syncookies.c revision 6281dcc94a96bd73017b2baa8fa83925405109ef
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 24extern int sysctl_tcp_syncookies; 25extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS]; 26 27#define COOKIEBITS 24 /* Upper bits store count */ 28#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) 29 30/* Table must be sorted. */ 31static __u16 const msstab[] = { 32 64, 33 512, 34 536, 35 1280 - 60, 36 1480 - 60, 37 1500 - 60, 38 4460 - 60, 39 9000 - 60, 40}; 41 42/* 43 * This (misnamed) value is the age of syncookie which is permitted. 44 * Its ideal value should be dependent on TCP_TIMEOUT_INIT and 45 * sysctl_tcp_retries1. It's a rather complicated formula (exponential 46 * backoff) to compute at runtime so it's currently hardcoded here. 47 */ 48#define COUNTER_TRIES 4 49 50static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, 51 struct request_sock *req, 52 struct dst_entry *dst) 53{ 54 struct inet_connection_sock *icsk = inet_csk(sk); 55 struct sock *child; 56 57 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst); 58 if (child) 59 inet_csk_reqsk_queue_add(sk, req, child); 60 else 61 reqsk_free(req); 62 63 return child; 64} 65 66static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], 67 ipv6_cookie_scratch); 68 69static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr, 70 __be16 sport, __be16 dport, u32 count, int c) 71{ 72 __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch); 73 74 /* 75 * we have 320 bits of information to hash, copy in the remaining 76 * 192 bits required for sha_transform, from the syncookie_secret 77 * and overwrite the digest with the secret 78 */ 79 memcpy(tmp + 10, syncookie_secret[c], 44); 80 memcpy(tmp, saddr, 16); 81 memcpy(tmp + 4, daddr, 16); 82 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; 83 tmp[9] = count; 84 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); 85 86 return tmp[17]; 87} 88 89static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr, 90 __be16 sport, __be16 dport, __u32 sseq, 91 __u32 count, __u32 data) 92{ 93 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + 94 sseq + (count << COOKIEBITS) + 95 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) 96 & COOKIEMASK)); 97} 98 99static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr, 100 struct in6_addr *daddr, __be16 sport, 101 __be16 dport, __u32 sseq, __u32 count, 102 __u32 maxdiff) 103{ 104 __u32 diff; 105 106 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; 107 108 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); 109 if (diff >= maxdiff) 110 return (__u32)-1; 111 112 return (cookie - 113 cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) 114 & COOKIEMASK; 115} 116 117__u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp) 118{ 119 struct ipv6hdr *iph = ipv6_hdr(skb); 120 const struct tcphdr *th = tcp_hdr(skb); 121 int mssind; 122 const __u16 mss = *mssp; 123 124 tcp_synq_overflow(sk); 125 126 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) 127 if (mss >= msstab[mssind]) 128 break; 129 130 *mssp = msstab[mssind]; 131 132 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); 133 134 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, 135 th->dest, ntohl(th->seq), 136 jiffies / (HZ * 60), mssind); 137} 138 139static inline int cookie_check(struct sk_buff *skb, __u32 cookie) 140{ 141 struct ipv6hdr *iph = ipv6_hdr(skb); 142 const struct tcphdr *th = tcp_hdr(skb); 143 __u32 seq = ntohl(th->seq) - 1; 144 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, 145 th->source, th->dest, seq, 146 jiffies / (HZ * 60), COUNTER_TRIES); 147 148 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; 149} 150 151struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 152{ 153 struct tcp_options_received tcp_opt; 154 u8 *hash_location; 155 struct inet_request_sock *ireq; 156 struct inet6_request_sock *ireq6; 157 struct tcp_request_sock *treq; 158 struct ipv6_pinfo *np = inet6_sk(sk); 159 struct tcp_sock *tp = tcp_sk(sk); 160 const struct tcphdr *th = tcp_hdr(skb); 161 __u32 cookie = ntohl(th->ack_seq) - 1; 162 struct sock *ret = sk; 163 struct request_sock *req; 164 int mss; 165 struct dst_entry *dst; 166 __u8 rcv_wscale; 167 bool ecn_ok; 168 169 if (!sysctl_tcp_syncookies || !th->ack || th->rst) 170 goto out; 171 172 if (tcp_synq_no_recent_overflow(sk) || 173 (mss = cookie_check(skb, cookie)) == 0) { 174 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); 175 goto out; 176 } 177 178 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); 179 180 /* check for timestamp cookie support */ 181 memset(&tcp_opt, 0, sizeof(tcp_opt)); 182 tcp_parse_options(skb, &tcp_opt, &hash_location, 0); 183 184 if (!cookie_check_timestamp(&tcp_opt, &ecn_ok)) 185 goto out; 186 187 ret = NULL; 188 req = inet6_reqsk_alloc(&tcp6_request_sock_ops); 189 if (!req) 190 goto out; 191 192 ireq = inet_rsk(req); 193 ireq6 = inet6_rsk(req); 194 treq = tcp_rsk(req); 195 196 if (security_inet_conn_request(sk, skb, req)) 197 goto out_free; 198 199 req->mss = mss; 200 ireq->rmt_port = th->source; 201 ireq->loc_port = th->dest; 202 ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr); 203 ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr); 204 if (ipv6_opt_accepted(sk, skb) || 205 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || 206 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { 207 atomic_inc(&skb->users); 208 ireq6->pktopts = skb; 209 } 210 211 ireq6->iif = sk->sk_bound_dev_if; 212 /* So that link locals have meaning */ 213 if (!sk->sk_bound_dev_if && 214 ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL) 215 ireq6->iif = inet6_iif(skb); 216 217 req->expires = 0UL; 218 req->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->rcv_isn = ntohl(th->seq) - 1; 226 treq->snt_isn = cookie; 227 228 /* 229 * We need to lookup the dst_entry to get the correct window size. 230 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten 231 * me if there is a preferred way. 232 */ 233 { 234 struct in6_addr *final_p, final; 235 struct flowi fl; 236 memset(&fl, 0, sizeof(fl)); 237 fl.flowi_proto = IPPROTO_TCP; 238 ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr); 239 final_p = fl6_update_dst(&fl, np->opt, &final); 240 ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr); 241 fl.flowi_oif = sk->sk_bound_dev_if; 242 fl.flowi_mark = sk->sk_mark; 243 fl.fl6_dport = inet_rsk(req)->rmt_port; 244 fl.fl6_sport = inet_sk(sk)->inet_sport; 245 security_req_classify_flow(req, &fl); 246 247 dst = ip6_dst_lookup_flow(sk, &fl, final_p, false); 248 if (IS_ERR(dst)) 249 goto out_free; 250 } 251 252 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); 253 tcp_select_initial_window(tcp_full_space(sk), req->mss, 254 &req->rcv_wnd, &req->window_clamp, 255 ireq->wscale_ok, &rcv_wscale, 256 dst_metric(dst, RTAX_INITRWND)); 257 258 ireq->rcv_wscale = rcv_wscale; 259 260 ret = get_cookie_sock(sk, skb, req, dst); 261out: 262 return ret; 263out_free: 264 reqsk_free(req); 265 return NULL; 266} 267 268