Commit | Line | Data |
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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 | ||
c6aefafb GG |
24 | #define COOKIEBITS 24 /* Upper bits store count */ |
25 | #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) | |
26 | ||
b23a002f HFS |
27 | static u32 syncookie6_secret[2][16-4+SHA_DIGEST_WORDS]; |
28 | ||
08629354 FW |
29 | /* RFC 2460, Section 8.3: |
30 | * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..] | |
31 | * | |
32 | * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows | |
33 | * using higher values than ipv4 tcp syncookies. | |
34 | * The other values are chosen based on ethernet (1500 and 9k MTU), plus | |
35 | * one that accounts for common encap (PPPoe) overhead. Table must be sorted. | |
36 | */ | |
c6aefafb | 37 | static __u16 const msstab[] = { |
08629354 | 38 | 1280 - 60, /* IPV6_MIN_MTU - 60 */ |
5918e2fb FW |
39 | 1480 - 60, |
40 | 1500 - 60, | |
5918e2fb | 41 | 9000 - 60, |
c6aefafb | 42 | }; |
c6aefafb | 43 | |
c6aefafb GG |
44 | static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, |
45 | struct request_sock *req, | |
46 | struct dst_entry *dst) | |
47 | { | |
48 | struct inet_connection_sock *icsk = inet_csk(sk); | |
49 | struct sock *child; | |
50 | ||
51 | child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst); | |
52 | if (child) | |
53 | inet_csk_reqsk_queue_add(sk, req, child); | |
54 | else | |
55 | reqsk_free(req); | |
56 | ||
57 | return child; | |
58 | } | |
59 | ||
245b2e70 TH |
60 | static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], |
61 | ipv6_cookie_scratch); | |
c6aefafb | 62 | |
b71d1d42 | 63 | static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr, |
c6aefafb GG |
64 | __be16 sport, __be16 dport, u32 count, int c) |
65 | { | |
b23a002f HFS |
66 | __u32 *tmp; |
67 | ||
68 | net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret)); | |
69 | ||
70 | tmp = __get_cpu_var(ipv6_cookie_scratch); | |
c6aefafb GG |
71 | |
72 | /* | |
73 | * we have 320 bits of information to hash, copy in the remaining | |
b23a002f | 74 | * 192 bits required for sha_transform, from the syncookie6_secret |
c6aefafb GG |
75 | * and overwrite the digest with the secret |
76 | */ | |
b23a002f | 77 | memcpy(tmp + 10, syncookie6_secret[c], 44); |
c6aefafb GG |
78 | memcpy(tmp, saddr, 16); |
79 | memcpy(tmp + 4, daddr, 16); | |
80 | tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; | |
81 | tmp[9] = count; | |
82 | sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); | |
83 | ||
84 | return tmp[17]; | |
85 | } | |
86 | ||
b71d1d42 ED |
87 | static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, |
88 | const struct in6_addr *daddr, | |
c6aefafb | 89 | __be16 sport, __be16 dport, __u32 sseq, |
8c27bd75 | 90 | __u32 data) |
c6aefafb | 91 | { |
8c27bd75 | 92 | u32 count = tcp_cookie_time(); |
c6aefafb GG |
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 | ||
b71d1d42 ED |
99 | static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, |
100 | const struct in6_addr *daddr, __be16 sport, | |
8c27bd75 | 101 | __be16 dport, __u32 sseq) |
c6aefafb | 102 | { |
8c27bd75 | 103 | __u32 diff, count = tcp_cookie_time(); |
c6aefafb GG |
104 | |
105 | cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; | |
106 | ||
107 | diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); | |
8c27bd75 | 108 | if (diff >= MAX_SYNCOOKIE_AGE) |
c6aefafb GG |
109 | return (__u32)-1; |
110 | ||
111 | return (cookie - | |
112 | cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) | |
113 | & COOKIEMASK; | |
114 | } | |
115 | ||
81eb6a14 PM |
116 | u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph, |
117 | const struct tcphdr *th, __u16 *mssp) | |
c6aefafb | 118 | { |
c6aefafb GG |
119 | int mssind; |
120 | const __u16 mss = *mssp; | |
121 | ||
5918e2fb FW |
122 | for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) |
123 | if (mss >= msstab[mssind]) | |
124 | break; | |
125 | ||
126 | *mssp = msstab[mssind]; | |
c6aefafb | 127 | |
c6aefafb | 128 | return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, |
8c27bd75 | 129 | th->dest, ntohl(th->seq), mssind); |
c6aefafb | 130 | } |
81eb6a14 | 131 | EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence); |
c6aefafb | 132 | |
81eb6a14 | 133 | __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp) |
c6aefafb | 134 | { |
b71d1d42 | 135 | const struct ipv6hdr *iph = ipv6_hdr(skb); |
c6aefafb | 136 | const struct tcphdr *th = tcp_hdr(skb); |
81eb6a14 PM |
137 | |
138 | tcp_synq_overflow(sk); | |
139 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); | |
140 | ||
141 | return __cookie_v6_init_sequence(iph, th, mssp); | |
142 | } | |
143 | ||
144 | int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, | |
145 | __u32 cookie) | |
146 | { | |
c6aefafb GG |
147 | __u32 seq = ntohl(th->seq) - 1; |
148 | __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, | |
8c27bd75 | 149 | th->source, th->dest, seq); |
c6aefafb | 150 | |
5918e2fb | 151 | return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; |
c6aefafb | 152 | } |
81eb6a14 | 153 | EXPORT_SYMBOL_GPL(__cookie_v6_check); |
c6aefafb GG |
154 | |
155 | struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) | |
156 | { | |
4957faad | 157 | struct tcp_options_received tcp_opt; |
c6aefafb | 158 | struct inet_request_sock *ireq; |
c6aefafb GG |
159 | struct tcp_request_sock *treq; |
160 | struct ipv6_pinfo *np = inet6_sk(sk); | |
161 | struct tcp_sock *tp = tcp_sk(sk); | |
162 | const struct tcphdr *th = tcp_hdr(skb); | |
163 | __u32 cookie = ntohl(th->ack_seq) - 1; | |
164 | struct sock *ret = sk; | |
165 | struct request_sock *req; | |
166 | int mss; | |
167 | struct dst_entry *dst; | |
168 | __u8 rcv_wscale; | |
f0e3d068 | 169 | bool ecn_ok = false; |
c6aefafb | 170 | |
af9b4738 | 171 | if (!sysctl_tcp_syncookies || !th->ack || th->rst) |
c6aefafb GG |
172 | goto out; |
173 | ||
a0f82f64 | 174 | if (tcp_synq_no_recent_overflow(sk) || |
81eb6a14 | 175 | (mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie)) == 0) { |
de0744af | 176 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); |
c6aefafb GG |
177 | goto out; |
178 | } | |
179 | ||
de0744af | 180 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); |
c6aefafb | 181 | |
bb5b7c11 DM |
182 | /* check for timestamp cookie support */ |
183 | memset(&tcp_opt, 0, sizeof(tcp_opt)); | |
1a2c6181 | 184 | tcp_parse_options(skb, &tcp_opt, 0, NULL); |
bb5b7c11 | 185 | |
5d134f1c | 186 | if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok)) |
8c763681 | 187 | goto out; |
bb5b7c11 | 188 | |
c6aefafb GG |
189 | ret = NULL; |
190 | req = inet6_reqsk_alloc(&tcp6_request_sock_ops); | |
191 | if (!req) | |
192 | goto out; | |
193 | ||
194 | ireq = inet_rsk(req); | |
c6aefafb | 195 | treq = tcp_rsk(req); |
8336886f | 196 | treq->listener = NULL; |
c6aefafb | 197 | |
1730554f FW |
198 | if (security_inet_conn_request(sk, skb, req)) |
199 | goto out_free; | |
c6aefafb GG |
200 | |
201 | req->mss = mss; | |
634fb979 | 202 | ireq->ir_rmt_port = th->source; |
b44084c2 | 203 | ireq->ir_num = ntohs(th->dest); |
634fb979 ED |
204 | ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; |
205 | ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; | |
c6aefafb GG |
206 | if (ipv6_opt_accepted(sk, skb) || |
207 | np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || | |
208 | np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { | |
209 | atomic_inc(&skb->users); | |
634fb979 | 210 | ireq->pktopts = skb; |
c6aefafb GG |
211 | } |
212 | ||
634fb979 | 213 | ireq->ir_iif = sk->sk_bound_dev_if; |
c6aefafb GG |
214 | /* So that link locals have meaning */ |
215 | if (!sk->sk_bound_dev_if && | |
634fb979 ED |
216 | ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) |
217 | ireq->ir_iif = inet6_iif(skb); | |
c6aefafb GG |
218 | |
219 | req->expires = 0UL; | |
e6c022a4 | 220 | req->num_retrans = 0; |
172d69e6 | 221 | ireq->ecn_ok = ecn_ok; |
bb5b7c11 | 222 | ireq->snd_wscale = tcp_opt.snd_wscale; |
bb5b7c11 DM |
223 | ireq->sack_ok = tcp_opt.sack_ok; |
224 | ireq->wscale_ok = tcp_opt.wscale_ok; | |
225 | ireq->tstamp_ok = tcp_opt.saw_tstamp; | |
226 | req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; | |
9ad7c049 | 227 | treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; |
c6aefafb GG |
228 | treq->rcv_isn = ntohl(th->seq) - 1; |
229 | treq->snt_isn = cookie; | |
230 | ||
231 | /* | |
232 | * We need to lookup the dst_entry to get the correct window size. | |
233 | * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten | |
234 | * me if there is a preferred way. | |
235 | */ | |
236 | { | |
20c59de2 | 237 | struct in6_addr *final_p, final; |
4c9483b2 DM |
238 | struct flowi6 fl6; |
239 | memset(&fl6, 0, sizeof(fl6)); | |
240 | fl6.flowi6_proto = IPPROTO_TCP; | |
634fb979 | 241 | fl6.daddr = ireq->ir_v6_rmt_addr; |
4c9483b2 | 242 | final_p = fl6_update_dst(&fl6, np->opt, &final); |
634fb979 | 243 | fl6.saddr = ireq->ir_v6_loc_addr; |
4c9483b2 DM |
244 | fl6.flowi6_oif = sk->sk_bound_dev_if; |
245 | fl6.flowi6_mark = sk->sk_mark; | |
634fb979 | 246 | fl6.fl6_dport = ireq->ir_rmt_port; |
1958b856 | 247 | fl6.fl6_sport = inet_sk(sk)->inet_sport; |
4c9483b2 DM |
248 | security_req_classify_flow(req, flowi6_to_flowi(&fl6)); |
249 | ||
250 | dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false); | |
68d0c6d3 | 251 | if (IS_ERR(dst)) |
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 |