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c6aefafb GG |
1 | /* |
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 | ||
24 | extern int sysctl_tcp_syncookies; | |
2051f11f | 25 | extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS]; |
c6aefafb GG |
26 | |
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 | */ | |
39 | static __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 | ||
61 | static 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 | ||
204fba4a | 77 | static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], cookie_scratch); |
c6aefafb GG |
78 | |
79 | static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr, | |
80 | __be16 sport, __be16 dport, u32 count, int c) | |
81 | { | |
82 | __u32 *tmp = __get_cpu_var(cookie_scratch); | |
83 | ||
84 | /* | |
85 | * we have 320 bits of information to hash, copy in the remaining | |
86 | * 192 bits required for sha_transform, from the syncookie_secret | |
87 | * and overwrite the digest with the secret | |
88 | */ | |
89 | memcpy(tmp + 10, syncookie_secret[c], 44); | |
90 | memcpy(tmp, saddr, 16); | |
91 | memcpy(tmp + 4, daddr, 16); | |
92 | tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; | |
93 | tmp[9] = count; | |
94 | sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); | |
95 | ||
96 | return tmp[17]; | |
97 | } | |
98 | ||
99 | static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr, | |
100 | __be16 sport, __be16 dport, __u32 sseq, | |
101 | __u32 count, __u32 data) | |
102 | { | |
103 | return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + | |
104 | sseq + (count << COOKIEBITS) + | |
105 | ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) | |
106 | & COOKIEMASK)); | |
107 | } | |
108 | ||
109 | static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr, | |
110 | struct in6_addr *daddr, __be16 sport, | |
111 | __be16 dport, __u32 sseq, __u32 count, | |
112 | __u32 maxdiff) | |
113 | { | |
114 | __u32 diff; | |
115 | ||
116 | cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; | |
117 | ||
118 | diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); | |
119 | if (diff >= maxdiff) | |
120 | return (__u32)-1; | |
121 | ||
122 | return (cookie - | |
123 | cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) | |
124 | & COOKIEMASK; | |
125 | } | |
126 | ||
127 | __u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp) | |
128 | { | |
129 | struct ipv6hdr *iph = ipv6_hdr(skb); | |
130 | const struct tcphdr *th = tcp_hdr(skb); | |
131 | int mssind; | |
132 | const __u16 mss = *mssp; | |
133 | ||
a0f82f64 | 134 | tcp_synq_overflow(sk); |
c6aefafb GG |
135 | |
136 | for (mssind = 0; mss > msstab[mssind + 1]; mssind++) | |
137 | ; | |
138 | *mssp = msstab[mssind] + 1; | |
139 | ||
de0744af | 140 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); |
c6aefafb GG |
141 | |
142 | return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, | |
143 | th->dest, ntohl(th->seq), | |
144 | jiffies / (HZ * 60), mssind); | |
145 | } | |
146 | ||
147 | static inline int cookie_check(struct sk_buff *skb, __u32 cookie) | |
148 | { | |
149 | struct ipv6hdr *iph = ipv6_hdr(skb); | |
150 | const struct tcphdr *th = tcp_hdr(skb); | |
151 | __u32 seq = ntohl(th->seq) - 1; | |
152 | __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, | |
153 | th->source, th->dest, seq, | |
154 | jiffies / (HZ * 60), COUNTER_TRIES); | |
155 | ||
156 | return mssind < NUM_MSS ? msstab[mssind] + 1 : 0; | |
157 | } | |
158 | ||
159 | struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) | |
160 | { | |
161 | struct inet_request_sock *ireq; | |
162 | struct inet6_request_sock *ireq6; | |
163 | struct tcp_request_sock *treq; | |
164 | struct ipv6_pinfo *np = inet6_sk(sk); | |
165 | struct tcp_sock *tp = tcp_sk(sk); | |
166 | const struct tcphdr *th = tcp_hdr(skb); | |
167 | __u32 cookie = ntohl(th->ack_seq) - 1; | |
168 | struct sock *ret = sk; | |
169 | struct request_sock *req; | |
170 | int mss; | |
171 | struct dst_entry *dst; | |
172 | __u8 rcv_wscale; | |
4dfc2817 | 173 | struct tcp_options_received tcp_opt; |
c6aefafb GG |
174 | |
175 | if (!sysctl_tcp_syncookies || !th->ack) | |
176 | goto out; | |
177 | ||
a0f82f64 | 178 | if (tcp_synq_no_recent_overflow(sk) || |
c6aefafb | 179 | (mss = cookie_check(skb, cookie)) == 0) { |
de0744af | 180 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); |
c6aefafb GG |
181 | goto out; |
182 | } | |
183 | ||
de0744af | 184 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); |
c6aefafb | 185 | |
4dfc2817 FW |
186 | /* check for timestamp cookie support */ |
187 | memset(&tcp_opt, 0, sizeof(tcp_opt)); | |
188 | tcp_parse_options(skb, &tcp_opt, 0); | |
189 | ||
190 | if (tcp_opt.saw_tstamp) | |
191 | cookie_check_timestamp(&tcp_opt); | |
192 | ||
c6aefafb GG |
193 | ret = NULL; |
194 | req = inet6_reqsk_alloc(&tcp6_request_sock_ops); | |
195 | if (!req) | |
196 | goto out; | |
197 | ||
198 | ireq = inet_rsk(req); | |
199 | ireq6 = inet6_rsk(req); | |
200 | treq = tcp_rsk(req); | |
c6aefafb | 201 | |
1730554f FW |
202 | if (security_inet_conn_request(sk, skb, req)) |
203 | goto out_free; | |
c6aefafb GG |
204 | |
205 | req->mss = mss; | |
206 | ireq->rmt_port = th->source; | |
fd507037 | 207 | ireq->loc_port = th->dest; |
c6aefafb GG |
208 | ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr); |
209 | ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr); | |
210 | if (ipv6_opt_accepted(sk, skb) || | |
211 | np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || | |
212 | np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { | |
213 | atomic_inc(&skb->users); | |
214 | ireq6->pktopts = skb; | |
215 | } | |
216 | ||
217 | ireq6->iif = sk->sk_bound_dev_if; | |
218 | /* So that link locals have meaning */ | |
219 | if (!sk->sk_bound_dev_if && | |
220 | ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL) | |
221 | ireq6->iif = inet6_iif(skb); | |
222 | ||
223 | req->expires = 0UL; | |
224 | req->retrans = 0; | |
16df845f | 225 | ireq->ecn_ok = 0; |
4dfc2817 FW |
226 | ireq->snd_wscale = tcp_opt.snd_wscale; |
227 | ireq->rcv_wscale = tcp_opt.rcv_wscale; | |
228 | ireq->sack_ok = tcp_opt.sack_ok; | |
229 | ireq->wscale_ok = tcp_opt.wscale_ok; | |
230 | ireq->tstamp_ok = tcp_opt.saw_tstamp; | |
231 | req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; | |
c6aefafb GG |
232 | treq->rcv_isn = ntohl(th->seq) - 1; |
233 | treq->snt_isn = cookie; | |
234 | ||
235 | /* | |
236 | * We need to lookup the dst_entry to get the correct window size. | |
237 | * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten | |
238 | * me if there is a preferred way. | |
239 | */ | |
240 | { | |
241 | struct in6_addr *final_p = NULL, final; | |
242 | struct flowi fl; | |
243 | memset(&fl, 0, sizeof(fl)); | |
244 | fl.proto = IPPROTO_TCP; | |
245 | ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr); | |
246 | if (np->opt && np->opt->srcrt) { | |
247 | struct rt0_hdr *rt0 = (struct rt0_hdr *) np->opt->srcrt; | |
248 | ipv6_addr_copy(&final, &fl.fl6_dst); | |
249 | ipv6_addr_copy(&fl.fl6_dst, rt0->addr); | |
250 | final_p = &final; | |
251 | } | |
252 | ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr); | |
253 | fl.oif = sk->sk_bound_dev_if; | |
254 | fl.fl_ip_dport = inet_rsk(req)->rmt_port; | |
255 | fl.fl_ip_sport = inet_sk(sk)->sport; | |
256 | security_req_classify_flow(req, &fl); | |
1730554f FW |
257 | if (ip6_dst_lookup(sk, &dst, &fl)) |
258 | goto out_free; | |
259 | ||
c6aefafb GG |
260 | if (final_p) |
261 | ipv6_addr_copy(&fl.fl6_dst, final_p); | |
52479b62 | 262 | if ((xfrm_lookup(sock_net(sk), &dst, &fl, sk, 0)) < 0) |
1730554f | 263 | goto out_free; |
c6aefafb GG |
264 | } |
265 | ||
4dfc2817 | 266 | req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); |
c6aefafb GG |
267 | tcp_select_initial_window(tcp_full_space(sk), req->mss, |
268 | &req->rcv_wnd, &req->window_clamp, | |
4dfc2817 | 269 | ireq->wscale_ok, &rcv_wscale); |
c6aefafb GG |
270 | |
271 | ireq->rcv_wscale = rcv_wscale; | |
272 | ||
273 | ret = get_cookie_sock(sk, skb, req, dst); | |
1730554f FW |
274 | out: |
275 | return ret; | |
276 | out_free: | |
277 | reqsk_free(req); | |
278 | return NULL; | |
c6aefafb GG |
279 | } |
280 |