return 0; 2837} 2838 2839static inline void tcp_complete_cwr(struct sock *sk) 2840{ 2841 struct tcp_sock *tp = tcp_sk(sk); 2842 2843 /* Do not moderate cwnd if it's already undone in cwr or recovery. */ 2844 if (tp->undo_marker) { 2845 if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR) 2846 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh); 2847 else /* PRR */ 2848 tp->snd_cwnd = tp->snd_ssthresh; 2849 tp->snd_cwnd_stamp = tcp_time_stamp; 2850 } 2851 tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR); 2852} 2853 2854static void tcp_try_keep_open(struct sock *sk) 2855{ 2856 struct tcp_sock *tp = tcp_sk(sk); 2857 int state = TCP_CA_Open; 2858 2859 if (tcp_left_out(tp) || tcp_any_retrans_done(sk)) 2860 state = TCP_CA_Disorder; 2861 2862 if (inet_csk(sk)->icsk_ca_state != state) { 2863 tcp_set_ca_state(sk, state); 2864 tp->high_seq = tp->snd_nxt; 2865 } 2866} 2867 2868static void tcp_try_to_open(struct sock *sk, int flag) 2869{ 2870 struct tcp_sock *tp = tcp_sk(sk); 2871 2872 tcp_verify_left_out(tp); 2873 2874 if (!tp->frto_counter && !tcp_any_retrans_done(sk)) 2875 tp->retrans_stamp = 0; 2876 2877 if (flag & FLAG_ECE) 2878 tcp_enter_cwr(sk, 1); 2879 2880 if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) { 2881 tcp_try_keep_open(sk); 2882 if (inet_csk(sk)->icsk_ca_state != TCP_CA_Open) 2883 tcp_moderate_cwnd(tp); 2884 } else { 2885 tcp_cwnd_down(sk, flag); 2886 } 2887} 2888 2889static void tcp_mtup_probe_failed(struct sock *sk) 2890{ 2891 struct inet_connection_sock *icsk = inet_csk(sk); 2892 2893 icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1; 2894 icsk->icsk_mtup.probe_size = 0; 2895} 2896 2897static void tcp_mtup_probe_success(struct sock *sk) 2898{ 2899 struct tcp_sock *tp = tcp_sk(sk); 2900 struct inet_connection_sock *icsk = inet_csk(sk); 2901 2902 /* FIXME: breaks with very large cwnd */ 2903 tp->prior_ssthresh = tcp_current_ssthresh(sk); 2904 tp->snd_cwnd = tp->snd_cwnd * 2905 tcp_mss_to_mtu(sk, tp->mss_cache) / 2906 icsk->icsk_mtup.probe_size; 2907 tp->snd_cwnd_cnt = 0; 2908 tp->snd_cwnd_stamp = tcp_time_stamp; 2909 tp->snd_ssthresh = tcp_current_ssthresh(sk); 2910 2911 icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size; 2912 icsk->icsk_mtup.probe_size = 0; 2913 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 2914} 2915 2916/* Do a simple retransmit without using the backoff mechanisms in 2917 * tcp_timer. This is used for path mtu discovery. 2918 * The socket is already locked here. 2919 */ 2920void tcp_simple_retransmit(struct sock *sk) 2921{ 2922 const struct inet_connection_sock *icsk = inet_csk(sk); 2923 struct tcp_sock *tp = tcp_sk(sk); 2924 struct sk_buff *skb; 2925 unsigned int mss = tcp_current_mss(sk); 2926 u32 prior_lost = tp->lost_out; 2927 2928 tcp_for_write_queue(skb, sk) { 2929 if (skb == tcp_send_head(sk)) 2930 break; 2931 if (tcp_skb_seglen(skb) > mss && 2932 !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) { 2933 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) { 2934 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; 2935 tp->retrans_out -= tcp_skb_pcount(skb); 2936 } 2937 tcp_skb_mark_lost_uncond_verify(tp, skb); 2938 } 2939 } 2940 2941 tcp_clear_retrans_hints_partial(tp); 2942 2943 if (prior_lost == tp->lost_out) 2944 return; 2945 2946 if (tcp_is_reno(tp)) 2947 tcp_limit_reno_sacked(tp); 2948 2949 tcp_verify_left_out(tp); 2950 2951 /* Don't muck with the congestion window here. 2952 * Reason is that we do not increase amount of _data_ 2953 * in network, but units changed and effective 2954 * cwnd/ssthresh really reduced now. 2955 */ 2956 if (icsk->icsk_ca_state != TCP_CA_Loss) { 2957 tp->high_seq = tp->snd_nxt; 2958 tp->snd_ssthresh = tcp_current_ssthresh(sk); 2959 tp->prior_ssthresh = 0; 2960 tp->undo_marker = 0; 2961 tcp_set_ca_state(sk, TCP_CA_Loss); 2962 } 2963 tcp_xmit_retransmit_queue(sk); 2964} 2965EXPORT_SYMBOL(tcp_simple_retransmit); 2966 2967/* This function implements the PRR algorithm, specifcally the PRR-SSRB 2968 * (proportional rate reduction with slow start reduction bound) as described in 2969 * http://www.ietf.org/id/draft-mathis-tcpm-proportional-rate-reduction-01.txt. 2970 * It computes the number of packets to send (sndcnt) based on packets newly 2971 * delivered: 2972 * 1) If the packets in flight is larger than ssthresh, PRR spreads the 2973 * cwnd reductions across a full RTT. 2974 * 2) If packets in flight is lower than ssthresh (such as due to excess 2975 * losses and/or application stalls), do not perform any further cwnd 2976 * reductions, but instead slow start up to ssthresh. 2977 */ 2978static void tcp_update_cwnd_in_recovery(struct sock *sk, int newly_acked_sacked, 2979 int fast_rexmit, int flag) 2980{ 2981 struct tcp_sock *tp = tcp_sk(sk); 2982 int sndcnt = 0; 2983 int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp); 2984 2985 if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) { 2986 u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered + 2987 tp->prior_cwnd - 1; 2988 sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out; 2989 } else { 2990 sndcnt = min_t(int, delta, 2991 max_t(int, tp->prr_delivered - tp->prr_out, 2992 newly_acked_sacked) + 1); 2993 } 2994 2995 sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0)); 2996 tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt; 2997} 2998 2999/* Process an event, which can update packets-in-flight not trivially. 3000 * Main goal of this function is to calculate new estimate for left_out, 3001 * taking into account both packets sitting in receiver's buffer and 3002 * packets lost by network. 3003 * 3004 * Besides that it does CWND reduction, when packet loss is detected 3005 * and changes state of machine. 3006 * 3007 * It does _not_ decide what to send, it is made in function 3008 * tcp_xmit_retransmit_queue(). 3009 */ 3010static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, 3011 int newly_acked_sacked, bool is_dupack, 3012 int flag) 3013{ 3014 struct inet_connection_sock *icsk = inet_csk(sk); 3015 struct tcp_sock *tp = tcp_sk(sk); 3016 int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) && 3017 (tcp_fackets_out(tp) > tp->reordering)); 3018 int fast_rexmit = 0, mib_idx; 3019 3020 if (WARN_ON(!tp->packets_out && tp->sacked_out)) 3021 tp->sacked_out = 0; 3022 if (WARN_ON(!tp->sacked_out && tp->fackets_out)) 3023 tp->fackets_out = 0; 3024 3025 /* Now state machine starts. 3026 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */ 3027 if (flag & FLAG_ECE) 3028 tp->prior_ssthresh = 0; 3029 3030 /* B. In all the states check for reneging SACKs. */ 3031 if (tcp_check_sack_reneging(sk, flag)) 3032 return; 3033 3034 /* C. Check consistency of the current state. */ 3035 tcp_verify_left_out(tp); 3036 3037 /* D. Check state exit conditions. State can be terminated 3038 * when high_seq is ACKed. */ 3039 if (icsk->icsk_ca_state == TCP_CA_Open) { 3040 WARN_ON(tp->retrans_out != 0); 3041 tp->retrans_stamp = 0; 3042 } else if (!before(tp->snd_una, tp->high_seq)) { 3043 switch (icsk->icsk_ca_state) { 3044 case TCP_CA_Loss: 3045 icsk->icsk_retransmits = 0; 3046 if (tcp_try_undo_recovery(sk)) 3047 return; 3048 break; 3049 3050 case TCP_CA_CWR: 3051 /* CWR is to be held something *above* high_seq 3052 * is ACKed for CWR bit to reach receiver. */ 3053 if (tp->snd_una != tp->high_seq) { 3054 tcp_complete_cwr(sk); 3055 tcp_set_ca_state(sk, TCP_CA_Open); 3056 } 3057 break; 3058 3059 case TCP_CA_Recovery: 3060 if (tcp_is_reno(tp)) 3061 tcp_reset_reno_sack(tp); 3062 if (tcp_try_undo_recovery(sk)) 3063 return; 3064 tcp_complete_cwr(sk); 3065 break; 3066 } 3067 } 3068 3069 /* E. Process state. */ 3070 switch (icsk->icsk_ca_state) { 3071 case TCP_CA_Recovery: 3072 if (!(flag & FLAG_SND_UNA_ADVANCED)) { 3073 if (tcp_is_reno(tp) && is_dupack) 3074 tcp_add_reno_sack(sk); 3075 } else 3076 do_lost = tcp_try_undo_partial(sk, pkts_acked); 3077 break; 3078 case TCP_CA_Loss: 3079 if (flag & FLAG_DATA_ACKED) 3080 icsk->icsk_retransmits = 0; 3081 if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED) 3082 tcp_reset_reno_sack(tp); 3083 if (!tcp_try_undo_loss(sk)) { 3084 tcp_moderate_cwnd(tp); 3085 tcp_xmit_retransmit_queue(sk); 3086 return; 3087 } 3088 if (icsk->icsk_ca_state != TCP_CA_Open) 3089 return; 3090 /* Loss is undone; fall through to processing in Open state. */ 3091 default: 3092 if (tcp_is_reno(tp)) { 3093 if (flag & FLAG_SND_UNA_ADVANCED) 3094 tcp_reset_reno_sack(tp); 3095 if (is_dupack) 3096 tcp_add_reno_sack(sk); 3097 } 3098 3099 if (icsk->icsk_ca_state <= TCP_CA_Disorder) 3100 tcp_try_undo_dsack(sk); 3101 3102 if (!tcp_time_to_recover(sk)) { 3103 tcp_try_to_open(sk, flag); 3104 return; 3105 } 3106 3107 /* MTU probe failure: don't reduce cwnd */ 3108 if (icsk->icsk_ca_state < TCP_CA_CWR && 3109 icsk->icsk_mtup.probe_size && 3110 tp->snd_una == tp->mtu_probe.probe_seq_start) { 3111 tcp_mtup_probe_failed(sk); 3112 /* Restores the reduction we did in tcp_mtup_probe() */ 3113 tp->snd_cwnd++; 3114 tcp_simple_retransmit(sk); 3115 return; 3116 } 3117 3118 /* Otherwise enter Recovery state */ 3119 3120 if (tcp_is_reno(tp)) 3121 mib_idx = LINUX_MIB_TCPRENORECOVERY; 3122 else 3123 mib_idx = LINUX_MIB_TCPSACKRECOVERY; 3124 3125 NET_INC_STATS_BH(sock_net(sk), mib_idx); 3126 3127 tp->high_seq = tp->snd_nxt; 3128 tp->prior_ssthresh = 0; 3129 tp->undo_marker = tp->snd_una; 3130 tp->undo_retrans = tp->retrans_out; 3131 3132 if (icsk->icsk_ca_state < TCP_CA_CWR) { 3133 if (!(flag & FLAG_ECE)) 3134 tp->prior_ssthresh = tcp_current_ssthresh(sk); 3135 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); 3136 TCP_ECN_queue_cwr(tp); 3137 } 3138 3139 tp->bytes_acked = 0; 3140 tp->snd_cwnd_cnt = 0; 3141 tp->prior_cwnd = tp->snd_cwnd; 3142 tp->prr_delivered = 0; 3143 tp->prr_out = 0; 3144 tcp_set_ca_state(sk, TCP_CA_Recovery); 3145 fast_rexmit = 1; 3146 } 3147 3148 if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk))) 3149 tcp_update_scoreboard(sk, fast_rexmit); 3150 tp->prr_delivered += newly_acked_sacked; 3151 tcp_update_cwnd_in_recovery(sk, newly_acked_sacked, fast_rexmit, flag); 3152 tcp_xmit_retransmit_queue(sk); 3153} 3154 3155void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt) 3156{ 3157 tcp_rtt_estimator(sk, seq_rtt); 3158 tcp_set_rto(sk); 3159 inet_csk(sk)->icsk_backoff = 0; 3160} 3161EXPORT_SYMBOL(tcp_valid_rtt_meas); 3162 3163/* Read draft-ietf-tcplw-high-performance before mucking 3164 * with this code. (Supersedes RFC1323) 3165 */ 3166static void tcp_ack_saw_tstamp(struct sock *sk, int flag) 3167{ 3168 /* RTTM Rule: A TSecr value received in a segment is used to 3169 * update the averaged RTT measurement only if the segment 3170 * acknowledges some new data, i.e., only if it advances the 3171 * left edge of the send window. 3172 * 3173 * See draft-ietf-tcplw-high-performance-00, section 3.3. 3174 * 1998/04/10 Andrey V. Savochkin <saw@msu.ru> 3175 * 3176 * Changed: reset backoff as soon as we see the first valid sample. 3177 * If we do not, we get strongly overestimated rto. With timestamps 3178 * samples are accepted even from very old segments: f.e., when rtt=1 3179 * increases to 8, we retransmit 5 times and after 8 seconds delayed 3180 * answer arrives rto becomes 120 seconds! If at least one of segments 3181 * in window is lost... Voila. --ANK (010210) 3182 */ 3183 struct tcp_sock *tp = tcp_sk(sk); 3184 3185 tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr); 3186} 3187 3188static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag) 3189{ 3190 /* We don't have a timestamp. Can only use 3191 * packets that are not retransmitted to determine 3192 * rtt estimates. Also, we must not reset the 3193 * backoff for rto until we get a non-retransmitted 3194 * packet. This allows us to deal with a situation 3195 * where the network delay has increased suddenly. 3196 * I.e. Karn's algorithm. (SIGCOMM '87, p5.) 3197 */ 3198 3199 if (flag & FLAG_RETRANS_DATA_ACKED) 3200 return; 3201 3202 tcp_valid_rtt_meas(sk, seq_rtt); 3203} 3204 3205static inline void tcp_ack_update_rtt(struct sock *sk, const int flag, 3206 const s32 seq_rtt) 3207{ 3208 const struct tcp_sock *tp = tcp_sk(sk); 3209 /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */ 3210 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) 3211 tcp_ack_saw_tstamp(sk, flag); 3212 else if (seq_rtt >= 0) 3213 tcp_ack_no_tstamp(sk, seq_rtt, flag); 3214} 3215 3216static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) 3217{ 3218 const struct inet_connection_sock *icsk = inet_csk(sk); 3219 icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight); 3220 tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp; 3221} 3222 3223/* Restart timer after forward progress on connection. 3224 * RFC2988 recommends to restart timer to now+rto. 3225 */ 3226static void tcp_rearm_rto(struct sock *sk) 3227{ 3228 const struct tcp_sock *tp = tcp_sk(sk); 3229 3230 if (!tp->packets_out) { 3231 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS); 3232 } else { 3233 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 3234 inet_csk(sk)->icsk_rto, TCP_RTO_MAX); 3235 } 3236} 3237 3238/* If we get here, the whole TSO packet has not been acked. */ 3239static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb) 3240{ 3241 struct tcp_sock *tp = tcp_sk(sk); 3242 u32 packets_acked; 3243 3244 BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)); 3245 3246 packets_acked = tcp_skb_pcount(skb); 3247 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) 3248 return 0; 3249 packets_acked -= tcp_skb_pcount(skb); 3250 3251 if (packets_acked) { 3252 BUG_ON(tcp_skb_pcount(skb) == 0); 3253 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)); 3254 } 3255 3256 return packets_acked; 3257} 3258 3259/* Remove acknowledged frames from the retransmission queue. If our packet 3260 * is before the ack sequence we can discard it as it's confirmed to have 3261 * arrived at the other end. 3262 */ 3263static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets, 3264 u32 prior_snd_una) 3265{ 3266 struct tcp_sock *tp = tcp_sk(sk); 3267 const struct inet_connection_sock *icsk = inet_csk(sk); 3268 struct sk_buff *skb; 3269 u32 now = tcp_time_stamp; 3270 int fully_acked = 1; 3271 int flag = 0; 3272 u32 pkts_acked = 0; 3273 u32 reord = tp->packets_out; 3274 u32 prior_sacked = tp->sacked_out; 3275 s32 seq_rtt = -1; 3276 s32 ca_seq_rtt = -1; 3277 ktime_t last_ackt = net_invalid_timestamp(); 3278 3279 while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) { 3280 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 3281 u32 acked_pcount; 3282 u8 sacked = scb->sacked; 3283 3284 /* Determine how many packets and what bytes were acked, tso and else */ 3285 if (after(scb->end_seq, tp->snd_una)) { 3286 if (tcp_skb_pcount(skb) == 1 || 3287 !after(tp->snd_una, scb->seq)) 3288 break; 3289 3290 acked_pcount = tcp_tso_acked(sk, skb); 3291 if (!acked_pcount) 3292 break; 3293 3294 fully_acked = 0; 3295 } else { 3296 acked_pcount = tcp_skb_pcount(skb); 3297 } 3298 3299 if (sacked & TCPCB_RETRANS) { 3300 if (sacked & TCPCB_SACKED_RETRANS) 3301 tp->retrans_out -= acked_pcount; 3302 flag |= FLAG_RETRANS_DATA_ACKED; 3303 ca_seq_rtt = -1; 3304 seq_rtt = -1; 3305 if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1)) 3306 flag |= FLAG_NONHEAD_RETRANS_ACKED; 3307 } else { 3308 ca_seq_rtt = now - scb->when; 3309 last_ackt = skb->tstamp; 3310 if (seq_rtt < 0) { 3311 seq_rtt = ca_seq_rtt; 3312 } 3313 if (!(sacked & TCPCB_SACKED_ACKED)) 3314 reord = min(pkts_acked, reord); 3315 } 3316 3317 if (sacked & TCPCB_SACKED_ACKED) 3318 tp->sacked_out -= acked_pcount; 3319 if (sacked & TCPCB_LOST) 3320 tp->lost_out -= acked_pcount; 3321 3322 tp->packets_out -= acked_pcount; 3323 pkts_acked += acked_pcount; 3324 3325 /* Initial outgoing SYN's get put onto the write_queue 3326 * just like anything else we transmit. It is not 3327 * true data, and if we misinform our callers that 3328 * this ACK acks real data, we will erroneously exit 3329 * connection startup slow start one packet too 3330 * quickly. This is severely frowned upon behavior. 3331 */ 3332 if (!(scb->tcp_flags & TCPHDR_SYN)) { 3333 flag |= FLAG_DATA_ACKED; 3334 } else { 3335 flag |= FLAG_SYN_ACKED; 3336 tp->retrans_stamp = 0; 3337 } 3338 3339 if (!fully_acked) 3340 break; 3341 3342 tcp_unlink_write_queue(skb, sk); 3343 sk_wmem_free_skb(sk, skb); 3344 tp->scoreboard_skb_hint = NULL; 3345 if (skb == tp->retransmit_skb_hint) 3346 tp->retransmit_skb_hint = NULL; 3347 if (skb == tp->lost_skb_hint) 3348 tp->lost_skb_hint = NULL; 3349 } 3350 3351 if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una))) 3352 tp->snd_up = tp->snd_una; 3353 3354 if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) 3355 flag |= FLAG_SACK_RENEGING; 3356 3357 if (flag & FLAG_ACKED) { 3358 const struct tcp_congestion_ops *ca_ops 3359 = inet_csk(sk)->icsk_ca_ops; 3360 3361 if (unlikely(icsk->icsk_mtup.probe_size && 3362 !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) { 3363 tcp_mtup_probe_success(sk); 3364 } 3365 3366 tcp_ack_update_rtt(sk, flag, seq_rtt); 3367 tcp_rearm_rto(sk); 3368 3369 if (tcp_is_reno(tp)) { 3370 tcp_remove_reno_sacks(sk, pkts_acked); 3371 } else { 3372 int delta; 3373 3374 /* Non-retransmitted hole got filled? That's reordering */ 3375 if (reord < prior_fackets) 3376 tcp_update_reordering(sk, tp->fackets_out - reord, 0); 3377 3378 delta = tcp_is_fack(tp) ? pkts_acked : 3379 prior_sacked - tp->sacked_out; 3380 tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta); 3381 } 3382 3383 tp->fackets_out -= min(pkts_acked, tp->fackets_out); 3384 3385 if (ca_ops->pkts_acked) { 3386 s32 rtt_us = -1; 3387 3388 /* Is the ACK triggering packet unambiguous? */ 3389 if (!(flag & FLAG_RETRANS_DATA_ACKED)) { 3390 /* High resolution needed and available? */ 3391 if (ca_ops->flags & TCP_CONG_RTT_STAMP && 3392 !ktime_equal(last_ackt, 3393 net_invalid_timestamp())) 3394 rtt_us = ktime_us_delta(ktime_get_real(), 3395 last_ackt); 3396 else if (ca_seq_rtt >= 0) 3397 rtt_us = jiffies_to_usecs(ca_seq_rtt); 3398 } 3399 3400 ca_ops->pkts_acked(sk, pkts_acked, rtt_us); 3401 } 3402 } 3403 3404#if FASTRETRANS_DEBUG > 0 3405 WARN_ON((int)tp->sacked_out < 0); 3406 WARN_ON((int)tp->lost_out < 0); 3407 WARN_ON((int)tp->retrans_out < 0); 3408 if (!tp->packets_out && tcp_is_sack(tp)) { 3409 icsk = inet_csk(sk); 3410 if (tp->lost_out) { 3411 printk(KERN_DEBUG "Leak l=%u %d\n", 3412 tp->lost_out, icsk->icsk_ca_state); 3413 tp->lost_out = 0; 3414 } 3415 if (tp->sacked_out) { 3416 printk(KERN_DEBUG "Leak s=%u %d\n", 3417 tp->sacked_out, icsk->icsk_ca_state); 3418 tp->sacked_out = 0; 3419 } 3420 if (tp->retrans_out) { 3421 printk(KERN_DEBUG "Leak r=%u %d\n", 3422 tp->retrans_out, icsk->icsk_ca_state); 3423 tp->retrans_out = 0; 3424 } 3425 } 3426#endif 3427 return flag; 3428} 3429 3430static void tcp_ack_probe(struct sock *sk) 3431{ 3432 const struct tcp_sock *tp = tcp_sk(sk); 3433 struct inet_connection_sock *icsk = inet_csk(sk); 3434 3435 /* Was it a usable window open? */ 3436 3437 if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) { 3438 icsk->icsk_backoff = 0; 3439 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0); 3440 /* Socket must be waked up by subsequent tcp_data_snd_check(). 3441 * This function is not for random using! 3442 */ 3443 } else { 3444 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, 3445 min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX), 3446 TCP_RTO_MAX); 3447 } 3448} 3449 3450static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag) 3451{ 3452 return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) || 3453 inet_csk(sk)->icsk_ca_state != TCP_CA_Open; 3454} 3455 3456static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag) 3457{ 3458 const struct tcp_sock *tp = tcp_sk(sk); 3459 return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) && 3460 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR)); 3461} 3462 3463/* Check that window update is acceptable. 3464 * The function assumes that snd_una<=ack<=snd_next. 3465 */ 3466static inline int tcp_may_update_window(const struct tcp_sock *tp, 3467 const u32 ack, const u32 ack_seq, 3468 const u32 nwin) 3469{ 3470 return after(ack, tp->snd_una) || 3471 after(ack_seq, tp->snd_wl1) || 3472 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd); 3473} 3474 3475/* Update our send window. 3476 * 3477 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2 3478 * and in FreeBSD. NetBSD's one is even worse.) is wrong. 3479 */ 3480static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack, 3481 u32 ack_seq) 3482{ 3483 struct tcp_sock *tp = tcp_sk(sk); 3484 int flag = 0; 3485 u32 nwin = ntohs(tcp_hdr(skb)->window); 3486 3487 if (likely(!tcp_hdr(skb)->syn)) 3488 nwin <<= tp->rx_opt.snd_wscale; 3489 3490 if (tcp_may_update_window(tp, ack, ack_seq, nwin)) { 3491 flag |= FLAG_WIN_UPDATE; 3492 tcp_update_wl(tp, ack_seq); 3493 3494 if (tp->snd_wnd != nwin) { 3495 tp->snd_wnd = nwin; 3496 3497 /* Note, it is the only place, where 3498 * fast path is recovered for sending TCP. 3499 */ 3500 tp->pred_flags = 0; 3501 tcp_fast_path_check(sk); 3502 3503 if (nwin > tp->max_window) { 3504 tp->max_window = nwin; 3505 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie); 3506 } 3507 } 3508 } 3509 3510 tp->snd_una = ack; 3511 3512 return flag; 3513} 3514 3515/* A very conservative spurious RTO response algorithm: reduce cwnd and 3516 * continue in congestion avoidance. 3517 */ 3518static void tcp_conservative_spur_to_response(struct tcp_sock *tp) 3519{ 3520 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh); 3521 tp->snd_cwnd_cnt = 0; 3522 tp->bytes_acked = 0; 3523 TCP_ECN_queue_cwr(tp); 3524 tcp_moderate_cwnd(tp); 3525} 3526 3527/* A conservative spurious RTO response algorithm: reduce cwnd using 3528 * rate halving and continue in congestion avoidance. 3529 */ 3530static void tcp_ratehalving_spur_to_response(struct sock *sk) 3531{ 3532 tcp_enter_cwr(sk, 0); 3533} 3534 3535static void tcp_undo_spur_to_response(struct sock *sk, int flag) 3536{ 3537 if (flag & FLAG_ECE) 3538 tcp_ratehalving_spur_to_response(sk); 3539 else 3540 tcp_undo_cwr(sk, true); 3541} 3542 3543/* F-RTO spurious RTO detection algorithm (RFC4138) 3544 * 3545 * F-RTO affects during two new ACKs following RTO (well, almost, see inline 3546 * comments). State (ACK number) is kept in frto_counter. When ACK advances 3547 * window (but not to or beyond highest sequence sent before RTO): 3548 * On First ACK, send two new segments out. 3549 * On Second ACK, RTO was likely spurious. Do spurious response (response 3550 * algorithm is not part of the F-RTO detection algorithm 3551 * given in RFC4138 but can be selected separately). 3552 * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss 3553 * and TCP falls back to conventional RTO recovery. F-RTO allows overriding 3554 * of Nagle, this is done using frto_counter states 2 and 3, when a new data 3555 * segment of any size sent during F-RTO, state 2 is upgraded to 3. 3556 * 3557 * Rationale: if the RTO was spurious, new ACKs should arrive from the 3558 * original window even after we transmit two new data segments. 3559 * 3560 * SACK version: 3561 * on first step, wait until first cumulative ACK arrives, then move to 3562 * the second step. In second step, the next ACK decides. 3563 * 3564 * F-RTO is implemented (mainly) in four functions: 3565 * - tcp_use_frto() is used to determine if TCP is can use F-RTO 3566 * - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is 3567 * called when tcp_use_frto() showed green light 3568 * - tcp_process_frto() handles incoming ACKs during F-RTO algorithm 3569 * - tcp_enter_frto_loss() is called if there is not enough evidence 3570 * to prove that the RTO is indeed spurious. It transfers the control 3571 * from F-RTO to the conventional RTO recovery 3572 */ 3573static int tcp_process_frto(struct sock *sk, int flag) 3574{ 3575 struct tcp_sock *tp = tcp_sk(sk); 3576 3577 tcp_verify_left_out(tp); 3578 3579 /* Duplicate the behavior from Loss state (fastretrans_alert) */ 3580 if (flag & FLAG_DATA_ACKED) 3581 inet_csk(sk)->icsk_retransmits = 0; 3582 3583 if ((flag & FLAG_NONHEAD_RETRANS_ACKED) || 3584 ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED))) 3585 tp->undo_marker = 0; 3586 3587 if (!before(tp->snd_una, tp->frto_highmark)) { 3588 tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag); 3589 return 1; 3590 } 3591 3592 if (!tcp_is_sackfrto(tp)) { 3593 /* RFC4138 shortcoming in step 2; should also have case c): 3594 * ACK isn't duplicate nor advances window, e.g., opposite dir 3595 * data, winupdate 3596 */ 3597 if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP)) 3598 return 1; 3599 3600 if (!(flag & FLAG_DATA_ACKED)) { 3601 tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3), 3602 flag); 3603 return 1; 3604 } 3605 } else { 3606 if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) { 3607 /* Prevent sending of new data. */ 3608 tp->snd_cwnd = min(tp->snd_cwnd, 3609 tcp_packets_in_flight(tp)); 3610 return 1; 3611 } 3612 3613 if ((tp->frto_counter >= 2) && 3614 (!(flag & FLAG_FORWARD_PROGRESS) || 3615 ((flag & FLAG_DATA_SACKED) && 3616 !(flag & FLAG_ONLY_ORIG_SACKED)))) { 3617 /* RFC4138 shortcoming (see comment above) */ 3618 if (!(flag & FLAG_FORWARD_PROGRESS) && 3619 (flag & FLAG_NOT_DUP)) 3620 return 1; 3621 3622 tcp_enter_frto_loss(sk, 3, flag); 3623 return 1; 3624 } 3625 } 3626 3627 if (tp->frto_counter == 1) { 3628 /* tcp_may_send_now needs to see updated state */ 3629 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2; 3630 tp->frto_counter = 2; 3631 3632 if (!tcp_may_send_now(sk)) 3633 tcp_enter_frto_loss(sk, 2, flag); 3634 3635 return 1; 3636 } else { 3637 switch (sysctl_tcp_frto_response) { 3638 case 2: 3639 tcp_undo_spur_to_response(sk, flag); 3640 break; 3641 case 1: 3642 tcp_conservative_spur_to_response(tp); 3643 break; 3644 default: 3645 tcp_ratehalving_spur_to_response(sk); 3646 break; 3647 } 3648 tp->frto_counter = 0; 3649 tp->undo_marker = 0; 3650 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS); 3651 } 3652 return 0; 3653} 3654 3655/* This routine deals with incoming acks, but not outgoing ones. */ 3656static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 3657{ 3658 struct inet_connection_sock *icsk = inet_csk(sk); 3659 struct tcp_sock *tp = tcp_sk(sk); 3660 u32 prior_snd_una = tp->snd_una; 3661 u32 ack_seq = TCP_SKB_CB(skb)->seq; 3662 u32 ack = TCP_SKB_CB(skb)->ack_seq; 3663 bool is_dupack = false; 3664 u32 prior_in_flight; 3665 u32 prior_fackets; 3666 int prior_packets; 3667 int prior_sacked = tp->sacked_out; 3668 int pkts_acked = 0; 3669 int newly_acked_sacked = 0; 3670 int frto_cwnd = 0; 3671 3672 /* If the ack is older than previous acks 3673 * then we can probably ignore it. 3674 */ 3675 if (before(ack, prior_snd_una)) 3676 goto old_ack; 3677 3678 /* If the ack includes data we haven't sent yet, discard 3679 * this segment (RFC793 Section 3.9). 3680 */ 3681 if (after(ack, tp->snd_nxt)) 3682 goto invalid_ack; 3683 3684 if (after(ack, prior_snd_una)) 3685 flag |= FLAG_SND_UNA_ADVANCED; 3686 3687 if (sysctl_tcp_abc) { 3688 if (icsk->icsk_ca_state < TCP_CA_CWR) 3689 tp->bytes_acked += ack - prior_snd_una; 3690 else if (icsk->icsk_ca_state == TCP_CA_Loss) 3691 /* we assume just one segment left network */ 3692 tp->bytes_acked += min(ack - prior_snd_una, 3693 tp->mss_cache); 3694 } 3695 3696 prior_fackets = tp->fackets_out; 3697 prior_in_flight = tcp_packets_in_flight(tp); 3698 3699 if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) { 3700 /* Window is constant, pure forward advance. 3701 * No more checks are required. 3702 * Note, we use the fact that SND.UNA>=SND.WL2. 3703 */ 3704 tcp_update_wl(tp, ack_seq); 3705 tp->snd_una = ack; 3706 flag |= FLAG_WIN_UPDATE; 3707 3708 tcp_ca_event(sk, CA_EVENT_FAST_ACK); 3709 3710 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS); 3711 } else { 3712 if (ack_seq != TCP_SKB_CB(skb)->end_seq) 3713 flag |= FLAG_DATA; 3714 else 3715 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS); 3716 3717 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq); 3718 3719 if (TCP_SKB_CB(skb)->sacked) 3720 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una); 3721 3722 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb))) 3723 flag |= FLAG_ECE; 3724 3725 tcp_ca_event(sk, CA_EVENT_SLOW_ACK); 3726 } 3727 3728 /* We passed data and got it acked, remove any soft error 3729 * log. Something worked... 3730 */ 3731 sk->sk_err_soft = 0; 3732 icsk->icsk_probes_out = 0; 3733 tp->rcv_tstamp = tcp_time_stamp; 3734 prior_packets = tp->packets_out; 3735 if (!prior_packets) 3736 goto no_queue; 3737 3738 /* See if we can take anything off of the retransmit queue. */ 3739 flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una); 3740 3741 pkts_acked = prior_packets - tp->packets_out; 3742 newly_acked_sacked = (prior_packets - prior_sacked) - 3743 (tp->packets_out - tp->sacked_out); 3744 3745 if (tp->frto_counter) 3746 frto_cwnd = tcp_process_frto(sk, flag); 3747 /* Guarantee sacktag reordering detection against wrap-arounds */ 3748 if (before(tp->frto_highmark, tp->snd_una)) 3749 tp->frto_highmark = 0; 3750 3751 if (tcp_ack_is_dubious(sk, flag)) { 3752 /* Advance CWND, if state allows this. */ 3753 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd && 3754 tcp_may_raise_cwnd(sk, flag)) 3755 tcp_cong_avoid(sk, ack, prior_in_flight); 3756 is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP)); 3757 tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked, 3758 is_dupack, flag); 3759 } else { 3760 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd) 3761 tcp_cong_avoid(sk, ack, prior_in_flight); 3762 } 3763 3764 if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) 3765 dst_confirm(__sk_dst_get(sk)); 3766 3767 return 1; 3768 3769no_queue: 3770 /* If data was DSACKed, see if we can undo a cwnd reduction. */ 3771 if (flag & FLAG_DSACKING_ACK) 3772 tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked, 3773 is_dupack, flag); 3774 /* If this ack opens up a zero window, clear backoff. It was 3775 * being used to time the probes, and is probably far higher than 3776 * it needs to be for normal retransmission. 3777 */ 3778 if (tcp_send_head(sk)) 3779 tcp_ack_probe(sk); 3780 return 1; 3781 3782invalid_ack: 3783 SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt); 3784 return -1; 3785 3786old_ack: 3787 /* If data was SACKed, tag it and see if we should send more data. 3788 * If data was DSACKed, see if we can undo a cwnd reduction. 3789 */ 3790 if (TCP_SKB_CB(skb)->sacked) { 3791 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una); 3792 newly_acked_sacked = tp->sacked_out - prior_sacked; 3793 tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked, 3794 is_dupack, flag); 3795 } 3796 3797 SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt); 3798 return 0; 3799} 3800 3801/* Look for tcp options. Normally only called on SYN and SYNACK packets. 3802 * But, this can also be called on packets in the established flow when 3803 * the fast version below fails. 3804 */ 3805void tcp_parse_options(const struct sk_buff *skb, struct tcp_options_received *opt_rx, 3806 const u8 **hvpp, int estab) 3807{ 3808 const unsigned char *ptr; 3809 const struct tcphdr *th = tcp_hdr(skb); 3810 int length = (th->doff * 4) - sizeof(struct tcphdr); 3811 3812 ptr = (const unsigned char *)(th + 1); 3813 opt_rx->saw_tstamp = 0; 3814 3815 while (length > 0) { 3816 int opcode = *ptr++; 3817 int opsize; 3818 3819 switch (opcode) { 3820 case TCPOPT_EOL: 3821 return; 3822 case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */ 3823 length--; 3824 continue; 3825 default: 3826 opsize = *ptr++; 3827 if (opsize < 2) /* "silly options" */ 3828 return; 3829 if (opsize > length) 3830 return; /* don't parse partial options */ 3831 switch (opcode) { 3832 case TCPOPT_MSS: 3833 if (opsize == TCPOLEN_MSS && th->syn && !estab) { 3834 u16 in_mss = get_unaligned_be16(ptr); 3835 if (in_mss) { 3836 if (opt_rx->user_mss && 3837 opt_rx->user_mss < in_mss) 3838 in_mss = opt_rx->user_mss; 3839 opt_rx->mss_clamp = in_mss; 3840 } 3841 } 3842 break; 3843 case TCPOPT_WINDOW: 3844 if (opsize == TCPOLEN_WINDOW && th->syn && 3845 !estab && sysctl_tcp_window_scaling) { 3846 __u8 snd_wscale = *(__u8 *)ptr; 3847 opt_rx->wscale_ok = 1; 3848 if (snd_wscale > 14) { 3849 if (net_ratelimit()) 3850 printk(KERN_INFO "tcp_parse_options: Illegal window " 3851 "scaling value %d >14 received.\n", 3852 snd_wscale); 3853 snd_wscale = 14; 3854 } 3855 opt_rx->snd_wscale = snd_wscale; 3856 } 3857 break; 3858 case TCPOPT_TIMESTAMP: 3859 if ((opsize == TCPOLEN_TIMESTAMP) && 3860 ((estab && opt_rx->tstamp_ok) || 3861 (!estab && sysctl_tcp_timestamps))) { 3862 opt_rx->saw_tstamp = 1; 3863 opt_rx->rcv_tsval = get_unaligned_be32(ptr); 3864 opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4); 3865 } 3866 break; 3867 case TCPOPT_SACK_PERM: 3868 if (opsize == TCPOLEN_SACK_PERM && th->syn && 3869 !estab && sysctl_tcp_sack) { 3870 opt_rx->sack_ok = TCP_SACK_SEEN; 3871 tcp_sack_reset(opt_rx); 3872 } 3873 break; 3874 3875 case TCPOPT_SACK: 3876 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) && 3877 !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) && 3878 opt_rx->sack_ok) { 3879 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th; 3880 } 3881 break; 3882#ifdef CONFIG_TCP_MD5SIG 3883 case TCPOPT_MD5SIG: 3884 /* 3885 * The MD5 Hash has already been 3886 * checked (see tcp_v{4,6}_do_rcv()). 3887 */ 3888 break; 3889#endif 3890 case TCPOPT_COOKIE: 3891 /* This option is variable length. 3892 */ 3893 switch (opsize) { 3894 case TCPOLEN_COOKIE_BASE: 3895 /* not yet implemented */ 3896 break; 3897 case TCPOLEN_COOKIE_PAIR: 3898 /* not yet implemented */ 3899 break; 3900 case TCPOLEN_COOKIE_MIN+0: 3901 case TCPOLEN_COOKIE_MIN+2: 3902 case TCPOLEN_COOKIE_MIN+4: 3903 case TCPOLEN_COOKIE_MIN+6: 3904 case TCPOLEN_COOKIE_MAX: 3905 /* 16-bit multiple */ 3906 opt_rx->cookie_plus = opsize; 3907 *hvpp = ptr; 3908 break; 3909 default: 3910 /* ignore option */ 3911 break; 3912 } 3913 break; 3914 } 3915 3916 ptr += opsize-2; 3917 length -= opsize; 3918 } 3919 } 3920} 3921EXPORT_SYMBOL(tcp_parse_options); 3922 3923static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th) 3924{ 3925 const __be32 *ptr = (const __be32 *)(th + 1); 3926 3927 if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) 3928 | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) { 3929 tp->rx_opt.saw_tstamp = 1; 3930 ++ptr; 3931 tp->rx_opt.rcv_tsval = ntohl(*ptr); 3932 ++ptr; 3933 tp->rx_opt.rcv_tsecr = ntohl(*ptr); 3934 return 1; 3935 } 3936 return 0; 3937} 3938 3939/* Fast parse options. This hopes to only see timestamps. 3940 * If it is wrong it falls back on tcp_parse_options(). 3941 */ 3942static int tcp_fast_parse_options(const struct sk_buff *skb, 3943 const struct tcphdr *th, 3944 struct tcp_sock *tp, const u8 **hvpp) 3945{ 3946 /* In the spirit of fast parsing, compare doff directly to constant 3947 * values. Because equality is used, short doff can be ignored here. 3948 */ 3949 if (th->doff == (sizeof(*th) / 4)) { 3950 tp->rx_opt.saw_tstamp = 0; 3951 return 0; 3952 } else if (tp->rx_opt.tstamp_ok && 3953 th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) { 3954 if (tcp_parse_aligned_timestamp(tp, th)) 3955 return 1; 3956 } 3957 tcp_parse_options(skb, &tp->rx_opt, hvpp, 1); 3958 return 1; 3959} 3960 3961#ifdef CONFIG_TCP_MD5SIG 3962/* 3963 * Parse MD5 Signature option 3964 */ 3965const u8 *tcp_parse_md5sig_option(const struct tcphdr *th) 3966{ 3967 int length = (th->doff << 2) - sizeof(*th); 3968 const u8 *ptr = (const u8 *)(th + 1); 3969 3970 /* If the TCP option is too short, we can short cut */ 3971 if (length < TCPOLEN_MD5SIG) 3972 return NULL; 3973 3974 while (length > 0) { 3975 int opcode = *ptr++; 3976 int opsize; 3977 3978 switch(opcode) { 3979 case TCPOPT_EOL: 3980 return NULL; 3981 case TCPOPT_NOP: 3982 length--; 3983 continue; 3984 default: 3985 opsize = *ptr++; 3986 if (opsize < 2 || opsize > length) 3987 return NULL; 3988 if (opcode == TCPOPT_MD5SIG) 3989 return opsize == TCPOLEN_MD5SIG ? ptr : NULL; 3990 } 3991 ptr += opsize - 2; 3992 length -= opsize; 3993 } 3994 return NULL; 3995} 3996EXPORT_SYMBOL(tcp_parse_md5sig_option); 3997#endif 3998 3999static inline void tcp_store_ts_recent(struct tcp_sock *tp) 4000{ 4001 tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval; 4002 tp->rx_opt.ts_recent_stamp = get_seconds(); 4003} 4004 4005static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq) 4006{ 4007 if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) { 4008 /* PAWS bug workaround wrt. ACK frames, the PAWS discard 4009 * extra check below makes sure this can only happen 4010 * for pure ACK frames. -DaveM 4011 * 4012 * Not only, also it occurs for expired timestamps. 4013 */ 4014 4015 if (tcp_paws_check(&tp->rx_opt, 0)) 4016 tcp_store_ts_recent(tp); 4017 } 4018} 4019 4020/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM 4021 * 4022 * It is not fatal. If this ACK does _not_ change critical state (seqs, window) 4023 * it can pass through stack. So, the following predicate verifies that 4024 * this segment is not used for anything but congestion avoidance or 4025 * fast retransmit. Moreover, we even are able to eliminate most of such 4026 * second order effects, if we apply some small "replay" window (~RTO) 4027 * to timestamp space. 4028 * 4029 * All these measures still do not guarantee that we reject wrapped ACKs 4030 * on networks with high bandwidth, when sequence space is recycled fastly, 4031 * but it guarantees that such events will be very rare and do not affect 4032 * connection seriously. This doesn't look nice, but alas, PAWS is really 4033 * buggy extension. 4034 * 4035 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC 4036 * states that events when retransmit arrives after original data are rare. 4037 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is 4038 * the biggest problem on large power networks even with minor reordering. 4039 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe 4040 * up to bandwidth of 18Gigabit/sec. 8) ] 4041 */ 4042 4043static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb) 4044{ 4045 const struct tcp_sock *tp = tcp_sk(sk); 4046 const struct tcphdr *th = tcp_hdr(skb); 4047 u32 seq = TCP_SKB_CB(skb)->seq; 4048 u32 ack = TCP_SKB_CB(skb)->ack_seq; 4049 4050 return (/* 1. Pure ACK with correct sequence number. */ 4051 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) && 4052 4053 /* 2. ... and duplicate ACK. */ 4054 ack == tp->snd_una && 4055 4056 /* 3. ... and does not update window. */ 4057 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) && 4058 4059 /* 4. ... and sits in replay window. */ 4060 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ); 4061} 4062 4063static inline int tcp_paws_discard(const struct sock *sk, 4064 const struct sk_buff *skb) 4065{ 4066 const struct tcp_sock *tp = tcp_sk(sk); 4067 4068 return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) && 4069 !tcp_disordered_ack(sk, skb); 4070} 4071 4072/* Check segment sequence number for validity. 4073 * 4074 * Segment controls are considered valid, if the segment 4075 * fits to the window after truncation to the window. Acceptability 4076 * of data (and SYN, FIN, of course) is checked separately. 4077 * See tcp_data_queue(), for example. 4078 * 4079 * Also, controls (RST is main one) are accepted using RCV.WUP instead 4080 * of RCV.NXT. Peer still did not advance his SND.UNA when we 4081 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP. 4082 * (borrowed from freebsd) 4083 */ 4084 4085static inline int tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq) 4086{ 4087 return !before(end_seq, tp->rcv_wup) && 4088 !after(seq, tp->rcv_nxt + tcp_receive_window(tp)); 4089} 4090 4091/* When we get a reset we do this. */ 4092static void tcp_reset(struct sock *sk) 4093{ 4094 /* We want the right error as BSD sees it (and indeed as we do). */ 4095 switch (sk->sk_state) { 4096 case TCP_SYN_SENT: 4097 sk->sk_err = ECONNREFUSED; 4098 break; 4099 case TCP_CLOSE_WAIT: 4100 sk->sk_err = EPIPE; 4101 break; 4102 case TCP_CLOSE: 4103 return; 4104 default: 4105 sk->sk_err = ECONNRESET; 4106 } 4107 /* This barrier is coupled with smp_rmb() in tcp_poll() */ 4108 smp_wmb(); 4109 4110 if (!sock_flag(sk, SOCK_DEAD)) 4111 sk->sk_error_report(sk); 4112 4113 tcp_done(sk); 4114} 4115 4116/* 4117 * Process the FIN bit. This now behaves as it is supposed to work 4118 * and the FIN takes effect when it is validly part of sequence 4119 * space. Not before when we get holes. 4120 * 4121 * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT 4122 * (and thence onto LAST-ACK and finally, CLOSE, we never enter 4123 * TIME-WAIT) 4124 * 4125 * If we are in FINWAIT-1, a received FIN indicates simultaneous 4126 * close and we go into CLOSING (and later onto TIME-WAIT) 4127 * 4128 * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT. 4129 */ 4130static void tcp_fin(struct sock *sk) 4131{ 4132 struct tcp_sock *tp = tcp_sk(sk); 4133 4134 inet_csk_schedule_ack(sk); 4135 4136 sk->sk_shutdown |= RCV_SHUTDOWN; 4137 sock_set_flag(sk, SOCK_DONE); 4138 4139 switch (sk->sk_state) { 4140 case TCP_SYN_RECV: 4141 case TCP_ESTABLISHED: 4142 /* Move to CLOSE_WAIT */ 4143 tcp_set_state(sk, TCP_CLOSE_WAIT); 4144 inet_csk(sk)->icsk_ack.pingpong = 1; 4145 break; 4146 4147 case TCP_CLOSE_WAIT: 4148 case TCP_CLOSING: 4149 /* Received a retransmission of the FIN, do 4150 * nothing. 4151 */ 4152 break; 4153 case TCP_LAST_ACK: 4154 /* RFC793: Remain in the LAST-ACK state. */ 4155 break; 4156 4157 case TCP_FIN_WAIT1: 4158 /* This case occurs when a simultaneous close 4159 * happens, we must ack the received FIN and 4160 * enter the CLOSING state. 4161 */ 4162 tcp_send_ack(sk); 4163 tcp_set_state(sk, TCP_CLOSING); 4164 break; 4165 case TCP_FIN_WAIT2: 4166 /* Received a FIN -- send ACK and enter TIME_WAIT. */ 4167 tcp_send_ack(sk); 4168 tcp_time_wait(sk, TCP_TIME_WAIT, 0); 4169 break; 4170 default: 4171 /* Only TCP_LISTEN and TCP_CLOSE are left, in these 4172 * cases we should never reach this piece of code. 4173 */ 4174 printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n", 4175 __func__, sk->sk_state); 4176 break; 4177 } 4178 4179 /* It _is_ possible, that we have something out-of-order _after_ FIN. 4180 * Probably, we should reset in this case. For now drop them. 4181 */ 4182 __skb_queue_purge(&tp->out_of_order_queue); 4183 if (tcp_is_sack(tp)) 4184 tcp_sack_reset(&tp->rx_opt); 4185 sk_mem_reclaim(sk); 4186 4187 if (!sock_flag(sk, SOCK_DEAD)) { 4188 sk->sk_state_change(sk); 4189 4190 /* Do not send POLL_HUP for half duplex close. */ 4191 if (sk->sk_shutdown == SHUTDOWN_MASK || 4192 sk->sk_state == TCP_CLOSE) 4193 sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP); 4194 else 4195 sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN); 4196 } 4197} 4198 4199static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, 4200 u32 end_seq) 4201{ 4202 if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) { 4203 if (before(seq, sp->start_seq)) 4204 sp->start_seq = seq; 4205 if (after(end_seq, sp->end_seq)) 4206 sp->end_seq = end_seq; 4207 return 1; 4208 } 4209 return 0; 4210} 4211 4212static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq) 4213{ 4214 struct tcp_sock *tp = tcp_sk(sk); 4215 4216 if (tcp_is_sack(tp) && sysctl_tcp_dsack) { 4217 int mib_idx; 4218 4219 if (before(seq, tp->rcv_nxt)) 4220 mib_idx = LINUX_MIB_TCPDSACKOLDSENT; 4221 else 4222 mib_idx = LINUX_MIB_TCPDSACKOFOSENT; 4223 4224 NET_INC_STATS_BH(sock_net(sk), mib_idx); 4225 4226 tp->rx_opt.dsack = 1; 4227 tp->duplicate_sack[0].start_seq = seq; 4228 tp->duplicate_sack[0].end_seq = end_seq; 4229 } 4230} 4231 4232static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq) 4233{ 4234 struct tcp_sock *tp = tcp_sk(sk); 4235 4236 if (!tp->rx_opt.dsack) 4237 tcp_dsack_set(sk, seq, end_seq); 4238 else 4239 tcp_sack_extend(tp->duplicate_sack, seq, end_seq); 4240} 4241 4242static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb) 4243{ 4244 struct tcp_sock *tp = tcp_sk(sk); 4245 4246 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && 4247 before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { 4248 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST); 4249 tcp_enter_quickack_mode(sk); 4250 4251 if (tcp_is_sack(tp) && sysctl_tcp_dsack) { 4252 u32 end_seq = TCP_SKB_CB(skb)->end_seq; 4253 4254 if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) 4255 end_seq = tp->rcv_nxt; 4256 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq); 4257 } 4258 } 4259 4260 tcp_send_ack(sk); 4261} 4262 4263/* These routines update the SACK block as out-of-order packets arrive or 4264 * in-order packets close up the sequence space. 4265 */ 4266static void tcp_sack_maybe_coalesce(struct tcp_sock *tp) 4267{ 4268 int this_sack; 4269 struct tcp_sack_block *sp = &tp->selective_acks[0]; 4270 struct tcp_sack_block *swalk = sp + 1; 4271 4272 /* See if the recent change to the first SACK eats into 4273 * or hits the sequence space of other SACK blocks, if so coalesce. 4274 */ 4275 for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) { 4276 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) { 4277 int i; 4278 4279 /* Zap SWALK, by moving every further SACK up by one slot. 4280 * Decrease num_sacks. 4281 */ 4282 tp->rx_opt.num_sacks--; 4283 for (i = this_sack; i < tp->rx_opt.num_sacks; i++) 4284 sp[i] = sp[i + 1]; 4285 continue; 4286 } 4287 this_sack++, swalk++; 4288 } 4289} 4290 4291static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq) 4292{ 4293 struct tcp_sock *tp = tcp_sk(sk); 4294 struct tcp_sack_block *sp = &tp->selective_acks[0]; 4295 int cur_sacks = tp->rx_opt.num_sacks; 4296 int this_sack; 4297 4298 if (!cur_sacks) 4299 goto new_sack; 4300 4301 for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) { 4302 if (tcp_sack_extend(sp, seq, end_seq)) { 4303 /* Rotate this_sack to the first one. */ 4304 for (; this_sack > 0; this_sack--, sp--) 4305 swap(*sp, *(sp - 1)); 4306 if (cur_sacks > 1) 4307 tcp_sack_maybe_coalesce(tp); 4308 return; 4309 } 4310 } 4311 4312 /* Could not find an adjacent existing SACK, build a new one, 4313 * put it at the front, and shift everyone else down. We 4314 * always know there is at least one SACK present already here. 4315 * 4316 * If the sack array is full, forget about the last one. 4317 */ 4318 if (this_sack >= TCP_NUM_SACKS) { 4319 this_sack--; 4320 tp->rx_opt.num_sacks--; 4321 sp--; 4322 } 4323 for (; this_sack > 0; this_sack--, sp--) 4324 *sp = *(sp - 1); 4325 4326new_sack: 4327 /* Build the new head SACK, and we're done. */ 4328 sp->start_seq = seq; 4329 sp->end_seq = end_seq; 4330 tp->rx_opt.num_sacks++; 4331} 4332 4333/* RCV.NXT advances, some SACKs should be eaten. */ 4334 4335static void tcp_sack_remove(struct tcp_sock *tp) 4336{ 4337 struct tcp_sack_block *sp = &tp->selective_acks[0]; 4338 int num_sacks = tp->rx_opt.num_sacks; 4339 int this_sack; 4340 4341 /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */ 4342 if (skb_queue_empty(&tp->out_of_order_queue)) { 4343 tp->rx_opt.num_sacks = 0; 4344 return; 4345 } 4346 4347 for (this_sack = 0; this_sack < num_sacks;) { 4348 /* Check if the start of the sack is covered by RCV.NXT. */ 4349 if (!before(tp->rcv_nxt, sp->start_seq)) { 4350 int i; 4351 4352 /* RCV.NXT must cover all the block! */ 4353 WARN_ON(before(tp->rcv_nxt, sp->end_seq)); 4354 4355 /* Zap this SACK, by moving forward any other SACKS. */ 4356 for (i=this_sack+1; i < num_sacks; i++) 4357 tp->selective_acks[i-1] = tp->selective_acks[i]; 4358 num_sacks--; 4359 continue; 4360 } 4361 this_sack++; 4362 sp++; 4363 } 4364 tp->rx_opt.num_sacks = num_sacks; 4365} 4366 4367/* This one checks to see if we can put data from the 4368 * out_of_order queue into the receive_queue. 4369 */ 4370static void tcp_ofo_queue(struct sock *sk) 4371{ 4372 struct tcp_sock *tp = tcp_sk(sk); 4373 __u32 dsack_high = tp->rcv_nxt; 4374 struct sk_buff *skb; 4375 4376 while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) { 4377 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) 4378 break; 4379 4380 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) { 4381 __u32 dsack = dsack_high; 4382 if (before(TCP_SKB_CB(skb)->end_seq, dsack_high)) 4383 dsack_high = TCP_SKB_CB(skb)->end_seq; 4384 tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack); 4385 } 4386 4387 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) { 4388 SOCK_DEBUG(sk, "ofo packet was already received\n"); 4389 __skb_unlink(skb, &tp->out_of_order_queue); 4390 __kfree_skb(skb); 4391 continue; 4392 } 4393 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n", 4394 tp->rcv_nxt, TCP_SKB_CB(skb)->seq, 4395 TCP_SKB_CB(skb)->end_seq); 4396 4397 __skb_unlink(skb, &tp->out_of_order_queue); 4398 __skb_queue_tail(&sk->sk_receive_queue, skb); 4399 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; 4400 if (tcp_hdr(skb)->fin) 4401 tcp_fin(sk); 4402 } 4403} 4404 4405static int tcp_prune_ofo_queue(struct sock *sk); 4406static int tcp_prune_queue(struct sock *sk); 4407 4408static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size) 4409{ 4410 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf || 4411 !sk_rmem_schedule(sk, size)) { 4412 4413 if (tcp_prune_queue(sk) < 0) 4414 return -1; 4415 4416 if (!sk_rmem_schedule(sk, size)) { 4417 if (!tcp_prune_ofo_queue(sk)) 4418 return -1; 4419 4420 if (!sk_rmem_schedule(sk, size)) 4421 return -1; 4422 } 4423 } 4424 return 0; 4425} 4426 4427static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) 4428{ 4429 const struct tcphdr *th = tcp_hdr(skb); 4430 struct tcp_sock *tp = tcp_sk(sk); 4431 int eaten = -1; 4432 4433 if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) 4434 goto drop; 4435 4436 skb_dst_drop(skb); 4437 __skb_pull(skb, th->doff * 4); 4438 4439 TCP_ECN_accept_cwr(tp, skb); 4440 4441 tp->rx_opt.dsack = 0; 4442 4443 /* Queue data for delivery to the user. 4444 * Packets in sequence go to the receive queue. 4445 * Out of sequence packets to the out_of_order_queue. 4446 */ 4447 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) { 4448 if (tcp_receive_window(tp) == 0) 4449 goto out_of_window; 4450 4451 /* Ok. In sequence. In window. */ 4452 if (tp->ucopy.task == current && 4453 tp->copied_seq == tp->rcv_nxt && tp->ucopy.len && 4454 sock_owned_by_user(sk) && !tp->urg_data) { 4455 int chunk = min_t(unsigned int, skb->len, 4456 tp->ucopy.len); 4457 4458 __set_current_state(TASK_RUNNING); 4459 4460 local_bh_enable(); 4461 if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) { 4462 tp->ucopy.len -= chunk; 4463 tp->copied_seq += chunk; 4464 eaten = (chunk == skb->len); 4465 tcp_rcv_space_adjust(sk); 4466 } 4467 local_bh_disable(); 4468 } 4469 4470 if (eaten <= 0) { 4471queue_and_out: 4472 if (eaten < 0 && 4473 tcp_try_rmem_schedule(sk, skb->truesize)) 4474 goto drop; 4475 4476 skb_set_owner_r(skb, sk); 4477 __skb_queue_tail(&sk->sk_receive_queue, skb); 4478 } 4479 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; 4480 if (skb->len) 4481 tcp_event_data_recv(sk, skb); 4482 if (th->fin) 4483 tcp_fin(sk); 4484 4485 if (!skb_queue_empty(&tp->out_of_order_queue)) { 4486 tcp_ofo_queue(sk); 4487 4488 /* RFC2581. 4.2. SHOULD send immediate ACK, when 4489 * gap in queue is filled. 4490 */ 4491 if (skb_queue_empty(&tp->out_of_order_queue)) 4492 inet_csk(sk)->icsk_ack.pingpong = 0; 4493 } 4494 4495 if (tp->rx_opt.num_sacks) 4496 tcp_sack_remove(tp); 4497 4498 tcp_fast_path_check(sk); 4499 4500 if (eaten > 0) 4501 __kfree_skb(skb); 4502 else if (!sock_flag(sk, SOCK_DEAD)) 4503 sk->sk_data_ready(sk, 0); 4504 return; 4505 } 4506 4507 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) { 4508 /* A retransmit, 2nd most common case. Force an immediate ack. */ 4509 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST); 4510 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); 4511 4512out_of_window: 4513 tcp_enter_quickack_mode(sk); 4514 inet_csk_schedule_ack(sk); 4515drop: 4516 __kfree_skb(skb); 4517 return; 4518 } 4519 4520 /* Out of window. F.e. zero window probe. */ 4521 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp))) 4522 goto out_of_window; 4523 4524 tcp_enter_quickack_mode(sk); 4525 4526 if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { 4527 /* Partial packet, seq < rcv_next < end_seq */ 4528 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n", 4529 tp->rcv_nxt, TCP_SKB_CB(skb)->seq, 4530 TCP_SKB_CB(skb)->end_seq); 4531 4532 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt); 4533 4534 /* If window is closed, drop tail of packet. But after 4535 * remembering D-SACK for its head made in previous line. 4536 */ 4537 if (!tcp_receive_window(tp)) 4538 goto out_of_window; 4539 goto queue_and_out; 4540 } 4541 4542 TCP_ECN_check_ce(tp, skb); 4543 4544 if (tcp_try_rmem_schedule(sk, skb->truesize)) 4545 goto drop; 4546 4547 /* Disable header prediction. */ 4548 tp->pred_flags = 0; 4549 inet_csk_schedule_ack(sk); 4550 4551 SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n", 4552 tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); 4553 4554 skb_set_owner_r(skb, sk); 4555 4556 if (!skb_peek(&tp->out_of_order_queue)) { 4557 /* Initial out of order segment, build 1 SACK. */ 4558 if (tcp_is_sack(tp)) { 4559 tp->rx_opt.num_sacks = 1; 4560 tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq; 4561 tp->selective_acks[0].end_seq = 4562 TCP_SKB_CB(skb)->end_seq; 4563 } 4564 __skb_queue_head(&tp->out_of_order_queue, skb); 4565 } else { 4566 struct sk_buff *skb1 = skb_peek_tail(&tp->out_of_order_queue); 4567 u32 seq = TCP_SKB_CB(skb)->seq; 4568 u32 end_seq = TCP_SKB_CB(skb)->end_seq; 4569 4570 if (seq == TCP_SKB_CB(skb1)->end_seq) { 4571 __skb_queue_after(&tp->out_of_order_queue, skb1, skb); 4572 4573 if (!tp->rx_opt.num_sacks || 4574 tp->selective_acks[0].end_seq != seq) 4575 goto add_sack; 4576 4577 /* Common case: data arrive in order after hole. */ 4578 tp->selective_acks[0].end_seq = end_seq; 4579 return; 4580 } 4581 4582 /* Find place to insert this segment. */ 4583 while (1) { 4584 if (!after(TCP_SKB_CB(skb1)->seq, seq)) 4585 break; 4586 if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) { 4587 skb1 = NULL; 4588 break; 4589 } 4590 skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1); 4591 } 4592 4593 /* Do skb overlap to previous one? */ 4594 if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) { 4595 if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) { 4596 /* All the bits are present. Drop. */ 4597 __kfree_skb(skb); 4598 tcp_dsack_set(sk, seq, end_seq); 4599 goto add_sack; 4600 } 4601 if (after(seq, TCP_SKB_CB(skb1)->seq)) { 4602 /* Partial overlap. */ 4603 tcp_dsack_set(sk, seq, 4604 TCP_SKB_CB(skb1)->end_seq); 4605 } else { 4606 if (skb_queue_is_first(&tp->out_of_order_queue, 4607 skb1)) 4608 skb1 = NULL; 4609 else 4610 skb1 = skb_queue_prev( 4611 &tp->out_of_order_queue, 4612 skb1); 4613 } 4614 } 4615 if (!skb1) 4616 __skb_queue_head(&tp->out_of_order_queue, skb); 4617 else 4618 __skb_queue_after(&tp->out_of_order_queue, skb1, skb); 4619 4620 /* And clean segments covered by new one as whole. */ 4621 while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) { 4622 skb1 = skb_queue_next(&tp->out_of_order_queue, skb); 4623 4624 if (!after(end_seq, TCP_SKB_CB(skb1)->seq)) 4625 break; 4626 if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) { 4627 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq, 4628 end_seq); 4629 break; 4630 } 4631 __skb_unlink(skb1, &tp->out_of_order_queue); 4632 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq, 4633 TCP_SKB_CB(skb1)->end_seq); 4634 __kfree_skb(skb1); 4635 } 4636 4637add_sack: 4638 if (tcp_is_sack(tp)) 4639 tcp_sack_new_ofo_skb(sk, seq, end_seq); 4640 } 4641} 4642 4643static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb, 4644 struct sk_buff_head *list) 4645{ 4646 struct sk_buff *next = NULL; 4647 4648 if (!skb_queue_is_last(list, skb)) 4649 next = skb_queue_next(list, skb); 4650 4651 __skb_unlink(skb, list); 4652 __kfree_skb(skb); 4653 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED); 4654 4655 return next; 4656} 4657 4658/* Collapse contiguous sequence of skbs head..tail with 4659 * sequence numbers start..end. 4660 * 4661 * If tail is NULL, this means until the end of the list. 4662 * 4663 * Segments with FIN/SYN are not collapsed (only because this 4664 * simplifies code) 4665 */ 4666static void 4667tcp_collapse(struct sock *sk, struct sk_buff_head *list, 4668 struct sk_buff *head, struct sk_buff *tail, 4669 u32 start, u32 end) 4670{ 4671 struct sk_buff *skb, *n; 4672 bool end_of_skbs; 4673 4674 /* First, check that queue is collapsible and find 4675 * the point where collapsing can be useful. */ 4676 skb = head; 4677restart: 4678 end_of_skbs = true; 4679 skb_queue_walk_from_safe(list, skb, n) { 4680 if (skb == tail) 4681 break; 4682 /* No new bits? It is possible on ofo queue. */ 4683 if (!before(start, TCP_SKB_CB(skb)->end_seq)) { 4684 skb = tcp_collapse_one(sk, skb, list); 4685 if (!skb) 4686 break; 4687 goto restart; 4688 } 4689 4690 /* The first skb to collapse is: 4691 * - not SYN/FIN and 4692 * - bloated or contains data before "start" or 4693 * overlaps to the next one. 4694 */ 4695 if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin && 4696 (tcp_win_from_space(skb->truesize) > skb->len || 4697 before(TCP_SKB_CB(skb)->seq, start))) { 4698 end_of_skbs = false; 4699 break; 4700 } 4701 4702 if (!skb_queue_is_last(list, skb)) { 4703 struct sk_buff *next = skb_queue_next(list, skb); 4704 if (next != tail && 4705 TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) { 4706 end_of_skbs = false; 4707 break; 4708 } 4709 } 4710 4711 /* Decided to skip this, advance start seq. */ 4712 start = TCP_SKB_CB(skb)->end_seq; 4713 } 4714 if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin) 4715 return; 4716 4717 while (before(start, end)) { 4718 struct sk_buff *nskb; 4719 unsigned int header = skb_headroom(skb); 4720 int copy = SKB_MAX_ORDER(header, 0); 4721 4722 /* Too big header? This can happen with IPv6. */ 4723 if (copy < 0) 4724 return; 4725 if (end - start < copy) 4726 copy = end - start; 4727 nskb = alloc_skb(copy + header, GFP_ATOMIC); 4728 if (!nskb) 4729 return; 4730 4731 skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head); 4732 skb_set_network_header(nskb, (skb_network_header(skb) - 4733 skb->head)); 4734 skb_set_transport_header(nskb, (skb_transport_header(skb) - 4735 skb->head)); 4736 skb_reserve(nskb, header); 4737 memcpy(nskb->head, skb->head, header); 4738 memcpy(nskb->cb, skb->cb, sizeof(skb->cb)); 4739 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start; 4740 __skb_queue_before(list, skb, nskb); 4741 skb_set_owner_r(nskb, sk); 4742 4743 /* Copy data, releasing collapsed skbs. */ 4744 while (copy > 0) { 4745 int offset = start - TCP_SKB_CB(skb)->seq; 4746 int size = TCP_SKB_CB(skb)->end_seq - start; 4747 4748 BUG_ON(offset < 0); 4749 if (size > 0) { 4750 size = min(copy, size); 4751 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size)) 4752 BUG(); 4753 TCP_SKB_CB(nskb)->end_seq += size; 4754 copy -= size; 4755 start += size; 4756 } 4757 if (!before(start, TCP_SKB_CB(skb)->end_seq)) { 4758 skb = tcp_collapse_one(sk, skb, list); 4759 if (!skb || 4760 skb == tail || 4761 tcp_hdr(skb)->syn || 4762 tcp_hdr(skb)->fin) 4763 return; 4764 } 4765 } 4766 } 4767} 4768 4769/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs 4770 * and tcp_collapse() them until all the queue is collapsed. 4771 */ 4772static void tcp_collapse_ofo_queue(struct sock *sk) 4773{ 4774 struct tcp_sock *tp = tcp_sk(sk); 4775 struct sk_buff *skb = skb_peek(&tp->out_of_order_queue); 4776 struct sk_buff *head; 4777 u32 start, end; 4778 4779 if (skb == NULL) 4780 return; 4781 4782 start = TCP_SKB_CB(skb)->seq; 4783 end = TCP_SKB_CB(skb)->end_seq; 4784 head = skb; 4785 4786 for (;;) { 4787 struct sk_buff *next = NULL; 4788 4789 if (!skb_queue_is_last(&tp->out_of_order_queue, skb)) 4790 next = skb_queue_next(&tp->out_of_order_queue, skb); 4791 skb = next; 4792 4793 /* Segment is terminated when we see gap or when 4794 * we are at the end of all the queue. */ 4795 if (!skb || 4796 after(TCP_SKB_CB(skb)->seq, end) || 4797 before(TCP_SKB_CB(skb)->end_seq, start)) { 4798 tcp_collapse(sk, &tp->out_of_order_queue, 4799 head, skb, start, end); 4800 head = skb; 4801 if (!skb) 4802 break; 4803 /* Start new segment */ 4804 start = TCP_SKB_CB(skb)->seq; 4805 end = TCP_SKB_CB(skb)->end_seq; 4806 } else { 4807 if (before(TCP_SKB_CB(skb)->seq, start)) 4808 start = TCP_SKB_CB(skb)->seq; 4809 if (after(TCP_SKB_CB(skb)->end_seq, end)) 4810 end = TCP_SKB_CB(skb)->end_seq; 4811 } 4812 } 4813} 4814 4815/* 4816 * Purge the out-of-order queue. 4817 * Return true if queue was pruned. 4818 */ 4819static int tcp_prune_ofo_queue(struct sock *sk) 4820{ 4821 struct tcp_sock *tp = tcp_sk(sk); 4822 int res = 0; 4823 4824 if (!skb_queue_empty(&tp->out_of_order_queue)) { 4825 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED); 4826 __skb_queue_purge(&tp->out_of_order_queue); 4827 4828 /* Reset SACK state. A conforming SACK implementation will 4829 * do the same at a timeout based retransmit. When a connection 4830 * is in a sad state like this, we care only about integrity 4831 * of the connection not performance. 4832 */ 4833 if (tp->rx_opt.sack_ok) 4834 tcp_sack_reset(&tp->rx_opt); 4835 sk_mem_reclaim(sk); 4836 res = 1; 4837 } 4838 return res; 4839} 4840 4841/* Reduce allocated memory if we can, trying to get 4842 * the socket within its memory limits again. 4843 * 4844 * Return less than zero if we should start dropping frames 4845 * until the socket owning process reads some of the data 4846 * to stabilize the situation. 4847 */ 4848static int tcp_prune_queue(struct sock *sk) 4849{ 4850 struct tcp_sock *tp = tcp_sk(sk); 4851 4852 SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq); 4853 4854 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED); 4855 4856 if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) 4857 tcp_clamp_window(sk); 4858 else if (sk_under_memory_pressure(sk)) 4859 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss); 4860 4861 tcp_collapse_ofo_queue(sk); 4862 if (!skb_queue_empty(&sk->sk_receive_queue)) 4863 tcp_collapse(sk, &sk->sk_receive_queue, 4864 skb_peek(&sk->sk_receive_queue), 4865 NULL, 4866 tp->copied_seq, tp->rcv_nxt); 4867 sk_mem_reclaim(sk); 4868 4869 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) 4870 return 0; 4871 4872 /* Collapsing did not help, destructive actions follow. 4873 * This must not ever occur. */ 4874 4875 tcp_prune_ofo_queue(sk); 4876 4877 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) 4878 return 0; 4879 4880 /* If we are really being abused, tell the caller to silently 4881 * drop receive data on the floor. It will get retransmitted 4882 * and hopefully then we'll have sufficient space. 4883 */ 4884 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED); 4885 4886 /* Massive buffer overcommit. */ 4887 tp->pred_flags = 0; 4888 return -1; 4889} 4890 4891/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto. 4892 * As additional protections, we do not touch cwnd in retransmission phases, 4893 * and if application hit its sndbuf limit recently. 4894 */ 4895void tcp_cwnd_application_limited(struct sock *sk) 4896{ 4897 struct tcp_sock *tp = tcp_sk(sk); 4898 4899 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open && 4900 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) { 4901 /* Limited by application or receiver window. */ 4902 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk)); 4903 u32 win_used = max(tp->snd_cwnd_used, init_win); 4904 if (win_used < tp->snd_cwnd) { 4905 tp->snd_ssthresh = tcp_current_ssthresh(sk); 4906 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1; 4907 } 4908 tp->snd_cwnd_used = 0; 4909 } 4910 tp->snd_cwnd_stamp = tcp_time_stamp; 4911} 4912 4913static int tcp_should_expand_sndbuf(const struct sock *sk) 4914{ 4915 const struct tcp_sock *tp = tcp_sk(sk); 4916 4917 /* If the user specified a specific send buffer setting, do 4918 * not modify it. 4919 */ 4920 if (sk->sk_userlocks & SOCK_SNDBUF_LOCK) 4921 return 0; 4922 4923 /* If we are under global TCP memory pressure, do not expand. */ 4924 if (sk_under_memory_pressure(sk)) 4925 return 0; 4926 4927 /* If we are under soft global TCP memory pressure, do not expand. */ 4928 if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0)) 4929 return 0; 4930 4931 /* If we filled the congestion window, do not expand. */ 4932 if (tp->packets_out >= tp->snd_cwnd) 4933 return 0; 4934 4935 return 1; 4936} 4937 4938/* When incoming ACK allowed to free some skb from write_queue, 4939 * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket 4940 * on the exit from tcp input handler. 4941 * 4942 * PROBLEM: sndbuf expansion does not work well with largesend. 4943 */ 4944static void tcp_new_space(struct sock *sk) 4945{ 4946 struct tcp_sock *tp = tcp_sk(sk); 4947 4948 if (tcp_should_expand_sndbuf(sk)) { 4949 int sndmem = SKB_TRUESIZE(max_t(u32, 4950 tp->rx_opt.mss_clamp, 4951 tp->mss_cache) + 4952 MAX_TCP_HEADER); 4953 int demanded = max_t(unsigned int, tp->snd_cwnd, 4954 tp->reordering + 1); 4955 sndmem *= 2 * demanded; 4956 if (sndmem > sk->sk_sndbuf) 4957 sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]); 4958 tp->snd_cwnd_stamp = tcp_time_stamp; 4959 } 4960 4961 sk->sk_write_space(sk); 4962} 4963 4964static void tcp_check_space(struct sock *sk) 4965{ 4966 if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) { 4967 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK); 4968 if (sk->sk_socket && 4969 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) 4970 tcp_new_space(sk); 4971 } 4972} 4973 4974static inline void tcp_data_snd_check(struct sock *sk) 4975{ 4976 tcp_push_pending_frames(sk); 4977 tcp_check_space(sk); 4978} 4979 4980/* 4981 * Check if sending an ack is needed. 4982 */ 4983static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible) 4984{ 4985 struct tcp_sock *tp = tcp_sk(sk); 4986 4987 /* More than one full frame received... */ 4988 if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss && 4989 /* ... and right edge of window advances far enough. 4990 * (tcp_recvmsg() will send ACK otherwise). Or... 4991 */ 4992 __tcp_select_window(sk) >= tp->rcv_wnd) || 4993 /* We ACK each frame or... */ 4994 tcp_in_quickack_mode(sk) || 4995 /* We have out of order data. */ 4996 (ofo_possible && skb_peek(&tp->out_of_order_queue))) { 4997 /* Then ack it now */ 4998 tcp_send_ack(sk); 4999 } else { 5000 /* Else, send delayed ack. */ 5001 tcp_send_delayed_ack(sk); 5002 } 5003} 5004 5005static inline void tcp_ack_snd_check(struct sock *sk) 5006{ 5007 if (!inet_csk_ack_scheduled(sk)) { 5008 /* We sent a data segment already. */ 5009 return; 5010 } 5011 __tcp_ack_snd_check(sk, 1); 5012} 5013 5014/* 5015 * This routine is only called when we have urgent data 5016 * signaled. Its the 'slow' part of tcp_urg. It could be 5017 * moved inline now as tcp_urg is only called from one 5018 * place. We handle URGent data wrong. We have to - as 5019 * BSD still doesn't use the correction from RFC961. 5020 * For 1003.1g we should support a new option TCP_STDURG to permit 5021 * either form (or just set the sysctl tcp_stdurg). 5022 */ 5023 5024static void tcp_check_urg(struct sock *sk, const struct tcphdr *th) 5025{ 5026 struct tcp_sock *tp = tcp_sk(sk); 5027 u32 ptr = ntohs(th->urg_ptr); 5028 5029 if (ptr && !sysctl_tcp_stdurg) 5030 ptr--; 5031 ptr += ntohl(th->seq); 5032 5033 /* Ignore urgent data that we've already seen and read. */ 5034 if (after(tp->copied_seq, ptr)) 5035 return; 5036 5037 /* Do not replay urg ptr. 5038 * 5039 * NOTE: interesting situation not covered by specs. 5040 * Misbehaving sender may send urg ptr, pointing to segment, 5041 * which we already have in ofo queue. We are not able to fetch 5042 * such data and will stay in TCP_URG_NOTYET until will be eaten 5043 * by recvmsg(). Seems, we are not obliged to handle such wicked 5044 * situations. But it is worth to think about possibility of some 5045 * DoSes using some hypothetical application level deadlock. 5046 */ 5047 if (before(ptr, tp->rcv_nxt)) 5048 return; 5049 5050 /* Do we already have a newer (or duplicate) urgent pointer? */ 5051 if (tp->urg_data && !after(ptr, tp->urg_seq)) 5052 return; 5053 5054 /* Tell the world about our new urgent pointer. */ 5055 sk_send_sigurg(sk); 5056 5057 /* We may be adding urgent data when the last byte read was 5058 * urgent. To do this requires some care. We cannot just ignore 5059 * tp->copied_seq since we would read the last urgent byte again 5060 * as data, nor can we alter copied_seq until this data arrives 5061 * or we break the semantics of SIOCATMARK (and thus sockatmark()) 5062 * 5063 * NOTE. Double Dutch. Rendering to plain English: author of comment 5064 * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB); 5065 * and expect that both A and B disappear from stream. This is _wrong_. 5066 * Though this happens in BSD with high probability, this is occasional. 5067 * Any application relying on this is buggy. Note also, that fix "works" 5068 * only in this artificial test. Insert some normal data between A and B and we will 5069 * decline of BSD again. Verdict: it is better to remove to trap 5070 * buggy users. 5071 */ 5072 if (tp->urg_seq == tp->copied_seq && tp->urg_data && 5073 !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) { 5074 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue); 5075 tp->copied_seq++; 5076 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) { 5077 __skb_unlink(skb, &sk->sk_receive_queue); 5078 __kfree_skb(skb); 5079 } 5080 } 5081 5082 tp->urg_data = TCP_URG_NOTYET; 5083 tp->urg_seq = ptr; 5084 5085 /* Disable header prediction. */ 5086 tp->pred_flags = 0; 5087} 5088 5089/* This is the 'fast' part of urgent handling. */ 5090static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th) 5091{ 5092 struct tcp_sock *tp = tcp_sk(sk); 5093 5094 /* Check if we get a new urgent pointer - normally not. */ 5095 if (th->urg) 5096 tcp_check_urg(sk, th); 5097 5098 /* Do we wait for any urgent data? - normally not... */ 5099 if (tp->urg_data == TCP_URG_NOTYET) { 5100 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) - 5101 th->syn; 5102 5103 /* Is the urgent pointer pointing into this packet? */ 5104 if (ptr < skb->len) { 5105 u8 tmp; 5106 if (skb_copy_bits(skb, ptr, &tmp, 1)) 5107 BUG(); 5108 tp->urg_data = TCP_URG_VALID | tmp; 5109 if (!sock_flag(sk, SOCK_DEAD)) 5110 sk->sk_data_ready(sk, 0); 5111 } 5112 } 5113} 5114 5115static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen) 5116{ 5117 struct tcp_sock *tp = tcp_sk(sk); 5118 int chunk = skb->len - hlen; 5119 int err; 5120 5121 local_bh_enable(); 5122 if (skb_csum_unnecessary(skb)) 5123 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk); 5124 else 5125 err = skb_copy_and_csum_datagram_iovec(skb, hlen, 5126 tp->ucopy.iov); 5127 5128 if (!err) { 5129 tp->ucopy.len -= chunk; 5130 tp->copied_seq += chunk; 5131 tcp_rcv_space_adjust(sk); 5132 } 5133 5134 local_bh_disable(); 5135 return err; 5136} 5137 5138static __sum16 __tcp_checksum_complete_user(struct sock *sk, 5139 struct sk_buff *skb) 5140{ 5141 __sum16 result; 5142 5143 if (sock_owned_by_user(sk)) { 5144 local_bh_enable(); 5145 result = __tcp_checksum_complete(skb); 5146 local_bh_disable(); 5147 } else { 5148 result = __tcp_checksum_complete(skb); 5149 } 5150 return result; 5151} 5152 5153static inline int tcp_checksum_complete_user(struct sock *sk, 5154 struct sk_buff *skb) 5155{ 5156 return !skb_csum_unnecessary(skb) && 5157 __tcp_checksum_complete_user(sk, skb); 5158} 5159 5160#ifdef CONFIG_NET_DMA 5161static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb, 5162 int hlen) 5163{ 5164 struct tcp_sock *tp = tcp_sk(sk); 5165 int chunk = skb->len - hlen; 5166 int dma_cookie; 5167 int copied_early = 0; 5168 5169 if (tp->ucopy.wakeup) 5170 return 0; 5171 5172 if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list) 5173 tp->ucopy.dma_chan = dma_find_channel(DMA_MEMCPY); 5174 5175 if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) { 5176 5177 dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan, 5178 skb, hlen, 5179 tp->ucopy.iov, chunk, 5180 tp->ucopy.pinned_list); 5181 5182 if (dma_cookie < 0) 5183 goto out; 5184 5185 tp->ucopy.dma_cookie = dma_cookie; 5186 copied_early = 1; 5187 5188 tp->ucopy.len -= chunk; 5189 tp->copied_seq += chunk; 5190 tcp_rcv_space_adjust(sk); 5191 5192 if ((tp->ucopy.len == 0) || 5193 (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) || 5194 (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) { 5195 tp->ucopy.wakeup = 1; 5196 sk->sk_data_ready(sk, 0); 5197 } 5198 } else if (chunk > 0) { 5199 tp->ucopy.wakeup = 1; 5200 sk->sk_data_ready(sk, 0); 5201 } 5202out: 5203 return copied_early; 5204} 5205#endif /* CONFIG_NET_DMA */ 5206 5207/* Does PAWS and seqno based validation of an incoming segment, flags will 5208 * play significant role here. 5209 */ 5210static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, 5211 const struct tcphdr *th, int syn_inerr) 5212{ 5213 const u8 *hash_location; 5214 struct tcp_sock *tp = tcp_sk(sk); 5215 5216 /* RFC1323: H1. Apply PAWS check first. */ 5217 if (tcp_fast_parse_options(skb, th, tp, &hash_location) && 5218 tp->rx_opt.saw_tstamp && 5219 tcp_paws_discard(sk, skb)) { 5220 if (!th->rst) { 5221 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 5222 tcp_send_dupack(sk, skb); 5223 goto discard; 5224 } 5225 /* Reset is accepted even if it did not pass PAWS. */ 5226 } 5227 5228 /* Step 1: check sequence number */ 5229 if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) { 5230 /* RFC793, page 37: "In all states except SYN-SENT, all reset 5231 * (RST) segments are validated by checking their SEQ-fields." 5232 * And page 69: "If an incoming segment is not acceptable, 5233 * an acknowledgment should be sent in reply (unless the RST 5234 * bit is set, if so drop the segment and return)". 5235 */ 5236 if (!th->rst) 5237 tcp_send_dupack(sk, skb); 5238 goto discard; 5239 } 5240 5241 /* Step 2: check RST bit */ 5242 if (th->rst) { 5243 tcp_reset(sk); 5244 goto discard; 5245 } 5246 5247 /* ts_recent update must be made after we are sure that the packet 5248 * is in window. 5249 */ 5250 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); 5251 5252 /* step 3: check security and precedence [ignored] */ 5253 5254 /* step 4: Check for a SYN in window. */ 5255 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { 5256 if (syn_inerr) 5257 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS); 5258 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONSYN); 5259 tcp_reset(sk); 5260 return -1; 5261 } 5262 5263 return 1; 5264 5265discard: 5266 __kfree_skb(skb); 5267 return 0; 5268} 5269 5270/* 5271 * TCP receive function for the ESTABLISHED state. 5272 * 5273 * It is split into a fast path and a slow path. The fast path is 5274 * disabled when: 5275 * - A zero window was announced from us - zero window probing 5276 * is only handled properly in the slow path. 5277 * - Out of order segments arrived. 5278 * - Urgent data is expected. 5279 * - There is no buffer space left 5280 * - Unexpected TCP flags/window values/header lengths are received 5281 * (detected by checking the TCP header against pred_flags) 5282 * - Data is sent in both directions. Fast path only supports pure senders 5283 * or pure receivers (this means either the sequence number or the ack 5284 * value must stay constant) 5285 * - Unexpected TCP option. 5286 * 5287 * When these conditions are not satisfied it drops into a standard 5288 * receive procedure patterned after RFC793 to handle all cases. 5289 * The first three cases are guaranteed by proper pred_flags setting, 5290 * the rest is checked inline. Fast processing is turned on in 5291 * tcp_data_queue when everything is OK. 5292 */ 5293int tcp_rcv_established(struct sock *sk, struct sk_buff *skb, 5294 const struct tcphdr *th, unsigned int len) 5295{ 5296 struct tcp_sock *tp = tcp_sk(sk); 5297 int res; 5298 5299 /* 5300 * Header prediction. 5301 * The code loosely follows the one in the famous 5302 * "30 instruction TCP receive" Van Jacobson mail. 5303 * 5304 * Van's trick is to deposit buffers into socket queue 5305 * on a device interrupt, to call tcp_recv function 5306 * on the receive process context and checksum and copy 5307 * the buffer to user space. smart... 5308 * 5309 * Our current scheme is not silly either but we take the 5310 * extra cost of the net_bh soft interrupt processing... 5311 * We do checksum and copy also but from device to kernel. 5312 */ 5313 5314 tp->rx_opt.saw_tstamp = 0; 5315 5316 /* pred_flags is 0xS?10 << 16 + snd_wnd 5317 * if header_prediction is to be made 5318 * 'S' will always be tp->tcp_header_len >> 2 5319 * '?' will be 0 for the fast path, otherwise pred_flags is 0 to 5320 * turn it off (when there are holes in the receive 5321 * space for instance) 5322 * PSH flag is ignored. 5323 */ 5324 5325 if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags && 5326 TCP_SKB_CB(skb)->seq == tp->rcv_nxt && 5327 !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) { 5328 int tcp_header_len = tp->tcp_header_len; 5329 5330 /* Timestamp header prediction: tcp_header_len 5331 * is automatically equal to th->doff*4 due to pred_flags 5332 * match. 5333 */ 5334 5335 /* Check timestamp */ 5336 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) { 5337 /* No? Slow path! */ 5338 if (!tcp_parse_aligned_timestamp(tp, th)) 5339 goto slow_path; 5340 5341 /* If PAWS failed, check it more carefully in slow path */ 5342 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0) 5343 goto slow_path; 5344 5345 /* DO NOT update ts_recent here, if checksum fails 5346 * and timestamp was corrupted part, it will result 5347 * in a hung connection since we will drop all 5348 * future packets due to the PAWS test. 5349 */ 5350 } 5351 5352 if (len <= tcp_header_len) { 5353 /* Bulk data transfer: sender */ 5354 if (len == tcp_header_len) { 5355 /* Predicted packet is in window by definition. 5356 * seq == rcv_nxt and rcv_wup <= rcv_nxt. 5357 * Hence, check seq<=rcv_wup reduces to: 5358 */ 5359 if (tcp_header_len == 5360 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && 5361 tp->rcv_nxt == tp->rcv_wup) 5362 tcp_store_ts_recent(tp); 5363 5364 /* We know that such packets are checksummed 5365 * on entry. 5366 */ 5367 tcp_ack(sk, skb, 0); 5368 __kfree_skb(skb); 5369 tcp_data_snd_check(sk); 5370 return 0; 5371 } else { /* Header too small */ 5372 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS); 5373 goto discard; 5374 } 5375 } else { 5376 int eaten = 0; 5377 int copied_early = 0; 5378 5379 if (tp->copied_seq == tp->rcv_nxt && 5380 len - tcp_header_len <= tp->ucopy.len) { 5381#ifdef CONFIG_NET_DMA 5382 if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) { 5383 copied_early = 1; 5384 eaten = 1; 5385 } 5386#endif 5387 if (tp->ucopy.task == current && 5388 sock_owned_by_user(sk) && !copied_early) { 5389 __set_current_state(TASK_RUNNING); 5390 5391 if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) 5392 eaten = 1; 5393 } 5394 if (eaten) { 5395 /* Predicted packet is in window by definition. 5396 * seq == rcv_nxt and rcv_wup <= rcv_nxt. 5397 * Hence, check seq<=rcv_wup reduces to: 5398 */ 5399 if (tcp_header_len == 5400 (sizeof(struct tcphdr) + 5401 TCPOLEN_TSTAMP_ALIGNED) && 5402 tp->rcv_nxt == tp->rcv_wup) 5403 tcp_store_ts_recent(tp); 5404 5405 tcp_rcv_rtt_measure_ts(sk, skb); 5406 5407 __skb_pull(skb, tcp_header_len); 5408 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; 5409 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER); 5410 } 5411 if (copied_early) 5412 tcp_cleanup_rbuf(sk, skb->len); 5413 } 5414 if (!eaten) { 5415 if (tcp_checksum_complete_user(sk, skb)) 5416 goto csum_error; 5417 5418 /* Predicted packet is in window by definition. 5419 * seq == rcv_nxt and rcv_wup <= rcv_nxt. 5420 * Hence, check seq<=rcv_wup reduces to: 5421 */ 5422 if (tcp_header_len == 5423 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && 5424 tp->rcv_nxt == tp->rcv_wup) 5425 tcp_store_ts_recent(tp); 5426 5427 tcp_rcv_rtt_measure_ts(sk, skb); 5428 5429 if ((int)skb->truesize > sk->sk_forward_alloc) 5430 goto step5; 5431 5432 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS); 5433 5434 /* Bulk data transfer: receiver */ 5435 __skb_pull(skb, tcp_header_len); 5436 __skb_queue_tail(&sk->sk_receive_queue, skb); 5437 skb_set_owner_r(skb, sk); 5438 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; 5439 } 5440 5441 tcp_event_data_recv(sk, skb); 5442 5443 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) { 5444 /* Well, only one small jumplet in fast path... */ 5445 tcp_ack(sk, skb, FLAG_DATA); 5446 tcp_data_snd_check(sk); 5447 if (!inet_csk_ack_scheduled(sk)) 5448 goto no_ack; 5449 } 5450 5451 if (!copied_early || tp->rcv_nxt != tp->rcv_wup) 5452 __tcp_ack_snd_check(sk, 0); 5453no_ack: 5454#ifdef CONFIG_NET_DMA 5455 if (copied_early) 5456 __skb_queue_tail(&sk->sk_async_wait_queue, skb); 5457 else 5458#endif 5459 if (eaten) 5460 __kfree_skb(skb); 5461 else 5462 sk->sk_data_ready(sk, 0); 5463 return 0; 5464 } 5465 } 5466 5467slow_path: 5468 if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb)) 5469 goto csum_error; 5470 5471 /* 5472 * Standard slow path. 5473 */ 5474 5475 res = tcp_validate_incoming(sk, skb, th, 1); 5476 if (res <= 0) 5477 return -res; 5478 5479step5: 5480 if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0) 5481 goto discard; 5482 5483 tcp_rcv_rtt_measure_ts(sk, skb); 5484 5485 /* Process urgent data. */ 5486 tcp_urg(sk, skb, th); 5487 5488 /* step 7: process the segment text */ 5489 tcp_data_queue(sk, skb); 5490 5491 tcp_data_snd_check(sk); 5492 tcp_ack_snd_check(sk); 5493 return 0; 5494 5495csum_error: 5496 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS); 5497 5498discard: 5499 __kfree_skb(skb); 5500 return 0; 5501} 5502EXPORT_SYMBOL(tcp_rcv_established); 5503 5504static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, 5505 const struct tcphdr *th, unsigned int len) 5506{ 5507 const u8 *hash_location; 5508 struct inet_connection_sock *icsk = inet_csk(sk); 5509 struct tcp_sock *tp = tcp_sk(sk); 5510 struct tcp_cookie_values *cvp = tp->cookie_values; 5511 int saved_clamp = tp->rx_opt.mss_clamp; 5512 5513 tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0); 5514 5515 if (th->ack) { 5516 /* rfc793: 5517 * "If the state is SYN-SENT then 5518 * first check the ACK bit 5519 * If the ACK bit is set 5520 * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send 5521 * a reset (unless the RST bit is set, if so drop 5522 * the segment and return)" 5523 * 5524 * We do not send data with SYN, so that RFC-correct 5525 * test reduces to: 5526 */ 5527 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt) 5528 goto reset_and_undo; 5529 5530 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && 5531 !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp, 5532 tcp_time_stamp)) { 5533 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED); 5534 goto reset_and_undo; 5535 } 5536 5537 /* Now ACK is acceptable. 5538 * 5539 * "If the RST bit is set 5540 * If the ACK was acceptable then signal the user "error: 5541 * connection reset", drop the segment, enter CLOSED state, 5542 * delete TCB, and return." 5543 */ 5544 5545 if (th->rst) { 5546 tcp_reset(sk); 5547 goto discard; 5548 } 5549 5550 /* rfc793: 5551 * "fifth, if neither of the SYN or RST bits is set then 5552 * drop the segment and return." 5553 * 5554 * See note below! 5555 * --ANK(990513) 5556 */ 5557 if (!th->syn) 5558 goto discard_and_undo; 5559 5560 /* rfc793: 5561 * "If the SYN bit is on ... 5562 * are acceptable then ... 5563 * (our SYN has been ACKed), change the connection 5564 * state to ESTABLISHED..." 5565 */ 5566 5567 TCP_ECN_rcv_synack(tp, th); 5568 5569 tp->snd_wl1 = TCP_SKB_CB(skb)->seq; 5570 tcp_ack(sk, skb, FLAG_SLOWPATH); 5571 5572 /* Ok.. it's good. Set up sequence numbers and 5573 * move to established. 5574 */ 5575 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; 5576 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; 5577 5578 /* RFC1323: The window in SYN & SYN/ACK segments is 5579 * never scaled. 5580 */ 5581 tp->snd_wnd = ntohs(th->window); 5582 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq); 5583 5584 if (!tp->rx_opt.wscale_ok) { 5585 tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0; 5586 tp->window_clamp = min(tp->window_clamp, 65535U); 5587 } 5588 5589 if (tp->rx_opt.saw_tstamp) { 5590 tp->rx_opt.tstamp_ok = 1; 5591 tp->tcp_header_len = 5592 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 5593 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; 5594 tcp_store_ts_recent(tp); 5595 } else { 5596 tp->tcp_header_len = sizeof(struct tcphdr); 5597 } 5598 5599 if (tcp_is_sack(tp) && sysctl_tcp_fack) 5600 tcp_enable_fack(tp); 5601 5602 tcp_mtup_init(sk); 5603 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 5604 tcp_initialize_rcv_mss(sk); 5605 5606 /* Remember, tcp_poll() does not lock socket! 5607 * Change state from SYN-SENT only after copied_seq 5608 * is initialized. */ 5609 tp->copied_seq = tp->rcv_nxt; 5610 5611 if (cvp != NULL && 5612 cvp->cookie_pair_size > 0 && 5613 tp->rx_opt.cookie_plus > 0) { 5614 int cookie_size = tp->rx_opt.cookie_plus 5615 - TCPOLEN_COOKIE_BASE; 5616 int cookie_pair_size = cookie_size 5617 + cvp->cookie_desired; 5618 5619 /* A cookie extension option was sent and returned. 5620 * Note that each incoming SYNACK replaces the 5621 * Responder cookie. The initial exchange is most 5622 * fragile, as protection against spoofing relies 5623 * entirely upon the sequence and timestamp (above). 5624 * This replacement strategy allows the correct pair to 5625 * pass through, while any others will be filtered via 5626 * Responder verification later. 5627 */ 5628 if (sizeof(cvp->cookie_pair) >= cookie_pair_size) { 5629 memcpy(&cvp->cookie_pair[cvp->cookie_desired], 5630 hash_location, cookie_size); 5631 cvp->cookie_pair_size = cookie_pair_size; 5632 } 5633 } 5634 5635 smp_mb(); 5636 tcp_set_state(sk, TCP_ESTABLISHED); 5637 5638 security_inet_conn_established(sk, skb); 5639 5640 /* Make sure socket is routed, for correct metrics. */ 5641 icsk->icsk_af_ops->rebuild_header(sk); 5642 5643 tcp_init_metrics(sk); 5644 5645 tcp_init_congestion_control(sk); 5646 5647 /* Prevent spurious tcp_cwnd_restart() on first data 5648 * packet. 5649 */ 5650 tp->lsndtime = tcp_time_stamp; 5651 5652 tcp_init_buffer_space(sk); 5653 5654 if (sock_flag(sk, SOCK_KEEPOPEN)) 5655 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp)); 5656 5657 if (!tp->rx_opt.snd_wscale) 5658 __tcp_fast_path_on(tp, tp->snd_wnd); 5659 else 5660 tp->pred_flags = 0; 5661 5662 if (!sock_flag(sk, SOCK_DEAD)) { 5663 sk->sk_state_change(sk); 5664 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT); 5665 } 5666 5667 if (sk->sk_write_pending || 5668 icsk->icsk_accept_queue.rskq_defer_accept || 5669 icsk->icsk_ack.pingpong) { 5670 /* Save one ACK. Data will be ready after 5671 * several ticks, if write_pending is set. 5672 * 5673 * It may be deleted, but with this feature tcpdumps 5674 * look so _wonderfully_ clever, that I was not able 5675 * to stand against the temptation 8) --ANK 5676 */ 5677 inet_csk_schedule_ack(sk); 5678 icsk->icsk_ack.lrcvtime = tcp_time_stamp; 5679 icsk->icsk_ack.ato = TCP_ATO_MIN; 5680 tcp_incr_quickack(sk); 5681 tcp_enter_quickack_mode(sk); 5682 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, 5683 TCP_DELACK_MAX, TCP_RTO_MAX); 5684 5685discard: 5686 __kfree_skb(skb); 5687 return 0; 5688 } else { 5689 tcp_send_ack(sk); 5690 } 5691 return -1; 5692 } 5693 5694 /* No ACK in the segment */ 5695 5696 if (th->rst) { 5697 /* rfc793: 5698 * "If the RST bit is set 5699 * 5700 * Otherwise (no ACK) drop the segment and return." 5701 */ 5702 5703 goto discard_and_undo; 5704 } 5705 5706 /* PAWS check. */ 5707 if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && 5708 tcp_paws_reject(&tp->rx_opt, 0)) 5709 goto discard_and_undo; 5710 5711 if (th->syn) { 5712 /* We see SYN without ACK. It is attempt of 5713 * simultaneous connect with crossed SYNs. 5714 * Particularly, it can be connect to self. 5715 */ 5716 tcp_set_state(sk, TCP_SYN_RECV); 5717 5718 if (tp->rx_opt.saw_tstamp) { 5719 tp->rx_opt.tstamp_ok = 1; 5720 tcp_store_ts_recent(tp); 5721 tp->tcp_header_len = 5722 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 5723 } else { 5724 tp->tcp_header_len = sizeof(struct tcphdr); 5725 } 5726 5727 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; 5728 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; 5729 5730 /* RFC1323: The window in SYN & SYN/ACK segments is 5731 * never scaled. 5732 */ 5733 tp->snd_wnd = ntohs(th->window); 5734 tp->snd_wl1 = TCP_SKB_CB(skb)->seq; 5735 tp->max_window = tp->snd_wnd; 5736 5737 TCP_ECN_rcv_syn(tp, th); 5738 5739 tcp_mtup_init(sk); 5740 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 5741 tcp_initialize_rcv_mss(sk); 5742 5743 tcp_send_synack(sk); 5744#if 0 5745 /* Note, we could accept data and URG from this segment. 5746 * There are no obstacles to make this. 5747 * 5748 * However, if we ignore data in ACKless segments sometimes, 5749 * we have no reasons to accept it sometimes. 5750 * Also, seems the code doing it in step6 of tcp_rcv_state_process 5751 * is not flawless. So, discard packet for sanity. 5752 * Uncomment this return to process the data. 5753 */ 5754 return -1; 5755#else 5756 goto discard; 5757#endif 5758 } 5759 /* "fifth, if neither of the SYN or RST bits is set then 5760 * drop the segment and return." 5761 */ 5762 5763discard_and_undo: 5764 tcp_clear_options(&tp->rx_opt); 5765 tp->rx_opt.mss_clamp = saved_clamp; 5766 goto discard; 5767 5768reset_and_undo: 5769 tcp_clear_options(&tp->rx_opt); 5770 tp->rx_opt.mss_clamp = saved_clamp; 5771 return 1; 5772} 5773 5774/* 5775 * This function implements the receiving procedure of RFC 793 for 5776 * all states except ESTABLISHED and TIME_WAIT. 5777 * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be 5778 * address independent. 5779 */ 5780 5781int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 5782 const struct tcphdr *th, unsigned int len) 5783{ 5784 struct tcp_sock *tp = tcp_sk(sk); 5785 struct inet_connection_sock *icsk = inet_csk(sk); 5786 int queued = 0; 5787 int res; 5788 5789 tp->rx_opt.saw_tstamp = 0; 5790 5791 switch (sk->sk_state) { 5792 case TCP_CLOSE: 5793 goto discard; 5794 5795 case TCP_LISTEN: 5796 if (th->ack) 5797 return 1; 5798 5799 if (th->rst) 5800 goto discard; 5801 5802 if (th->syn) { 5803 if (th->fin) 5804 goto discard; 5805 if (icsk->icsk_af_ops->conn_request(sk, skb) < 0) 5806 return 1; 5807 5808 /* Now we have several options: In theory there is 5809 * nothing else in the frame. KA9Q has an option to 5810 * send data with the syn, BSD accepts data with the 5811 * syn up to the [to be] advertised window and 5812 * Solaris 2.1 gives you a protocol error. For now 5813 * we just ignore it, that fits the spec precisely 5814 * and avoids incompatibilities. It would be nice in 5815 * future to drop through and process the data. 5816 * 5817 * Now that TTCP is starting to be used we ought to 5818 * queue this data. 5819 * But, this leaves one open to an easy denial of 5820 * service attack, and SYN cookies can't defend 5821 * against this problem. So, we drop the data 5822 * in the interest of security over speed unless 5823 * it's still in use. 5824 */ 5825 kfree_skb(skb); 5826 return 0; 5827 } 5828 goto discard; 5829 5830 case TCP_SYN_SENT: 5831 queued = tcp_rcv_synsent_state_process(sk, skb, th, len); 5832 if (queued >= 0) 5833 return queued; 5834 5835 /* Do step6 onward by hand. */ 5836 tcp_urg(sk, skb, th); 5837 __kfree_skb(skb); 5838 tcp_data_snd_check(sk); 5839 return 0; 5840 } 5841 5842 res = tcp_validate_incoming(sk, skb, th, 0); 5843 if (res <= 0) 5844 return -res; 5845 5846 /* step 5: check the ACK field */ 5847 if (th->ack) { 5848 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH) > 0; 5849 5850 switch (sk->sk_state) { 5851 case TCP_SYN_RECV: 5852 if (acceptable) { 5853 tp->copied_seq = tp->rcv_nxt; 5854 smp_mb(); 5855 tcp_set_state(sk, TCP_ESTABLISHED); 5856 sk->sk_state_change(sk); 5857 5858 /* Note, that this wakeup is only for marginal 5859 * crossed SYN case. Passively open sockets 5860 * are not waked up, because sk->sk_sleep == 5861 * NULL and sk->sk_socket == NULL. 5862 */ 5863 if (sk->sk_socket) 5864 sk_wake_async(sk, 5865 SOCK_WAKE_IO, POLL_OUT); 5866 5867 tp->snd_una = TCP_SKB_CB(skb)->ack_seq; 5868 tp->snd_wnd = ntohs(th->window) << 5869 tp->rx_opt.snd_wscale; 5870 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq); 5871 5872 if (tp->rx_opt.tstamp_ok) 5873 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; 5874 5875 /* Make sure socket is routed, for 5876 * correct metrics. 5877 */ 5878 icsk->icsk_af_ops->rebuild_header(sk); 5879 5880 tcp_init_metrics(sk); 5881 5882 tcp_init_congestion_control(sk); 5883 5884 /* Prevent spurious tcp_cwnd_restart() on 5885 * first data packet. 5886 */ 5887 tp->lsndtime = tcp_time_stamp; 5888 5889 tcp_mtup_init(sk); 5890 tcp_initialize_rcv_mss(sk); 5891 tcp_init_buffer_space(sk); 5892 tcp_fast_path_on(tp); 5893 } else { 5894 return 1; 5895 } 5896 break; 5897 5898 case TCP_FIN_WAIT1: 5899 if (tp->snd_una == tp->write_seq) { 5900 tcp_set_state(sk, TCP_FIN_WAIT2); 5901 sk->sk_shutdown |= SEND_SHUTDOWN; 5902 dst_confirm(__sk_dst_get(sk)); 5903 5904 if (!sock_flag(sk, SOCK_DEAD)) 5905 /* Wake up lingering close() */ 5906 sk->sk_state_change(sk); 5907 else { 5908 int tmo; 5909 5910 if (tp->linger2 < 0 || 5911 (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && 5912 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) { 5913 tcp_done(sk); 5914 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA); 5915 return 1; 5916 } 5917 5918 tmo = tcp_fin_time(sk); 5919 if (tmo > TCP_TIMEWAIT_LEN) { 5920 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN); 5921 } else if (th->fin || sock_owned_by_user(sk)) { 5922 /* Bad case. We could lose such FIN otherwise. 5923 * It is not a big problem, but it looks confusing 5924 * and not so rare event. We still can lose it now, 5925 * if it spins in bh_lock_sock(), but it is really 5926 * marginal case. 5927 */ 5928 inet_csk_reset_keepalive_timer(sk, tmo); 5929 } else { 5930 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 5931 goto discard; 5932 } 5933 } 5934 } 5935 break; 5936 5937 case TCP_CLOSING: 5938 if (tp->snd_una == tp->write_seq) { 5939 tcp_time_wait(sk, TCP_TIME_WAIT, 0); 5940 goto discard; 5941 } 5942 break; 5943 5944 case TCP_LAST_ACK: 5945 if (tp->snd_una == tp->write_seq) { 5946 tcp_update_metrics(sk); 5947 tcp_done(sk); 5948 goto discard; 5949 } 5950 break; 5951 } 5952 } else 5953 goto discard; 5954 5955 /* step 6: check the URG bit */ 5956 tcp_urg(sk, skb, th); 5957 5958 /* step 7: process the segment text */ 5959 switch (sk->sk_state) { 5960 case TCP_CLOSE_WAIT: 5961 case TCP_CLOSING: 5962 case TCP_LAST_ACK: 5963 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) 5964 break; 5965 case TCP_FIN_WAIT1: 5966 case TCP_FIN_WAIT2: 5967 /* RFC 793 says to queue data in these states, 5968 * RFC 1122 says we MUST send a reset. 5969 * BSD 4.4 also does reset. 5970 */ 5971 if (sk->sk_shutdown & RCV_SHUTDOWN) { 5972 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && 5973 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) { 5974 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA); 5975 tcp_reset(sk); 5976 return 1; 5977 } 5978 } 5979 /* Fall through */ 5980 case TCP_ESTABLISHED: 5981 tcp_data_queue(sk, skb); 5982 queued = 1; 5983 break; 5984 } 5985 5986 /* tcp_data could move socket to TIME-WAIT */ 5987 if (sk->sk_state != TCP_CLOSE) { 5988 tcp_data_snd_check(sk); 5989 tcp_ack_snd_check(sk); 5990 } 5991 5992 if (!queued) { 5993discard: 5994 __kfree_skb(skb); 5995 } 5996 return 0; 5997} 5998EXPORT_SYMBOL(tcp_rcv_state_process); 5999