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 extern int sysctl_tcp_syncookies; 25 extern __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 /* 31 * This table has to be sorted and terminated with (__u16)-1. 32 * XXX generate a better table. 33 * Unresolved Issues: HIPPI with a 64k MSS is not well supported. 34 * 35 * Taken directly from ipv4 implementation. 36 * Should this list be modified for ipv6 use or is it close enough? 37 * rfc 2460 8.3 suggests mss values 20 bytes less than ipv4 counterpart 38 */ 39 static __u16 const msstab[] = { 40 64 - 1, 41 256 - 1, 42 512 - 1, 43 536 - 1, 44 1024 - 1, 45 1440 - 1, 46 1460 - 1, 47 4312 - 1, 48 (__u16)-1 49 }; 50 /* The number doesn't include the -1 terminator */ 51 #define NUM_MSS (ARRAY_SIZE(msstab) - 1) 52 53 /* 54 * This (misnamed) value is the age of syncookie which is permitted. 55 * Its ideal value should be dependent on TCP_TIMEOUT_INIT and 56 * sysctl_tcp_retries1. It's a rather complicated formula (exponential 57 * backoff) to compute at runtime so it's currently hardcoded here. 58 */ 59 #define COUNTER_TRIES 4 60 61 static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, 62 struct request_sock *req, 63 struct dst_entry *dst) 64 { 65 struct inet_connection_sock *icsk = inet_csk(sk); 66 struct sock *child; 67 68 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst); 69 if (child) 70 inet_csk_reqsk_queue_add(sk, req, child); 71 else 72 reqsk_free(req); 73 74 return child; 75 } 76 77 static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], 78 ipv6_cookie_scratch); 79 80 static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr, 81 __be16 sport, __be16 dport, u32 count, int c) 82 { 83 __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch); 84 85 /* 86 * we have 320 bits of information to hash, copy in the remaining 87 * 192 bits required for sha_transform, from the syncookie_secret 88 * and overwrite the digest with the secret 89 */ 90 memcpy(tmp + 10, syncookie_secret[c], 44); 91 memcpy(tmp, saddr, 16); 92 memcpy(tmp + 4, daddr, 16); 93 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; 94 tmp[9] = count; 95 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); 96 97 return tmp[17]; 98 } 99 100 static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr, 101 __be16 sport, __be16 dport, __u32 sseq, 102 __u32 count, __u32 data) 103 { 104 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + 105 sseq + (count << COOKIEBITS) + 106 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) 107 & COOKIEMASK)); 108 } 109 110 static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr, 111 struct in6_addr *daddr, __be16 sport, 112 __be16 dport, __u32 sseq, __u32 count, 113 __u32 maxdiff) 114 { 115 __u32 diff; 116 117 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; 118 119 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); 120 if (diff >= maxdiff) 121 return (__u32)-1; 122 123 return (cookie - 124 cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) 125 & COOKIEMASK; 126 } 127 128 __u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp) 129 { 130 struct ipv6hdr *iph = ipv6_hdr(skb); 131 const struct tcphdr *th = tcp_hdr(skb); 132 int mssind; 133 const __u16 mss = *mssp; 134 135 tcp_synq_overflow(sk); 136 137 for (mssind = 0; mss > msstab[mssind + 1]; mssind++) 138 ; 139 *mssp = msstab[mssind] + 1; 140 141 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); 142 143 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, 144 th->dest, ntohl(th->seq), 145 jiffies / (HZ * 60), mssind); 146 } 147 148 static inline int cookie_check(struct sk_buff *skb, __u32 cookie) 149 { 150 struct ipv6hdr *iph = ipv6_hdr(skb); 151 const struct tcphdr *th = tcp_hdr(skb); 152 __u32 seq = ntohl(th->seq) - 1; 153 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, 154 th->source, th->dest, seq, 155 jiffies / (HZ * 60), COUNTER_TRIES); 156 157 return mssind < NUM_MSS ? msstab[mssind] + 1 : 0; 158 } 159 160 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 161 { 162 struct inet_request_sock *ireq; 163 struct inet6_request_sock *ireq6; 164 struct tcp_request_sock *treq; 165 struct ipv6_pinfo *np = inet6_sk(sk); 166 struct tcp_sock *tp = tcp_sk(sk); 167 const struct tcphdr *th = tcp_hdr(skb); 168 __u32 cookie = ntohl(th->ack_seq) - 1; 169 struct sock *ret = sk; 170 struct request_sock *req; 171 int mss; 172 struct dst_entry *dst; 173 __u8 rcv_wscale; 174 struct tcp_options_received tcp_opt; 175 176 if (!sysctl_tcp_syncookies || !th->ack) 177 goto out; 178 179 if (tcp_synq_no_recent_overflow(sk) || 180 (mss = cookie_check(skb, cookie)) == 0) { 181 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); 182 goto out; 183 } 184 185 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); 186 187 /* check for timestamp cookie support */ 188 memset(&tcp_opt, 0, sizeof(tcp_opt)); 189 tcp_parse_options(skb, &tcp_opt, 0); 190 191 if (tcp_opt.saw_tstamp) 192 cookie_check_timestamp(&tcp_opt); 193 194 ret = NULL; 195 req = inet6_reqsk_alloc(&tcp6_request_sock_ops); 196 if (!req) 197 goto out; 198 199 ireq = inet_rsk(req); 200 ireq6 = inet6_rsk(req); 201 treq = tcp_rsk(req); 202 203 if (security_inet_conn_request(sk, skb, req)) 204 goto out_free; 205 206 req->mss = mss; 207 ireq->rmt_port = th->source; 208 ireq->loc_port = th->dest; 209 ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr); 210 ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr); 211 if (ipv6_opt_accepted(sk, skb) || 212 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || 213 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { 214 atomic_inc(&skb->users); 215 ireq6->pktopts = skb; 216 } 217 218 ireq6->iif = sk->sk_bound_dev_if; 219 /* So that link locals have meaning */ 220 if (!sk->sk_bound_dev_if && 221 ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL) 222 ireq6->iif = inet6_iif(skb); 223 224 req->expires = 0UL; 225 req->retrans = 0; 226 ireq->ecn_ok = 0; 227 ireq->snd_wscale = tcp_opt.snd_wscale; 228 ireq->rcv_wscale = tcp_opt.rcv_wscale; 229 ireq->sack_ok = tcp_opt.sack_ok; 230 ireq->wscale_ok = tcp_opt.wscale_ok; 231 ireq->tstamp_ok = tcp_opt.saw_tstamp; 232 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; 233 treq->rcv_isn = ntohl(th->seq) - 1; 234 treq->snt_isn = cookie; 235 236 /* 237 * We need to lookup the dst_entry to get the correct window size. 238 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten 239 * me if there is a preferred way. 240 */ 241 { 242 struct in6_addr *final_p = NULL, final; 243 struct flowi fl; 244 memset(&fl, 0, sizeof(fl)); 245 fl.proto = IPPROTO_TCP; 246 ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr); 247 if (np->opt && np->opt->srcrt) { 248 struct rt0_hdr *rt0 = (struct rt0_hdr *) np->opt->srcrt; 249 ipv6_addr_copy(&final, &fl.fl6_dst); 250 ipv6_addr_copy(&fl.fl6_dst, rt0->addr); 251 final_p = &final; 252 } 253 ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr); 254 fl.oif = sk->sk_bound_dev_if; 255 fl.fl_ip_dport = inet_rsk(req)->rmt_port; 256 fl.fl_ip_sport = inet_sk(sk)->sport; 257 security_req_classify_flow(req, &fl); 258 if (ip6_dst_lookup(sk, &dst, &fl)) 259 goto out_free; 260 261 if (final_p) 262 ipv6_addr_copy(&fl.fl6_dst, final_p); 263 if ((xfrm_lookup(sock_net(sk), &dst, &fl, sk, 0)) < 0) 264 goto out_free; 265 } 266 267 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); 268 tcp_select_initial_window(tcp_full_space(sk), req->mss, 269 &req->rcv_wnd, &req->window_clamp, 270 ireq->wscale_ok, &rcv_wscale); 271 272 ireq->rcv_wscale = rcv_wscale; 273 274 ret = get_cookie_sock(sk, skb, req, dst); 275 out: 276 return ret; 277 out_free: 278 reqsk_free(req); 279 return NULL; 280 } 281 282