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 extern int sysctl_tcp_syncookies;
25 extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
27 #define COOKIEBITS 24 /* Upper bits store count */
28 #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
30 /* Table must be sorted. */
31 static __u16 const msstab[] = {
43 * This (misnamed) value is the age of syncookie which is permitted.
44 * Its ideal value should be dependent on TCP_TIMEOUT_INIT and
45 * sysctl_tcp_retries1. It's a rather complicated formula (exponential
46 * backoff) to compute at runtime so it's currently hardcoded here.
48 #define COUNTER_TRIES 4
50 static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
51 struct request_sock *req,
52 struct dst_entry *dst)
54 struct inet_connection_sock *icsk = inet_csk(sk);
57 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
59 inet_csk_reqsk_queue_add(sk, req, child);
66 static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
69 static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
70 __be16 sport, __be16 dport, u32 count, int c)
72 __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
75 * we have 320 bits of information to hash, copy in the remaining
76 * 192 bits required for sha_transform, from the syncookie_secret
77 * and overwrite the digest with the secret
79 memcpy(tmp + 10, syncookie_secret[c], 44);
80 memcpy(tmp, saddr, 16);
81 memcpy(tmp + 4, daddr, 16);
82 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport;
84 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
89 static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
90 const struct in6_addr *daddr,
91 __be16 sport, __be16 dport, __u32 sseq,
92 __u32 count, __u32 data)
94 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
95 sseq + (count << COOKIEBITS) +
96 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
100 static __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, __u32 count,
107 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
109 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
114 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
118 __u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
120 const struct ipv6hdr *iph = ipv6_hdr(skb);
121 const struct tcphdr *th = tcp_hdr(skb);
123 const __u16 mss = *mssp;
125 tcp_synq_overflow(sk);
127 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
128 if (mss >= msstab[mssind])
131 *mssp = msstab[mssind];
133 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
135 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
136 th->dest, ntohl(th->seq),
137 jiffies / (HZ * 60), mssind);
140 static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
142 const struct ipv6hdr *iph = ipv6_hdr(skb);
143 const struct tcphdr *th = tcp_hdr(skb);
144 __u32 seq = ntohl(th->seq) - 1;
145 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
146 th->source, th->dest, seq,
147 jiffies / (HZ * 60), COUNTER_TRIES);
149 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
152 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
154 struct tcp_options_received tcp_opt;
156 struct inet_request_sock *ireq;
157 struct inet6_request_sock *ireq6;
158 struct tcp_request_sock *treq;
159 struct ipv6_pinfo *np = inet6_sk(sk);
160 struct tcp_sock *tp = tcp_sk(sk);
161 const struct tcphdr *th = tcp_hdr(skb);
162 __u32 cookie = ntohl(th->ack_seq) - 1;
163 struct sock *ret = sk;
164 struct request_sock *req;
166 struct dst_entry *dst;
170 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
173 if (tcp_synq_no_recent_overflow(sk) ||
174 (mss = cookie_check(skb, cookie)) == 0) {
175 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
179 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
181 /* check for timestamp cookie support */
182 memset(&tcp_opt, 0, sizeof(tcp_opt));
183 tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
185 if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
189 req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
193 ireq = inet_rsk(req);
194 ireq6 = inet6_rsk(req);
197 if (security_inet_conn_request(sk, skb, req))
201 ireq->rmt_port = th->source;
202 ireq->loc_port = th->dest;
203 ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr);
204 ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr);
205 if (ipv6_opt_accepted(sk, skb) ||
206 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
207 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
208 atomic_inc(&skb->users);
209 ireq6->pktopts = skb;
212 ireq6->iif = sk->sk_bound_dev_if;
213 /* So that link locals have meaning */
214 if (!sk->sk_bound_dev_if &&
215 ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
216 ireq6->iif = inet6_iif(skb);
220 ireq->ecn_ok = ecn_ok;
221 ireq->snd_wscale = tcp_opt.snd_wscale;
222 ireq->sack_ok = tcp_opt.sack_ok;
223 ireq->wscale_ok = tcp_opt.wscale_ok;
224 ireq->tstamp_ok = tcp_opt.saw_tstamp;
225 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
226 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
227 treq->rcv_isn = ntohl(th->seq) - 1;
228 treq->snt_isn = cookie;
231 * We need to lookup the dst_entry to get the correct window size.
232 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
233 * me if there is a preferred way.
236 struct in6_addr *final_p, final;
238 memset(&fl6, 0, sizeof(fl6));
239 fl6.flowi6_proto = IPPROTO_TCP;
240 ipv6_addr_copy(&fl6.daddr, &ireq6->rmt_addr);
241 final_p = fl6_update_dst(&fl6, np->opt, &final);
242 ipv6_addr_copy(&fl6.saddr, &ireq6->loc_addr);
243 fl6.flowi6_oif = sk->sk_bound_dev_if;
244 fl6.flowi6_mark = sk->sk_mark;
245 fl6.fl6_dport = inet_rsk(req)->rmt_port;
246 fl6.fl6_sport = inet_sk(sk)->inet_sport;
247 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
249 dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false);
254 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
255 tcp_select_initial_window(tcp_full_space(sk), req->mss,
256 &req->rcv_wnd, &req->window_clamp,
257 ireq->wscale_ok, &rcv_wscale,
258 dst_metric(dst, RTAX_INITRWND));
260 ireq->rcv_wscale = rcv_wscale;
262 ret = get_cookie_sock(sk, skb, req, dst);