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 /* RFC 2460, Section 8.3:
28 * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..]
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.
35 static __u16 const msstab[] = {
36 1280 - 60, /* IPV6_MIN_MTU - 60 */
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)
46 struct inet_connection_sock *icsk = inet_csk(sk);
49 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
51 inet_csk_reqsk_queue_add(sk, req, child);
58 static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
61 static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
62 __be16 sport, __be16 dport, u32 count, int c)
64 __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
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
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;
76 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
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,
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)
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)
97 __u32 diff, count = tcp_cookie_time();
99 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
101 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
102 if (diff >= MAX_SYNCOOKIE_AGE)
106 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
110 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
111 const struct tcphdr *th, __u16 *mssp)
114 const __u16 mss = *mssp;
116 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
117 if (mss >= msstab[mssind])
120 *mssp = msstab[mssind];
122 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
123 th->dest, ntohl(th->seq), mssind);
125 EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
127 __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp)
129 const struct ipv6hdr *iph = ipv6_hdr(skb);
130 const struct tcphdr *th = tcp_hdr(skb);
132 tcp_synq_overflow(sk);
133 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
135 return __cookie_v6_init_sequence(iph, th, mssp);
138 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
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);
145 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
147 EXPORT_SYMBOL_GPL(__cookie_v6_check);
149 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
151 struct tcp_options_received tcp_opt;
152 struct inet_request_sock *ireq;
153 struct tcp_request_sock *treq;
154 struct ipv6_pinfo *np = inet6_sk(sk);
155 struct tcp_sock *tp = tcp_sk(sk);
156 const struct tcphdr *th = tcp_hdr(skb);
157 __u32 cookie = ntohl(th->ack_seq) - 1;
158 struct sock *ret = sk;
159 struct request_sock *req;
161 struct dst_entry *dst;
165 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
168 if (tcp_synq_no_recent_overflow(sk) ||
169 (mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie)) == 0) {
170 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
174 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
176 /* check for timestamp cookie support */
177 memset(&tcp_opt, 0, sizeof(tcp_opt));
178 tcp_parse_options(skb, &tcp_opt, 0, NULL);
180 if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok))
184 req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
188 ireq = inet_rsk(req);
190 treq->listener = NULL;
192 if (security_inet_conn_request(sk, skb, req))
196 ireq->ir_rmt_port = th->source;
197 ireq->ir_num = ntohs(th->dest);
198 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
199 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
200 if (ipv6_opt_accepted(sk, skb) ||
201 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
202 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
203 atomic_inc(&skb->users);
207 ireq->ir_iif = sk->sk_bound_dev_if;
208 /* So that link locals have meaning */
209 if (!sk->sk_bound_dev_if &&
210 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
211 ireq->ir_iif = inet6_iif(skb);
214 req->num_retrans = 0;
215 ireq->ecn_ok = ecn_ok;
216 ireq->snd_wscale = tcp_opt.snd_wscale;
217 ireq->sack_ok = tcp_opt.sack_ok;
218 ireq->wscale_ok = tcp_opt.wscale_ok;
219 ireq->tstamp_ok = tcp_opt.saw_tstamp;
220 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
221 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
222 treq->rcv_isn = ntohl(th->seq) - 1;
223 treq->snt_isn = cookie;
226 * We need to lookup the dst_entry to get the correct window size.
227 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
228 * me if there is a preferred way.
231 struct in6_addr *final_p, final;
233 memset(&fl6, 0, sizeof(fl6));
234 fl6.flowi6_proto = IPPROTO_TCP;
235 fl6.daddr = ireq->ir_v6_rmt_addr;
236 final_p = fl6_update_dst(&fl6, np->opt, &final);
237 fl6.saddr = ireq->ir_v6_loc_addr;
238 fl6.flowi6_oif = sk->sk_bound_dev_if;
239 fl6.flowi6_mark = sk->sk_mark;
240 fl6.fl6_dport = ireq->ir_rmt_port;
241 fl6.fl6_sport = inet_sk(sk)->inet_sport;
242 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
244 dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false);
249 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
250 tcp_select_initial_window(tcp_full_space(sk), req->mss,
251 &req->rcv_wnd, &req->window_clamp,
252 ireq->wscale_ok, &rcv_wscale,
253 dst_metric(dst, RTAX_INITRWND));
255 ireq->rcv_wscale = rcv_wscale;
257 ret = get_cookie_sock(sk, skb, req, dst);