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 static u32 syncookie6_secret[2][16-4+SHA_DIGEST_WORDS]; 28 29 /* RFC 2460, Section 8.3: 30 * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..] 31 * 32 * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows 33 * using higher values than ipv4 tcp syncookies. 34 * The other values are chosen based on ethernet (1500 and 9k MTU), plus 35 * one that accounts for common encap (PPPoe) overhead. Table must be sorted. 36 */ 37 static __u16 const msstab[] = { 38 1280 - 60, /* IPV6_MIN_MTU - 60 */ 39 1480 - 60, 40 1500 - 60, 41 9000 - 60, 42 }; 43 44 static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, 45 struct request_sock *req, 46 struct dst_entry *dst) 47 { 48 struct inet_connection_sock *icsk = inet_csk(sk); 49 struct sock *child; 50 51 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst); 52 if (child) 53 inet_csk_reqsk_queue_add(sk, req, child); 54 else 55 reqsk_free(req); 56 57 return child; 58 } 59 60 static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], 61 ipv6_cookie_scratch); 62 63 static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr, 64 __be16 sport, __be16 dport, u32 count, int c) 65 { 66 __u32 *tmp; 67 68 net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret)); 69 70 tmp = __get_cpu_var(ipv6_cookie_scratch); 71 72 /* 73 * we have 320 bits of information to hash, copy in the remaining 74 * 192 bits required for sha_transform, from the syncookie6_secret 75 * and overwrite the digest with the secret 76 */ 77 memcpy(tmp + 10, syncookie6_secret[c], 44); 78 memcpy(tmp, saddr, 16); 79 memcpy(tmp + 4, daddr, 16); 80 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; 81 tmp[9] = count; 82 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); 83 84 return tmp[17]; 85 } 86 87 static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, 88 const struct in6_addr *daddr, 89 __be16 sport, __be16 dport, __u32 sseq, 90 __u32 data) 91 { 92 u32 count = tcp_cookie_time(); 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 99 static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, 100 const struct in6_addr *daddr, __be16 sport, 101 __be16 dport, __u32 sseq) 102 { 103 __u32 diff, count = tcp_cookie_time(); 104 105 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; 106 107 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); 108 if (diff >= MAX_SYNCOOKIE_AGE) 109 return (__u32)-1; 110 111 return (cookie - 112 cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) 113 & COOKIEMASK; 114 } 115 116 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph, 117 const struct tcphdr *th, __u16 *mssp) 118 { 119 int mssind; 120 const __u16 mss = *mssp; 121 122 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) 123 if (mss >= msstab[mssind]) 124 break; 125 126 *mssp = msstab[mssind]; 127 128 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, 129 th->dest, ntohl(th->seq), mssind); 130 } 131 EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence); 132 133 __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp) 134 { 135 const struct ipv6hdr *iph = ipv6_hdr(skb); 136 const struct tcphdr *th = tcp_hdr(skb); 137 138 tcp_synq_overflow(sk); 139 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); 140 141 return __cookie_v6_init_sequence(iph, th, mssp); 142 } 143 144 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, 145 __u32 cookie) 146 { 147 __u32 seq = ntohl(th->seq) - 1; 148 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, 149 th->source, th->dest, seq); 150 151 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; 152 } 153 EXPORT_SYMBOL_GPL(__cookie_v6_check); 154 155 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 156 { 157 struct tcp_options_received tcp_opt; 158 struct inet_request_sock *ireq; 159 struct tcp_request_sock *treq; 160 struct ipv6_pinfo *np = inet6_sk(sk); 161 struct tcp_sock *tp = tcp_sk(sk); 162 const struct tcphdr *th = tcp_hdr(skb); 163 __u32 cookie = ntohl(th->ack_seq) - 1; 164 struct sock *ret = sk; 165 struct request_sock *req; 166 int mss; 167 struct dst_entry *dst; 168 __u8 rcv_wscale; 169 bool ecn_ok = false; 170 171 if (!sysctl_tcp_syncookies || !th->ack || th->rst) 172 goto out; 173 174 if (tcp_synq_no_recent_overflow(sk) || 175 (mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie)) == 0) { 176 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); 177 goto out; 178 } 179 180 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); 181 182 /* check for timestamp cookie support */ 183 memset(&tcp_opt, 0, sizeof(tcp_opt)); 184 tcp_parse_options(skb, &tcp_opt, 0, NULL); 185 186 if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok)) 187 goto out; 188 189 ret = NULL; 190 req = inet6_reqsk_alloc(&tcp6_request_sock_ops); 191 if (!req) 192 goto out; 193 194 ireq = inet_rsk(req); 195 treq = tcp_rsk(req); 196 treq->listener = NULL; 197 198 if (security_inet_conn_request(sk, skb, req)) 199 goto out_free; 200 201 req->mss = mss; 202 ireq->ir_rmt_port = th->source; 203 ireq->ir_num = ntohs(th->dest); 204 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; 205 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; 206 if (ipv6_opt_accepted(sk, skb) || 207 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || 208 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { 209 atomic_inc(&skb->users); 210 ireq->pktopts = skb; 211 } 212 213 ireq->ir_iif = sk->sk_bound_dev_if; 214 /* So that link locals have meaning */ 215 if (!sk->sk_bound_dev_if && 216 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) 217 ireq->ir_iif = inet6_iif(skb); 218 219 req->expires = 0UL; 220 req->num_retrans = 0; 221 ireq->ecn_ok = ecn_ok; 222 ireq->snd_wscale = tcp_opt.snd_wscale; 223 ireq->sack_ok = tcp_opt.sack_ok; 224 ireq->wscale_ok = tcp_opt.wscale_ok; 225 ireq->tstamp_ok = tcp_opt.saw_tstamp; 226 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; 227 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; 228 treq->rcv_isn = ntohl(th->seq) - 1; 229 treq->snt_isn = cookie; 230 231 /* 232 * We need to lookup the dst_entry to get the correct window size. 233 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten 234 * me if there is a preferred way. 235 */ 236 { 237 struct in6_addr *final_p, final; 238 struct flowi6 fl6; 239 memset(&fl6, 0, sizeof(fl6)); 240 fl6.flowi6_proto = IPPROTO_TCP; 241 fl6.daddr = ireq->ir_v6_rmt_addr; 242 final_p = fl6_update_dst(&fl6, np->opt, &final); 243 fl6.saddr = ireq->ir_v6_loc_addr; 244 fl6.flowi6_oif = sk->sk_bound_dev_if; 245 fl6.flowi6_mark = sk->sk_mark; 246 fl6.fl6_dport = ireq->ir_rmt_port; 247 fl6.fl6_sport = inet_sk(sk)->inet_sport; 248 security_req_classify_flow(req, flowi6_to_flowi(&fl6)); 249 250 dst = ip6_dst_lookup_flow(sk, &fl6, final_p); 251 if (IS_ERR(dst)) 252 goto out_free; 253 } 254 255 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); 256 tcp_select_initial_window(tcp_full_space(sk), req->mss, 257 &req->rcv_wnd, &req->window_clamp, 258 ireq->wscale_ok, &rcv_wscale, 259 dst_metric(dst, RTAX_INITRWND)); 260 261 ireq->rcv_wscale = rcv_wscale; 262 263 ret = get_cookie_sock(sk, skb, req, dst); 264 out: 265 return ret; 266 out_free: 267 reqsk_free(req); 268 return NULL; 269 } 270 271