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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * Syncookies implementation for the Linux kernel
3 *
4 * Copyright (C) 1997 Andi Kleen
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +09005 * Based on ideas by D.J.Bernstein and Eric Schenk.
Linus Torvalds1da177e2005-04-16 15:20:36 -07006 *
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.
Linus Torvalds1da177e2005-04-16 15:20:36 -070011 */
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>
Paul Gortmakerbc3b2d72011-07-15 11:47:34 -040018#include <linux/export.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070019#include <net/tcp.h>
KOVACS Krisztian86b08d82008-10-01 07:44:42 -070020#include <net/route.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070021
Florian Westphal253ff512014-08-26 12:55:53 +020022static u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly;
Linus Torvalds1da177e2005-04-16 15:20:36 -070023
24#define COOKIEBITS 24 /* Upper bits store count */
25#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
26
Florian Westphal274e2da2014-11-03 17:35:01 +010027/* TCP Timestamp: 6 lowest bits of timestamp sent in the cookie SYN-ACK
28 * stores TCP options:
29 *
30 * MSB LSB
31 * | 31 ... 6 | 5 | 4 | 3 2 1 0 |
32 * | Timestamp | ECN | SACK | WScale |
33 *
34 * When we receive a valid cookie-ACK, we look at the echoed tsval (if
35 * any) to figure out which TCP options we should use for the rebuilt
36 * connection.
37 *
38 * A WScale setting of '0xf' (which is an invalid scaling value)
39 * means that original syn did not include the TCP window scaling option.
40 */
41#define TS_OPT_WSCALE_MASK 0xf
42#define TS_OPT_SACK BIT(4)
43#define TS_OPT_ECN BIT(5)
44/* There is no TS_OPT_TIMESTAMP:
45 * if ACK contains timestamp option, we already know it was
46 * requested/supported by the syn/synack exchange.
47 */
48#define TSBITS 6
49#define TSMASK (((__u32)1 << TSBITS) - 1)
50
Peter Zijlstra25528212016-03-15 14:52:49 -070051static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], ipv4_cookie_scratch);
Eric Dumazet11baab72008-02-07 10:40:19 +010052
Al Viro714e85b2006-11-14 20:51:49 -080053static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
Linus Torvalds1da177e2005-04-16 15:20:36 -070054 u32 count, int c)
55{
Hannes Frederic Sowab23a0022013-10-19 21:48:56 +020056 __u32 *tmp;
Linus Torvalds1da177e2005-04-16 15:20:36 -070057
Hannes Frederic Sowab23a0022013-10-19 21:48:56 +020058 net_get_random_once(syncookie_secret, sizeof(syncookie_secret));
59
Christoph Lameter903ceff2014-08-17 12:30:35 -050060 tmp = this_cpu_ptr(ipv4_cookie_scratch);
Florian Westphal2051f112008-03-23 22:21:28 -070061 memcpy(tmp + 4, syncookie_secret[c], sizeof(syncookie_secret[c]));
Al Viro714e85b2006-11-14 20:51:49 -080062 tmp[0] = (__force u32)saddr;
63 tmp[1] = (__force u32)daddr;
64 tmp[2] = ((__force u32)sport << 16) + (__force u32)dport;
Linus Torvalds1da177e2005-04-16 15:20:36 -070065 tmp[3] = count;
66 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
67
68 return tmp[17];
69}
70
Florian Westphal4dfc2812008-04-10 03:12:40 -070071
72/*
73 * when syncookies are in effect and tcp timestamps are enabled we encode
Florian Westphal734f6142010-06-21 11:48:44 +000074 * tcp options in the lower bits of the timestamp value that will be
Florian Westphal4dfc2812008-04-10 03:12:40 -070075 * sent in the syn-ack.
76 * Since subsequent timestamps use the normal tcp_time_stamp value, we
77 * must make sure that the resulting initial timestamp is <= tcp_time_stamp.
78 */
79__u32 cookie_init_timestamp(struct request_sock *req)
80{
81 struct inet_request_sock *ireq;
82 u32 ts, ts_now = tcp_time_stamp;
83 u32 options = 0;
84
85 ireq = inet_rsk(req);
Florian Westphal734f6142010-06-21 11:48:44 +000086
Florian Westphal274e2da2014-11-03 17:35:01 +010087 options = ireq->wscale_ok ? ireq->snd_wscale : TS_OPT_WSCALE_MASK;
88 if (ireq->sack_ok)
89 options |= TS_OPT_SACK;
90 if (ireq->ecn_ok)
91 options |= TS_OPT_ECN;
Florian Westphal4dfc2812008-04-10 03:12:40 -070092
93 ts = ts_now & ~TSMASK;
94 ts |= options;
95 if (ts > ts_now) {
96 ts >>= TSBITS;
97 ts--;
98 ts <<= TSBITS;
99 ts |= options;
100 }
101 return ts;
102}
103
104
Al Viro714e85b2006-11-14 20:51:49 -0800105static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
Florian Westphal8c27bd72013-09-20 22:32:55 +0200106 __be16 dport, __u32 sseq, __u32 data)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700107{
108 /*
109 * Compute the secure sequence number.
110 * The output should be:
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900111 * HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700112 * + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24).
113 * Where sseq is their sequence number and count increases every
114 * minute by 1.
115 * As an extra hack, we add a small "data" value that encodes the
116 * MSS into the second hash value.
117 */
Florian Westphal8c27bd72013-09-20 22:32:55 +0200118 u32 count = tcp_cookie_time();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
120 sseq + (count << COOKIEBITS) +
121 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
122 & COOKIEMASK));
123}
124
125/*
126 * This retrieves the small "data" value from the syncookie.
127 * If the syncookie is bad, the data returned will be out of
128 * range. This must be checked by the caller.
129 *
Florian Westphal8c27bd72013-09-20 22:32:55 +0200130 * The count value used to generate the cookie must be less than
131 * MAX_SYNCOOKIE_AGE minutes in the past.
132 * The return value (__u32)-1 if this test fails.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700133 */
Al Viro714e85b2006-11-14 20:51:49 -0800134static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
Florian Westphal8c27bd72013-09-20 22:32:55 +0200135 __be16 sport, __be16 dport, __u32 sseq)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700136{
Florian Westphal8c27bd72013-09-20 22:32:55 +0200137 u32 diff, count = tcp_cookie_time();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700138
139 /* Strip away the layers from the cookie */
140 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
141
142 /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */
Weilong Chen0c9a67d2013-12-23 14:37:27 +0800143 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
Florian Westphal8c27bd72013-09-20 22:32:55 +0200144 if (diff >= MAX_SYNCOOKIE_AGE)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700145 return (__u32)-1;
146
147 return (cookie -
148 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
149 & COOKIEMASK; /* Leaving the data behind */
150}
151
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900152/*
Florian Westphal08629352013-09-20 22:32:56 +0200153 * MSS Values are chosen based on the 2011 paper
154 * 'An Analysis of TCP Maximum Segement Sizes' by S. Alcock and R. Nelson.
155 * Values ..
156 * .. lower than 536 are rare (< 0.2%)
157 * .. between 537 and 1299 account for less than < 1.5% of observed values
158 * .. in the 1300-1349 range account for about 15 to 20% of observed mss values
159 * .. exceeding 1460 are very rare (< 0.04%)
Florian Westphal5918e2f2010-06-03 00:43:57 +0000160 *
Florian Westphal08629352013-09-20 22:32:56 +0200161 * 1460 is the single most frequently announced mss value (30 to 46% depending
162 * on monitor location). Table must be sorted.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700163 */
164static __u16 const msstab[] = {
Florian Westphal5918e2f2010-06-03 00:43:57 +0000165 536,
Florian Westphal08629352013-09-20 22:32:56 +0200166 1300,
167 1440, /* 1440, 1452: PPPoE */
Florian Westphal5918e2f2010-06-03 00:43:57 +0000168 1460,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700169};
Linus Torvalds1da177e2005-04-16 15:20:36 -0700170
171/*
172 * Generate a syncookie. mssp points to the mss, which is returned
173 * rounded down to the value encoded in the cookie.
174 */
Patrick McHardy01982302013-08-27 08:50:13 +0200175u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
176 u16 *mssp)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700177{
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178 int mssind;
179 const __u16 mss = *mssp;
180
Florian Westphal5918e2f2010-06-03 00:43:57 +0000181 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
182 if (mss >= msstab[mssind])
183 break;
184 *mssp = msstab[mssind];
Linus Torvalds1da177e2005-04-16 15:20:36 -0700185
Arnaldo Carvalho de Meloaa8223c2007-04-10 21:04:22 -0700186 return secure_tcp_syn_cookie(iph->saddr, iph->daddr,
187 th->source, th->dest, ntohl(th->seq),
Florian Westphal8c27bd72013-09-20 22:32:55 +0200188 mssind);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700189}
Patrick McHardy01982302013-08-27 08:50:13 +0200190EXPORT_SYMBOL_GPL(__cookie_v4_init_sequence);
191
Eric Dumazet3f684b42015-09-29 07:42:49 -0700192__u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mssp)
Patrick McHardy01982302013-08-27 08:50:13 +0200193{
194 const struct iphdr *iph = ip_hdr(skb);
195 const struct tcphdr *th = tcp_hdr(skb);
196
Patrick McHardy01982302013-08-27 08:50:13 +0200197 return __cookie_v4_init_sequence(iph, th, mssp);
198}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700199
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900200/*
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900201 * Check if a ack sequence number is a valid syncookie.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700202 * Return the decoded mss if it is, or 0 if not.
203 */
Patrick McHardy01982302013-08-27 08:50:13 +0200204int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
205 u32 cookie)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700206{
Arnaldo Carvalho de Meloaa8223c2007-04-10 21:04:22 -0700207 __u32 seq = ntohl(th->seq) - 1;
208 __u32 mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr,
Florian Westphal8c27bd72013-09-20 22:32:55 +0200209 th->source, th->dest, seq);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700210
Florian Westphal5918e2f2010-06-03 00:43:57 +0000211 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700212}
Patrick McHardy01982302013-08-27 08:50:13 +0200213EXPORT_SYMBOL_GPL(__cookie_v4_check);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700214
Eric Dumazetb80c0e72015-06-04 18:30:43 -0700215struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
216 struct request_sock *req,
217 struct dst_entry *dst)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700218{
Arnaldo Carvalho de Melo8292a172005-12-13 23:15:52 -0800219 struct inet_connection_sock *icsk = inet_csk(sk);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700220 struct sock *child;
Eric Dumazet5e0724d2015-10-22 08:20:46 -0700221 bool own_req;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700222
Eric Dumazet5e0724d2015-10-22 08:20:46 -0700223 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst,
224 NULL, &own_req);
Eric Dumazet0470c8c2015-03-17 18:32:31 -0700225 if (child) {
226 atomic_set(&req->rsk_refcnt, 1);
Eric Dumazet6bcfd7f2015-10-08 11:16:48 -0700227 sock_rps_save_rxhash(child, skb);
Arnaldo Carvalho de Melo463c84b2005-08-09 20:10:42 -0700228 inet_csk_reqsk_queue_add(sk, req, child);
Eric Dumazet0470c8c2015-03-17 18:32:31 -0700229 } else {
Arnaldo Carvalho de Melo60236fd2005-06-18 22:47:21 -0700230 reqsk_free(req);
Eric Dumazet0470c8c2015-03-17 18:32:31 -0700231 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700232 return child;
233}
Eric Dumazetb80c0e72015-06-04 18:30:43 -0700234EXPORT_SYMBOL(tcp_get_cookie_sock);
Florian Westphal4dfc2812008-04-10 03:12:40 -0700235
236/*
237 * when syncookies are in effect and tcp timestamps are enabled we stored
238 * additional tcp options in the timestamp.
239 * This extracts these options from the timestamp echo.
240 *
Florian Westphalf1673382014-11-03 17:35:02 +0100241 * return false if we decode a tcp option that is disabled
242 * on the host.
Florian Westphal4dfc2812008-04-10 03:12:40 -0700243 */
Florian Westphalf1673382014-11-03 17:35:02 +0100244bool cookie_timestamp_decode(struct tcp_options_received *tcp_opt)
Florian Westphal4dfc2812008-04-10 03:12:40 -0700245{
Florian Westphal734f6142010-06-21 11:48:44 +0000246 /* echoed timestamp, lowest bits contain options */
Florian Westphal274e2da2014-11-03 17:35:01 +0100247 u32 options = tcp_opt->rcv_tsecr;
Florian Westphal4dfc2812008-04-10 03:12:40 -0700248
Florian Westphal8c763682010-06-16 14:42:15 -0700249 if (!tcp_opt->saw_tstamp) {
250 tcp_clear_options(tcp_opt);
251 return true;
252 }
253
254 if (!sysctl_tcp_timestamps)
255 return false;
256
Florian Westphal274e2da2014-11-03 17:35:01 +0100257 tcp_opt->sack_ok = (options & TS_OPT_SACK) ? TCP_SACK_SEEN : 0;
Florian Westphal4dfc2812008-04-10 03:12:40 -0700258
Florian Westphal8c763682010-06-16 14:42:15 -0700259 if (tcp_opt->sack_ok && !sysctl_tcp_sack)
260 return false;
Florian Westphal4dfc2812008-04-10 03:12:40 -0700261
Florian Westphal274e2da2014-11-03 17:35:01 +0100262 if ((options & TS_OPT_WSCALE_MASK) == TS_OPT_WSCALE_MASK)
Florian Westphal734f6142010-06-21 11:48:44 +0000263 return true; /* no window scaling */
264
265 tcp_opt->wscale_ok = 1;
Florian Westphal274e2da2014-11-03 17:35:01 +0100266 tcp_opt->snd_wscale = options & TS_OPT_WSCALE_MASK;
267
Florian Westphal734f6142010-06-21 11:48:44 +0000268 return sysctl_tcp_window_scaling != 0;
Florian Westphal4dfc2812008-04-10 03:12:40 -0700269}
Florian Westphalf1673382014-11-03 17:35:02 +0100270EXPORT_SYMBOL(cookie_timestamp_decode);
271
272bool cookie_ecn_ok(const struct tcp_options_received *tcp_opt,
Florian Westphalf7b3bec2014-11-03 17:35:03 +0100273 const struct net *net, const struct dst_entry *dst)
Florian Westphalf1673382014-11-03 17:35:02 +0100274{
275 bool ecn_ok = tcp_opt->rcv_tsecr & TS_OPT_ECN;
276
277 if (!ecn_ok)
278 return false;
279
280 if (net->ipv4.sysctl_tcp_ecn)
281 return true;
282
Florian Westphalf7b3bec2014-11-03 17:35:03 +0100283 return dst_feature(dst, RTAX_FEATURE_ECN);
Florian Westphalf1673382014-11-03 17:35:02 +0100284}
285EXPORT_SYMBOL(cookie_ecn_ok);
Florian Westphal4dfc2812008-04-10 03:12:40 -0700286
Eric Dumazet079096f2015-10-02 11:43:32 -0700287/* On input, sk is a listener.
288 * Output is listener if incoming packet would not create a child
289 * NULL if memory could not be allocated.
290 */
Cong Wang461b74c2014-10-15 14:33:22 -0700291struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700292{
Cong Wang461b74c2014-10-15 14:33:22 -0700293 struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
William Allen Simpson4957faade2009-12-02 18:25:27 +0000294 struct tcp_options_received tcp_opt;
Arnaldo Carvalho de Melo2e6599c2005-06-18 22:46:52 -0700295 struct inet_request_sock *ireq;
296 struct tcp_request_sock *treq;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700297 struct tcp_sock *tp = tcp_sk(sk);
Arnaldo Carvalho de Meloaa8223c2007-04-10 21:04:22 -0700298 const struct tcphdr *th = tcp_hdr(skb);
299 __u32 cookie = ntohl(th->ack_seq) - 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700300 struct sock *ret = sk;
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900301 struct request_sock *req;
302 int mss;
303 struct rtable *rt;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700304 __u8 rcv_wscale;
Eric Dumazetdfd25ff2012-03-10 09:20:21 +0000305 struct flowi4 fl4;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700306
Nikolay Borisov12ed8242016-02-03 09:46:51 +0200307 if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700308 goto out;
309
Florian Westphal646697b2014-10-30 02:55:38 +0100310 if (tcp_synq_no_recent_overflow(sk))
311 goto out;
312
313 mss = __cookie_v4_check(ip_hdr(skb), th, cookie);
314 if (mss == 0) {
Eric Dumazet02a1d6e2016-04-27 16:44:39 -0700315 __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700316 goto out;
317 }
318
Eric Dumazet02a1d6e2016-04-27 16:44:39 -0700319 __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700320
David S. Millerbb5b7c12009-12-15 20:56:42 -0800321 /* check for timestamp cookie support */
322 memset(&tcp_opt, 0, sizeof(tcp_opt));
Christoph Paasch1a2c6182013-03-17 08:23:34 +0000323 tcp_parse_options(skb, &tcp_opt, 0, NULL);
David S. Millerbb5b7c12009-12-15 20:56:42 -0800324
Florian Westphalf1673382014-11-03 17:35:02 +0100325 if (!cookie_timestamp_decode(&tcp_opt))
Florian Westphal8c763682010-06-16 14:42:15 -0700326 goto out;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800327
Linus Torvalds1da177e2005-04-16 15:20:36 -0700328 ret = NULL;
Eric Dumazeta1a53442015-10-04 21:08:11 -0700329 req = inet_reqsk_alloc(&tcp_request_sock_ops, sk, false); /* for safety */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700330 if (!req)
331 goto out;
332
Arnaldo Carvalho de Melo2e6599c2005-06-18 22:46:52 -0700333 ireq = inet_rsk(req);
334 treq = tcp_rsk(req);
Arnaldo Carvalho de Meloaa8223c2007-04-10 21:04:22 -0700335 treq->rcv_isn = ntohl(th->seq) - 1;
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900336 treq->snt_isn = cookie;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700337 req->mss = mss;
Eric Dumazetb44084c2013-10-10 00:04:37 -0700338 ireq->ir_num = ntohs(th->dest);
339 ireq->ir_rmt_port = th->source;
Eric Dumazet08d2cc3b2015-03-18 14:05:38 -0700340 sk_rcv_saddr_set(req_to_sk(req), ip_hdr(skb)->daddr);
341 sk_daddr_set(req_to_sk(req), ip_hdr(skb)->saddr);
Lorenzo Colitti84f39b02014-05-13 10:17:35 -0700342 ireq->ir_mark = inet_request_mark(sk, skb);
David S. Millerbb5b7c12009-12-15 20:56:42 -0800343 ireq->snd_wscale = tcp_opt.snd_wscale;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800344 ireq->sack_ok = tcp_opt.sack_ok;
345 ireq->wscale_ok = tcp_opt.wscale_ok;
346 ireq->tstamp_ok = tcp_opt.saw_tstamp;
347 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
Yuchung Cheng0f1c28a2015-09-18 11:36:14 -0700348 treq->snt_synack.v64 = 0;
Eric Dumazet9439ce02015-03-17 18:32:29 -0700349 treq->tfo_listener = false;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700350
David Ahern6dd9a142015-12-16 13:20:44 -0800351 ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
Eric Dumazet16f86162015-03-13 15:51:10 -0700352
Linus Torvalds1da177e2005-04-16 15:20:36 -0700353 /* We throwed the options of the initial SYN away, so we hope
354 * the ACK carries the same options again (see RFC1122 4.2.3.8)
355 */
Cong Wange25f8662014-10-15 14:33:21 -0700356 ireq->opt = tcp_v4_save_options(skb);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700357
Paul Moore284904a2009-03-27 17:10:28 -0400358 if (security_inet_conn_request(sk, skb, req)) {
Eric Dumazet0470c8c2015-03-17 18:32:31 -0700359 reqsk_free(req);
Paul Moore284904a2009-03-27 17:10:28 -0400360 goto out;
361 }
362
Eric Dumazete6c022a2012-10-27 23:16:46 +0000363 req->num_retrans = 0;
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900364
Linus Torvalds1da177e2005-04-16 15:20:36 -0700365 /*
366 * We need to lookup the route here to get at the correct
367 * window size. We should better make sure that the window size
368 * hasn't changed since we received the original syn, but I see
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900369 * no easy way to do this.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700370 */
David Ahern6dd9a142015-12-16 13:20:44 -0800371 flowi4_init_output(&fl4, ireq->ir_iif, ireq->ir_mark,
Dmitry Popovd66954a2013-04-11 08:55:07 +0000372 RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE, IPPROTO_TCP,
Eric Dumazetdfd25ff2012-03-10 09:20:21 +0000373 inet_sk_flowi_flags(sk),
Cong Wang461b74c2014-10-15 14:33:22 -0700374 opt->srr ? opt->faddr : ireq->ir_rmt_addr,
Eric Dumazet634fb9792013-10-09 15:21:29 -0700375 ireq->ir_loc_addr, th->source, th->dest);
Eric Dumazetdfd25ff2012-03-10 09:20:21 +0000376 security_req_classify_flow(req, flowi4_to_flowi(&fl4));
377 rt = ip_route_output_key(sock_net(sk), &fl4);
378 if (IS_ERR(rt)) {
Eric Dumazet0470c8c2015-03-17 18:32:31 -0700379 reqsk_free(req);
Eric Dumazetdfd25ff2012-03-10 09:20:21 +0000380 goto out;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700381 }
382
383 /* Try to redo what tcp_v4_send_synack did. */
Eric Dumazeted53d0a2015-10-08 19:33:23 -0700384 req->rsk_window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
Florian Westphal4dfc2812008-04-10 03:12:40 -0700385
Linus Torvalds1da177e2005-04-16 15:20:36 -0700386 tcp_select_initial_window(tcp_full_space(sk), req->mss,
Eric Dumazeted53d0a2015-10-08 19:33:23 -0700387 &req->rsk_rcv_wnd, &req->rsk_window_clamp,
laurent chavey31d12922009-12-15 11:15:28 +0000388 ireq->wscale_ok, &rcv_wscale,
Changli Gaod8d1f302010-06-10 23:31:35 -0700389 dst_metric(&rt->dst, RTAX_INITRWND));
Florian Westphal4dfc2812008-04-10 03:12:40 -0700390
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900391 ireq->rcv_wscale = rcv_wscale;
Florian Westphalf7b3bec2014-11-03 17:35:03 +0100392 ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), &rt->dst);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700393
Eric Dumazetb80c0e72015-06-04 18:30:43 -0700394 ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst);
Eric Dumazetdfd25ff2012-03-10 09:20:21 +0000395 /* ip_queue_xmit() depends on our flow being setup
396 * Normal sockets get it right from inet_csk_route_child_sock()
397 */
398 if (ret)
399 inet_sk(ret)->cork.fl.u.ip4 = fl4;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700400out: return ret;
401}