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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
24#define COOKIEBITS 24 /* Upper bits store count */
25#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
26
27static u32 syncookie6_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly;
28
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 */
37static __u16 const msstab[] = {
38 1280 - 60, /* IPV6_MIN_MTU - 60 */
39 1480 - 60,
40 1500 - 60,
41 9000 - 60,
42};
43
44static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], ipv6_cookie_scratch);
45
46static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
47 __be16 sport, __be16 dport, u32 count, int c)
48{
49 __u32 *tmp;
50
51 net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret));
52
53 tmp = this_cpu_ptr(ipv6_cookie_scratch);
54
55 /*
56 * we have 320 bits of information to hash, copy in the remaining
57 * 192 bits required for sha_transform, from the syncookie6_secret
58 * and overwrite the digest with the secret
59 */
60 memcpy(tmp + 10, syncookie6_secret[c], 44);
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
70static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
71 const struct in6_addr *daddr,
72 __be16 sport, __be16 dport, __u32 sseq,
73 __u32 data)
74{
75 u32 count = tcp_cookie_time();
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
82static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
83 const struct in6_addr *daddr, __be16 sport,
84 __be16 dport, __u32 sseq)
85{
86 __u32 diff, count = tcp_cookie_time();
87
88 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
89
90 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
91 if (diff >= MAX_SYNCOOKIE_AGE)
92 return (__u32)-1;
93
94 return (cookie -
95 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
96 & COOKIEMASK;
97}
98
99u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
100 const struct tcphdr *th, __u16 *mssp)
101{
102 int mssind;
103 const __u16 mss = *mssp;
104
105 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
106 if (mss >= msstab[mssind])
107 break;
108
109 *mssp = msstab[mssind];
110
111 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
112 th->dest, ntohl(th->seq), mssind);
113}
114EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
115
116__u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp)
117{
118 const struct ipv6hdr *iph = ipv6_hdr(skb);
119 const struct tcphdr *th = tcp_hdr(skb);
120
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{
127 __u32 seq = ntohl(th->seq) - 1;
128 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
129 th->source, th->dest, seq);
130
131 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
132}
133EXPORT_SYMBOL_GPL(__cookie_v6_check);
134
135struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
136{
137 struct tcp_options_received tcp_opt;
138 struct inet_request_sock *ireq;
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
150 if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
151 goto out;
152
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) {
158 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
159 goto out;
160 }
161
162 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
163
164 /* check for timestamp cookie support */
165 memset(&tcp_opt, 0, sizeof(tcp_opt));
166 tcp_parse_options(skb, &tcp_opt, 0, NULL);
167
168 if (!cookie_timestamp_decode(&tcp_opt))
169 goto out;
170
171 ret = NULL;
172 req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false);
173 if (!req)
174 goto out;
175
176 ireq = inet_rsk(req);
177 treq = tcp_rsk(req);
178 treq->tfo_listener = false;
179
180 if (security_inet_conn_request(sk, skb, req))
181 goto out_free;
182
183 req->mss = mss;
184 ireq->ir_rmt_port = th->source;
185 ireq->ir_num = ntohs(th->dest);
186 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
187 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
188 if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
189 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
190 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
191 atomic_inc(&skb->users);
192 ireq->pktopts = skb;
193 }
194
195 ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
196 /* So that link locals have meaning */
197 if (!sk->sk_bound_dev_if &&
198 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
199 ireq->ir_iif = tcp_v6_iif(skb);
200
201 ireq->ir_mark = inet_request_mark(sk, skb);
202
203 req->num_retrans = 0;
204 ireq->snd_wscale = tcp_opt.snd_wscale;
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;
209 treq->snt_synack.v64 = 0;
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 {
219 struct in6_addr *final_p, final;
220 struct flowi6 fl6;
221 memset(&fl6, 0, sizeof(fl6));
222 fl6.flowi6_proto = IPPROTO_TCP;
223 fl6.daddr = ireq->ir_v6_rmt_addr;
224 final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final);
225 fl6.saddr = ireq->ir_v6_loc_addr;
226 fl6.flowi6_oif = ireq->ir_iif;
227 fl6.flowi6_mark = ireq->ir_mark;
228 fl6.fl6_dport = ireq->ir_rmt_port;
229 fl6.fl6_sport = inet_sk(sk)->inet_sport;
230 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
231
232 dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
233 if (IS_ERR(dst))
234 goto out_free;
235 }
236
237 req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
238 tcp_select_initial_window(tcp_full_space(sk), req->mss,
239 &req->rsk_rcv_wnd, &req->rsk_window_clamp,
240 ireq->wscale_ok, &rcv_wscale,
241 dst_metric(dst, RTAX_INITRWND));
242
243 ireq->rcv_wscale = rcv_wscale;
244 ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst);
245
246 ret = tcp_get_cookie_sock(sk, skb, req, dst);
247out:
248 return ret;
249out_free:
250 reqsk_free(req);
251 return NULL;
252}
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * IPv6 Syncookies implementation for the Linux kernel
4 *
5 * Authors:
6 * Glenn Griffin <ggriffin.kernel@gmail.com>
7 *
8 * Based on IPv4 implementation by Andi Kleen
9 * linux/net/ipv4/syncookies.c
10 */
11
12#include <linux/tcp.h>
13#include <linux/random.h>
14#include <linux/siphash.h>
15#include <linux/kernel.h>
16#include <net/secure_seq.h>
17#include <net/ipv6.h>
18#include <net/tcp.h>
19
20#define COOKIEBITS 24 /* Upper bits store count */
21#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
22
23static siphash_key_t syncookie6_secret[2] __read_mostly;
24
25/* RFC 2460, Section 8.3:
26 * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..]
27 *
28 * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows
29 * using higher values than ipv4 tcp syncookies.
30 * The other values are chosen based on ethernet (1500 and 9k MTU), plus
31 * one that accounts for common encap (PPPoe) overhead. Table must be sorted.
32 */
33static __u16 const msstab[] = {
34 1280 - 60, /* IPV6_MIN_MTU - 60 */
35 1480 - 60,
36 1500 - 60,
37 9000 - 60,
38};
39
40static u32 cookie_hash(const struct in6_addr *saddr,
41 const struct in6_addr *daddr,
42 __be16 sport, __be16 dport, u32 count, int c)
43{
44 const struct {
45 struct in6_addr saddr;
46 struct in6_addr daddr;
47 u32 count;
48 __be16 sport;
49 __be16 dport;
50 } __aligned(SIPHASH_ALIGNMENT) combined = {
51 .saddr = *saddr,
52 .daddr = *daddr,
53 .count = count,
54 .sport = sport,
55 .dport = dport
56 };
57
58 net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret));
59 return siphash(&combined, offsetofend(typeof(combined), dport),
60 &syncookie6_secret[c]);
61}
62
63static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
64 const struct in6_addr *daddr,
65 __be16 sport, __be16 dport, __u32 sseq,
66 __u32 data)
67{
68 u32 count = tcp_cookie_time();
69 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
70 sseq + (count << COOKIEBITS) +
71 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
72 & COOKIEMASK));
73}
74
75static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
76 const struct in6_addr *daddr, __be16 sport,
77 __be16 dport, __u32 sseq)
78{
79 __u32 diff, count = tcp_cookie_time();
80
81 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
82
83 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
84 if (diff >= MAX_SYNCOOKIE_AGE)
85 return (__u32)-1;
86
87 return (cookie -
88 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
89 & COOKIEMASK;
90}
91
92u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
93 const struct tcphdr *th, __u16 *mssp)
94{
95 int mssind;
96 const __u16 mss = *mssp;
97
98 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
99 if (mss >= msstab[mssind])
100 break;
101
102 *mssp = msstab[mssind];
103
104 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
105 th->dest, ntohl(th->seq), mssind);
106}
107EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
108
109__u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp)
110{
111 const struct ipv6hdr *iph = ipv6_hdr(skb);
112 const struct tcphdr *th = tcp_hdr(skb);
113
114 return __cookie_v6_init_sequence(iph, th, mssp);
115}
116
117int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
118 __u32 cookie)
119{
120 __u32 seq = ntohl(th->seq) - 1;
121 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
122 th->source, th->dest, seq);
123
124 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
125}
126EXPORT_SYMBOL_GPL(__cookie_v6_check);
127
128struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
129{
130 struct tcp_options_received tcp_opt;
131 struct inet_request_sock *ireq;
132 struct tcp_request_sock *treq;
133 struct ipv6_pinfo *np = inet6_sk(sk);
134 struct tcp_sock *tp = tcp_sk(sk);
135 const struct tcphdr *th = tcp_hdr(skb);
136 __u32 cookie = ntohl(th->ack_seq) - 1;
137 struct sock *ret = sk;
138 struct request_sock *req;
139 int mss;
140 struct dst_entry *dst;
141 __u8 rcv_wscale;
142 u32 tsoff = 0;
143
144 if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
145 goto out;
146
147 if (tcp_synq_no_recent_overflow(sk))
148 goto out;
149
150 mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie);
151 if (mss == 0) {
152 __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
153 goto out;
154 }
155
156 __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
157
158 /* check for timestamp cookie support */
159 memset(&tcp_opt, 0, sizeof(tcp_opt));
160 tcp_parse_options(sock_net(sk), skb, &tcp_opt, 0, NULL);
161
162 if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) {
163 tsoff = secure_tcpv6_ts_off(sock_net(sk),
164 ipv6_hdr(skb)->daddr.s6_addr32,
165 ipv6_hdr(skb)->saddr.s6_addr32);
166 tcp_opt.rcv_tsecr -= tsoff;
167 }
168
169 if (!cookie_timestamp_decode(sock_net(sk), &tcp_opt))
170 goto out;
171
172 ret = NULL;
173 req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false);
174 if (!req)
175 goto out;
176
177 ireq = inet_rsk(req);
178 treq = tcp_rsk(req);
179 treq->tfo_listener = false;
180
181 if (security_inet_conn_request(sk, skb, req))
182 goto out_free;
183
184 req->mss = mss;
185 ireq->ir_rmt_port = th->source;
186 ireq->ir_num = ntohs(th->dest);
187 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
188 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
189 if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
190 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
191 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
192 refcount_inc(&skb->users);
193 ireq->pktopts = skb;
194 }
195
196 ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
197 /* So that link locals have meaning */
198 if (!sk->sk_bound_dev_if &&
199 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
200 ireq->ir_iif = tcp_v6_iif(skb);
201
202 ireq->ir_mark = inet_request_mark(sk, skb);
203
204 req->num_retrans = 0;
205 ireq->snd_wscale = tcp_opt.snd_wscale;
206 ireq->sack_ok = tcp_opt.sack_ok;
207 ireq->wscale_ok = tcp_opt.wscale_ok;
208 ireq->tstamp_ok = tcp_opt.saw_tstamp;
209 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
210 treq->snt_synack = 0;
211 treq->rcv_isn = ntohl(th->seq) - 1;
212 treq->snt_isn = cookie;
213 treq->ts_off = 0;
214 treq->txhash = net_tx_rndhash();
215 if (IS_ENABLED(CONFIG_SMC))
216 ireq->smc_ok = 0;
217
218 /*
219 * We need to lookup the dst_entry to get the correct window size.
220 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
221 * me if there is a preferred way.
222 */
223 {
224 struct in6_addr *final_p, final;
225 struct flowi6 fl6;
226 memset(&fl6, 0, sizeof(fl6));
227 fl6.flowi6_proto = IPPROTO_TCP;
228 fl6.daddr = ireq->ir_v6_rmt_addr;
229 final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final);
230 fl6.saddr = ireq->ir_v6_loc_addr;
231 fl6.flowi6_oif = ireq->ir_iif;
232 fl6.flowi6_mark = ireq->ir_mark;
233 fl6.fl6_dport = ireq->ir_rmt_port;
234 fl6.fl6_sport = inet_sk(sk)->inet_sport;
235 fl6.flowi6_uid = sk->sk_uid;
236 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
237
238 dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
239 if (IS_ERR(dst))
240 goto out_free;
241 }
242
243 req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
244 tcp_select_initial_window(sk, tcp_full_space(sk), req->mss,
245 &req->rsk_rcv_wnd, &req->rsk_window_clamp,
246 ireq->wscale_ok, &rcv_wscale,
247 dst_metric(dst, RTAX_INITRWND));
248
249 ireq->rcv_wscale = rcv_wscale;
250 ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst);
251
252 ret = tcp_get_cookie_sock(sk, skb, req, dst, tsoff);
253out:
254 return ret;
255out_free:
256 reqsk_free(req);
257 return NULL;
258}