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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
24extern int sysctl_tcp_syncookies;
25extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
26
27#define COOKIEBITS 24 /* Upper bits store count */
28#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
29
30/* Table must be sorted. */
31static __u16 const msstab[] = {
32 64,
33 512,
34 536,
35 1280 - 60,
36 1480 - 60,
37 1500 - 60,
38 4460 - 60,
39 9000 - 60,
40};
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
50static 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
66static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
67 ipv6_cookie_scratch);
68
69static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
70 __be16 sport, __be16 dport, u32 count, int c)
71{
72 __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
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
89static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
90 const struct in6_addr *daddr,
91 __be16 sport, __be16 dport, __u32 sseq,
92 __u32 count, __u32 data)
93{
94 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
95 sseq + (count << COOKIEBITS) +
96 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
97 & COOKIEMASK));
98}
99
100static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
101 const struct in6_addr *daddr, __be16 sport,
102 __be16 dport, __u32 sseq, __u32 count,
103 __u32 maxdiff)
104{
105 __u32 diff;
106
107 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
108
109 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
110 if (diff >= maxdiff)
111 return (__u32)-1;
112
113 return (cookie -
114 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
115 & COOKIEMASK;
116}
117
118__u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp)
119{
120 const struct ipv6hdr *iph = ipv6_hdr(skb);
121 const struct tcphdr *th = tcp_hdr(skb);
122 int mssind;
123 const __u16 mss = *mssp;
124
125 tcp_synq_overflow(sk);
126
127 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
128 if (mss >= msstab[mssind])
129 break;
130
131 *mssp = msstab[mssind];
132
133 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
134
135 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
136 th->dest, ntohl(th->seq),
137 jiffies / (HZ * 60), mssind);
138}
139
140static inline int cookie_check(const struct sk_buff *skb, __u32 cookie)
141{
142 const struct ipv6hdr *iph = ipv6_hdr(skb);
143 const struct tcphdr *th = tcp_hdr(skb);
144 __u32 seq = ntohl(th->seq) - 1;
145 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
146 th->source, th->dest, seq,
147 jiffies / (HZ * 60), COUNTER_TRIES);
148
149 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
150}
151
152struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
153{
154 struct tcp_options_received tcp_opt;
155 const u8 *hash_location;
156 struct inet_request_sock *ireq;
157 struct inet6_request_sock *ireq6;
158 struct tcp_request_sock *treq;
159 struct ipv6_pinfo *np = inet6_sk(sk);
160 struct tcp_sock *tp = tcp_sk(sk);
161 const struct tcphdr *th = tcp_hdr(skb);
162 __u32 cookie = ntohl(th->ack_seq) - 1;
163 struct sock *ret = sk;
164 struct request_sock *req;
165 int mss;
166 struct dst_entry *dst;
167 __u8 rcv_wscale;
168 bool ecn_ok = false;
169
170 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
171 goto out;
172
173 if (tcp_synq_no_recent_overflow(sk) ||
174 (mss = cookie_check(skb, cookie)) == 0) {
175 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
176 goto out;
177 }
178
179 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
180
181 /* check for timestamp cookie support */
182 memset(&tcp_opt, 0, sizeof(tcp_opt));
183 tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
184
185 if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
186 goto out;
187
188 ret = NULL;
189 req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
190 if (!req)
191 goto out;
192
193 ireq = inet_rsk(req);
194 ireq6 = inet6_rsk(req);
195 treq = tcp_rsk(req);
196
197 if (security_inet_conn_request(sk, skb, req))
198 goto out_free;
199
200 req->mss = mss;
201 ireq->rmt_port = th->source;
202 ireq->loc_port = th->dest;
203 ireq6->rmt_addr = ipv6_hdr(skb)->saddr;
204 ireq6->loc_addr = ipv6_hdr(skb)->daddr;
205 if (ipv6_opt_accepted(sk, skb) ||
206 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
207 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
208 atomic_inc(&skb->users);
209 ireq6->pktopts = skb;
210 }
211
212 ireq6->iif = sk->sk_bound_dev_if;
213 /* So that link locals have meaning */
214 if (!sk->sk_bound_dev_if &&
215 ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
216 ireq6->iif = inet6_iif(skb);
217
218 req->expires = 0UL;
219 req->retrans = 0;
220 ireq->ecn_ok = ecn_ok;
221 ireq->snd_wscale = tcp_opt.snd_wscale;
222 ireq->sack_ok = tcp_opt.sack_ok;
223 ireq->wscale_ok = tcp_opt.wscale_ok;
224 ireq->tstamp_ok = tcp_opt.saw_tstamp;
225 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
226 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
227 treq->rcv_isn = ntohl(th->seq) - 1;
228 treq->snt_isn = cookie;
229
230 /*
231 * We need to lookup the dst_entry to get the correct window size.
232 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
233 * me if there is a preferred way.
234 */
235 {
236 struct in6_addr *final_p, final;
237 struct flowi6 fl6;
238 memset(&fl6, 0, sizeof(fl6));
239 fl6.flowi6_proto = IPPROTO_TCP;
240 fl6.daddr = ireq6->rmt_addr;
241 final_p = fl6_update_dst(&fl6, np->opt, &final);
242 fl6.saddr = ireq6->loc_addr;
243 fl6.flowi6_oif = sk->sk_bound_dev_if;
244 fl6.flowi6_mark = sk->sk_mark;
245 fl6.fl6_dport = inet_rsk(req)->rmt_port;
246 fl6.fl6_sport = inet_sk(sk)->inet_sport;
247 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
248
249 dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false);
250 if (IS_ERR(dst))
251 goto out_free;
252 }
253
254 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
255 tcp_select_initial_window(tcp_full_space(sk), req->mss,
256 &req->rcv_wnd, &req->window_clamp,
257 ireq->wscale_ok, &rcv_wscale,
258 dst_metric(dst, RTAX_INITRWND));
259
260 ireq->rcv_wscale = rcv_wscale;
261
262 ret = get_cookie_sock(sk, skb, req, dst);
263out:
264 return ret;
265out_free:
266 reqsk_free(req);
267 return NULL;
268}
269
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}