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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
30/*
31 * This table has to be sorted and terminated with (__u16)-1.
32 * XXX generate a better table.
33 * Unresolved Issues: HIPPI with a 64k MSS is not well supported.
34 *
35 * Taken directly from ipv4 implementation.
36 * Should this list be modified for ipv6 use or is it close enough?
37 * rfc 2460 8.3 suggests mss values 20 bytes less than ipv4 counterpart
38 */
39static __u16 const msstab[] = {
40 64 - 1,
41 256 - 1,
42 512 - 1,
43 536 - 1,
44 1024 - 1,
45 1440 - 1,
46 1460 - 1,
47 4312 - 1,
48 (__u16)-1
49};
50/* The number doesn't include the -1 terminator */
51#define NUM_MSS (ARRAY_SIZE(msstab) - 1)
52
53/*
54 * This (misnamed) value is the age of syncookie which is permitted.
55 * Its ideal value should be dependent on TCP_TIMEOUT_INIT and
56 * sysctl_tcp_retries1. It's a rather complicated formula (exponential
57 * backoff) to compute at runtime so it's currently hardcoded here.
58 */
59#define COUNTER_TRIES 4
60
61static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
62 struct request_sock *req,
63 struct dst_entry *dst)
64{
65 struct inet_connection_sock *icsk = inet_csk(sk);
66 struct sock *child;
67
68 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
69 if (child)
70 inet_csk_reqsk_queue_add(sk, req, child);
71 else
72 reqsk_free(req);
73
74 return child;
75}
76
Tejun Heo245b2e72009-06-24 15:13:48 +090077static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
78 ipv6_cookie_scratch);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080079
80static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr,
81 __be16 sport, __be16 dport, u32 count, int c)
82{
Tejun Heo245b2e72009-06-24 15:13:48 +090083 __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -080084
85 /*
86 * we have 320 bits of information to hash, copy in the remaining
87 * 192 bits required for sha_transform, from the syncookie_secret
88 * and overwrite the digest with the secret
89 */
90 memcpy(tmp + 10, syncookie_secret[c], 44);
91 memcpy(tmp, saddr, 16);
92 memcpy(tmp + 4, daddr, 16);
93 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport;
94 tmp[9] = count;
95 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
96
97 return tmp[17];
98}
99
100static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr,
101 __be16 sport, __be16 dport, __u32 sseq,
102 __u32 count, __u32 data)
103{
104 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
105 sseq + (count << COOKIEBITS) +
106 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
107 & COOKIEMASK));
108}
109
110static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr,
111 struct in6_addr *daddr, __be16 sport,
112 __be16 dport, __u32 sseq, __u32 count,
113 __u32 maxdiff)
114{
115 __u32 diff;
116
117 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
118
119 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
120 if (diff >= maxdiff)
121 return (__u32)-1;
122
123 return (cookie -
124 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
125 & COOKIEMASK;
126}
127
128__u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
129{
130 struct ipv6hdr *iph = ipv6_hdr(skb);
131 const struct tcphdr *th = tcp_hdr(skb);
132 int mssind;
133 const __u16 mss = *mssp;
134
Florian Westphala0f82f62009-04-19 09:43:48 +0000135 tcp_synq_overflow(sk);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800136
137 for (mssind = 0; mss > msstab[mssind + 1]; mssind++)
138 ;
139 *mssp = msstab[mssind] + 1;
140
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700141 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800142
143 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
144 th->dest, ntohl(th->seq),
145 jiffies / (HZ * 60), mssind);
146}
147
148static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
149{
150 struct ipv6hdr *iph = ipv6_hdr(skb);
151 const struct tcphdr *th = tcp_hdr(skb);
152 __u32 seq = ntohl(th->seq) - 1;
153 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
154 th->source, th->dest, seq,
155 jiffies / (HZ * 60), COUNTER_TRIES);
156
157 return mssind < NUM_MSS ? msstab[mssind] + 1 : 0;
158}
159
160struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
161{
162 struct inet_request_sock *ireq;
163 struct inet6_request_sock *ireq6;
164 struct tcp_request_sock *treq;
165 struct ipv6_pinfo *np = inet6_sk(sk);
166 struct tcp_sock *tp = tcp_sk(sk);
167 const struct tcphdr *th = tcp_hdr(skb);
168 __u32 cookie = ntohl(th->ack_seq) - 1;
169 struct sock *ret = sk;
170 struct request_sock *req;
171 int mss;
172 struct dst_entry *dst;
173 __u8 rcv_wscale;
Florian Westphal4dfc2812008-04-10 03:12:40 -0700174 struct tcp_options_received tcp_opt;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800175
176 if (!sysctl_tcp_syncookies || !th->ack)
177 goto out;
178
Florian Westphala0f82f62009-04-19 09:43:48 +0000179 if (tcp_synq_no_recent_overflow(sk) ||
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800180 (mss = cookie_check(skb, cookie)) == 0) {
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700181 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800182 goto out;
183 }
184
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700185 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800186
Florian Westphal4dfc2812008-04-10 03:12:40 -0700187 /* check for timestamp cookie support */
188 memset(&tcp_opt, 0, sizeof(tcp_opt));
189 tcp_parse_options(skb, &tcp_opt, 0);
190
191 if (tcp_opt.saw_tstamp)
192 cookie_check_timestamp(&tcp_opt);
193
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800194 ret = NULL;
195 req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
196 if (!req)
197 goto out;
198
199 ireq = inet_rsk(req);
200 ireq6 = inet6_rsk(req);
201 treq = tcp_rsk(req);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800202
Florian Westphal17305542008-08-03 18:13:44 -0700203 if (security_inet_conn_request(sk, skb, req))
204 goto out_free;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800205
206 req->mss = mss;
207 ireq->rmt_port = th->source;
KOVACS Krisztianfd507032008-10-19 23:35:58 -0700208 ireq->loc_port = th->dest;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800209 ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr);
210 ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr);
211 if (ipv6_opt_accepted(sk, skb) ||
212 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
213 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
214 atomic_inc(&skb->users);
215 ireq6->pktopts = skb;
216 }
217
218 ireq6->iif = sk->sk_bound_dev_if;
219 /* So that link locals have meaning */
220 if (!sk->sk_bound_dev_if &&
221 ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
222 ireq6->iif = inet6_iif(skb);
223
224 req->expires = 0UL;
225 req->retrans = 0;
Florian Westphal16df8452008-07-26 02:21:54 -0700226 ireq->ecn_ok = 0;
Florian Westphal4dfc2812008-04-10 03:12:40 -0700227 ireq->snd_wscale = tcp_opt.snd_wscale;
228 ireq->rcv_wscale = tcp_opt.rcv_wscale;
229 ireq->sack_ok = tcp_opt.sack_ok;
230 ireq->wscale_ok = tcp_opt.wscale_ok;
231 ireq->tstamp_ok = tcp_opt.saw_tstamp;
232 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800233 treq->rcv_isn = ntohl(th->seq) - 1;
234 treq->snt_isn = cookie;
235
236 /*
237 * We need to lookup the dst_entry to get the correct window size.
238 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
239 * me if there is a preferred way.
240 */
241 {
242 struct in6_addr *final_p = NULL, final;
243 struct flowi fl;
244 memset(&fl, 0, sizeof(fl));
245 fl.proto = IPPROTO_TCP;
246 ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr);
247 if (np->opt && np->opt->srcrt) {
248 struct rt0_hdr *rt0 = (struct rt0_hdr *) np->opt->srcrt;
249 ipv6_addr_copy(&final, &fl.fl6_dst);
250 ipv6_addr_copy(&fl.fl6_dst, rt0->addr);
251 final_p = &final;
252 }
253 ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr);
254 fl.oif = sk->sk_bound_dev_if;
255 fl.fl_ip_dport = inet_rsk(req)->rmt_port;
256 fl.fl_ip_sport = inet_sk(sk)->sport;
257 security_req_classify_flow(req, &fl);
Florian Westphal17305542008-08-03 18:13:44 -0700258 if (ip6_dst_lookup(sk, &dst, &fl))
259 goto out_free;
260
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800261 if (final_p)
262 ipv6_addr_copy(&fl.fl6_dst, final_p);
Alexey Dobriyan52479b62008-11-25 17:35:18 -0800263 if ((xfrm_lookup(sock_net(sk), &dst, &fl, sk, 0)) < 0)
Florian Westphal17305542008-08-03 18:13:44 -0700264 goto out_free;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800265 }
266
Florian Westphal4dfc2812008-04-10 03:12:40 -0700267 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800268 tcp_select_initial_window(tcp_full_space(sk), req->mss,
269 &req->rcv_wnd, &req->window_clamp,
Florian Westphal4dfc2812008-04-10 03:12:40 -0700270 ireq->wscale_ok, &rcv_wscale);
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800271
272 ireq->rcv_wscale = rcv_wscale;
273
274 ret = get_cookie_sock(sk, skb, req, dst);
Florian Westphal17305542008-08-03 18:13:44 -0700275out:
276 return ret;
277out_free:
278 reqsk_free(req);
279 return NULL;
Glenn Griffinc6aefaf2008-02-07 21:49:26 -0800280}
281