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 27static 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 */ 37static __u16 const msstab[] = { 38 1280 - 60, /* IPV6_MIN_MTU - 60 */ 39 1480 - 60, 40 1500 - 60, 41 9000 - 60, 42}; 43 44static 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 atomic_set(&req->rsk_refcnt, 1); 54 inet_csk_reqsk_queue_add(sk, req, child); 55 } else { 56 reqsk_free(req); 57 } 58 return child; 59} 60 61static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], 62 ipv6_cookie_scratch); 63 64static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr, 65 __be16 sport, __be16 dport, u32 count, int c) 66{ 67 __u32 *tmp; 68 69 net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret)); 70 71 tmp = this_cpu_ptr(ipv6_cookie_scratch); 72 73 /* 74 * we have 320 bits of information to hash, copy in the remaining 75 * 192 bits required for sha_transform, from the syncookie6_secret 76 * and overwrite the digest with the secret 77 */ 78 memcpy(tmp + 10, syncookie6_secret[c], 44); 79 memcpy(tmp, saddr, 16); 80 memcpy(tmp + 4, daddr, 16); 81 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; 82 tmp[9] = count; 83 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); 84 85 return tmp[17]; 86} 87 88static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, 89 const struct in6_addr *daddr, 90 __be16 sport, __be16 dport, __u32 sseq, 91 __u32 data) 92{ 93 u32 count = tcp_cookie_time(); 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 100static __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) 103{ 104 __u32 diff, count = tcp_cookie_time(); 105 106 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; 107 108 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); 109 if (diff >= MAX_SYNCOOKIE_AGE) 110 return (__u32)-1; 111 112 return (cookie - 113 cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) 114 & COOKIEMASK; 115} 116 117u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph, 118 const struct tcphdr *th, __u16 *mssp) 119{ 120 int mssind; 121 const __u16 mss = *mssp; 122 123 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) 124 if (mss >= msstab[mssind]) 125 break; 126 127 *mssp = msstab[mssind]; 128 129 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, 130 th->dest, ntohl(th->seq), mssind); 131} 132EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence); 133 134__u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp) 135{ 136 const struct ipv6hdr *iph = ipv6_hdr(skb); 137 const struct tcphdr *th = tcp_hdr(skb); 138 139 tcp_synq_overflow(sk); 140 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); 141 142 return __cookie_v6_init_sequence(iph, th, mssp); 143} 144 145int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, 146 __u32 cookie) 147{ 148 __u32 seq = ntohl(th->seq) - 1; 149 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, 150 th->source, th->dest, seq); 151 152 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; 153} 154EXPORT_SYMBOL_GPL(__cookie_v6_check); 155 156struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) 157{ 158 struct tcp_options_received tcp_opt; 159 struct inet_request_sock *ireq; 160 struct tcp_request_sock *treq; 161 struct ipv6_pinfo *np = inet6_sk(sk); 162 struct tcp_sock *tp = tcp_sk(sk); 163 const struct tcphdr *th = tcp_hdr(skb); 164 __u32 cookie = ntohl(th->ack_seq) - 1; 165 struct sock *ret = sk; 166 struct request_sock *req; 167 int mss; 168 struct dst_entry *dst; 169 __u8 rcv_wscale; 170 171 if (!sysctl_tcp_syncookies || !th->ack || th->rst) 172 goto out; 173 174 if (tcp_synq_no_recent_overflow(sk)) 175 goto out; 176 177 mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie); 178 if (mss == 0) { 179 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); 180 goto out; 181 } 182 183 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); 184 185 /* check for timestamp cookie support */ 186 memset(&tcp_opt, 0, sizeof(tcp_opt)); 187 tcp_parse_options(skb, &tcp_opt, 0, NULL); 188 189 if (!cookie_timestamp_decode(&tcp_opt)) 190 goto out; 191 192 ret = NULL; 193 req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk); 194 if (!req) 195 goto out; 196 197 ireq = inet_rsk(req); 198 treq = tcp_rsk(req); 199 treq->tfo_listener = false; 200 201 if (security_inet_conn_request(sk, skb, req)) 202 goto out_free; 203 204 req->mss = mss; 205 ireq->ir_rmt_port = th->source; 206 ireq->ir_num = ntohs(th->dest); 207 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; 208 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; 209 if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) || 210 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || 211 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { 212 atomic_inc(&skb->users); 213 ireq->pktopts = skb; 214 } 215 216 ireq->ir_iif = sk->sk_bound_dev_if; 217 /* So that link locals have meaning */ 218 if (!sk->sk_bound_dev_if && 219 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) 220 ireq->ir_iif = tcp_v6_iif(skb); 221 222 ireq->ir_mark = inet_request_mark(sk, skb); 223 224 req->num_retrans = 0; 225 ireq->snd_wscale = tcp_opt.snd_wscale; 226 ireq->sack_ok = tcp_opt.sack_ok; 227 ireq->wscale_ok = tcp_opt.wscale_ok; 228 ireq->tstamp_ok = tcp_opt.saw_tstamp; 229 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; 230 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; 231 treq->rcv_isn = ntohl(th->seq) - 1; 232 treq->snt_isn = cookie; 233 234 /* 235 * We need to lookup the dst_entry to get the correct window size. 236 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten 237 * me if there is a preferred way. 238 */ 239 { 240 struct in6_addr *final_p, final; 241 struct flowi6 fl6; 242 memset(&fl6, 0, sizeof(fl6)); 243 fl6.flowi6_proto = IPPROTO_TCP; 244 fl6.daddr = ireq->ir_v6_rmt_addr; 245 final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final); 246 fl6.saddr = ireq->ir_v6_loc_addr; 247 fl6.flowi6_oif = sk->sk_bound_dev_if; 248 fl6.flowi6_mark = ireq->ir_mark; 249 fl6.fl6_dport = ireq->ir_rmt_port; 250 fl6.fl6_sport = inet_sk(sk)->inet_sport; 251 security_req_classify_flow(req, flowi6_to_flowi(&fl6)); 252 253 dst = ip6_dst_lookup_flow(sk, &fl6, final_p); 254 if (IS_ERR(dst)) 255 goto out_free; 256 } 257 258 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); 259 tcp_select_initial_window(tcp_full_space(sk), req->mss, 260 &req->rcv_wnd, &req->window_clamp, 261 ireq->wscale_ok, &rcv_wscale, 262 dst_metric(dst, RTAX_INITRWND)); 263 264 ireq->rcv_wscale = rcv_wscale; 265 ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst); 266 267 ret = get_cookie_sock(sk, skb, req, dst); 268out: 269 return ret; 270out_free: 271 reqsk_free(req); 272 return NULL; 273} 274