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1/*
2 * Syncookies implementation for the Linux kernel
3 *
4 * Copyright (C) 1997 Andi Kleen
5 * Based on ideas by D.J.Bernstein and Eric Schenk.
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; either version
10 * 2 of the License, or (at your option) any later version.
11 */
12
13#include <linux/tcp.h>
14#include <linux/slab.h>
15#include <linux/random.h>
16#include <linux/cryptohash.h>
17#include <linux/kernel.h>
18#include <linux/export.h>
19#include <net/tcp.h>
20#include <net/route.h>
21
22/* Timestamps: lowest bits store TCP options */
23#define TSBITS 6
24#define TSMASK (((__u32)1 << TSBITS) - 1)
25
26extern int sysctl_tcp_syncookies;
27
28static u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
29
30#define COOKIEBITS 24 /* Upper bits store count */
31#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
32
33static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
34 ipv4_cookie_scratch);
35
36static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
37 u32 count, int c)
38{
39 __u32 *tmp;
40
41 net_get_random_once(syncookie_secret, sizeof(syncookie_secret));
42
43 tmp = __get_cpu_var(ipv4_cookie_scratch);
44 memcpy(tmp + 4, syncookie_secret[c], sizeof(syncookie_secret[c]));
45 tmp[0] = (__force u32)saddr;
46 tmp[1] = (__force u32)daddr;
47 tmp[2] = ((__force u32)sport << 16) + (__force u32)dport;
48 tmp[3] = count;
49 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
50
51 return tmp[17];
52}
53
54
55/*
56 * when syncookies are in effect and tcp timestamps are enabled we encode
57 * tcp options in the lower bits of the timestamp value that will be
58 * sent in the syn-ack.
59 * Since subsequent timestamps use the normal tcp_time_stamp value, we
60 * must make sure that the resulting initial timestamp is <= tcp_time_stamp.
61 */
62__u32 cookie_init_timestamp(struct request_sock *req)
63{
64 struct inet_request_sock *ireq;
65 u32 ts, ts_now = tcp_time_stamp;
66 u32 options = 0;
67
68 ireq = inet_rsk(req);
69
70 options = ireq->wscale_ok ? ireq->snd_wscale : 0xf;
71 options |= ireq->sack_ok << 4;
72 options |= ireq->ecn_ok << 5;
73
74 ts = ts_now & ~TSMASK;
75 ts |= options;
76 if (ts > ts_now) {
77 ts >>= TSBITS;
78 ts--;
79 ts <<= TSBITS;
80 ts |= options;
81 }
82 return ts;
83}
84
85
86static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
87 __be16 dport, __u32 sseq, __u32 data)
88{
89 /*
90 * Compute the secure sequence number.
91 * The output should be:
92 * HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24)
93 * + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24).
94 * Where sseq is their sequence number and count increases every
95 * minute by 1.
96 * As an extra hack, we add a small "data" value that encodes the
97 * MSS into the second hash value.
98 */
99 u32 count = tcp_cookie_time();
100 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
101 sseq + (count << COOKIEBITS) +
102 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
103 & COOKIEMASK));
104}
105
106/*
107 * This retrieves the small "data" value from the syncookie.
108 * If the syncookie is bad, the data returned will be out of
109 * range. This must be checked by the caller.
110 *
111 * The count value used to generate the cookie must be less than
112 * MAX_SYNCOOKIE_AGE minutes in the past.
113 * The return value (__u32)-1 if this test fails.
114 */
115static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
116 __be16 sport, __be16 dport, __u32 sseq)
117{
118 u32 diff, count = tcp_cookie_time();
119
120 /* Strip away the layers from the cookie */
121 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
122
123 /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */
124 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
125 if (diff >= MAX_SYNCOOKIE_AGE)
126 return (__u32)-1;
127
128 return (cookie -
129 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
130 & COOKIEMASK; /* Leaving the data behind */
131}
132
133/*
134 * MSS Values are chosen based on the 2011 paper
135 * 'An Analysis of TCP Maximum Segement Sizes' by S. Alcock and R. Nelson.
136 * Values ..
137 * .. lower than 536 are rare (< 0.2%)
138 * .. between 537 and 1299 account for less than < 1.5% of observed values
139 * .. in the 1300-1349 range account for about 15 to 20% of observed mss values
140 * .. exceeding 1460 are very rare (< 0.04%)
141 *
142 * 1460 is the single most frequently announced mss value (30 to 46% depending
143 * on monitor location). Table must be sorted.
144 */
145static __u16 const msstab[] = {
146 536,
147 1300,
148 1440, /* 1440, 1452: PPPoE */
149 1460,
150};
151
152/*
153 * Generate a syncookie. mssp points to the mss, which is returned
154 * rounded down to the value encoded in the cookie.
155 */
156u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
157 u16 *mssp)
158{
159 int mssind;
160 const __u16 mss = *mssp;
161
162 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
163 if (mss >= msstab[mssind])
164 break;
165 *mssp = msstab[mssind];
166
167 return secure_tcp_syn_cookie(iph->saddr, iph->daddr,
168 th->source, th->dest, ntohl(th->seq),
169 mssind);
170}
171EXPORT_SYMBOL_GPL(__cookie_v4_init_sequence);
172
173__u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
174{
175 const struct iphdr *iph = ip_hdr(skb);
176 const struct tcphdr *th = tcp_hdr(skb);
177
178 tcp_synq_overflow(sk);
179 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
180
181 return __cookie_v4_init_sequence(iph, th, mssp);
182}
183
184/*
185 * Check if a ack sequence number is a valid syncookie.
186 * Return the decoded mss if it is, or 0 if not.
187 */
188int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
189 u32 cookie)
190{
191 __u32 seq = ntohl(th->seq) - 1;
192 __u32 mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr,
193 th->source, th->dest, seq);
194
195 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
196}
197EXPORT_SYMBOL_GPL(__cookie_v4_check);
198
199static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
200 struct request_sock *req,
201 struct dst_entry *dst)
202{
203 struct inet_connection_sock *icsk = inet_csk(sk);
204 struct sock *child;
205
206 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
207 if (child)
208 inet_csk_reqsk_queue_add(sk, req, child);
209 else
210 reqsk_free(req);
211
212 return child;
213}
214
215
216/*
217 * when syncookies are in effect and tcp timestamps are enabled we stored
218 * additional tcp options in the timestamp.
219 * This extracts these options from the timestamp echo.
220 *
221 * The lowest 4 bits store snd_wscale.
222 * next 2 bits indicate SACK and ECN support.
223 *
224 * return false if we decode an option that should not be.
225 */
226bool cookie_check_timestamp(struct tcp_options_received *tcp_opt,
227 struct net *net, bool *ecn_ok)
228{
229 /* echoed timestamp, lowest bits contain options */
230 u32 options = tcp_opt->rcv_tsecr & TSMASK;
231
232 if (!tcp_opt->saw_tstamp) {
233 tcp_clear_options(tcp_opt);
234 return true;
235 }
236
237 if (!sysctl_tcp_timestamps)
238 return false;
239
240 tcp_opt->sack_ok = (options & (1 << 4)) ? TCP_SACK_SEEN : 0;
241 *ecn_ok = (options >> 5) & 1;
242 if (*ecn_ok && !net->ipv4.sysctl_tcp_ecn)
243 return false;
244
245 if (tcp_opt->sack_ok && !sysctl_tcp_sack)
246 return false;
247
248 if ((options & 0xf) == 0xf)
249 return true; /* no window scaling */
250
251 tcp_opt->wscale_ok = 1;
252 tcp_opt->snd_wscale = options & 0xf;
253 return sysctl_tcp_window_scaling != 0;
254}
255EXPORT_SYMBOL(cookie_check_timestamp);
256
257struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
258 struct ip_options *opt)
259{
260 struct tcp_options_received tcp_opt;
261 struct inet_request_sock *ireq;
262 struct tcp_request_sock *treq;
263 struct tcp_sock *tp = tcp_sk(sk);
264 const struct tcphdr *th = tcp_hdr(skb);
265 __u32 cookie = ntohl(th->ack_seq) - 1;
266 struct sock *ret = sk;
267 struct request_sock *req;
268 int mss;
269 struct rtable *rt;
270 __u8 rcv_wscale;
271 bool ecn_ok = false;
272 struct flowi4 fl4;
273
274 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
275 goto out;
276
277 if (tcp_synq_no_recent_overflow(sk) ||
278 (mss = __cookie_v4_check(ip_hdr(skb), th, cookie)) == 0) {
279 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
280 goto out;
281 }
282
283 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
284
285 /* check for timestamp cookie support */
286 memset(&tcp_opt, 0, sizeof(tcp_opt));
287 tcp_parse_options(skb, &tcp_opt, 0, NULL);
288
289 if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok))
290 goto out;
291
292 ret = NULL;
293 req = inet_reqsk_alloc(&tcp_request_sock_ops); /* for safety */
294 if (!req)
295 goto out;
296
297 ireq = inet_rsk(req);
298 treq = tcp_rsk(req);
299 treq->rcv_isn = ntohl(th->seq) - 1;
300 treq->snt_isn = cookie;
301 req->mss = mss;
302 ireq->ir_num = ntohs(th->dest);
303 ireq->ir_rmt_port = th->source;
304 ireq->ir_loc_addr = ip_hdr(skb)->daddr;
305 ireq->ir_rmt_addr = ip_hdr(skb)->saddr;
306 ireq->ecn_ok = ecn_ok;
307 ireq->snd_wscale = tcp_opt.snd_wscale;
308 ireq->sack_ok = tcp_opt.sack_ok;
309 ireq->wscale_ok = tcp_opt.wscale_ok;
310 ireq->tstamp_ok = tcp_opt.saw_tstamp;
311 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
312 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
313 treq->listener = NULL;
314
315 /* We throwed the options of the initial SYN away, so we hope
316 * the ACK carries the same options again (see RFC1122 4.2.3.8)
317 */
318 if (opt && opt->optlen) {
319 int opt_size = sizeof(struct ip_options_rcu) + opt->optlen;
320
321 ireq->opt = kmalloc(opt_size, GFP_ATOMIC);
322 if (ireq->opt != NULL && ip_options_echo(&ireq->opt->opt, skb)) {
323 kfree(ireq->opt);
324 ireq->opt = NULL;
325 }
326 }
327
328 if (security_inet_conn_request(sk, skb, req)) {
329 reqsk_free(req);
330 goto out;
331 }
332
333 req->expires = 0UL;
334 req->num_retrans = 0;
335
336 /*
337 * We need to lookup the route here to get at the correct
338 * window size. We should better make sure that the window size
339 * hasn't changed since we received the original syn, but I see
340 * no easy way to do this.
341 */
342 flowi4_init_output(&fl4, sk->sk_bound_dev_if, sk->sk_mark,
343 RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE, IPPROTO_TCP,
344 inet_sk_flowi_flags(sk),
345 (opt && opt->srr) ? opt->faddr : ireq->ir_rmt_addr,
346 ireq->ir_loc_addr, th->source, th->dest);
347 security_req_classify_flow(req, flowi4_to_flowi(&fl4));
348 rt = ip_route_output_key(sock_net(sk), &fl4);
349 if (IS_ERR(rt)) {
350 reqsk_free(req);
351 goto out;
352 }
353
354 /* Try to redo what tcp_v4_send_synack did. */
355 req->window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
356
357 tcp_select_initial_window(tcp_full_space(sk), req->mss,
358 &req->rcv_wnd, &req->window_clamp,
359 ireq->wscale_ok, &rcv_wscale,
360 dst_metric(&rt->dst, RTAX_INITRWND));
361
362 ireq->rcv_wscale = rcv_wscale;
363
364 ret = get_cookie_sock(sk, skb, req, &rt->dst);
365 /* ip_queue_xmit() depends on our flow being setup
366 * Normal sockets get it right from inet_csk_route_child_sock()
367 */
368 if (ret)
369 inet_sk(ret)->cork.fl.u.ip4 = fl4;
370out: return ret;
371}
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Syncookies implementation for the Linux kernel
4 *
5 * Copyright (C) 1997 Andi Kleen
6 * Based on ideas by D.J.Bernstein and Eric Schenk.
7 */
8
9#include <linux/tcp.h>
10#include <linux/siphash.h>
11#include <linux/kernel.h>
12#include <linux/export.h>
13#include <net/secure_seq.h>
14#include <net/tcp.h>
15#include <net/route.h>
16
17static siphash_aligned_key_t syncookie_secret[2];
18
19#define COOKIEBITS 24 /* Upper bits store count */
20#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
21
22/* TCP Timestamp: 6 lowest bits of timestamp sent in the cookie SYN-ACK
23 * stores TCP options:
24 *
25 * MSB LSB
26 * | 31 ... 6 | 5 | 4 | 3 2 1 0 |
27 * | Timestamp | ECN | SACK | WScale |
28 *
29 * When we receive a valid cookie-ACK, we look at the echoed tsval (if
30 * any) to figure out which TCP options we should use for the rebuilt
31 * connection.
32 *
33 * A WScale setting of '0xf' (which is an invalid scaling value)
34 * means that original syn did not include the TCP window scaling option.
35 */
36#define TS_OPT_WSCALE_MASK 0xf
37#define TS_OPT_SACK BIT(4)
38#define TS_OPT_ECN BIT(5)
39/* There is no TS_OPT_TIMESTAMP:
40 * if ACK contains timestamp option, we already know it was
41 * requested/supported by the syn/synack exchange.
42 */
43#define TSBITS 6
44#define TSMASK (((__u32)1 << TSBITS) - 1)
45
46static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
47 u32 count, int c)
48{
49 net_get_random_once(syncookie_secret, sizeof(syncookie_secret));
50 return siphash_4u32((__force u32)saddr, (__force u32)daddr,
51 (__force u32)sport << 16 | (__force u32)dport,
52 count, &syncookie_secret[c]);
53}
54
55
56/*
57 * when syncookies are in effect and tcp timestamps are enabled we encode
58 * tcp options in the lower bits of the timestamp value that will be
59 * sent in the syn-ack.
60 * Since subsequent timestamps use the normal tcp_time_stamp value, we
61 * must make sure that the resulting initial timestamp is <= tcp_time_stamp.
62 */
63u64 cookie_init_timestamp(struct request_sock *req, u64 now)
64{
65 struct inet_request_sock *ireq;
66 u32 ts, ts_now = tcp_ns_to_ts(now);
67 u32 options = 0;
68
69 ireq = inet_rsk(req);
70
71 options = ireq->wscale_ok ? ireq->snd_wscale : TS_OPT_WSCALE_MASK;
72 if (ireq->sack_ok)
73 options |= TS_OPT_SACK;
74 if (ireq->ecn_ok)
75 options |= TS_OPT_ECN;
76
77 ts = ts_now & ~TSMASK;
78 ts |= options;
79 if (ts > ts_now) {
80 ts >>= TSBITS;
81 ts--;
82 ts <<= TSBITS;
83 ts |= options;
84 }
85 return (u64)ts * (NSEC_PER_SEC / TCP_TS_HZ);
86}
87
88
89static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
90 __be16 dport, __u32 sseq, __u32 data)
91{
92 /*
93 * Compute the secure sequence number.
94 * The output should be:
95 * HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24)
96 * + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24).
97 * Where sseq is their sequence number and count increases every
98 * minute by 1.
99 * As an extra hack, we add a small "data" value that encodes the
100 * MSS into the second hash value.
101 */
102 u32 count = tcp_cookie_time();
103 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
104 sseq + (count << COOKIEBITS) +
105 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
106 & COOKIEMASK));
107}
108
109/*
110 * This retrieves the small "data" value from the syncookie.
111 * If the syncookie is bad, the data returned will be out of
112 * range. This must be checked by the caller.
113 *
114 * The count value used to generate the cookie must be less than
115 * MAX_SYNCOOKIE_AGE minutes in the past.
116 * The return value (__u32)-1 if this test fails.
117 */
118static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
119 __be16 sport, __be16 dport, __u32 sseq)
120{
121 u32 diff, count = tcp_cookie_time();
122
123 /* Strip away the layers from the cookie */
124 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
125
126 /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */
127 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
128 if (diff >= MAX_SYNCOOKIE_AGE)
129 return (__u32)-1;
130
131 return (cookie -
132 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
133 & COOKIEMASK; /* Leaving the data behind */
134}
135
136/*
137 * MSS Values are chosen based on the 2011 paper
138 * 'An Analysis of TCP Maximum Segement Sizes' by S. Alcock and R. Nelson.
139 * Values ..
140 * .. lower than 536 are rare (< 0.2%)
141 * .. between 537 and 1299 account for less than < 1.5% of observed values
142 * .. in the 1300-1349 range account for about 15 to 20% of observed mss values
143 * .. exceeding 1460 are very rare (< 0.04%)
144 *
145 * 1460 is the single most frequently announced mss value (30 to 46% depending
146 * on monitor location). Table must be sorted.
147 */
148static __u16 const msstab[] = {
149 536,
150 1300,
151 1440, /* 1440, 1452: PPPoE */
152 1460,
153};
154
155/*
156 * Generate a syncookie. mssp points to the mss, which is returned
157 * rounded down to the value encoded in the cookie.
158 */
159u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
160 u16 *mssp)
161{
162 int mssind;
163 const __u16 mss = *mssp;
164
165 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
166 if (mss >= msstab[mssind])
167 break;
168 *mssp = msstab[mssind];
169
170 return secure_tcp_syn_cookie(iph->saddr, iph->daddr,
171 th->source, th->dest, ntohl(th->seq),
172 mssind);
173}
174EXPORT_SYMBOL_GPL(__cookie_v4_init_sequence);
175
176__u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mssp)
177{
178 const struct iphdr *iph = ip_hdr(skb);
179 const struct tcphdr *th = tcp_hdr(skb);
180
181 return __cookie_v4_init_sequence(iph, th, mssp);
182}
183
184/*
185 * Check if a ack sequence number is a valid syncookie.
186 * Return the decoded mss if it is, or 0 if not.
187 */
188int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
189 u32 cookie)
190{
191 __u32 seq = ntohl(th->seq) - 1;
192 __u32 mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr,
193 th->source, th->dest, seq);
194
195 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
196}
197EXPORT_SYMBOL_GPL(__cookie_v4_check);
198
199struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
200 struct request_sock *req,
201 struct dst_entry *dst, u32 tsoff)
202{
203 struct inet_connection_sock *icsk = inet_csk(sk);
204 struct sock *child;
205 bool own_req;
206
207 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst,
208 NULL, &own_req);
209 if (child) {
210 refcount_set(&req->rsk_refcnt, 1);
211 tcp_sk(child)->tsoffset = tsoff;
212 sock_rps_save_rxhash(child, skb);
213
214 if (rsk_drop_req(req)) {
215 reqsk_put(req);
216 return child;
217 }
218
219 if (inet_csk_reqsk_queue_add(sk, req, child))
220 return child;
221
222 bh_unlock_sock(child);
223 sock_put(child);
224 }
225 __reqsk_free(req);
226
227 return NULL;
228}
229EXPORT_SYMBOL(tcp_get_cookie_sock);
230
231/*
232 * when syncookies are in effect and tcp timestamps are enabled we stored
233 * additional tcp options in the timestamp.
234 * This extracts these options from the timestamp echo.
235 *
236 * return false if we decode a tcp option that is disabled
237 * on the host.
238 */
239bool cookie_timestamp_decode(const struct net *net,
240 struct tcp_options_received *tcp_opt)
241{
242 /* echoed timestamp, lowest bits contain options */
243 u32 options = tcp_opt->rcv_tsecr;
244
245 if (!tcp_opt->saw_tstamp) {
246 tcp_clear_options(tcp_opt);
247 return true;
248 }
249
250 if (!READ_ONCE(net->ipv4.sysctl_tcp_timestamps))
251 return false;
252
253 tcp_opt->sack_ok = (options & TS_OPT_SACK) ? TCP_SACK_SEEN : 0;
254
255 if (tcp_opt->sack_ok && !READ_ONCE(net->ipv4.sysctl_tcp_sack))
256 return false;
257
258 if ((options & TS_OPT_WSCALE_MASK) == TS_OPT_WSCALE_MASK)
259 return true; /* no window scaling */
260
261 tcp_opt->wscale_ok = 1;
262 tcp_opt->snd_wscale = options & TS_OPT_WSCALE_MASK;
263
264 return READ_ONCE(net->ipv4.sysctl_tcp_window_scaling) != 0;
265}
266EXPORT_SYMBOL(cookie_timestamp_decode);
267
268bool cookie_ecn_ok(const struct tcp_options_received *tcp_opt,
269 const struct net *net, const struct dst_entry *dst)
270{
271 bool ecn_ok = tcp_opt->rcv_tsecr & TS_OPT_ECN;
272
273 if (!ecn_ok)
274 return false;
275
276 if (READ_ONCE(net->ipv4.sysctl_tcp_ecn))
277 return true;
278
279 return dst_feature(dst, RTAX_FEATURE_ECN);
280}
281EXPORT_SYMBOL(cookie_ecn_ok);
282
283struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
284 const struct tcp_request_sock_ops *af_ops,
285 struct sock *sk,
286 struct sk_buff *skb)
287{
288 struct tcp_request_sock *treq;
289 struct request_sock *req;
290
291 if (sk_is_mptcp(sk))
292 req = mptcp_subflow_reqsk_alloc(ops, sk, false);
293 else
294 req = inet_reqsk_alloc(ops, sk, false);
295
296 if (!req)
297 return NULL;
298
299 treq = tcp_rsk(req);
300
301 /* treq->af_specific might be used to perform TCP_MD5 lookup */
302 treq->af_specific = af_ops;
303
304 treq->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
305#if IS_ENABLED(CONFIG_MPTCP)
306 treq->is_mptcp = sk_is_mptcp(sk);
307 if (treq->is_mptcp) {
308 int err = mptcp_subflow_init_cookie_req(req, sk, skb);
309
310 if (err) {
311 reqsk_free(req);
312 return NULL;
313 }
314 }
315#endif
316
317 return req;
318}
319EXPORT_SYMBOL_GPL(cookie_tcp_reqsk_alloc);
320
321/* On input, sk is a listener.
322 * Output is listener if incoming packet would not create a child
323 * NULL if memory could not be allocated.
324 */
325struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
326{
327 struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
328 struct tcp_options_received tcp_opt;
329 struct inet_request_sock *ireq;
330 struct tcp_request_sock *treq;
331 struct tcp_sock *tp = tcp_sk(sk);
332 const struct tcphdr *th = tcp_hdr(skb);
333 __u32 cookie = ntohl(th->ack_seq) - 1;
334 struct sock *ret = sk;
335 struct request_sock *req;
336 int full_space, mss;
337 struct rtable *rt;
338 __u8 rcv_wscale;
339 struct flowi4 fl4;
340 u32 tsoff = 0;
341
342 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) ||
343 !th->ack || th->rst)
344 goto out;
345
346 if (tcp_synq_no_recent_overflow(sk))
347 goto out;
348
349 mss = __cookie_v4_check(ip_hdr(skb), th, cookie);
350 if (mss == 0) {
351 __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
352 goto out;
353 }
354
355 __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
356
357 /* check for timestamp cookie support */
358 memset(&tcp_opt, 0, sizeof(tcp_opt));
359 tcp_parse_options(sock_net(sk), skb, &tcp_opt, 0, NULL);
360
361 if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) {
362 tsoff = secure_tcp_ts_off(sock_net(sk),
363 ip_hdr(skb)->daddr,
364 ip_hdr(skb)->saddr);
365 tcp_opt.rcv_tsecr -= tsoff;
366 }
367
368 if (!cookie_timestamp_decode(sock_net(sk), &tcp_opt))
369 goto out;
370
371 ret = NULL;
372 req = cookie_tcp_reqsk_alloc(&tcp_request_sock_ops,
373 &tcp_request_sock_ipv4_ops, sk, skb);
374 if (!req)
375 goto out;
376
377 ireq = inet_rsk(req);
378 treq = tcp_rsk(req);
379 treq->rcv_isn = ntohl(th->seq) - 1;
380 treq->snt_isn = cookie;
381 treq->ts_off = 0;
382 treq->txhash = net_tx_rndhash();
383 req->mss = mss;
384 ireq->ir_num = ntohs(th->dest);
385 ireq->ir_rmt_port = th->source;
386 sk_rcv_saddr_set(req_to_sk(req), ip_hdr(skb)->daddr);
387 sk_daddr_set(req_to_sk(req), ip_hdr(skb)->saddr);
388 ireq->ir_mark = inet_request_mark(sk, skb);
389 ireq->snd_wscale = tcp_opt.snd_wscale;
390 ireq->sack_ok = tcp_opt.sack_ok;
391 ireq->wscale_ok = tcp_opt.wscale_ok;
392 ireq->tstamp_ok = tcp_opt.saw_tstamp;
393 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
394 treq->snt_synack = 0;
395 treq->tfo_listener = false;
396
397 if (IS_ENABLED(CONFIG_SMC))
398 ireq->smc_ok = 0;
399
400 ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
401
402 /* We throwed the options of the initial SYN away, so we hope
403 * the ACK carries the same options again (see RFC1122 4.2.3.8)
404 */
405 RCU_INIT_POINTER(ireq->ireq_opt, tcp_v4_save_options(sock_net(sk), skb));
406
407 if (security_inet_conn_request(sk, skb, req)) {
408 reqsk_free(req);
409 goto out;
410 }
411
412 req->num_retrans = 0;
413
414 /*
415 * We need to lookup the route here to get at the correct
416 * window size. We should better make sure that the window size
417 * hasn't changed since we received the original syn, but I see
418 * no easy way to do this.
419 */
420 flowi4_init_output(&fl4, ireq->ir_iif, ireq->ir_mark,
421 RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE, IPPROTO_TCP,
422 inet_sk_flowi_flags(sk),
423 opt->srr ? opt->faddr : ireq->ir_rmt_addr,
424 ireq->ir_loc_addr, th->source, th->dest, sk->sk_uid);
425 security_req_classify_flow(req, flowi4_to_flowi_common(&fl4));
426 rt = ip_route_output_key(sock_net(sk), &fl4);
427 if (IS_ERR(rt)) {
428 reqsk_free(req);
429 goto out;
430 }
431
432 /* Try to redo what tcp_v4_send_synack did. */
433 req->rsk_window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
434 /* limit the window selection if the user enforce a smaller rx buffer */
435 full_space = tcp_full_space(sk);
436 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
437 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
438 req->rsk_window_clamp = full_space;
439
440 tcp_select_initial_window(sk, full_space, req->mss,
441 &req->rsk_rcv_wnd, &req->rsk_window_clamp,
442 ireq->wscale_ok, &rcv_wscale,
443 dst_metric(&rt->dst, RTAX_INITRWND));
444
445 ireq->rcv_wscale = rcv_wscale;
446 ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), &rt->dst);
447
448 ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst, tsoff);
449 /* ip_queue_xmit() depends on our flow being setup
450 * Normal sockets get it right from inet_csk_route_child_sock()
451 */
452 if (ret)
453 inet_sk(ret)->cork.fl.u.ip4 = fl4;
454out: return ret;
455}