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Glenn Griffinc6aefaf2008-02-07 21:49:26 -08001/*
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
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080024#define COOKIEBITS 24 /* Upper bits store count */
25#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
26
Florian Westphal253ff512014-08-26 12:55:53 +020027static u32 syncookie6_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly;
Hannes Frederic Sowab23a0022013-10-19 21:48:56 +020028
Florian Westphal08629352013-09-20 22:32:56 +020029/* 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 */
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080037static __u16 const msstab[] = {
Florian Westphal08629352013-09-20 22:32:56 +020038 1280 - 60, /* IPV6_MIN_MTU - 60 */
Florian Westphal5918e2f2010-06-03 00:43:57 +000039 1480 - 60,
40 1500 - 60,
Florian Westphal5918e2f2010-06-03 00:43:57 +000041 9000 - 60,
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080042};
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080043
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080044static 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);
Eric Dumazet0470c8c2015-03-17 18:32:31 -070052 if (child) {
53 atomic_set(&req->rsk_refcnt, 1);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080054 inet_csk_reqsk_queue_add(sk, req, child);
Eric Dumazet0470c8c2015-03-17 18:32:31 -070055 } else {
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080056 reqsk_free(req);
Eric Dumazet0470c8c2015-03-17 18:32:31 -070057 }
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080058 return child;
59}
60
Tejun Heo245b2e72009-06-24 15:13:48 +090061static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
62 ipv6_cookie_scratch);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080063
Eric Dumazetb71d1d42011-04-22 04:53:02 +000064static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080065 __be16 sport, __be16 dport, u32 count, int c)
66{
Hannes Frederic Sowab23a0022013-10-19 21:48:56 +020067 __u32 *tmp;
68
69 net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret));
70
Christoph Lameter903ceff2014-08-17 12:30:35 -050071 tmp = this_cpu_ptr(ipv6_cookie_scratch);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080072
73 /*
74 * we have 320 bits of information to hash, copy in the remaining
Hannes Frederic Sowab23a0022013-10-19 21:48:56 +020075 * 192 bits required for sha_transform, from the syncookie6_secret
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080076 * and overwrite the digest with the secret
77 */
Hannes Frederic Sowab23a0022013-10-19 21:48:56 +020078 memcpy(tmp + 10, syncookie6_secret[c], 44);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080079 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
Eric Dumazetb71d1d42011-04-22 04:53:02 +000088static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
89 const struct in6_addr *daddr,
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080090 __be16 sport, __be16 dport, __u32 sseq,
Florian Westphal8c27bd72013-09-20 22:32:55 +020091 __u32 data)
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080092{
Florian Westphal8c27bd72013-09-20 22:32:55 +020093 u32 count = tcp_cookie_time();
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080094 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
Eric Dumazetb71d1d42011-04-22 04:53:02 +0000100static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
101 const struct in6_addr *daddr, __be16 sport,
Florian Westphal8c27bd72013-09-20 22:32:55 +0200102 __be16 dport, __u32 sseq)
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800103{
Florian Westphal8c27bd72013-09-20 22:32:55 +0200104 __u32 diff, count = tcp_cookie_time();
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800105
106 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
107
108 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
Florian Westphal8c27bd72013-09-20 22:32:55 +0200109 if (diff >= MAX_SYNCOOKIE_AGE)
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800110 return (__u32)-1;
111
112 return (cookie -
113 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
114 & COOKIEMASK;
115}
116
Patrick McHardy81eb6a12013-08-27 08:50:15 +0200117u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
118 const struct tcphdr *th, __u16 *mssp)
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800119{
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800120 int mssind;
121 const __u16 mss = *mssp;
122
Florian Westphal5918e2f2010-06-03 00:43:57 +0000123 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
124 if (mss >= msstab[mssind])
125 break;
126
127 *mssp = msstab[mssind];
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800128
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800129 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
Florian Westphal8c27bd72013-09-20 22:32:55 +0200130 th->dest, ntohl(th->seq), mssind);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800131}
Patrick McHardy81eb6a12013-08-27 08:50:15 +0200132EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800133
Patrick McHardy81eb6a12013-08-27 08:50:15 +0200134__u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp)
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800135{
Eric Dumazetb71d1d42011-04-22 04:53:02 +0000136 const struct ipv6hdr *iph = ipv6_hdr(skb);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800137 const struct tcphdr *th = tcp_hdr(skb);
Patrick McHardy81eb6a12013-08-27 08:50:15 +0200138
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{
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800148 __u32 seq = ntohl(th->seq) - 1;
149 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
Florian Westphal8c27bd72013-09-20 22:32:55 +0200150 th->source, th->dest, seq);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800151
Florian Westphal5918e2f2010-06-03 00:43:57 +0000152 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800153}
Patrick McHardy81eb6a12013-08-27 08:50:15 +0200154EXPORT_SYMBOL_GPL(__cookie_v6_check);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800155
156struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
157{
William Allen Simpson4957faade2009-12-02 18:25:27 +0000158 struct tcp_options_received tcp_opt;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800159 struct inet_request_sock *ireq;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800160 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
Florian Westphalaf9b4732010-06-03 00:43:44 +0000171 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800172 goto out;
173
Florian Westphal646697b2014-10-30 02:55:38 +0100174 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) {
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700179 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800180 goto out;
181 }
182
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700183 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800184
David S. Millerbb5b7c12009-12-15 20:56:42 -0800185 /* check for timestamp cookie support */
186 memset(&tcp_opt, 0, sizeof(tcp_opt));
Christoph Paasch1a2c6182013-03-17 08:23:34 +0000187 tcp_parse_options(skb, &tcp_opt, 0, NULL);
David S. Millerbb5b7c12009-12-15 20:56:42 -0800188
Florian Westphalf1673382014-11-03 17:35:02 +0100189 if (!cookie_timestamp_decode(&tcp_opt))
Florian Westphal8c763682010-06-16 14:42:15 -0700190 goto out;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800191
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800192 ret = NULL;
Eric Dumazet407640d2015-03-17 18:32:26 -0700193 req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800194 if (!req)
195 goto out;
196
197 ireq = inet_rsk(req);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800198 treq = tcp_rsk(req);
Eric Dumazet9439ce02015-03-17 18:32:29 -0700199 treq->tfo_listener = false;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800200
Florian Westphal17305542008-08-03 18:13:44 -0700201 if (security_inet_conn_request(sk, skb, req))
202 goto out_free;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800203
204 req->mss = mss;
Eric Dumazet634fb9792013-10-09 15:21:29 -0700205 ireq->ir_rmt_port = th->source;
Eric Dumazetb44084c2013-10-10 00:04:37 -0700206 ireq->ir_num = ntohs(th->dest);
Eric Dumazet634fb9792013-10-09 15:21:29 -0700207 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
208 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
Eric Dumazeta2247722014-09-27 09:50:56 -0700209 if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800210 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
211 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
212 atomic_inc(&skb->users);
Eric Dumazet634fb9792013-10-09 15:21:29 -0700213 ireq->pktopts = skb;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800214 }
215
Eric Dumazet634fb9792013-10-09 15:21:29 -0700216 ireq->ir_iif = sk->sk_bound_dev_if;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800217 /* So that link locals have meaning */
218 if (!sk->sk_bound_dev_if &&
Eric Dumazet634fb9792013-10-09 15:21:29 -0700219 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
Eric Dumazet870c3152014-10-17 09:17:20 -0700220 ireq->ir_iif = tcp_v6_iif(skb);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800221
Lorenzo Colitti84f39b02014-05-13 10:17:35 -0700222 ireq->ir_mark = inet_request_mark(sk, skb);
223
Eric Dumazete6c022a2012-10-27 23:16:46 +0000224 req->num_retrans = 0;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800225 ireq->snd_wscale = tcp_opt.snd_wscale;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800226 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;
Jerry Chu9ad7c042011-06-08 11:08:38 +0000230 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800231 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 {
Arnaud Ebalard20c59de2010-06-01 21:35:01 +0000240 struct in6_addr *final_p, final;
David S. Miller4c9483b2011-03-12 16:22:43 -0500241 struct flowi6 fl6;
242 memset(&fl6, 0, sizeof(fl6));
243 fl6.flowi6_proto = IPPROTO_TCP;
Eric Dumazet634fb9792013-10-09 15:21:29 -0700244 fl6.daddr = ireq->ir_v6_rmt_addr;
David S. Miller4c9483b2011-03-12 16:22:43 -0500245 final_p = fl6_update_dst(&fl6, np->opt, &final);
Eric Dumazet634fb9792013-10-09 15:21:29 -0700246 fl6.saddr = ireq->ir_v6_loc_addr;
David S. Miller4c9483b2011-03-12 16:22:43 -0500247 fl6.flowi6_oif = sk->sk_bound_dev_if;
Lorenzo Colitti84f39b02014-05-13 10:17:35 -0700248 fl6.flowi6_mark = ireq->ir_mark;
Eric Dumazet634fb9792013-10-09 15:21:29 -0700249 fl6.fl6_dport = ireq->ir_rmt_port;
David S. Miller1958b852011-03-12 16:36:19 -0500250 fl6.fl6_sport = inet_sk(sk)->inet_sport;
David S. Miller4c9483b2011-03-12 16:22:43 -0500251 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
Florian Westphal17305542008-08-03 18:13:44 -0700252
Steffen Klassert0e0d44a2013-08-28 08:04:14 +0200253 dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
David S. Miller68d0c6d2011-03-01 13:19:07 -0800254 if (IS_ERR(dst))
Florian Westphal17305542008-08-03 18:13:44 -0700255 goto out_free;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800256 }
257
Florian Westphal4dfc2812008-04-10 03:12:40 -0700258 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800259 tcp_select_initial_window(tcp_full_space(sk), req->mss,
260 &req->rcv_wnd, &req->window_clamp,
laurent chavey31d12922009-12-15 11:15:28 +0000261 ireq->wscale_ok, &rcv_wscale,
262 dst_metric(dst, RTAX_INITRWND));
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800263
264 ireq->rcv_wscale = rcv_wscale;
Florian Westphalf7b3bec2014-11-03 17:35:03 +0100265 ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800266
267 ret = get_cookie_sock(sk, skb, req, dst);
Florian Westphal17305542008-08-03 18:13:44 -0700268out:
269 return ret;
270out_free:
271 reqsk_free(req);
272 return NULL;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800273}