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 /* Table must be sorted. */ 31 static __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 50 static 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 66 static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], 67 ipv6_cookie_scratch); 68 69 static u32 cookie_hash(const struct in6_addr *saddr, const 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 89 static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, 90 const struct in6_addr *daddr, 91 __be16 sport, __be16 dport, __u32 sseq, 92 __u32 count, __u32 data) 93 { 94 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + 95 sseq + (count << COOKIEBITS) + 96 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) 97 & COOKIEMASK)); 98 } 99 100 static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, 101 const struct in6_addr *daddr, __be16 sport, 102 __be16 dport, __u32 sseq, __u32 count, 103 __u32 maxdiff) 104 { 105 __u32 diff; 106 107 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; 108 109 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); 110 if (diff >= maxdiff) 111 return (__u32)-1; 112 113 return (cookie - 114 cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) 115 & COOKIEMASK; 116 } 117 118 __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp) 119 { 120 const struct ipv6hdr *iph = ipv6_hdr(skb); 121 const struct tcphdr *th = tcp_hdr(skb); 122 int mssind; 123 const __u16 mss = *mssp; 124 125 tcp_synq_overflow(sk); 126 127 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) 128 if (mss >= msstab[mssind]) 129 break; 130 131 *mssp = msstab[mssind]; 132 133 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); 134 135 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, 136 th->dest, ntohl(th->seq), 137 jiffies / (HZ * 60), mssind); 138 } 139 140 static inline int cookie_check(const struct sk_buff *skb, __u32 cookie) 141 { 142 const struct ipv6hdr *iph = ipv6_hdr(skb); 143 const struct tcphdr *th = tcp_hdr(skb); 144 __u32 seq = ntohl(th->seq) - 1; 145 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, 146 th->source, th->dest, seq, 147 jiffies / (HZ * 60), COUNTER_TRIES); 148 149 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; 150 } 151 152 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 153 { 154 struct tcp_options_received tcp_opt; 155 const u8 *hash_location; 156 struct inet_request_sock *ireq; 157 struct inet6_request_sock *ireq6; 158 struct tcp_request_sock *treq; 159 struct ipv6_pinfo *np = inet6_sk(sk); 160 struct tcp_sock *tp = tcp_sk(sk); 161 const struct tcphdr *th = tcp_hdr(skb); 162 __u32 cookie = ntohl(th->ack_seq) - 1; 163 struct sock *ret = sk; 164 struct request_sock *req; 165 int mss; 166 struct dst_entry *dst; 167 __u8 rcv_wscale; 168 bool ecn_ok = false; 169 170 if (!sysctl_tcp_syncookies || !th->ack || th->rst) 171 goto out; 172 173 if (tcp_synq_no_recent_overflow(sk) || 174 (mss = cookie_check(skb, cookie)) == 0) { 175 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); 176 goto out; 177 } 178 179 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); 180 181 /* check for timestamp cookie support */ 182 memset(&tcp_opt, 0, sizeof(tcp_opt)); 183 tcp_parse_options(skb, &tcp_opt, &hash_location, 0); 184 185 if (!cookie_check_timestamp(&tcp_opt, &ecn_ok)) 186 goto out; 187 188 ret = NULL; 189 req = inet6_reqsk_alloc(&tcp6_request_sock_ops); 190 if (!req) 191 goto out; 192 193 ireq = inet_rsk(req); 194 ireq6 = inet6_rsk(req); 195 treq = tcp_rsk(req); 196 197 if (security_inet_conn_request(sk, skb, req)) 198 goto out_free; 199 200 req->mss = mss; 201 ireq->rmt_port = th->source; 202 ireq->loc_port = th->dest; 203 ireq6->rmt_addr = ipv6_hdr(skb)->saddr; 204 ireq6->loc_addr = ipv6_hdr(skb)->daddr; 205 if (ipv6_opt_accepted(sk, skb) || 206 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || 207 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { 208 atomic_inc(&skb->users); 209 ireq6->pktopts = skb; 210 } 211 212 ireq6->iif = sk->sk_bound_dev_if; 213 /* So that link locals have meaning */ 214 if (!sk->sk_bound_dev_if && 215 ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL) 216 ireq6->iif = inet6_iif(skb); 217 218 req->expires = 0UL; 219 req->retrans = 0; 220 ireq->ecn_ok = ecn_ok; 221 ireq->snd_wscale = tcp_opt.snd_wscale; 222 ireq->sack_ok = tcp_opt.sack_ok; 223 ireq->wscale_ok = tcp_opt.wscale_ok; 224 ireq->tstamp_ok = tcp_opt.saw_tstamp; 225 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; 226 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; 227 treq->rcv_isn = ntohl(th->seq) - 1; 228 treq->snt_isn = cookie; 229 230 /* 231 * We need to lookup the dst_entry to get the correct window size. 232 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten 233 * me if there is a preferred way. 234 */ 235 { 236 struct in6_addr *final_p, final; 237 struct flowi6 fl6; 238 memset(&fl6, 0, sizeof(fl6)); 239 fl6.flowi6_proto = IPPROTO_TCP; 240 fl6.daddr = ireq6->rmt_addr; 241 final_p = fl6_update_dst(&fl6, np->opt, &final); 242 fl6.saddr = ireq6->loc_addr; 243 fl6.flowi6_oif = sk->sk_bound_dev_if; 244 fl6.flowi6_mark = sk->sk_mark; 245 fl6.fl6_dport = inet_rsk(req)->rmt_port; 246 fl6.fl6_sport = inet_sk(sk)->inet_sport; 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); 263 out: 264 return ret; 265 out_free: 266 reqsk_free(req); 267 return NULL; 268 } 269 270