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] __read_mostly; 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 DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], 45 ipv6_cookie_scratch); 46 47 static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr, 48 __be16 sport, __be16 dport, u32 count, int c) 49 { 50 __u32 *tmp; 51 52 net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret)); 53 54 tmp = this_cpu_ptr(ipv6_cookie_scratch); 55 56 /* 57 * we have 320 bits of information to hash, copy in the remaining 58 * 192 bits required for sha_transform, from the syncookie6_secret 59 * and overwrite the digest with the secret 60 */ 61 memcpy(tmp + 10, syncookie6_secret[c], 44); 62 memcpy(tmp, saddr, 16); 63 memcpy(tmp + 4, daddr, 16); 64 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; 65 tmp[9] = count; 66 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); 67 68 return tmp[17]; 69 } 70 71 static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, 72 const struct in6_addr *daddr, 73 __be16 sport, __be16 dport, __u32 sseq, 74 __u32 data) 75 { 76 u32 count = tcp_cookie_time(); 77 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + 78 sseq + (count << COOKIEBITS) + 79 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) 80 & COOKIEMASK)); 81 } 82 83 static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, 84 const struct in6_addr *daddr, __be16 sport, 85 __be16 dport, __u32 sseq) 86 { 87 __u32 diff, count = tcp_cookie_time(); 88 89 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; 90 91 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); 92 if (diff >= MAX_SYNCOOKIE_AGE) 93 return (__u32)-1; 94 95 return (cookie - 96 cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) 97 & COOKIEMASK; 98 } 99 100 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph, 101 const struct tcphdr *th, __u16 *mssp) 102 { 103 int mssind; 104 const __u16 mss = *mssp; 105 106 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) 107 if (mss >= msstab[mssind]) 108 break; 109 110 *mssp = msstab[mssind]; 111 112 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, 113 th->dest, ntohl(th->seq), mssind); 114 } 115 EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence); 116 117 __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp) 118 { 119 const struct ipv6hdr *iph = ipv6_hdr(skb); 120 const struct tcphdr *th = tcp_hdr(skb); 121 122 tcp_synq_overflow(sk); 123 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); 124 125 return __cookie_v6_init_sequence(iph, th, mssp); 126 } 127 128 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, 129 __u32 cookie) 130 { 131 __u32 seq = ntohl(th->seq) - 1; 132 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, 133 th->source, th->dest, seq); 134 135 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; 136 } 137 EXPORT_SYMBOL_GPL(__cookie_v6_check); 138 139 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 140 { 141 struct tcp_options_received tcp_opt; 142 struct inet_request_sock *ireq; 143 struct tcp_request_sock *treq; 144 struct ipv6_pinfo *np = inet6_sk(sk); 145 struct tcp_sock *tp = tcp_sk(sk); 146 const struct tcphdr *th = tcp_hdr(skb); 147 __u32 cookie = ntohl(th->ack_seq) - 1; 148 struct sock *ret = sk; 149 struct request_sock *req; 150 int mss; 151 struct dst_entry *dst; 152 __u8 rcv_wscale; 153 154 if (!sysctl_tcp_syncookies || !th->ack || th->rst) 155 goto out; 156 157 if (tcp_synq_no_recent_overflow(sk)) 158 goto out; 159 160 mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie); 161 if (mss == 0) { 162 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); 163 goto out; 164 } 165 166 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); 167 168 /* check for timestamp cookie support */ 169 memset(&tcp_opt, 0, sizeof(tcp_opt)); 170 tcp_parse_options(skb, &tcp_opt, 0, NULL); 171 172 if (!cookie_timestamp_decode(&tcp_opt)) 173 goto out; 174 175 ret = NULL; 176 req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk); 177 if (!req) 178 goto out; 179 180 ireq = inet_rsk(req); 181 treq = tcp_rsk(req); 182 treq->tfo_listener = false; 183 184 if (security_inet_conn_request(sk, skb, req)) 185 goto out_free; 186 187 req->mss = mss; 188 ireq->ir_rmt_port = th->source; 189 ireq->ir_num = ntohs(th->dest); 190 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; 191 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; 192 if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) || 193 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || 194 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { 195 atomic_inc(&skb->users); 196 ireq->pktopts = skb; 197 } 198 199 ireq->ir_iif = sk->sk_bound_dev_if; 200 /* So that link locals have meaning */ 201 if (!sk->sk_bound_dev_if && 202 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) 203 ireq->ir_iif = tcp_v6_iif(skb); 204 205 ireq->ir_mark = inet_request_mark(sk, skb); 206 207 req->num_retrans = 0; 208 ireq->snd_wscale = tcp_opt.snd_wscale; 209 ireq->sack_ok = tcp_opt.sack_ok; 210 ireq->wscale_ok = tcp_opt.wscale_ok; 211 ireq->tstamp_ok = tcp_opt.saw_tstamp; 212 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; 213 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; 214 treq->rcv_isn = ntohl(th->seq) - 1; 215 treq->snt_isn = cookie; 216 217 /* 218 * We need to lookup the dst_entry to get the correct window size. 219 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten 220 * me if there is a preferred way. 221 */ 222 { 223 struct in6_addr *final_p, final; 224 struct flowi6 fl6; 225 memset(&fl6, 0, sizeof(fl6)); 226 fl6.flowi6_proto = IPPROTO_TCP; 227 fl6.daddr = ireq->ir_v6_rmt_addr; 228 final_p = fl6_update_dst(&fl6, np->opt, &final); 229 fl6.saddr = ireq->ir_v6_loc_addr; 230 fl6.flowi6_oif = sk->sk_bound_dev_if; 231 fl6.flowi6_mark = ireq->ir_mark; 232 fl6.fl6_dport = ireq->ir_rmt_port; 233 fl6.fl6_sport = inet_sk(sk)->inet_sport; 234 security_req_classify_flow(req, flowi6_to_flowi(&fl6)); 235 236 dst = ip6_dst_lookup_flow(sk, &fl6, final_p); 237 if (IS_ERR(dst)) 238 goto out_free; 239 } 240 241 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); 242 tcp_select_initial_window(tcp_full_space(sk), req->mss, 243 &req->rcv_wnd, &req->window_clamp, 244 ireq->wscale_ok, &rcv_wscale, 245 dst_metric(dst, RTAX_INITRWND)); 246 247 ireq->rcv_wscale = rcv_wscale; 248 ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst); 249 250 ret = tcp_get_cookie_sock(sk, skb, req, dst); 251 out: 252 return ret; 253 out_free: 254 reqsk_free(req); 255 return NULL; 256 } 257