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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 Westphal734f6142010-06-21 11:48:44 +000022/* Timestamps: lowest bits store TCP options */
Florian Westphal172d69e2010-06-21 11:48:45 +000023#define TSBITS 6
Florian Westphal4dfc2812008-04-10 03:12:40 -070024#define TSMASK (((__u32)1 << TSBITS) - 1)
25
Linus Torvalds1da177e2005-04-16 15:20:36 -070026extern int sysctl_tcp_syncookies;
27
Hannes Frederic Sowab23a0022013-10-19 21:48:56 +020028static u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
Linus Torvalds1da177e2005-04-16 15:20:36 -070029
30#define COOKIEBITS 24 /* Upper bits store count */
31#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
32
Tejun Heo245b2e72009-06-24 15:13:48 +090033static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
34 ipv4_cookie_scratch);
Eric Dumazet11baab72008-02-07 10:40:19 +010035
Al Viro714e85b2006-11-14 20:51:49 -080036static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
Linus Torvalds1da177e2005-04-16 15:20:36 -070037 u32 count, int c)
38{
Hannes Frederic Sowab23a0022013-10-19 21:48:56 +020039 __u32 *tmp;
Linus Torvalds1da177e2005-04-16 15:20:36 -070040
Hannes Frederic Sowab23a0022013-10-19 21:48:56 +020041 net_get_random_once(syncookie_secret, sizeof(syncookie_secret));
42
43 tmp = __get_cpu_var(ipv4_cookie_scratch);
Florian Westphal2051f112008-03-23 22:21:28 -070044 memcpy(tmp + 4, syncookie_secret[c], sizeof(syncookie_secret[c]));
Al Viro714e85b2006-11-14 20:51:49 -080045 tmp[0] = (__force u32)saddr;
46 tmp[1] = (__force u32)daddr;
47 tmp[2] = ((__force u32)sport << 16) + (__force u32)dport;
Linus Torvalds1da177e2005-04-16 15:20:36 -070048 tmp[3] = count;
49 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
50
51 return tmp[17];
52}
53
Florian Westphal4dfc2812008-04-10 03:12:40 -070054
55/*
56 * when syncookies are in effect and tcp timestamps are enabled we encode
Florian Westphal734f6142010-06-21 11:48:44 +000057 * tcp options in the lower bits of the timestamp value that will be
Florian Westphal4dfc2812008-04-10 03:12:40 -070058 * 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);
Florian Westphal734f6142010-06-21 11:48:44 +000069
70 options = ireq->wscale_ok ? ireq->snd_wscale : 0xf;
71 options |= ireq->sack_ok << 4;
Florian Westphal172d69e2010-06-21 11:48:45 +000072 options |= ireq->ecn_ok << 5;
Florian Westphal4dfc2812008-04-10 03:12:40 -070073
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
Al Viro714e85b2006-11-14 20:51:49 -080086static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
Florian Westphal8c27bd72013-09-20 22:32:55 +020087 __be16 dport, __u32 sseq, __u32 data)
Linus Torvalds1da177e2005-04-16 15:20:36 -070088{
89 /*
90 * Compute the secure sequence number.
91 * The output should be:
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +090092 * HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24)
Linus Torvalds1da177e2005-04-16 15:20:36 -070093 * + (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 */
Florian Westphal8c27bd72013-09-20 22:32:55 +020099 u32 count = tcp_cookie_time();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700100 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 *
Florian Westphal8c27bd72013-09-20 22:32:55 +0200111 * 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.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700114 */
Al Viro714e85b2006-11-14 20:51:49 -0800115static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
Florian Westphal8c27bd72013-09-20 22:32:55 +0200116 __be16 sport, __be16 dport, __u32 sseq)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700117{
Florian Westphal8c27bd72013-09-20 22:32:55 +0200118 u32 diff, count = tcp_cookie_time();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119
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) */
Weilong Chen0c9a67d2013-12-23 14:37:27 +0800124 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
Florian Westphal8c27bd72013-09-20 22:32:55 +0200125 if (diff >= MAX_SYNCOOKIE_AGE)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700126 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
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900133/*
Florian Westphal08629352013-09-20 22:32:56 +0200134 * 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%)
Florian Westphal5918e2f2010-06-03 00:43:57 +0000141 *
Florian Westphal08629352013-09-20 22:32:56 +0200142 * 1460 is the single most frequently announced mss value (30 to 46% depending
143 * on monitor location). Table must be sorted.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700144 */
145static __u16 const msstab[] = {
Florian Westphal5918e2f2010-06-03 00:43:57 +0000146 536,
Florian Westphal08629352013-09-20 22:32:56 +0200147 1300,
148 1440, /* 1440, 1452: PPPoE */
Florian Westphal5918e2f2010-06-03 00:43:57 +0000149 1460,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700150};
Linus Torvalds1da177e2005-04-16 15:20:36 -0700151
152/*
153 * Generate a syncookie. mssp points to the mss, which is returned
154 * rounded down to the value encoded in the cookie.
155 */
Patrick McHardy01982302013-08-27 08:50:13 +0200156u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
157 u16 *mssp)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700158{
Linus Torvalds1da177e2005-04-16 15:20:36 -0700159 int mssind;
160 const __u16 mss = *mssp;
161
Florian Westphal5918e2f2010-06-03 00:43:57 +0000162 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
163 if (mss >= msstab[mssind])
164 break;
165 *mssp = msstab[mssind];
Linus Torvalds1da177e2005-04-16 15:20:36 -0700166
Arnaldo Carvalho de Meloaa8223c2007-04-10 21:04:22 -0700167 return secure_tcp_syn_cookie(iph->saddr, iph->daddr,
168 th->source, th->dest, ntohl(th->seq),
Florian Westphal8c27bd72013-09-20 22:32:55 +0200169 mssind);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700170}
Patrick McHardy01982302013-08-27 08:50:13 +0200171EXPORT_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}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700183
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900184/*
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900185 * Check if a ack sequence number is a valid syncookie.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700186 * Return the decoded mss if it is, or 0 if not.
187 */
Patrick McHardy01982302013-08-27 08:50:13 +0200188int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
189 u32 cookie)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700190{
Arnaldo Carvalho de Meloaa8223c2007-04-10 21:04:22 -0700191 __u32 seq = ntohl(th->seq) - 1;
192 __u32 mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr,
Florian Westphal8c27bd72013-09-20 22:32:55 +0200193 th->source, th->dest, seq);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700194
Florian Westphal5918e2f2010-06-03 00:43:57 +0000195 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700196}
Patrick McHardy01982302013-08-27 08:50:13 +0200197EXPORT_SYMBOL_GPL(__cookie_v4_check);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700198
Linus Torvalds1da177e2005-04-16 15:20:36 -0700199static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
Arnaldo Carvalho de Melo60236fd2005-06-18 22:47:21 -0700200 struct request_sock *req,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700201 struct dst_entry *dst)
202{
Arnaldo Carvalho de Melo8292a172005-12-13 23:15:52 -0800203 struct inet_connection_sock *icsk = inet_csk(sk);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700204 struct sock *child;
205
Arnaldo Carvalho de Melo8292a172005-12-13 23:15:52 -0800206 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700207 if (child)
Arnaldo Carvalho de Melo463c84b2005-08-09 20:10:42 -0700208 inet_csk_reqsk_queue_add(sk, req, child);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700209 else
Arnaldo Carvalho de Melo60236fd2005-06-18 22:47:21 -0700210 reqsk_free(req);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700211
212 return child;
213}
214
Florian Westphal4dfc2812008-04-10 03:12:40 -0700215
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 *
Florian Westphal734f6142010-06-21 11:48:44 +0000221 * The lowest 4 bits store snd_wscale.
Florian Westphal172d69e2010-06-21 11:48:45 +0000222 * next 2 bits indicate SACK and ECN support.
Florian Westphal8c763682010-06-16 14:42:15 -0700223 *
224 * return false if we decode an option that should not be.
Florian Westphal4dfc2812008-04-10 03:12:40 -0700225 */
Hannes Frederic Sowa5d134f12013-01-05 16:10:48 +0000226bool cookie_check_timestamp(struct tcp_options_received *tcp_opt,
227 struct net *net, bool *ecn_ok)
Florian Westphal4dfc2812008-04-10 03:12:40 -0700228{
Florian Westphal734f6142010-06-21 11:48:44 +0000229 /* echoed timestamp, lowest bits contain options */
Florian Westphal4dfc2812008-04-10 03:12:40 -0700230 u32 options = tcp_opt->rcv_tsecr & TSMASK;
231
Florian Westphal8c763682010-06-16 14:42:15 -0700232 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
Vijay Subramanianab562222011-12-20 13:23:24 +0000240 tcp_opt->sack_ok = (options & (1 << 4)) ? TCP_SACK_SEEN : 0;
Florian Westphal172d69e2010-06-21 11:48:45 +0000241 *ecn_ok = (options >> 5) & 1;
Hannes Frederic Sowa5d134f12013-01-05 16:10:48 +0000242 if (*ecn_ok && !net->ipv4.sysctl_tcp_ecn)
Florian Westphal172d69e2010-06-21 11:48:45 +0000243 return false;
Florian Westphal4dfc2812008-04-10 03:12:40 -0700244
Florian Westphal8c763682010-06-16 14:42:15 -0700245 if (tcp_opt->sack_ok && !sysctl_tcp_sack)
246 return false;
Florian Westphal4dfc2812008-04-10 03:12:40 -0700247
Florian Westphal734f6142010-06-21 11:48:44 +0000248 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;
Florian Westphal4dfc2812008-04-10 03:12:40 -0700254}
255EXPORT_SYMBOL(cookie_check_timestamp);
256
Linus Torvalds1da177e2005-04-16 15:20:36 -0700257struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
258 struct ip_options *opt)
259{
William Allen Simpson4957faade2009-12-02 18:25:27 +0000260 struct tcp_options_received tcp_opt;
Arnaldo Carvalho de Melo2e6599c2005-06-18 22:46:52 -0700261 struct inet_request_sock *ireq;
262 struct tcp_request_sock *treq;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700263 struct tcp_sock *tp = tcp_sk(sk);
Arnaldo Carvalho de Meloaa8223c2007-04-10 21:04:22 -0700264 const struct tcphdr *th = tcp_hdr(skb);
265 __u32 cookie = ntohl(th->ack_seq) - 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700266 struct sock *ret = sk;
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900267 struct request_sock *req;
268 int mss;
269 struct rtable *rt;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700270 __u8 rcv_wscale;
Mike Waychisonf0e3d0682011-08-10 21:59:57 -0700271 bool ecn_ok = false;
Eric Dumazetdfd25ff2012-03-10 09:20:21 +0000272 struct flowi4 fl4;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700273
Florian Westphalaf9b4732010-06-03 00:43:44 +0000274 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700275 goto out;
276
Florian Westphala0f82f62009-04-19 09:43:48 +0000277 if (tcp_synq_no_recent_overflow(sk) ||
Patrick McHardy01982302013-08-27 08:50:13 +0200278 (mss = __cookie_v4_check(ip_hdr(skb), th, cookie)) == 0) {
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700279 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700280 goto out;
281 }
282
Pavel Emelyanovde0744a2008-07-16 20:31:16 -0700283 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700284
David S. Millerbb5b7c12009-12-15 20:56:42 -0800285 /* check for timestamp cookie support */
286 memset(&tcp_opt, 0, sizeof(tcp_opt));
Christoph Paasch1a2c6182013-03-17 08:23:34 +0000287 tcp_parse_options(skb, &tcp_opt, 0, NULL);
David S. Millerbb5b7c12009-12-15 20:56:42 -0800288
Hannes Frederic Sowa5d134f12013-01-05 16:10:48 +0000289 if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok))
Florian Westphal8c763682010-06-16 14:42:15 -0700290 goto out;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800291
Linus Torvalds1da177e2005-04-16 15:20:36 -0700292 ret = NULL;
Arnaldo Carvalho de Meloce4a7d02008-06-10 12:39:35 -0700293 req = inet_reqsk_alloc(&tcp_request_sock_ops); /* for safety */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700294 if (!req)
295 goto out;
296
Arnaldo Carvalho de Melo2e6599c2005-06-18 22:46:52 -0700297 ireq = inet_rsk(req);
298 treq = tcp_rsk(req);
Arnaldo Carvalho de Meloaa8223c2007-04-10 21:04:22 -0700299 treq->rcv_isn = ntohl(th->seq) - 1;
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900300 treq->snt_isn = cookie;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700301 req->mss = mss;
Eric Dumazetb44084c2013-10-10 00:04:37 -0700302 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;
Florian Westphal172d69e2010-06-21 11:48:45 +0000306 ireq->ecn_ok = ecn_ok;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800307 ireq->snd_wscale = tcp_opt.snd_wscale;
David S. Millerbb5b7c12009-12-15 20:56:42 -0800308 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;
Jerry Chu9ad7c042011-06-08 11:08:38 +0000312 treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
Jerry Chu83368862012-08-31 12:29:12 +0000313 treq->listener = NULL;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700314
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) {
Eric Dumazetf6d8bd02011-04-21 09:45:37 +0000319 int opt_size = sizeof(struct ip_options_rcu) + opt->optlen;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700320
Arnaldo Carvalho de Melo2e6599c2005-06-18 22:46:52 -0700321 ireq->opt = kmalloc(opt_size, GFP_ATOMIC);
Eric Dumazetf6d8bd02011-04-21 09:45:37 +0000322 if (ireq->opt != NULL && ip_options_echo(&ireq->opt->opt, skb)) {
Arnaldo Carvalho de Melo2e6599c2005-06-18 22:46:52 -0700323 kfree(ireq->opt);
324 ireq->opt = NULL;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700325 }
326 }
327
Paul Moore284904a2009-03-27 17:10:28 -0400328 if (security_inet_conn_request(sk, skb, req)) {
329 reqsk_free(req);
330 goto out;
331 }
332
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900333 req->expires = 0UL;
Eric Dumazete6c022a2012-10-27 23:16:46 +0000334 req->num_retrans = 0;
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900335
Linus Torvalds1da177e2005-04-16 15:20:36 -0700336 /*
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
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900340 * no easy way to do this.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700341 */
Dmitry Popovd66954a2013-04-11 08:55:07 +0000342 flowi4_init_output(&fl4, sk->sk_bound_dev_if, sk->sk_mark,
343 RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE, IPPROTO_TCP,
Eric Dumazetdfd25ff2012-03-10 09:20:21 +0000344 inet_sk_flowi_flags(sk),
Eric Dumazet634fb9792013-10-09 15:21:29 -0700345 (opt && opt->srr) ? opt->faddr : ireq->ir_rmt_addr,
346 ireq->ir_loc_addr, th->source, th->dest);
Eric Dumazetdfd25ff2012-03-10 09:20:21 +0000347 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;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700352 }
353
354 /* Try to redo what tcp_v4_send_synack did. */
Changli Gaod8d1f302010-06-10 23:31:35 -0700355 req->window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
Florian Westphal4dfc2812008-04-10 03:12:40 -0700356
Linus Torvalds1da177e2005-04-16 15:20:36 -0700357 tcp_select_initial_window(tcp_full_space(sk), req->mss,
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900358 &req->rcv_wnd, &req->window_clamp,
laurent chavey31d12922009-12-15 11:15:28 +0000359 ireq->wscale_ok, &rcv_wscale,
Changli Gaod8d1f302010-06-10 23:31:35 -0700360 dst_metric(&rt->dst, RTAX_INITRWND));
Florian Westphal4dfc2812008-04-10 03:12:40 -0700361
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900362 ireq->rcv_wscale = rcv_wscale;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700363
Changli Gaod8d1f302010-06-10 23:31:35 -0700364 ret = get_cookie_sock(sk, skb, req, &rt->dst);
Eric Dumazetdfd25ff2012-03-10 09:20:21 +0000365 /* 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;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700370out: return ret;
371}