2 * IPv6 Syncookies implementation for the Linux kernel
5 * Glenn Griffin <ggriffin.kernel@gmail.com>
7 * Based on IPv4 implementation by Andi Kleen
8 * linux/net/ipv4/syncookies.c
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.
17 #include <linux/tcp.h>
18 #include <linux/random.h>
19 #include <linux/cryptohash.h>
20 #include <linux/kernel.h>
24 #define COOKIEBITS 24 /* Upper bits store count */
25 #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
27 static u32 syncookie6_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly;
29 /* RFC 2460, Section 8.3:
30 * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..]
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.
37 static __u16 const msstab[] = {
38 1280 - 60, /* IPV6_MIN_MTU - 60 */
44 static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
47 static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
48 __be16 sport, __be16 dport, u32 count, int c)
52 net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret));
54 tmp = this_cpu_ptr(ipv6_cookie_scratch);
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
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;
66 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
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,
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)
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)
87 __u32 diff, count = tcp_cookie_time();
89 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
91 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
92 if (diff >= MAX_SYNCOOKIE_AGE)
96 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
100 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
101 const struct tcphdr *th, __u16 *mssp)
104 const __u16 mss = *mssp;
106 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
107 if (mss >= msstab[mssind])
110 *mssp = msstab[mssind];
112 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
113 th->dest, ntohl(th->seq), mssind);
115 EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
117 __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp)
119 const struct ipv6hdr *iph = ipv6_hdr(skb);
120 const struct tcphdr *th = tcp_hdr(skb);
122 return __cookie_v6_init_sequence(iph, th, mssp);
125 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
128 __u32 seq = ntohl(th->seq) - 1;
129 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
130 th->source, th->dest, seq);
132 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
134 EXPORT_SYMBOL_GPL(__cookie_v6_check);
136 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
138 struct tcp_options_received tcp_opt;
139 struct inet_request_sock *ireq;
140 struct tcp_request_sock *treq;
141 struct ipv6_pinfo *np = inet6_sk(sk);
142 struct tcp_sock *tp = tcp_sk(sk);
143 const struct tcphdr *th = tcp_hdr(skb);
144 __u32 cookie = ntohl(th->ack_seq) - 1;
145 struct sock *ret = sk;
146 struct request_sock *req;
148 struct dst_entry *dst;
151 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
154 if (tcp_synq_no_recent_overflow(sk))
157 mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie);
159 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
163 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
165 /* check for timestamp cookie support */
166 memset(&tcp_opt, 0, sizeof(tcp_opt));
167 tcp_parse_options(skb, &tcp_opt, 0, NULL);
169 if (!cookie_timestamp_decode(&tcp_opt))
173 req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false);
177 ireq = inet_rsk(req);
179 treq->tfo_listener = false;
181 if (security_inet_conn_request(sk, skb, req))
185 ireq->ir_rmt_port = th->source;
186 ireq->ir_num = ntohs(th->dest);
187 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
188 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
189 if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
190 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
191 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
192 atomic_inc(&skb->users);
196 ireq->ir_iif = sk->sk_bound_dev_if;
197 /* So that link locals have meaning */
198 if (!sk->sk_bound_dev_if &&
199 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
200 ireq->ir_iif = tcp_v6_iif(skb);
202 ireq->ir_mark = inet_request_mark(sk, skb);
204 req->num_retrans = 0;
205 ireq->snd_wscale = tcp_opt.snd_wscale;
206 ireq->sack_ok = tcp_opt.sack_ok;
207 ireq->wscale_ok = tcp_opt.wscale_ok;
208 ireq->tstamp_ok = tcp_opt.saw_tstamp;
209 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
210 treq->snt_synack.v64 = 0;
211 treq->rcv_isn = ntohl(th->seq) - 1;
212 treq->snt_isn = cookie;
215 * We need to lookup the dst_entry to get the correct window size.
216 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
217 * me if there is a preferred way.
220 struct in6_addr *final_p, final;
222 memset(&fl6, 0, sizeof(fl6));
223 fl6.flowi6_proto = IPPROTO_TCP;
224 fl6.daddr = ireq->ir_v6_rmt_addr;
225 final_p = fl6_update_dst(&fl6, np->opt, &final);
226 fl6.saddr = ireq->ir_v6_loc_addr;
227 fl6.flowi6_oif = sk->sk_bound_dev_if;
228 fl6.flowi6_mark = ireq->ir_mark;
229 fl6.fl6_dport = ireq->ir_rmt_port;
230 fl6.fl6_sport = inet_sk(sk)->inet_sport;
231 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
233 dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
238 req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
239 tcp_select_initial_window(tcp_full_space(sk), req->mss,
240 &req->rsk_rcv_wnd, &req->rsk_window_clamp,
241 ireq->wscale_ok, &rcv_wscale,
242 dst_metric(dst, RTAX_INITRWND));
244 ireq->rcv_wscale = rcv_wscale;
245 ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst);
247 ret = tcp_get_cookie_sock(sk, skb, req, dst);