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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];
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 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
60static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
61 ipv6_cookie_scratch);
62
63static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
64 __be16 sport, __be16 dport, u32 count, int c)
65{
66 __u32 *tmp;
67
68 net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret));
69
70 tmp = __get_cpu_var(ipv6_cookie_scratch);
71
72 /*
73 * we have 320 bits of information to hash, copy in the remaining
74 * 192 bits required for sha_transform, from the syncookie6_secret
75 * and overwrite the digest with the secret
76 */
77 memcpy(tmp + 10, syncookie6_secret[c], 44);
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
87static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
88 const struct in6_addr *daddr,
89 __be16 sport, __be16 dport, __u32 sseq,
90 __u32 data)
91{
92 u32 count = tcp_cookie_time();
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
99static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
100 const struct in6_addr *daddr, __be16 sport,
101 __be16 dport, __u32 sseq)
102{
103 __u32 diff, count = tcp_cookie_time();
104
105 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
106
107 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
108 if (diff >= MAX_SYNCOOKIE_AGE)
109 return (__u32)-1;
110
111 return (cookie -
112 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
113 & COOKIEMASK;
114}
115
116u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
117 const struct tcphdr *th, __u16 *mssp)
118{
119 int mssind;
120 const __u16 mss = *mssp;
121
122 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
123 if (mss >= msstab[mssind])
124 break;
125
126 *mssp = msstab[mssind];
127
128 return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
129 th->dest, ntohl(th->seq), mssind);
130}
131EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
132
133__u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp)
134{
135 const struct ipv6hdr *iph = ipv6_hdr(skb);
136 const struct tcphdr *th = tcp_hdr(skb);
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
144int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
145 __u32 cookie)
146{
147 __u32 seq = ntohl(th->seq) - 1;
148 __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
149 th->source, th->dest, seq);
150
151 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
152}
153EXPORT_SYMBOL_GPL(__cookie_v6_check);
154
155struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
156{
157 struct tcp_options_received tcp_opt;
158 struct inet_request_sock *ireq;
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;
169 bool ecn_ok = false;
170
171 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
172 goto out;
173
174 if (tcp_synq_no_recent_overflow(sk) ||
175 (mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie)) == 0) {
176 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
177 goto out;
178 }
179
180 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
181
182 /* check for timestamp cookie support */
183 memset(&tcp_opt, 0, sizeof(tcp_opt));
184 tcp_parse_options(skb, &tcp_opt, 0, NULL);
185
186 if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok))
187 goto out;
188
189 ret = NULL;
190 req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
191 if (!req)
192 goto out;
193
194 ireq = inet_rsk(req);
195 treq = tcp_rsk(req);
196 treq->listener = NULL;
197
198 if (security_inet_conn_request(sk, skb, req))
199 goto out_free;
200
201 req->mss = mss;
202 ireq->ir_rmt_port = th->source;
203 ireq->ir_num = ntohs(th->dest);
204 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
205 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
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);
210 ireq->pktopts = skb;
211 }
212
213 ireq->ir_iif = sk->sk_bound_dev_if;
214 /* So that link locals have meaning */
215 if (!sk->sk_bound_dev_if &&
216 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
217 ireq->ir_iif = inet6_iif(skb);
218
219 req->expires = 0UL;
220 req->num_retrans = 0;
221 ireq->ecn_ok = ecn_ok;
222 ireq->snd_wscale = tcp_opt.snd_wscale;
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;
227 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
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 {
237 struct in6_addr *final_p, final;
238 struct flowi6 fl6;
239 memset(&fl6, 0, sizeof(fl6));
240 fl6.flowi6_proto = IPPROTO_TCP;
241 fl6.daddr = ireq->ir_v6_rmt_addr;
242 final_p = fl6_update_dst(&fl6, np->opt, &final);
243 fl6.saddr = ireq->ir_v6_loc_addr;
244 fl6.flowi6_oif = sk->sk_bound_dev_if;
245 fl6.flowi6_mark = sk->sk_mark;
246 fl6.fl6_dport = ireq->ir_rmt_port;
247 fl6.fl6_sport = inet_sk(sk)->inet_sport;
248 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
249
250 dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
251 if (IS_ERR(dst))
252 goto out_free;
253 }
254
255 req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
256 tcp_select_initial_window(tcp_full_space(sk), req->mss,
257 &req->rcv_wnd, &req->window_clamp,
258 ireq->wscale_ok, &rcv_wscale,
259 dst_metric(dst, RTAX_INITRWND));
260
261 ireq->rcv_wscale = rcv_wscale;
262
263 ret = get_cookie_sock(sk, skb, req, dst);
264out:
265 return ret;
266out_free:
267 reqsk_free(req);
268 return NULL;
269}
270
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_aligned_key_t syncookie6_secret[2];
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{
119 __u32 cookie = ntohl(th->ack_seq) - 1;
120 __u32 seq = ntohl(th->seq) - 1;
121 __u32 mssind;
122
123 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
124 th->source, th->dest, seq);
125
126 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
127}
128EXPORT_SYMBOL_GPL(__cookie_v6_check);
129
130static struct request_sock *cookie_tcp_check(struct net *net, struct sock *sk,
131 struct sk_buff *skb)
132{
133 struct tcp_options_received tcp_opt;
134 u32 tsoff = 0;
135 int mss;
136
137 if (tcp_synq_no_recent_overflow(sk))
138 goto out;
139
140 mss = __cookie_v6_check(ipv6_hdr(skb), tcp_hdr(skb));
141 if (!mss) {
142 __NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESFAILED);
143 goto out;
144 }
145
146 __NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESRECV);
147
148 /* check for timestamp cookie support */
149 memset(&tcp_opt, 0, sizeof(tcp_opt));
150 tcp_parse_options(net, skb, &tcp_opt, 0, NULL);
151
152 if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) {
153 tsoff = secure_tcpv6_ts_off(net,
154 ipv6_hdr(skb)->daddr.s6_addr32,
155 ipv6_hdr(skb)->saddr.s6_addr32);
156 tcp_opt.rcv_tsecr -= tsoff;
157 }
158
159 if (!cookie_timestamp_decode(net, &tcp_opt))
160 goto out;
161
162 return cookie_tcp_reqsk_alloc(&tcp6_request_sock_ops, sk, skb,
163 &tcp_opt, mss, tsoff);
164out:
165 return ERR_PTR(-EINVAL);
166}
167
168struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
169{
170 const struct tcphdr *th = tcp_hdr(skb);
171 struct ipv6_pinfo *np = inet6_sk(sk);
172 struct tcp_sock *tp = tcp_sk(sk);
173 struct inet_request_sock *ireq;
174 struct net *net = sock_net(sk);
175 struct request_sock *req;
176 struct dst_entry *dst;
177 struct sock *ret = sk;
178 __u8 rcv_wscale;
179 int full_space;
180 SKB_DR(reason);
181
182 if (!READ_ONCE(net->ipv4.sysctl_tcp_syncookies) ||
183 !th->ack || th->rst)
184 goto out;
185
186 if (cookie_bpf_ok(skb)) {
187 req = cookie_bpf_check(sk, skb);
188 } else {
189 req = cookie_tcp_check(net, sk, skb);
190 if (IS_ERR(req))
191 goto out;
192 }
193 if (!req) {
194 SKB_DR_SET(reason, NO_SOCKET);
195 goto out_drop;
196 }
197
198 ireq = inet_rsk(req);
199
200 ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
201 ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
202
203 if (security_inet_conn_request(sk, skb, req)) {
204 SKB_DR_SET(reason, SECURITY_HOOK);
205 goto out_free;
206 }
207
208 if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
209 np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
210 np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
211 refcount_inc(&skb->users);
212 ireq->pktopts = skb;
213 }
214
215 /* So that link locals have meaning */
216 if (!sk->sk_bound_dev_if &&
217 ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
218 ireq->ir_iif = tcp_v6_iif(skb);
219
220 tcp_ao_syncookie(sk, skb, req, AF_INET6);
221
222 /*
223 * We need to lookup the dst_entry to get the correct window size.
224 * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
225 * me if there is a preferred way.
226 */
227 {
228 struct in6_addr *final_p, final;
229 struct flowi6 fl6;
230 memset(&fl6, 0, sizeof(fl6));
231 fl6.flowi6_proto = IPPROTO_TCP;
232 fl6.daddr = ireq->ir_v6_rmt_addr;
233 final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final);
234 fl6.saddr = ireq->ir_v6_loc_addr;
235 fl6.flowi6_oif = ireq->ir_iif;
236 fl6.flowi6_mark = ireq->ir_mark;
237 fl6.fl6_dport = ireq->ir_rmt_port;
238 fl6.fl6_sport = inet_sk(sk)->inet_sport;
239 fl6.flowi6_uid = sk->sk_uid;
240 security_req_classify_flow(req, flowi6_to_flowi_common(&fl6));
241
242 dst = ip6_dst_lookup_flow(net, sk, &fl6, final_p);
243 if (IS_ERR(dst)) {
244 SKB_DR_SET(reason, IP_OUTNOROUTES);
245 goto out_free;
246 }
247 }
248
249 req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? :dst_metric(dst, RTAX_WINDOW);
250 /* limit the window selection if the user enforce a smaller rx buffer */
251 full_space = tcp_full_space(sk);
252 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
253 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
254 req->rsk_window_clamp = full_space;
255
256 tcp_select_initial_window(sk, full_space, req->mss,
257 &req->rsk_rcv_wnd, &req->rsk_window_clamp,
258 ireq->wscale_ok, &rcv_wscale,
259 dst_metric(dst, RTAX_INITRWND));
260
261 /* req->syncookie is set true only if ACK is validated
262 * by BPF kfunc, then, rcv_wscale is already configured.
263 */
264 if (!req->syncookie)
265 ireq->rcv_wscale = rcv_wscale;
266 ireq->ecn_ok &= cookie_ecn_ok(net, dst);
267
268 ret = tcp_get_cookie_sock(sk, skb, req, dst);
269 if (!ret) {
270 SKB_DR_SET(reason, NO_SOCKET);
271 goto out_drop;
272 }
273out:
274 return ret;
275out_free:
276 reqsk_free(req);
277out_drop:
278 sk_skb_reason_drop(sk, skb, reason);
279 return NULL;
280}