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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 | ||
5918e2fb | 30 | /* Table must be sorted. */ |
c6aefafb | 31 | static __u16 const msstab[] = { |
5918e2fb FW |
32 | 64, |
33 | 512, | |
34 | 536, | |
35 | 1280 - 60, | |
36 | 1480 - 60, | |
37 | 1500 - 60, | |
38 | 4460 - 60, | |
39 | 9000 - 60, | |
c6aefafb | 40 | }; |
c6aefafb GG |
41 | |
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 | ||
50 | static 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 | ||
245b2e70 TH |
66 | static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], |
67 | ipv6_cookie_scratch); | |
c6aefafb GG |
68 | |
69 | static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr, | |
70 | __be16 sport, __be16 dport, u32 count, int c) | |
71 | { | |
245b2e70 | 72 | __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch); |
c6aefafb GG |
73 | |
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 | ||
89 | static __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 | ||
99 | static __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 | ||
a0f82f64 | 124 | tcp_synq_overflow(sk); |
c6aefafb | 125 | |
5918e2fb FW |
126 | for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) |
127 | if (mss >= msstab[mssind]) | |
128 | break; | |
129 | ||
130 | *mssp = msstab[mssind]; | |
c6aefafb | 131 | |
de0744af | 132 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); |
c6aefafb GG |
133 | |
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 | ||
139 | static 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 | ||
5918e2fb | 148 | return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; |
c6aefafb GG |
149 | } |
150 | ||
151 | struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) | |
152 | { | |
4957faad WAS |
153 | struct tcp_options_received tcp_opt; |
154 | u8 *hash_location; | |
c6aefafb GG |
155 | 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; | |
172d69e6 | 167 | bool ecn_ok; |
c6aefafb | 168 | |
af9b4738 | 169 | if (!sysctl_tcp_syncookies || !th->ack || th->rst) |
c6aefafb GG |
170 | goto out; |
171 | ||
a0f82f64 | 172 | if (tcp_synq_no_recent_overflow(sk) || |
c6aefafb | 173 | (mss = cookie_check(skb, cookie)) == 0) { |
de0744af | 174 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); |
c6aefafb GG |
175 | goto out; |
176 | } | |
177 | ||
de0744af | 178 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); |
c6aefafb | 179 | |
bb5b7c11 DM |
180 | /* check for timestamp cookie support */ |
181 | memset(&tcp_opt, 0, sizeof(tcp_opt)); | |
182 | tcp_parse_options(skb, &tcp_opt, &hash_location, 0); | |
183 | ||
172d69e6 | 184 | if (!cookie_check_timestamp(&tcp_opt, &ecn_ok)) |
8c763681 | 185 | goto out; |
bb5b7c11 | 186 | |
c6aefafb GG |
187 | 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); | |
c6aefafb | 195 | |
1730554f FW |
196 | if (security_inet_conn_request(sk, skb, req)) |
197 | goto out_free; | |
c6aefafb GG |
198 | |
199 | req->mss = mss; | |
200 | ireq->rmt_port = th->source; | |
fd507037 | 201 | ireq->loc_port = th->dest; |
c6aefafb GG |
202 | 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; | |
172d69e6 | 219 | ireq->ecn_ok = ecn_ok; |
bb5b7c11 | 220 | ireq->snd_wscale = tcp_opt.snd_wscale; |
bb5b7c11 DM |
221 | 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; | |
c6aefafb GG |
225 | 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 | { | |
20c59de2 | 234 | struct in6_addr *final_p, final; |
c6aefafb GG |
235 | struct flowi fl; |
236 | memset(&fl, 0, sizeof(fl)); | |
237 | fl.proto = IPPROTO_TCP; | |
238 | ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr); | |
20c59de2 | 239 | final_p = fl6_update_dst(&fl, np->opt, &final); |
c6aefafb GG |
240 | ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr); |
241 | fl.oif = sk->sk_bound_dev_if; | |
51953d5b | 242 | fl.mark = sk->sk_mark; |
c6aefafb | 243 | fl.fl_ip_dport = inet_rsk(req)->rmt_port; |
c720c7e8 | 244 | fl.fl_ip_sport = inet_sk(sk)->inet_sport; |
c6aefafb | 245 | security_req_classify_flow(req, &fl); |
1730554f FW |
246 | if (ip6_dst_lookup(sk, &dst, &fl)) |
247 | goto out_free; | |
248 | ||
c6aefafb GG |
249 | if (final_p) |
250 | ipv6_addr_copy(&fl.fl6_dst, final_p); | |
52479b62 | 251 | if ((xfrm_lookup(sock_net(sk), &dst, &fl, sk, 0)) < 0) |
1730554f | 252 | goto out_free; |
c6aefafb GG |
253 | } |
254 | ||
4dfc2817 | 255 | req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); |
c6aefafb GG |
256 | tcp_select_initial_window(tcp_full_space(sk), req->mss, |
257 | &req->rcv_wnd, &req->window_clamp, | |
31d12926 | 258 | ireq->wscale_ok, &rcv_wscale, |
259 | dst_metric(dst, RTAX_INITRWND)); | |
c6aefafb GG |
260 | |
261 | ireq->rcv_wscale = rcv_wscale; | |
262 | ||
263 | ret = get_cookie_sock(sk, skb, req, dst); | |
1730554f FW |
264 | out: |
265 | return ret; | |
266 | out_free: | |
267 | reqsk_free(req); | |
268 | return NULL; | |
c6aefafb GG |
269 | } |
270 |