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> | |
fe62d05b | 19 | #include <linux/siphash.h> |
c6aefafb | 20 | #include <linux/kernel.h> |
84b114b9 | 21 | #include <net/secure_seq.h> |
c6aefafb GG |
22 | #include <net/ipv6.h> |
23 | #include <net/tcp.h> | |
24 | ||
c6aefafb GG |
25 | #define COOKIEBITS 24 /* Upper bits store count */ |
26 | #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) | |
27 | ||
fe62d05b | 28 | static siphash_key_t syncookie6_secret[2] __read_mostly; |
b23a002f | 29 | |
08629354 FW |
30 | /* RFC 2460, Section 8.3: |
31 | * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..] | |
32 | * | |
33 | * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows | |
34 | * using higher values than ipv4 tcp syncookies. | |
35 | * The other values are chosen based on ethernet (1500 and 9k MTU), plus | |
36 | * one that accounts for common encap (PPPoe) overhead. Table must be sorted. | |
37 | */ | |
c6aefafb | 38 | static __u16 const msstab[] = { |
08629354 | 39 | 1280 - 60, /* IPV6_MIN_MTU - 60 */ |
5918e2fb FW |
40 | 1480 - 60, |
41 | 1500 - 60, | |
5918e2fb | 42 | 9000 - 60, |
c6aefafb | 43 | }; |
c6aefafb | 44 | |
fe62d05b JD |
45 | static u32 cookie_hash(const struct in6_addr *saddr, |
46 | const struct in6_addr *daddr, | |
c6aefafb GG |
47 | __be16 sport, __be16 dport, u32 count, int c) |
48 | { | |
fe62d05b JD |
49 | const struct { |
50 | struct in6_addr saddr; | |
51 | struct in6_addr daddr; | |
52 | u32 count; | |
53 | __be16 sport; | |
54 | __be16 dport; | |
55 | } __aligned(SIPHASH_ALIGNMENT) combined = { | |
56 | .saddr = *saddr, | |
57 | .daddr = *daddr, | |
58 | .count = count, | |
59 | .sport = sport, | |
60 | .dport = dport | |
61 | }; | |
b23a002f HFS |
62 | |
63 | net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret)); | |
fe62d05b JD |
64 | return siphash(&combined, offsetofend(typeof(combined), dport), |
65 | &syncookie6_secret[c]); | |
c6aefafb GG |
66 | } |
67 | ||
b71d1d42 ED |
68 | static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, |
69 | const struct in6_addr *daddr, | |
c6aefafb | 70 | __be16 sport, __be16 dport, __u32 sseq, |
8c27bd75 | 71 | __u32 data) |
c6aefafb | 72 | { |
8c27bd75 | 73 | u32 count = tcp_cookie_time(); |
c6aefafb GG |
74 | return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + |
75 | sseq + (count << COOKIEBITS) + | |
76 | ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) | |
77 | & COOKIEMASK)); | |
78 | } | |
79 | ||
b71d1d42 ED |
80 | static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, |
81 | const struct in6_addr *daddr, __be16 sport, | |
8c27bd75 | 82 | __be16 dport, __u32 sseq) |
c6aefafb | 83 | { |
8c27bd75 | 84 | __u32 diff, count = tcp_cookie_time(); |
c6aefafb GG |
85 | |
86 | cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; | |
87 | ||
88 | diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); | |
8c27bd75 | 89 | if (diff >= MAX_SYNCOOKIE_AGE) |
c6aefafb GG |
90 | return (__u32)-1; |
91 | ||
92 | return (cookie - | |
93 | cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) | |
94 | & COOKIEMASK; | |
95 | } | |
96 | ||
81eb6a14 PM |
97 | u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph, |
98 | const struct tcphdr *th, __u16 *mssp) | |
c6aefafb | 99 | { |
c6aefafb GG |
100 | int mssind; |
101 | const __u16 mss = *mssp; | |
102 | ||
5918e2fb FW |
103 | for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) |
104 | if (mss >= msstab[mssind]) | |
105 | break; | |
106 | ||
107 | *mssp = msstab[mssind]; | |
c6aefafb | 108 | |
c6aefafb | 109 | return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, |
8c27bd75 | 110 | th->dest, ntohl(th->seq), mssind); |
c6aefafb | 111 | } |
81eb6a14 | 112 | EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence); |
c6aefafb | 113 | |
3f684b4b | 114 | __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp) |
c6aefafb | 115 | { |
b71d1d42 | 116 | const struct ipv6hdr *iph = ipv6_hdr(skb); |
c6aefafb | 117 | const struct tcphdr *th = tcp_hdr(skb); |
81eb6a14 | 118 | |
81eb6a14 PM |
119 | return __cookie_v6_init_sequence(iph, th, mssp); |
120 | } | |
121 | ||
122 | int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, | |
123 | __u32 cookie) | |
124 | { | |
c6aefafb GG |
125 | __u32 seq = ntohl(th->seq) - 1; |
126 | __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, | |
8c27bd75 | 127 | th->source, th->dest, seq); |
c6aefafb | 128 | |
5918e2fb | 129 | return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; |
c6aefafb | 130 | } |
81eb6a14 | 131 | EXPORT_SYMBOL_GPL(__cookie_v6_check); |
c6aefafb GG |
132 | |
133 | struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) | |
134 | { | |
4957faad | 135 | struct tcp_options_received tcp_opt; |
c6aefafb | 136 | struct inet_request_sock *ireq; |
c6aefafb GG |
137 | struct tcp_request_sock *treq; |
138 | struct ipv6_pinfo *np = inet6_sk(sk); | |
139 | struct tcp_sock *tp = tcp_sk(sk); | |
140 | const struct tcphdr *th = tcp_hdr(skb); | |
141 | __u32 cookie = ntohl(th->ack_seq) - 1; | |
142 | struct sock *ret = sk; | |
143 | struct request_sock *req; | |
144 | int mss; | |
145 | struct dst_entry *dst; | |
146 | __u8 rcv_wscale; | |
84b114b9 | 147 | u32 tsoff = 0; |
c6aefafb | 148 | |
12ed8244 | 149 | if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst) |
c6aefafb GG |
150 | goto out; |
151 | ||
646697b9 FW |
152 | if (tcp_synq_no_recent_overflow(sk)) |
153 | goto out; | |
154 | ||
155 | mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie); | |
156 | if (mss == 0) { | |
02a1d6e7 | 157 | __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); |
c6aefafb GG |
158 | goto out; |
159 | } | |
160 | ||
02a1d6e7 | 161 | __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); |
c6aefafb | 162 | |
bb5b7c11 DM |
163 | /* check for timestamp cookie support */ |
164 | memset(&tcp_opt, 0, sizeof(tcp_opt)); | |
eed29f17 | 165 | tcp_parse_options(sock_net(sk), skb, &tcp_opt, 0, NULL); |
bb5b7c11 | 166 | |
84b114b9 | 167 | if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) { |
5d2ed052 ED |
168 | tsoff = secure_tcpv6_ts_off(sock_net(sk), |
169 | ipv6_hdr(skb)->daddr.s6_addr32, | |
84b114b9 ED |
170 | ipv6_hdr(skb)->saddr.s6_addr32); |
171 | tcp_opt.rcv_tsecr -= tsoff; | |
172 | } | |
173 | ||
f9301034 | 174 | if (!cookie_timestamp_decode(sock_net(sk), &tcp_opt)) |
8c763681 | 175 | goto out; |
bb5b7c11 | 176 | |
c6aefafb | 177 | ret = NULL; |
a1a5344d | 178 | req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false); |
c6aefafb GG |
179 | if (!req) |
180 | goto out; | |
181 | ||
182 | ireq = inet_rsk(req); | |
c6aefafb | 183 | treq = tcp_rsk(req); |
9439ce00 | 184 | treq->tfo_listener = false; |
c6aefafb | 185 | |
1730554f FW |
186 | if (security_inet_conn_request(sk, skb, req)) |
187 | goto out_free; | |
c6aefafb GG |
188 | |
189 | req->mss = mss; | |
634fb979 | 190 | ireq->ir_rmt_port = th->source; |
b44084c2 | 191 | ireq->ir_num = ntohs(th->dest); |
634fb979 ED |
192 | ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; |
193 | ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; | |
a224772d | 194 | if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) || |
c6aefafb GG |
195 | np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || |
196 | np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { | |
63354797 | 197 | refcount_inc(&skb->users); |
634fb979 | 198 | ireq->pktopts = skb; |
c6aefafb GG |
199 | } |
200 | ||
6dd9a14e | 201 | ireq->ir_iif = inet_request_bound_dev_if(sk, skb); |
c6aefafb GG |
202 | /* So that link locals have meaning */ |
203 | if (!sk->sk_bound_dev_if && | |
634fb979 | 204 | ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) |
870c3151 | 205 | ireq->ir_iif = tcp_v6_iif(skb); |
c6aefafb | 206 | |
84f39b08 LC |
207 | ireq->ir_mark = inet_request_mark(sk, skb); |
208 | ||
e6c022a4 | 209 | req->num_retrans = 0; |
bb5b7c11 | 210 | ireq->snd_wscale = tcp_opt.snd_wscale; |
bb5b7c11 DM |
211 | ireq->sack_ok = tcp_opt.sack_ok; |
212 | ireq->wscale_ok = tcp_opt.wscale_ok; | |
213 | ireq->tstamp_ok = tcp_opt.saw_tstamp; | |
214 | req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; | |
9a568de4 | 215 | treq->snt_synack = 0; |
c6aefafb GG |
216 | treq->rcv_isn = ntohl(th->seq) - 1; |
217 | treq->snt_isn = cookie; | |
95a22cae | 218 | treq->ts_off = 0; |
18bcf290 | 219 | treq->txhash = net_tx_rndhash(); |
bc58a1ba HW |
220 | if (IS_ENABLED(CONFIG_SMC)) |
221 | ireq->smc_ok = 0; | |
c6aefafb GG |
222 | |
223 | /* | |
224 | * We need to lookup the dst_entry to get the correct window size. | |
225 | * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten | |
226 | * me if there is a preferred way. | |
227 | */ | |
228 | { | |
20c59de2 | 229 | struct in6_addr *final_p, final; |
4c9483b2 DM |
230 | struct flowi6 fl6; |
231 | memset(&fl6, 0, sizeof(fl6)); | |
232 | fl6.flowi6_proto = IPPROTO_TCP; | |
634fb979 | 233 | fl6.daddr = ireq->ir_v6_rmt_addr; |
45f6fad8 | 234 | final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final); |
634fb979 | 235 | fl6.saddr = ireq->ir_v6_loc_addr; |
6dd9a14e | 236 | fl6.flowi6_oif = ireq->ir_iif; |
84f39b08 | 237 | fl6.flowi6_mark = ireq->ir_mark; |
634fb979 | 238 | fl6.fl6_dport = ireq->ir_rmt_port; |
1958b856 | 239 | fl6.fl6_sport = inet_sk(sk)->inet_sport; |
e2d118a1 | 240 | fl6.flowi6_uid = sk->sk_uid; |
4c9483b2 DM |
241 | security_req_classify_flow(req, flowi6_to_flowi(&fl6)); |
242 | ||
0e0d44ab | 243 | dst = ip6_dst_lookup_flow(sk, &fl6, final_p); |
68d0c6d3 | 244 | if (IS_ERR(dst)) |
1730554f | 245 | goto out_free; |
c6aefafb GG |
246 | } |
247 | ||
ed53d0ab | 248 | req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); |
ceef9ab6 | 249 | tcp_select_initial_window(sk, tcp_full_space(sk), req->mss, |
ed53d0ab | 250 | &req->rsk_rcv_wnd, &req->rsk_window_clamp, |
31d12926 | 251 | ireq->wscale_ok, &rcv_wscale, |
252 | dst_metric(dst, RTAX_INITRWND)); | |
c6aefafb GG |
253 | |
254 | ireq->rcv_wscale = rcv_wscale; | |
f7b3bec6 | 255 | ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst); |
c6aefafb | 256 | |
84b114b9 | 257 | ret = tcp_get_cookie_sock(sk, skb, req, dst, tsoff); |
1730554f FW |
258 | out: |
259 | return ret; | |
260 | out_free: | |
261 | reqsk_free(req); | |
262 | return NULL; | |
c6aefafb | 263 | } |