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, cookie_scratch)[16 + 5 + SHA_WORKSPACE_WORDS]; 78 79 static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr, 80 __be16 sport, __be16 dport, u32 count, int c) 81 { 82 __u32 *tmp = __get_cpu_var(cookie_scratch); 83 84 /* 85 * we have 320 bits of information to hash, copy in the remaining 86 * 192 bits required for sha_transform, from the syncookie_secret 87 * and overwrite the digest with the secret 88 */ 89 memcpy(tmp + 10, syncookie_secret[c], 44); 90 memcpy(tmp, saddr, 16); 91 memcpy(tmp + 4, daddr, 16); 92 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; 93 tmp[9] = count; 94 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); 95 96 return tmp[17]; 97 } 98 99 static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr, 100 __be16 sport, __be16 dport, __u32 sseq, 101 __u32 count, __u32 data) 102 { 103 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + 104 sseq + (count << COOKIEBITS) + 105 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) 106 & COOKIEMASK)); 107 } 108 109 static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr, 110 struct in6_addr *daddr, __be16 sport, 111 __be16 dport, __u32 sseq, __u32 count, 112 __u32 maxdiff) 113 { 114 __u32 diff; 115 116 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; 117 118 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); 119 if (diff >= maxdiff) 120 return (__u32)-1; 121 122 return (cookie - 123 cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) 124 & COOKIEMASK; 125 } 126 127 __u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp) 128 { 129 struct ipv6hdr *iph = ipv6_hdr(skb); 130 const struct tcphdr *th = tcp_hdr(skb); 131 int mssind; 132 const __u16 mss = *mssp; 133 134 tcp_synq_overflow(sk); 135 136 for (mssind = 0; mss > msstab[mssind + 1]; mssind++) 137 ; 138 *mssp = msstab[mssind] + 1; 139 140 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); 141 142 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, 143 th->dest, ntohl(th->seq), 144 jiffies / (HZ * 60), mssind); 145 } 146 147 static inline int cookie_check(struct sk_buff *skb, __u32 cookie) 148 { 149 struct ipv6hdr *iph = ipv6_hdr(skb); 150 const struct tcphdr *th = tcp_hdr(skb); 151 __u32 seq = ntohl(th->seq) - 1; 152 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, 153 th->source, th->dest, seq, 154 jiffies / (HZ * 60), COUNTER_TRIES); 155 156 return mssind < NUM_MSS ? msstab[mssind] + 1 : 0; 157 } 158 159 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 160 { 161 struct inet_request_sock *ireq; 162 struct inet6_request_sock *ireq6; 163 struct tcp_request_sock *treq; 164 struct ipv6_pinfo *np = inet6_sk(sk); 165 struct tcp_sock *tp = tcp_sk(sk); 166 const struct tcphdr *th = tcp_hdr(skb); 167 __u32 cookie = ntohl(th->ack_seq) - 1; 168 struct sock *ret = sk; 169 struct request_sock *req; 170 int mss; 171 struct dst_entry *dst; 172 __u8 rcv_wscale; 173 struct tcp_options_received tcp_opt; 174 175 if (!sysctl_tcp_syncookies || !th->ack) 176 goto out; 177 178 if (tcp_synq_no_recent_overflow(sk) || 179 (mss = cookie_check(skb, cookie)) == 0) { 180 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); 181 goto out; 182 } 183 184 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); 185 186 /* check for timestamp cookie support */ 187 memset(&tcp_opt, 0, sizeof(tcp_opt)); 188 tcp_parse_options(skb, &tcp_opt, 0); 189 190 if (tcp_opt.saw_tstamp) 191 cookie_check_timestamp(&tcp_opt); 192 193 ret = NULL; 194 req = inet6_reqsk_alloc(&tcp6_request_sock_ops); 195 if (!req) 196 goto out; 197 198 ireq = inet_rsk(req); 199 ireq6 = inet6_rsk(req); 200 treq = tcp_rsk(req); 201 202 if (security_inet_conn_request(sk, skb, req)) 203 goto out_free; 204 205 req->mss = mss; 206 ireq->rmt_port = th->source; 207 ireq->loc_port = th->dest; 208 ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr); 209 ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr); 210 if (ipv6_opt_accepted(sk, skb) || 211 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || 212 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { 213 atomic_inc(&skb->users); 214 ireq6->pktopts = skb; 215 } 216 217 ireq6->iif = sk->sk_bound_dev_if; 218 /* So that link locals have meaning */ 219 if (!sk->sk_bound_dev_if && 220 ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL) 221 ireq6->iif = inet6_iif(skb); 222 223 req->expires = 0UL; 224 req->retrans = 0; 225 ireq->ecn_ok = 0; 226 ireq->snd_wscale = tcp_opt.snd_wscale; 227 ireq->rcv_wscale = tcp_opt.rcv_wscale; 228 ireq->sack_ok = tcp_opt.sack_ok; 229 ireq->wscale_ok = tcp_opt.wscale_ok; 230 ireq->tstamp_ok = tcp_opt.saw_tstamp; 231 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; 232 treq->rcv_isn = ntohl(th->seq) - 1; 233 treq->snt_isn = cookie; 234 235 /* 236 * We need to lookup the dst_entry to get the correct window size. 237 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten 238 * me if there is a preferred way. 239 */ 240 { 241 struct in6_addr *final_p = NULL, final; 242 struct flowi fl; 243 memset(&fl, 0, sizeof(fl)); 244 fl.proto = IPPROTO_TCP; 245 ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr); 246 if (np->opt && np->opt->srcrt) { 247 struct rt0_hdr *rt0 = (struct rt0_hdr *) np->opt->srcrt; 248 ipv6_addr_copy(&final, &fl.fl6_dst); 249 ipv6_addr_copy(&fl.fl6_dst, rt0->addr); 250 final_p = &final; 251 } 252 ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr); 253 fl.oif = sk->sk_bound_dev_if; 254 fl.fl_ip_dport = inet_rsk(req)->rmt_port; 255 fl.fl_ip_sport = inet_sk(sk)->sport; 256 security_req_classify_flow(req, &fl); 257 if (ip6_dst_lookup(sk, &dst, &fl)) 258 goto out_free; 259 260 if (final_p) 261 ipv6_addr_copy(&fl.fl6_dst, final_p); 262 if ((xfrm_lookup(sock_net(sk), &dst, &fl, sk, 0)) < 0) 263 goto out_free; 264 } 265 266 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); 267 tcp_select_initial_window(tcp_full_space(sk), req->mss, 268 &req->rcv_wnd, &req->window_clamp, 269 ireq->wscale_ok, &rcv_wscale); 270 271 ireq->rcv_wscale = rcv_wscale; 272 273 ret = get_cookie_sock(sk, skb, req, dst); 274 out: 275 return ret; 276 out_free: 277 reqsk_free(req); 278 return NULL; 279 } 280 281