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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
24extern int sysctl_tcp_syncookies;
Florian Westphal2051f112008-03-23 22:21:28 -070025extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080026
27#define COOKIEBITS 24 /* Upper bits store count */
28#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
29
Florian Westphal5918e2f2010-06-03 00:43:57 +000030/* Table must be sorted. */
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080031static __u16 const msstab[] = {
Florian Westphal5918e2f2010-06-03 00:43:57 +000032 64,
33 512,
34 536,
35 1280 - 60,
36 1480 - 60,
37 1500 - 60,
38 4460 - 60,
39 9000 - 60,
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080040};
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080041
42/*
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.
47 */
48#define COUNTER_TRIES 4
49
50static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
51 struct request_sock *req,
52 struct dst_entry *dst)
53{
54 struct inet_connection_sock *icsk = inet_csk(sk);
55 struct sock *child;
56
57 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
58 if (child)
59 inet_csk_reqsk_queue_add(sk, req, child);
60 else
61 reqsk_free(req);
62
63 return child;
64}
65
Tejun Heo245b2e72009-06-24 15:13:48 +090066static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
67 ipv6_cookie_scratch);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080068
69static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr,
70 __be16 sport, __be16 dport, u32 count, int c)
71{
Tejun Heo245b2e72009-06-24 15:13:48 +090072 __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080073
74 /*
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
78 */
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;
83 tmp[9] = count;
84 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
85
86 return tmp[17];
87}
88
89static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr,
90 __be16 sport, __be16 dport, __u32 sseq,
91 __u32 count, __u32 data)
92{
93 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
94 sseq + (count << COOKIEBITS) +
95 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
96 & COOKIEMASK));
97}
98
99static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr,
100 struct in6_addr *daddr, __be16 sport,
101 __be16 dport, __u32 sseq, __u32 count,
102 __u32 maxdiff)
103{
104 __u32 diff;
105
106 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
107
108 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
109 if (diff >= maxdiff)
110 return (__u32)-1;
111
112 return (cookie -
113 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
114 & COOKIEMASK;
115}
116
117__u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
118{
119 struct ipv6hdr *iph = ipv6_hdr(skb);
120 const struct tcphdr *th = tcp_hdr(skb);
121 int mssind;
122 const __u16 mss = *mssp;
123
Florian Westphala0f82f62009-04-19 09:43:48 +0000124 tcp_synq_overflow(sk);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800125
Florian Westphal5918e2f2010-06-03 00:43:57 +0000126 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
127 if (mss >= msstab[mssind])
128 break;
129
130 *mssp = msstab[mssind];
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800131
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700132 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800133
134 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
135 th->dest, ntohl(th->seq),
136 jiffies / (HZ * 60), mssind);
137}
138
139static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
140{
141 struct ipv6hdr *iph = ipv6_hdr(skb);
142 const struct tcphdr *th = tcp_hdr(skb);
143 __u32 seq = ntohl(th->seq) - 1;
144 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
145 th->source, th->dest, seq,
146 jiffies / (HZ * 60), COUNTER_TRIES);
147
Florian Westphal5918e2f2010-06-03 00:43:57 +0000148 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800149}
150
151struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
152{
William Allen Simpson4957faade2009-12-02 18:25:27 +0000153 struct tcp_options_received tcp_opt;
154 u8 *hash_location;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800155 struct inet_request_sock *ireq;
156 struct inet6_request_sock *ireq6;
157 struct tcp_request_sock *treq;
158 struct ipv6_pinfo *np = inet6_sk(sk);
159 struct tcp_sock *tp = tcp_sk(sk);
160 const struct tcphdr *th = tcp_hdr(skb);
161 __u32 cookie = ntohl(th->ack_seq) - 1;
162 struct sock *ret = sk;
163 struct request_sock *req;
164 int mss;
165 struct dst_entry *dst;
166 __u8 rcv_wscale;
Florian Westphal172d69e2010-06-21 11:48:45 +0000167 bool ecn_ok;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800168
Florian Westphalaf9b4732010-06-03 00:43:44 +0000169 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800170 goto out;
171
Florian Westphala0f82f62009-04-19 09:43:48 +0000172 if (tcp_synq_no_recent_overflow(sk) ||
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800173 (mss = cookie_check(skb, cookie)) == 0) {
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700174 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800175 goto out;
176 }
177
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700178 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800179
David S. Millerbb5b7c12009-12-15 20:56:42 -0800180 /* check for timestamp cookie support */
181 memset(&tcp_opt, 0, sizeof(tcp_opt));
182 tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
183
Florian Westphal172d69e2010-06-21 11:48:45 +0000184 if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
Florian Westphal8c763682010-06-16 14:42:15 -0700185 goto out;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800186
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800187 ret = NULL;
188 req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
189 if (!req)
190 goto out;
191
192 ireq = inet_rsk(req);
193 ireq6 = inet6_rsk(req);
194 treq = tcp_rsk(req);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800195
Florian Westphal17305542008-08-03 18:13:44 -0700196 if (security_inet_conn_request(sk, skb, req))
197 goto out_free;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800198
199 req->mss = mss;
200 ireq->rmt_port = th->source;
KOVACS Krisztianfd507032008-10-19 23:35:58 -0700201 ireq->loc_port = th->dest;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800202 ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr);
203 ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr);
204 if (ipv6_opt_accepted(sk, skb) ||
205 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
206 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
207 atomic_inc(&skb->users);
208 ireq6->pktopts = skb;
209 }
210
211 ireq6->iif = sk->sk_bound_dev_if;
212 /* So that link locals have meaning */
213 if (!sk->sk_bound_dev_if &&
214 ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
215 ireq6->iif = inet6_iif(skb);
216
217 req->expires = 0UL;
218 req->retrans = 0;
Florian Westphal172d69e2010-06-21 11:48:45 +0000219 ireq->ecn_ok = ecn_ok;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800220 ireq->snd_wscale = tcp_opt.snd_wscale;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800221 ireq->sack_ok = tcp_opt.sack_ok;
222 ireq->wscale_ok = tcp_opt.wscale_ok;
223 ireq->tstamp_ok = tcp_opt.saw_tstamp;
224 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800225 treq->rcv_isn = ntohl(th->seq) - 1;
226 treq->snt_isn = cookie;
227
228 /*
229 * We need to lookup the dst_entry to get the correct window size.
230 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
231 * me if there is a preferred way.
232 */
233 {
Arnaud Ebalard20c59de2010-06-01 21:35:01 +0000234 struct in6_addr *final_p, final;
David S. Miller4c9483b2011-03-12 16:22:43 -0500235 struct flowi6 fl6;
236 memset(&fl6, 0, sizeof(fl6));
237 fl6.flowi6_proto = IPPROTO_TCP;
238 ipv6_addr_copy(&fl6.daddr, &ireq6->rmt_addr);
239 final_p = fl6_update_dst(&fl6, np->opt, &final);
240 ipv6_addr_copy(&fl6.saddr, &ireq6->loc_addr);
241 fl6.flowi6_oif = sk->sk_bound_dev_if;
242 fl6.flowi6_mark = sk->sk_mark;
243 fl6.uli.ports.dport = inet_rsk(req)->rmt_port;
244 fl6.uli.ports.sport = inet_sk(sk)->inet_sport;
245 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
Florian Westphal17305542008-08-03 18:13:44 -0700246
David S. Miller4c9483b2011-03-12 16:22:43 -0500247 dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false);
David S. Miller68d0c6d2011-03-01 13:19:07 -0800248 if (IS_ERR(dst))
Florian Westphal17305542008-08-03 18:13:44 -0700249 goto out_free;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800250 }
251
Florian Westphal4dfc2812008-04-10 03:12:40 -0700252 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800253 tcp_select_initial_window(tcp_full_space(sk), req->mss,
254 &req->rcv_wnd, &req->window_clamp,
laurent chavey31d12922009-12-15 11:15:28 +0000255 ireq->wscale_ok, &rcv_wscale,
256 dst_metric(dst, RTAX_INITRWND));
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800257
258 ireq->rcv_wscale = rcv_wscale;
259
260 ret = get_cookie_sock(sk, skb, req, dst);
Florian Westphal17305542008-08-03 18:13:44 -0700261out:
262 return ret;
263out_free:
264 reqsk_free(req);
265 return NULL;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800266}
267