1/* 2 * IPv6 Syncookies implementation for the Linux kernel 3 * 4 * Authors: 5 * Glenn Griffin <ggriffin.kernel@gmail.com> 6 * 7 * Based on IPv4 implementation by Andi Kleen 8 * linux/net/ipv4/syncookies.c 9 * 10 * This program is free software; you can redistribute it and/or 11 * modify it under the terms of the GNU General Public License 12 * as published by the Free Software Foundation; either version 13 * 2 of the License, or (at your option) any later version. 14 * 15 */ 16 17#include <linux/tcp.h> 18#include <linux/random.h> 19#include <linux/cryptohash.h> 20#include <linux/kernel.h> 21#include <net/ipv6.h> 22#include <net/tcp.h> 23 24#define COOKIEBITS 24 /* Upper bits store count */ 25#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) 26 27/* Table must be sorted. */ 28static __u16 const msstab[] = { 29 64, 30 512, 31 536, 32 1280 - 60, 33 1480 - 60, 34 1500 - 60, 35 4460 - 60, 36 9000 - 60, 37}; 38 39/* 40 * This (misnamed) value is the age of syncookie which is permitted. 41 * Its ideal value should be dependent on TCP_TIMEOUT_INIT and 42 * sysctl_tcp_retries1. It's a rather complicated formula (exponential 43 * backoff) to compute at runtime so it's currently hardcoded here. 44 */ 45#define COUNTER_TRIES 4 46 47static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, 48 struct request_sock *req, 49 struct dst_entry *dst) 50{ 51 struct inet_connection_sock *icsk = inet_csk(sk); 52 struct sock *child; 53 54 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst); 55 if (child) 56 inet_csk_reqsk_queue_add(sk, req, child); 57 else 58 reqsk_free(req); 59 60 return child; 61} 62 63static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], 64 ipv6_cookie_scratch); 65 66static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr, 67 __be16 sport, __be16 dport, u32 count, int c) 68{ 69 __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch); 70 71 /* 72 * we have 320 bits of information to hash, copy in the remaining 73 * 192 bits required for sha_transform, from the syncookie_secret 74 * and overwrite the digest with the secret 75 */ 76 memcpy(tmp + 10, syncookie_secret[c], 44); 77 memcpy(tmp, saddr, 16); 78 memcpy(tmp + 4, daddr, 16); 79 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; 80 tmp[9] = count; 81 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); 82 83 return tmp[17]; 84} 85 86static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, 87 const struct in6_addr *daddr, 88 __be16 sport, __be16 dport, __u32 sseq, 89 __u32 count, __u32 data) 90{ 91 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + 92 sseq + (count << COOKIEBITS) + 93 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) 94 & COOKIEMASK)); 95} 96 97static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, 98 const struct in6_addr *daddr, __be16 sport, 99 __be16 dport, __u32 sseq, __u32 count, 100 __u32 maxdiff) 101{ 102 __u32 diff; 103 104 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; 105 106 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); 107 if (diff >= maxdiff) 108 return (__u32)-1; 109 110 return (cookie - 111 cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) 112 & COOKIEMASK; 113} 114 115__u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp) 116{ 117 const struct ipv6hdr *iph = ipv6_hdr(skb); 118 const struct tcphdr *th = tcp_hdr(skb); 119 int mssind; 120 const __u16 mss = *mssp; 121 122 tcp_synq_overflow(sk); 123 124 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) 125 if (mss >= msstab[mssind]) 126 break; 127 128 *mssp = msstab[mssind]; 129 130 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); 131 132 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, 133 th->dest, ntohl(th->seq), 134 jiffies / (HZ * 60), mssind); 135} 136 137static inline int cookie_check(const struct sk_buff *skb, __u32 cookie) 138{ 139 const struct ipv6hdr *iph = ipv6_hdr(skb); 140 const struct tcphdr *th = tcp_hdr(skb); 141 __u32 seq = ntohl(th->seq) - 1; 142 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, 143 th->source, th->dest, seq, 144 jiffies / (HZ * 60), COUNTER_TRIES); 145 146 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; 147} 148 149struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 150{ 151 struct tcp_options_received tcp_opt; 152 struct inet_request_sock *ireq; 153 struct inet6_request_sock *ireq6; 154 struct tcp_request_sock *treq; 155 struct ipv6_pinfo *np = inet6_sk(sk); 156 struct tcp_sock *tp = tcp_sk(sk); 157 const struct tcphdr *th = tcp_hdr(skb); 158 __u32 cookie = ntohl(th->ack_seq) - 1; 159 struct sock *ret = sk; 160 struct request_sock *req; 161 int mss; 162 struct dst_entry *dst; 163 __u8 rcv_wscale; 164 bool ecn_ok = false; 165 166 if (!sysctl_tcp_syncookies || !th->ack || th->rst) 167 goto out; 168 169 if (tcp_synq_no_recent_overflow(sk) || 170 (mss = cookie_check(skb, cookie)) == 0) { 171 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); 172 goto out; 173 } 174 175 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); 176 177 /* check for timestamp cookie support */ 178 memset(&tcp_opt, 0, sizeof(tcp_opt)); 179 tcp_parse_options(skb, &tcp_opt, 0, NULL); 180 181 if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok)) 182 goto out; 183 184 ret = NULL; 185 req = inet6_reqsk_alloc(&tcp6_request_sock_ops); 186 if (!req) 187 goto out; 188 189 ireq = inet_rsk(req); 190 ireq6 = inet6_rsk(req); 191 treq = tcp_rsk(req); 192 treq->listener = NULL; 193 194 if (security_inet_conn_request(sk, skb, req)) 195 goto out_free; 196 197 req->mss = mss; 198 ireq->rmt_port = th->source; 199 ireq->loc_port = th->dest; 200 ireq6->rmt_addr = ipv6_hdr(skb)->saddr; 201 ireq6->loc_addr = ipv6_hdr(skb)->daddr; 202 if (ipv6_opt_accepted(sk, skb) || 203 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || 204 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { 205 atomic_inc(&skb->users); 206 ireq6->pktopts = skb; 207 } 208 209 ireq6->iif = sk->sk_bound_dev_if; 210 /* So that link locals have meaning */ 211 if (!sk->sk_bound_dev_if && 212 ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL) 213 ireq6->iif = inet6_iif(skb); 214 215 ireq->ir_mark = inet_request_mark(sk, skb); 216 217 req->expires = 0UL; 218 req->num_retrans = 0; 219 ireq->ecn_ok = ecn_ok; 220 ireq->snd_wscale = tcp_opt.snd_wscale; 221 ireq->sack_ok = tcp_opt.sack_ok; 222 ireq->wscale_ok = tcp_opt.wscale_ok; 223 ireq->tstamp_ok = tcp_opt.saw_tstamp; 224 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; 225 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; 226 treq->rcv_isn = ntohl(th->seq) - 1; 227 treq->snt_isn = cookie; 228 229 /* 230 * We need to lookup the dst_entry to get the correct window size. 231 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten 232 * me if there is a preferred way. 233 */ 234 { 235 struct in6_addr *final_p, final; 236 struct flowi6 fl6; 237 memset(&fl6, 0, sizeof(fl6)); 238 fl6.flowi6_proto = IPPROTO_TCP; 239 fl6.daddr = ireq6->rmt_addr; 240 final_p = fl6_update_dst(&fl6, np->opt, &final); 241 fl6.saddr = ireq6->loc_addr; 242 fl6.flowi6_oif = sk->sk_bound_dev_if; 243 fl6.flowi6_mark = ireq->ir_mark; 244 fl6.fl6_dport = inet_rsk(req)->rmt_port; 245 fl6.fl6_sport = inet_sk(sk)->inet_sport; 246 fl6.flowi6_uid = sock_i_uid(sk); 247 security_req_classify_flow(req, flowi6_to_flowi(&fl6)); 248 249 dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false); 250 if (IS_ERR(dst)) 251 goto out_free; 252 } 253 254 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); 255 tcp_select_initial_window(tcp_full_space(sk), req->mss, 256 &req->rcv_wnd, &req->window_clamp, 257 ireq->wscale_ok, &rcv_wscale, 258 dst_metric(dst, RTAX_INITRWND)); 259 260 ireq->rcv_wscale = rcv_wscale; 261 262 ret = get_cookie_sock(sk, skb, req, dst); 263out: 264 return ret; 265out_free: 266 reqsk_free(req); 267 return NULL; 268} 269 270