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CommitLineData
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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
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24#define COOKIEBITS 24 /* Upper bits store count */
25#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
26
253ff516 27static u32 syncookie6_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly;
b23a002f 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 37static __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
25528213 44static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], ipv6_cookie_scratch);
c6aefafb 45
b71d1d42 46static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
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47 __be16 sport, __be16 dport, u32 count, int c)
48{
b23a002f
HFS
49 __u32 *tmp;
50
51 net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret));
52
903ceff7 53 tmp = this_cpu_ptr(ipv6_cookie_scratch);
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54
55 /*
56 * we have 320 bits of information to hash, copy in the remaining
b23a002f 57 * 192 bits required for sha_transform, from the syncookie6_secret
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58 * and overwrite the digest with the secret
59 */
b23a002f 60 memcpy(tmp + 10, syncookie6_secret[c], 44);
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61 memcpy(tmp, saddr, 16);
62 memcpy(tmp + 4, daddr, 16);
63 tmp[8] = ((__force u32)sport << 16) + (__force u32)dport;
64 tmp[9] = count;
65 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
66
67 return tmp[17];
68}
69
b71d1d42
ED
70static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
71 const struct in6_addr *daddr,
c6aefafb 72 __be16 sport, __be16 dport, __u32 sseq,
8c27bd75 73 __u32 data)
c6aefafb 74{
8c27bd75 75 u32 count = tcp_cookie_time();
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76 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
77 sseq + (count << COOKIEBITS) +
78 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
79 & COOKIEMASK));
80}
81
b71d1d42
ED
82static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
83 const struct in6_addr *daddr, __be16 sport,
8c27bd75 84 __be16 dport, __u32 sseq)
c6aefafb 85{
8c27bd75 86 __u32 diff, count = tcp_cookie_time();
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87
88 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
89
90 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
8c27bd75 91 if (diff >= MAX_SYNCOOKIE_AGE)
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92 return (__u32)-1;
93
94 return (cookie -
95 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
96 & COOKIEMASK;
97}
98
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99u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
100 const struct tcphdr *th, __u16 *mssp)
c6aefafb 101{
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102 int mssind;
103 const __u16 mss = *mssp;
104
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105 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
106 if (mss >= msstab[mssind])
107 break;
108
109 *mssp = msstab[mssind];
c6aefafb 110
c6aefafb 111 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
8c27bd75 112 th->dest, ntohl(th->seq), mssind);
c6aefafb 113}
81eb6a14 114EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
c6aefafb 115
3f684b4b 116__u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp)
c6aefafb 117{
b71d1d42 118 const struct ipv6hdr *iph = ipv6_hdr(skb);
c6aefafb 119 const struct tcphdr *th = tcp_hdr(skb);
81eb6a14 120
81eb6a14
PM
121 return __cookie_v6_init_sequence(iph, th, mssp);
122}
123
124int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
125 __u32 cookie)
126{
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127 __u32 seq = ntohl(th->seq) - 1;
128 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
8c27bd75 129 th->source, th->dest, seq);
c6aefafb 130
5918e2fb 131 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
c6aefafb 132}
81eb6a14 133EXPORT_SYMBOL_GPL(__cookie_v6_check);
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134
135struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
136{
4957faad 137 struct tcp_options_received tcp_opt;
c6aefafb 138 struct inet_request_sock *ireq;
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139 struct tcp_request_sock *treq;
140 struct ipv6_pinfo *np = inet6_sk(sk);
141 struct tcp_sock *tp = tcp_sk(sk);
142 const struct tcphdr *th = tcp_hdr(skb);
143 __u32 cookie = ntohl(th->ack_seq) - 1;
144 struct sock *ret = sk;
145 struct request_sock *req;
146 int mss;
147 struct dst_entry *dst;
148 __u8 rcv_wscale;
149
12ed8244 150 if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
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151 goto out;
152
646697b9
FW
153 if (tcp_synq_no_recent_overflow(sk))
154 goto out;
155
156 mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie);
157 if (mss == 0) {
02a1d6e7 158 __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
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159 goto out;
160 }
161
02a1d6e7 162 __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
c6aefafb 163
bb5b7c11
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164 /* check for timestamp cookie support */
165 memset(&tcp_opt, 0, sizeof(tcp_opt));
1a2c6181 166 tcp_parse_options(skb, &tcp_opt, 0, NULL);
bb5b7c11 167
f1673381 168 if (!cookie_timestamp_decode(&tcp_opt))
8c763681 169 goto out;
bb5b7c11 170
c6aefafb 171 ret = NULL;
a1a5344d 172 req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false);
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173 if (!req)
174 goto out;
175
176 ireq = inet_rsk(req);
c6aefafb 177 treq = tcp_rsk(req);
9439ce00 178 treq->tfo_listener = false;
c6aefafb 179
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FW
180 if (security_inet_conn_request(sk, skb, req))
181 goto out_free;
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182
183 req->mss = mss;
634fb979 184 ireq->ir_rmt_port = th->source;
b44084c2 185 ireq->ir_num = ntohs(th->dest);
634fb979
ED
186 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
187 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
a224772d 188 if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
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189 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
190 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
191 atomic_inc(&skb->users);
634fb979 192 ireq->pktopts = skb;
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193 }
194
6dd9a14e 195 ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
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196 /* So that link locals have meaning */
197 if (!sk->sk_bound_dev_if &&
634fb979 198 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
870c3151 199 ireq->ir_iif = tcp_v6_iif(skb);
c6aefafb 200
84f39b08
LC
201 ireq->ir_mark = inet_request_mark(sk, skb);
202
e6c022a4 203 req->num_retrans = 0;
bb5b7c11 204 ireq->snd_wscale = tcp_opt.snd_wscale;
bb5b7c11
DM
205 ireq->sack_ok = tcp_opt.sack_ok;
206 ireq->wscale_ok = tcp_opt.wscale_ok;
207 ireq->tstamp_ok = tcp_opt.saw_tstamp;
208 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
0f1c28ae 209 treq->snt_synack.v64 = 0;
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210 treq->rcv_isn = ntohl(th->seq) - 1;
211 treq->snt_isn = cookie;
212
213 /*
214 * We need to lookup the dst_entry to get the correct window size.
215 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
216 * me if there is a preferred way.
217 */
218 {
20c59de2 219 struct in6_addr *final_p, final;
4c9483b2
DM
220 struct flowi6 fl6;
221 memset(&fl6, 0, sizeof(fl6));
222 fl6.flowi6_proto = IPPROTO_TCP;
634fb979 223 fl6.daddr = ireq->ir_v6_rmt_addr;
45f6fad8 224 final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final);
634fb979 225 fl6.saddr = ireq->ir_v6_loc_addr;
6dd9a14e 226 fl6.flowi6_oif = ireq->ir_iif;
84f39b08 227 fl6.flowi6_mark = ireq->ir_mark;
634fb979 228 fl6.fl6_dport = ireq->ir_rmt_port;
1958b856 229 fl6.fl6_sport = inet_sk(sk)->inet_sport;
4c9483b2
DM
230 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
231
0e0d44ab 232 dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
68d0c6d3 233 if (IS_ERR(dst))
1730554f 234 goto out_free;
c6aefafb
GG
235 }
236
ed53d0ab 237 req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
c6aefafb 238 tcp_select_initial_window(tcp_full_space(sk), req->mss,
ed53d0ab 239 &req->rsk_rcv_wnd, &req->rsk_window_clamp,
31d12926 240 ireq->wscale_ok, &rcv_wscale,
241 dst_metric(dst, RTAX_INITRWND));
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242
243 ireq->rcv_wscale = rcv_wscale;
f7b3bec6 244 ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst);
c6aefafb 245
b80c0e78 246 ret = tcp_get_cookie_sock(sk, skb, req, dst);
1730554f
FW
247out:
248 return ret;
249out_free:
250 reqsk_free(req);
251 return NULL;
c6aefafb 252}