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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 Westphal5918e2f2010-06-03 00:43:57 +000027/* Table must be sorted. */
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080028static __u16 const msstab[] = {
Florian Westphal5918e2f2010-06-03 00:43:57 +000029 64,
30 512,
31 536,
32 1280 - 60,
33 1480 - 60,
34 1500 - 60,
35 4460 - 60,
36 9000 - 60,
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080037};
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080038
39/*
40 * This (misnamed) value is the age of syncookie which is permitted.
41 * Its ideal value should be dependent on TCP_TIMEOUT_INIT and
42 * sysctl_tcp_retries1. It's a rather complicated formula (exponential
43 * backoff) to compute at runtime so it's currently hardcoded here.
44 */
45#define COUNTER_TRIES 4
46
47static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
48 struct request_sock *req,
49 struct dst_entry *dst)
50{
51 struct inet_connection_sock *icsk = inet_csk(sk);
52 struct sock *child;
53
54 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
55 if (child)
56 inet_csk_reqsk_queue_add(sk, req, child);
57 else
58 reqsk_free(req);
59
60 return child;
61}
62
Tejun Heo245b2e72009-06-24 15:13:48 +090063static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
64 ipv6_cookie_scratch);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080065
Eric Dumazetb71d1d42011-04-22 04:53:02 +000066static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080067 __be16 sport, __be16 dport, u32 count, int c)
68{
Tejun Heo245b2e72009-06-24 15:13:48 +090069 __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080070
71 /*
72 * we have 320 bits of information to hash, copy in the remaining
73 * 192 bits required for sha_transform, from the syncookie_secret
74 * and overwrite the digest with the secret
75 */
76 memcpy(tmp + 10, syncookie_secret[c], 44);
77 memcpy(tmp, saddr, 16);
78 memcpy(tmp + 4, daddr, 16);
79 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport;
80 tmp[9] = count;
81 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
82
83 return tmp[17];
84}
85
Eric Dumazetb71d1d42011-04-22 04:53:02 +000086static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
87 const struct in6_addr *daddr,
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080088 __be16 sport, __be16 dport, __u32 sseq,
89 __u32 count, __u32 data)
90{
91 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
92 sseq + (count << COOKIEBITS) +
93 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
94 & COOKIEMASK));
95}
96
Eric Dumazetb71d1d42011-04-22 04:53:02 +000097static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
98 const struct in6_addr *daddr, __be16 sport,
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080099 __be16 dport, __u32 sseq, __u32 count,
100 __u32 maxdiff)
101{
102 __u32 diff;
103
104 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
105
106 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
107 if (diff >= maxdiff)
108 return (__u32)-1;
109
110 return (cookie -
111 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
112 & COOKIEMASK;
113}
114
Eric Dumazetcf533ea2011-10-21 05:22:42 -0400115__u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp)
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800116{
Eric Dumazetb71d1d42011-04-22 04:53:02 +0000117 const struct ipv6hdr *iph = ipv6_hdr(skb);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800118 const struct tcphdr *th = tcp_hdr(skb);
119 int mssind;
120 const __u16 mss = *mssp;
121
Florian Westphala0f82f62009-04-19 09:43:48 +0000122 tcp_synq_overflow(sk);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800123
Florian Westphal5918e2f2010-06-03 00:43:57 +0000124 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
125 if (mss >= msstab[mssind])
126 break;
127
128 *mssp = msstab[mssind];
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800129
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700130 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800131
132 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
133 th->dest, ntohl(th->seq),
134 jiffies / (HZ * 60), mssind);
135}
136
Eric Dumazetcf533ea2011-10-21 05:22:42 -0400137static inline int cookie_check(const struct sk_buff *skb, __u32 cookie)
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800138{
Eric Dumazetb71d1d42011-04-22 04:53:02 +0000139 const struct ipv6hdr *iph = ipv6_hdr(skb);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800140 const struct tcphdr *th = tcp_hdr(skb);
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,
144 jiffies / (HZ * 60), COUNTER_TRIES);
145
Florian Westphal5918e2f2010-06-03 00:43:57 +0000146 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800147}
148
149struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
150{
William Allen Simpson4957faade2009-12-02 18:25:27 +0000151 struct tcp_options_received tcp_opt;
Eric Dumazetcf533ea2011-10-21 05:22:42 -0400152 const u8 *hash_location;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800153 struct inet_request_sock *ireq;
154 struct inet6_request_sock *ireq6;
155 struct tcp_request_sock *treq;
156 struct ipv6_pinfo *np = inet6_sk(sk);
157 struct tcp_sock *tp = tcp_sk(sk);
158 const struct tcphdr *th = tcp_hdr(skb);
159 __u32 cookie = ntohl(th->ack_seq) - 1;
160 struct sock *ret = sk;
161 struct request_sock *req;
162 int mss;
163 struct dst_entry *dst;
164 __u8 rcv_wscale;
Mike Waychisonf0e3d0682011-08-10 21:59:57 -0700165 bool ecn_ok = false;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800166
Florian Westphalaf9b4732010-06-03 00:43:44 +0000167 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800168 goto out;
169
Florian Westphala0f82f62009-04-19 09:43:48 +0000170 if (tcp_synq_no_recent_overflow(sk) ||
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800171 (mss = cookie_check(skb, cookie)) == 0) {
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700172 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800173 goto out;
174 }
175
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700176 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800177
David S. Millerbb5b7c12009-12-15 20:56:42 -0800178 /* check for timestamp cookie support */
179 memset(&tcp_opt, 0, sizeof(tcp_opt));
Yuchung Cheng2100c8d2012-07-19 06:43:05 +0000180 tcp_parse_options(skb, &tcp_opt, &hash_location, 0, NULL);
David S. Millerbb5b7c12009-12-15 20:56:42 -0800181
Florian Westphal172d69e2010-06-21 11:48:45 +0000182 if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
Florian Westphal8c763682010-06-16 14:42:15 -0700183 goto out;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800184
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800185 ret = NULL;
186 req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
187 if (!req)
188 goto out;
189
190 ireq = inet_rsk(req);
191 ireq6 = inet6_rsk(req);
192 treq = tcp_rsk(req);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800193
Florian Westphal17305542008-08-03 18:13:44 -0700194 if (security_inet_conn_request(sk, skb, req))
195 goto out_free;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800196
197 req->mss = mss;
198 ireq->rmt_port = th->source;
KOVACS Krisztianfd507032008-10-19 23:35:58 -0700199 ireq->loc_port = th->dest;
Alexey Dobriyan4e3fd7a2011-11-21 03:39:03 +0000200 ireq6->rmt_addr = ipv6_hdr(skb)->saddr;
201 ireq6->loc_addr = ipv6_hdr(skb)->daddr;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800202 if (ipv6_opt_accepted(sk, skb) ||
203 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
204 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
205 atomic_inc(&skb->users);
206 ireq6->pktopts = skb;
207 }
208
209 ireq6->iif = sk->sk_bound_dev_if;
210 /* So that link locals have meaning */
211 if (!sk->sk_bound_dev_if &&
212 ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
213 ireq6->iif = inet6_iif(skb);
214
215 req->expires = 0UL;
216 req->retrans = 0;
Florian Westphal172d69e2010-06-21 11:48:45 +0000217 ireq->ecn_ok = ecn_ok;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800218 ireq->snd_wscale = tcp_opt.snd_wscale;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800219 ireq->sack_ok = tcp_opt.sack_ok;
220 ireq->wscale_ok = tcp_opt.wscale_ok;
221 ireq->tstamp_ok = tcp_opt.saw_tstamp;
222 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
Jerry Chu9ad7c042011-06-08 11:08:38 +0000223 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800224 treq->rcv_isn = ntohl(th->seq) - 1;
225 treq->snt_isn = cookie;
226
227 /*
228 * We need to lookup the dst_entry to get the correct window size.
229 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
230 * me if there is a preferred way.
231 */
232 {
Arnaud Ebalard20c59de2010-06-01 21:35:01 +0000233 struct in6_addr *final_p, final;
David S. Miller4c9483b2011-03-12 16:22:43 -0500234 struct flowi6 fl6;
235 memset(&fl6, 0, sizeof(fl6));
236 fl6.flowi6_proto = IPPROTO_TCP;
Alexey Dobriyan4e3fd7a2011-11-21 03:39:03 +0000237 fl6.daddr = ireq6->rmt_addr;
David S. Miller4c9483b2011-03-12 16:22:43 -0500238 final_p = fl6_update_dst(&fl6, np->opt, &final);
Alexey Dobriyan4e3fd7a2011-11-21 03:39:03 +0000239 fl6.saddr = ireq6->loc_addr;
David S. Miller4c9483b2011-03-12 16:22:43 -0500240 fl6.flowi6_oif = sk->sk_bound_dev_if;
241 fl6.flowi6_mark = sk->sk_mark;
David S. Miller1958b852011-03-12 16:36:19 -0500242 fl6.fl6_dport = inet_rsk(req)->rmt_port;
243 fl6.fl6_sport = inet_sk(sk)->inet_sport;
David S. Miller4c9483b2011-03-12 16:22:43 -0500244 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
Florian Westphal17305542008-08-03 18:13:44 -0700245
David S. Miller4c9483b2011-03-12 16:22:43 -0500246 dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false);
David S. Miller68d0c6d2011-03-01 13:19:07 -0800247 if (IS_ERR(dst))
Florian Westphal17305542008-08-03 18:13:44 -0700248 goto out_free;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800249 }
250
Florian Westphal4dfc2812008-04-10 03:12:40 -0700251 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800252 tcp_select_initial_window(tcp_full_space(sk), req->mss,
253 &req->rcv_wnd, &req->window_clamp,
laurent chavey31d12922009-12-15 11:15:28 +0000254 ireq->wscale_ok, &rcv_wscale,
255 dst_metric(dst, RTAX_INITRWND));
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800256
257 ireq->rcv_wscale = rcv_wscale;
258
259 ret = get_cookie_sock(sk, skb, req, dst);
Florian Westphal17305542008-08-03 18:13:44 -0700260out:
261 return ret;
262out_free:
263 reqsk_free(req);
264 return NULL;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800265}
266