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 /* RFC 2460, Section 8.3: 28 * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..] 29 * 30 * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows 31 * using higher values than ipv4 tcp syncookies. 32 * The other values are chosen based on ethernet (1500 and 9k MTU), plus 33 * one that accounts for common encap (PPPoe) overhead. Table must be sorted. 34 */ 35 static __u16 const msstab[] = { 36 1280 - 60, /* IPV6_MIN_MTU - 60 */ 37 1480 - 60, 38 1500 - 60, 39 9000 - 60, 40 }; 41 42 static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, 43 struct request_sock *req, 44 struct dst_entry *dst) 45 { 46 struct inet_connection_sock *icsk = inet_csk(sk); 47 struct sock *child; 48 49 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst); 50 if (child) 51 inet_csk_reqsk_queue_add(sk, req, child); 52 else 53 reqsk_free(req); 54 55 return child; 56 } 57 58 static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], 59 ipv6_cookie_scratch); 60 61 static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr, 62 __be16 sport, __be16 dport, u32 count, int c) 63 { 64 __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch); 65 66 /* 67 * we have 320 bits of information to hash, copy in the remaining 68 * 192 bits required for sha_transform, from the syncookie_secret 69 * and overwrite the digest with the secret 70 */ 71 memcpy(tmp + 10, syncookie_secret[c], 44); 72 memcpy(tmp, saddr, 16); 73 memcpy(tmp + 4, daddr, 16); 74 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; 75 tmp[9] = count; 76 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); 77 78 return tmp[17]; 79 } 80 81 static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, 82 const struct in6_addr *daddr, 83 __be16 sport, __be16 dport, __u32 sseq, 84 __u32 data) 85 { 86 u32 count = tcp_cookie_time(); 87 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + 88 sseq + (count << COOKIEBITS) + 89 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) 90 & COOKIEMASK)); 91 } 92 93 static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, 94 const struct in6_addr *daddr, __be16 sport, 95 __be16 dport, __u32 sseq) 96 { 97 __u32 diff, count = tcp_cookie_time(); 98 99 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; 100 101 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); 102 if (diff >= MAX_SYNCOOKIE_AGE) 103 return (__u32)-1; 104 105 return (cookie - 106 cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) 107 & COOKIEMASK; 108 } 109 110 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph, 111 const struct tcphdr *th, __u16 *mssp) 112 { 113 int mssind; 114 const __u16 mss = *mssp; 115 116 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) 117 if (mss >= msstab[mssind]) 118 break; 119 120 *mssp = msstab[mssind]; 121 122 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, 123 th->dest, ntohl(th->seq), mssind); 124 } 125 EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence); 126 127 __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp) 128 { 129 const struct ipv6hdr *iph = ipv6_hdr(skb); 130 const struct tcphdr *th = tcp_hdr(skb); 131 132 tcp_synq_overflow(sk); 133 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); 134 135 return __cookie_v6_init_sequence(iph, th, mssp); 136 } 137 138 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, 139 __u32 cookie) 140 { 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); 144 145 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; 146 } 147 EXPORT_SYMBOL_GPL(__cookie_v6_check); 148 149 struct 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_v6_check(ipv6_hdr(skb), th, 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 req->expires = 0UL; 216 req->num_retrans = 0; 217 ireq->ecn_ok = ecn_ok; 218 ireq->snd_wscale = tcp_opt.snd_wscale; 219 ireq->sack_ok = tcp_opt.sack_ok; 220 ireq->wscale_ok = tcp_opt.wscale_ok; 221 ireq->tstamp_ok = tcp_opt.saw_tstamp; 222 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; 223 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; 224 treq->rcv_isn = ntohl(th->seq) - 1; 225 treq->snt_isn = cookie; 226 227 /* 228 * We need to lookup the dst_entry to get the correct window size. 229 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten 230 * me if there is a preferred way. 231 */ 232 { 233 struct in6_addr *final_p, final; 234 struct flowi6 fl6; 235 memset(&fl6, 0, sizeof(fl6)); 236 fl6.flowi6_proto = IPPROTO_TCP; 237 fl6.daddr = ireq6->rmt_addr; 238 final_p = fl6_update_dst(&fl6, np->opt, &final); 239 fl6.saddr = ireq6->loc_addr; 240 fl6.flowi6_oif = sk->sk_bound_dev_if; 241 fl6.flowi6_mark = sk->sk_mark; 242 fl6.fl6_dport = inet_rsk(req)->rmt_port; 243 fl6.fl6_sport = inet_sk(sk)->inet_sport; 244 security_req_classify_flow(req, flowi6_to_flowi(&fl6)); 245 246 dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false); 247 if (IS_ERR(dst)) 248 goto out_free; 249 } 250 251 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); 252 tcp_select_initial_window(tcp_full_space(sk), req->mss, 253 &req->rcv_wnd, &req->window_clamp, 254 ireq->wscale_ok, &rcv_wscale, 255 dst_metric(dst, RTAX_INITRWND)); 256 257 ireq->rcv_wscale = rcv_wscale; 258 259 ret = get_cookie_sock(sk, skb, req, dst); 260 out: 261 return ret; 262 out_free: 263 reqsk_free(req); 264 return NULL; 265 } 266 267