source: src/linux/universal/linux-3.18/net/ipv4/tcp_minisocks.c @ 31885

Last change on this file since 31885 was 31885, checked in by brainslayer, 5 weeks ago

update

File size: 24.9 KB
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1/*
2 * INET         An implementation of the TCP/IP protocol suite for the LINUX
3 *              operating system.  INET is implemented using the  BSD Socket
4 *              interface as the means of communication with the user level.
5 *
6 *              Implementation of the Transmission Control Protocol(TCP).
7 *
8 * Authors:     Ross Biro
9 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 *              Mark Evans, <evansmp@uhura.aston.ac.uk>
11 *              Corey Minyard <wf-rch!minyard@relay.EU.net>
12 *              Florian La Roche, <flla@stud.uni-sb.de>
13 *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 *              Linus Torvalds, <torvalds@cs.helsinki.fi>
15 *              Alan Cox, <gw4pts@gw4pts.ampr.org>
16 *              Matthew Dillon, <dillon@apollo.west.oic.com>
17 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 *              Jorge Cwik, <jorge@laser.satlink.net>
19 */
20
21#include <linux/mm.h>
22#include <linux/module.h>
23#include <linux/slab.h>
24#include <linux/sysctl.h>
25#include <linux/workqueue.h>
26#include <net/tcp.h>
27#include <net/inet_common.h>
28#include <net/xfrm.h>
29
30int sysctl_tcp_syncookies __read_mostly = 1;
31EXPORT_SYMBOL(sysctl_tcp_syncookies);
32
33int sysctl_tcp_abort_on_overflow __read_mostly;
34
35struct inet_timewait_death_row tcp_death_row = {
36        .sysctl_max_tw_buckets = NR_FILE * 2,
37        .period         = TCP_TIMEWAIT_LEN / INET_TWDR_TWKILL_SLOTS,
38        .death_lock     = __SPIN_LOCK_UNLOCKED(tcp_death_row.death_lock),
39        .hashinfo       = &tcp_hashinfo,
40        .tw_timer       = TIMER_INITIALIZER(inet_twdr_hangman, 0,
41                                            (unsigned long)&tcp_death_row),
42        .twkill_work    = __WORK_INITIALIZER(tcp_death_row.twkill_work,
43                                             inet_twdr_twkill_work),
44/* Short-time timewait calendar */
45
46        .twcal_hand     = -1,
47        .twcal_timer    = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0,
48                                            (unsigned long)&tcp_death_row),
49};
50EXPORT_SYMBOL_GPL(tcp_death_row);
51
52static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
53{
54        if (seq == s_win)
55                return true;
56        if (after(end_seq, s_win) && before(seq, e_win))
57                return true;
58        return seq == e_win && seq == end_seq;
59}
60
61/*
62 * * Main purpose of TIME-WAIT state is to close connection gracefully,
63 *   when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
64 *   (and, probably, tail of data) and one or more our ACKs are lost.
65 * * What is TIME-WAIT timeout? It is associated with maximal packet
66 *   lifetime in the internet, which results in wrong conclusion, that
67 *   it is set to catch "old duplicate segments" wandering out of their path.
68 *   It is not quite correct. This timeout is calculated so that it exceeds
69 *   maximal retransmission timeout enough to allow to lose one (or more)
70 *   segments sent by peer and our ACKs. This time may be calculated from RTO.
71 * * When TIME-WAIT socket receives RST, it means that another end
72 *   finally closed and we are allowed to kill TIME-WAIT too.
73 * * Second purpose of TIME-WAIT is catching old duplicate segments.
74 *   Well, certainly it is pure paranoia, but if we load TIME-WAIT
75 *   with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
76 * * If we invented some more clever way to catch duplicates
77 *   (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
78 *
79 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
80 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
81 * from the very beginning.
82 *
83 * NOTE. With recycling (and later with fin-wait-2) TW bucket
84 * is _not_ stateless. It means, that strictly speaking we must
85 * spinlock it. I do not want! Well, probability of misbehaviour
86 * is ridiculously low and, seems, we could use some mb() tricks
87 * to avoid misread sequence numbers, states etc.  --ANK
88 *
89 * We don't need to initialize tmp_out.sack_ok as we don't use the results
90 */
91enum tcp_tw_status
92tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
93                           const struct tcphdr *th)
94{
95        struct tcp_options_received tmp_opt;
96        struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
97        bool paws_reject = false;
98
99        tmp_opt.saw_tstamp = 0;
100        if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
101                tcp_parse_options(skb, &tmp_opt, 0, NULL);
102
103                if (tmp_opt.saw_tstamp) {
104                        tmp_opt.rcv_tsecr       -= tcptw->tw_ts_offset;
105                        tmp_opt.ts_recent       = tcptw->tw_ts_recent;
106                        tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
107                        paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
108                }
109        }
110
111        if (tw->tw_substate == TCP_FIN_WAIT2) {
112                /* Just repeat all the checks of tcp_rcv_state_process() */
113
114                /* Out of window, send ACK */
115                if (paws_reject ||
116                    !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
117                                   tcptw->tw_rcv_nxt,
118                                   tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
119                        return TCP_TW_ACK;
120
121                if (th->rst)
122                        goto kill;
123
124                if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
125                        goto kill_with_rst;
126
127                /* Dup ACK? */
128                if (!th->ack ||
129                    !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
130                    TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
131                        inet_twsk_put(tw);
132                        return TCP_TW_SUCCESS;
133                }
134
135                /* New data or FIN. If new data arrive after half-duplex close,
136                 * reset.
137                 */
138                if (!th->fin ||
139                    TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) {
140kill_with_rst:
141                        inet_twsk_deschedule(tw, &tcp_death_row);
142                        inet_twsk_put(tw);
143                        return TCP_TW_RST;
144                }
145
146                /* FIN arrived, enter true time-wait state. */
147                tw->tw_substate   = TCP_TIME_WAIT;
148                tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
149                if (tmp_opt.saw_tstamp) {
150                        tcptw->tw_ts_recent_stamp = get_seconds();
151                        tcptw->tw_ts_recent       = tmp_opt.rcv_tsval;
152                }
153
154                if (tcp_death_row.sysctl_tw_recycle &&
155                    tcptw->tw_ts_recent_stamp &&
156                    tcp_tw_remember_stamp(tw))
157                        inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout,
158                                           TCP_TIMEWAIT_LEN);
159                else
160                        inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
161                                           TCP_TIMEWAIT_LEN);
162                return TCP_TW_ACK;
163        }
164
165        /*
166         *      Now real TIME-WAIT state.
167         *
168         *      RFC 1122:
169         *      "When a connection is [...] on TIME-WAIT state [...]
170         *      [a TCP] MAY accept a new SYN from the remote TCP to
171         *      reopen the connection directly, if it:
172         *
173         *      (1)  assigns its initial sequence number for the new
174         *      connection to be larger than the largest sequence
175         *      number it used on the previous connection incarnation,
176         *      and
177         *
178         *      (2)  returns to TIME-WAIT state if the SYN turns out
179         *      to be an old duplicate".
180         */
181
182        if (!paws_reject &&
183            (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
184             (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
185                /* In window segment, it may be only reset or bare ack. */
186
187                if (th->rst) {
188                        /* This is TIME_WAIT assassination, in two flavors.
189                         * Oh well... nobody has a sufficient solution to this
190                         * protocol bug yet.
191                         */
192                        if (sysctl_tcp_rfc1337 == 0) {
193kill:
194                                inet_twsk_deschedule(tw, &tcp_death_row);
195                                inet_twsk_put(tw);
196                                return TCP_TW_SUCCESS;
197                        }
198                }
199                inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
200                                   TCP_TIMEWAIT_LEN);
201
202                if (tmp_opt.saw_tstamp) {
203                        tcptw->tw_ts_recent       = tmp_opt.rcv_tsval;
204                        tcptw->tw_ts_recent_stamp = get_seconds();
205                }
206
207                inet_twsk_put(tw);
208                return TCP_TW_SUCCESS;
209        }
210
211        /* Out of window segment.
212
213           All the segments are ACKed immediately.
214
215           The only exception is new SYN. We accept it, if it is
216           not old duplicate and we are not in danger to be killed
217           by delayed old duplicates. RFC check is that it has
218           newer sequence number works at rates <40Mbit/sec.
219           However, if paws works, it is reliable AND even more,
220           we even may relax silly seq space cutoff.
221
222           RED-PEN: we violate main RFC requirement, if this SYN will appear
223           old duplicate (i.e. we receive RST in reply to SYN-ACK),
224           we must return socket to time-wait state. It is not good,
225           but not fatal yet.
226         */
227
228        if (th->syn && !th->rst && !th->ack && !paws_reject &&
229            (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
230             (tmp_opt.saw_tstamp &&
231              (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
232                u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
233                if (isn == 0)
234                        isn++;
235                TCP_SKB_CB(skb)->tcp_tw_isn = isn;
236                return TCP_TW_SYN;
237        }
238
239        if (paws_reject)
240                NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
241
242        if (!th->rst) {
243                /* In this case we must reset the TIMEWAIT timer.
244                 *
245                 * If it is ACKless SYN it may be both old duplicate
246                 * and new good SYN with random sequence number <rcv_nxt.
247                 * Do not reschedule in the last case.
248                 */
249                if (paws_reject || th->ack)
250                        inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
251                                           TCP_TIMEWAIT_LEN);
252
253                /* Send ACK. Note, we do not put the bucket,
254                 * it will be released by caller.
255                 */
256                return TCP_TW_ACK;
257        }
258        inet_twsk_put(tw);
259        return TCP_TW_SUCCESS;
260}
261EXPORT_SYMBOL(tcp_timewait_state_process);
262
263/*
264 * Move a socket to time-wait or dead fin-wait-2 state.
265 */
266void tcp_time_wait(struct sock *sk, int state, int timeo)
267{
268        struct inet_timewait_sock *tw = NULL;
269        const struct inet_connection_sock *icsk = inet_csk(sk);
270        const struct tcp_sock *tp = tcp_sk(sk);
271        bool recycle_ok = false;
272
273        if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
274                recycle_ok = tcp_remember_stamp(sk);
275
276        if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
277                tw = inet_twsk_alloc(sk, state);
278
279        if (tw != NULL) {
280                struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
281                const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
282                struct inet_sock *inet = inet_sk(sk);
283
284                tw->tw_transparent      = inet->transparent;
285                tw->tw_rcv_wscale       = tp->rx_opt.rcv_wscale;
286                tcptw->tw_rcv_nxt       = tp->rcv_nxt;
287                tcptw->tw_snd_nxt       = tp->snd_nxt;
288                tcptw->tw_rcv_wnd       = tcp_receive_window(tp);
289                tcptw->tw_ts_recent     = tp->rx_opt.ts_recent;
290                tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
291                tcptw->tw_ts_offset     = tp->tsoffset;
292
293#if IS_ENABLED(CONFIG_IPV6)
294                if (tw->tw_family == PF_INET6) {
295                        struct ipv6_pinfo *np = inet6_sk(sk);
296
297                        tw->tw_v6_daddr = sk->sk_v6_daddr;
298                        tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
299                        tw->tw_tclass = np->tclass;
300                        tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK);
301                        tw->tw_ipv6only = sk->sk_ipv6only;
302                }
303#endif
304
305#ifdef CONFIG_TCP_MD5SIG
306                /*
307                 * The timewait bucket does not have the key DB from the
308                 * sock structure. We just make a quick copy of the
309                 * md5 key being used (if indeed we are using one)
310                 * so the timewait ack generating code has the key.
311                 */
312                do {
313                        struct tcp_md5sig_key *key;
314                        tcptw->tw_md5_key = NULL;
315                        key = tp->af_specific->md5_lookup(sk, sk);
316                        if (key != NULL) {
317                                tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
318                                if (tcptw->tw_md5_key && !tcp_alloc_md5sig_pool())
319                                        BUG();
320                        }
321                } while (0);
322#endif
323
324                /* Linkage updates. */
325                __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
326
327                /* Get the TIME_WAIT timeout firing. */
328                if (timeo < rto)
329                        timeo = rto;
330
331                if (recycle_ok) {
332                        tw->tw_timeout = rto;
333                } else {
334                        tw->tw_timeout = TCP_TIMEWAIT_LEN;
335                        if (state == TCP_TIME_WAIT)
336                                timeo = TCP_TIMEWAIT_LEN;
337                }
338
339                inet_twsk_schedule(tw, &tcp_death_row, timeo,
340                                   TCP_TIMEWAIT_LEN);
341                inet_twsk_put(tw);
342        } else {
343                /* Sorry, if we're out of memory, just CLOSE this
344                 * socket up.  We've got bigger problems than
345                 * non-graceful socket closings.
346                 */
347                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
348        }
349
350        tcp_update_metrics(sk);
351        tcp_done(sk);
352}
353
354void tcp_twsk_destructor(struct sock *sk)
355{
356#ifdef CONFIG_TCP_MD5SIG
357        struct tcp_timewait_sock *twsk = tcp_twsk(sk);
358
359        if (twsk->tw_md5_key)
360                kfree_rcu(twsk->tw_md5_key, rcu);
361#endif
362}
363EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
364
365void tcp_openreq_init_rwin(struct request_sock *req,
366                           struct sock *sk, struct dst_entry *dst)
367{
368        struct inet_request_sock *ireq = inet_rsk(req);
369        struct tcp_sock *tp = tcp_sk(sk);
370        __u8 rcv_wscale;
371        int mss = dst_metric_advmss(dst);
372
373        if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
374                mss = tp->rx_opt.user_mss;
375
376        /* Set this up on the first call only */
377        req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
378
379        /* limit the window selection if the user enforce a smaller rx buffer */
380        if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
381            (req->window_clamp > tcp_full_space(sk) || req->window_clamp == 0))
382                req->window_clamp = tcp_full_space(sk);
383
384        /* tcp_full_space because it is guaranteed to be the first packet */
385        tcp_select_initial_window(tcp_full_space(sk),
386                mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
387                &req->rcv_wnd,
388                &req->window_clamp,
389                ireq->wscale_ok,
390                &rcv_wscale,
391                dst_metric(dst, RTAX_INITRWND));
392        ireq->rcv_wscale = rcv_wscale;
393}
394EXPORT_SYMBOL(tcp_openreq_init_rwin);
395
396static void tcp_ecn_openreq_child(struct tcp_sock *tp,
397                                  const struct request_sock *req)
398{
399        tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
400}
401
402/* This is not only more efficient than what we used to do, it eliminates
403 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
404 *
405 * Actually, we could lots of memory writes here. tp of listening
406 * socket contains all necessary default parameters.
407 */
408struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
409{
410        struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
411
412        if (newsk != NULL) {
413                const struct inet_request_sock *ireq = inet_rsk(req);
414                struct tcp_request_sock *treq = tcp_rsk(req);
415                struct inet_connection_sock *newicsk = inet_csk(newsk);
416                struct tcp_sock *newtp = tcp_sk(newsk);
417
418                /* Now setup tcp_sock */
419                newtp->pred_flags = 0;
420
421                newtp->rcv_wup = newtp->copied_seq =
422                newtp->rcv_nxt = treq->rcv_isn + 1;
423
424                newtp->snd_sml = newtp->snd_una =
425                newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
426
427                tcp_prequeue_init(newtp);
428                INIT_LIST_HEAD(&newtp->tsq_node);
429
430                tcp_init_wl(newtp, treq->rcv_isn);
431
432                newtp->srtt_us = 0;
433                newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
434                newicsk->icsk_rto = TCP_TIMEOUT_INIT;
435                newicsk->icsk_ack.lrcvtime = tcp_time_stamp;
436
437                newtp->packets_out = 0;
438                newtp->retrans_out = 0;
439                newtp->sacked_out = 0;
440                newtp->fackets_out = 0;
441                newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
442                tcp_enable_early_retrans(newtp);
443                newtp->tlp_high_seq = 0;
444                newtp->lsndtime = treq->snt_synack;
445                newtp->total_retrans = req->num_retrans;
446
447                /* So many TCP implementations out there (incorrectly) count the
448                 * initial SYN frame in their delayed-ACK and congestion control
449                 * algorithms that we must have the following bandaid to talk
450                 * efficiently to them.  -DaveM
451                 */
452                newtp->snd_cwnd = TCP_INIT_CWND;
453                newtp->snd_cwnd_cnt = 0;
454
455                if (!newicsk->icsk_ca_setsockopt ||
456                    !try_module_get(newicsk->icsk_ca_ops->owner))
457                        tcp_assign_congestion_control(newsk);
458
459                tcp_set_ca_state(newsk, TCP_CA_Open);
460                tcp_init_xmit_timers(newsk);
461                __skb_queue_head_init(&newtp->out_of_order_queue);
462                newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
463
464                newtp->rx_opt.saw_tstamp = 0;
465
466                newtp->rx_opt.dsack = 0;
467                newtp->rx_opt.num_sacks = 0;
468
469                newtp->urg_data = 0;
470
471                if (sock_flag(newsk, SOCK_KEEPOPEN))
472                        inet_csk_reset_keepalive_timer(newsk,
473                                                       keepalive_time_when(newtp));
474
475                newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
476                if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
477                        if (sysctl_tcp_fack)
478                                tcp_enable_fack(newtp);
479                }
480                newtp->window_clamp = req->window_clamp;
481                newtp->rcv_ssthresh = req->rcv_wnd;
482                newtp->rcv_wnd = req->rcv_wnd;
483                newtp->rx_opt.wscale_ok = ireq->wscale_ok;
484                if (newtp->rx_opt.wscale_ok) {
485                        newtp->rx_opt.snd_wscale = ireq->snd_wscale;
486                        newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
487                } else {
488                        newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
489                        newtp->window_clamp = min(newtp->window_clamp, 65535U);
490                }
491                newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
492                                  newtp->rx_opt.snd_wscale);
493                newtp->max_window = newtp->snd_wnd;
494
495                if (newtp->rx_opt.tstamp_ok) {
496                        newtp->rx_opt.ts_recent = req->ts_recent;
497                        newtp->rx_opt.ts_recent_stamp = get_seconds();
498                        newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
499                } else {
500                        newtp->rx_opt.ts_recent_stamp = 0;
501                        newtp->tcp_header_len = sizeof(struct tcphdr);
502                }
503                newtp->tsoffset = 0;
504#ifdef CONFIG_TCP_MD5SIG
505                newtp->md5sig_info = NULL;      /*XXX*/
506                if (newtp->af_specific->md5_lookup(sk, newsk))
507                        newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
508#endif
509                if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
510                        newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
511                newtp->rx_opt.mss_clamp = req->mss;
512                tcp_ecn_openreq_child(newtp, req);
513                newtp->fastopen_rsk = NULL;
514                newtp->syn_data_acked = 0;
515
516                TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
517        }
518        return newsk;
519}
520EXPORT_SYMBOL(tcp_create_openreq_child);
521
522/*
523 * Process an incoming packet for SYN_RECV sockets represented as a
524 * request_sock. Normally sk is the listener socket but for TFO it
525 * points to the child socket.
526 *
527 * XXX (TFO) - The current impl contains a special check for ack
528 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
529 *
530 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
531 */
532
533struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
534                           struct request_sock *req,
535                           struct request_sock **prev,
536                           bool fastopen)
537{
538        struct tcp_options_received tmp_opt;
539        struct sock *child;
540        const struct tcphdr *th = tcp_hdr(skb);
541        __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
542        bool paws_reject = false;
543
544        BUG_ON(fastopen == (sk->sk_state == TCP_LISTEN));
545
546        tmp_opt.saw_tstamp = 0;
547        if (th->doff > (sizeof(struct tcphdr)>>2)) {
548                tcp_parse_options(skb, &tmp_opt, 0, NULL);
549
550                if (tmp_opt.saw_tstamp) {
551                        tmp_opt.ts_recent = req->ts_recent;
552                        /* We do not store true stamp, but it is not required,
553                         * it can be estimated (approximately)
554                         * from another data.
555                         */
556                        tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
557                        paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
558                }
559        }
560
561        /* Check for pure retransmitted SYN. */
562        if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
563            flg == TCP_FLAG_SYN &&
564            !paws_reject) {
565                /*
566                 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
567                 * this case on figure 6 and figure 8, but formal
568                 * protocol description says NOTHING.
569                 * To be more exact, it says that we should send ACK,
570                 * because this segment (at least, if it has no data)
571                 * is out of window.
572                 *
573                 *  CONCLUSION: RFC793 (even with RFC1122) DOES NOT
574                 *  describe SYN-RECV state. All the description
575                 *  is wrong, we cannot believe to it and should
576                 *  rely only on common sense and implementation
577                 *  experience.
578                 *
579                 * Enforce "SYN-ACK" according to figure 8, figure 6
580                 * of RFC793, fixed by RFC1122.
581                 *
582                 * Note that even if there is new data in the SYN packet
583                 * they will be thrown away too.
584                 *
585                 * Reset timer after retransmitting SYNACK, similar to
586                 * the idea of fast retransmit in recovery.
587                 */
588                if (!inet_rtx_syn_ack(sk, req))
589                        req->expires = min(TCP_TIMEOUT_INIT << req->num_timeout,
590                                           TCP_RTO_MAX) + jiffies;
591                return NULL;
592        }
593
594        /* Further reproduces section "SEGMENT ARRIVES"
595           for state SYN-RECEIVED of RFC793.
596           It is broken, however, it does not work only
597           when SYNs are crossed.
598
599           You would think that SYN crossing is impossible here, since
600           we should have a SYN_SENT socket (from connect()) on our end,
601           but this is not true if the crossed SYNs were sent to both
602           ends by a malicious third party.  We must defend against this,
603           and to do that we first verify the ACK (as per RFC793, page
604           36) and reset if it is invalid.  Is this a true full defense?
605           To convince ourselves, let us consider a way in which the ACK
606           test can still pass in this 'malicious crossed SYNs' case.
607           Malicious sender sends identical SYNs (and thus identical sequence
608           numbers) to both A and B:
609
610                A: gets SYN, seq=7
611                B: gets SYN, seq=7
612
613           By our good fortune, both A and B select the same initial
614           send sequence number of seven :-)
615
616                A: sends SYN|ACK, seq=7, ack_seq=8
617                B: sends SYN|ACK, seq=7, ack_seq=8
618
619           So we are now A eating this SYN|ACK, ACK test passes.  So
620           does sequence test, SYN is truncated, and thus we consider
621           it a bare ACK.
622
623           If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
624           bare ACK.  Otherwise, we create an established connection.  Both
625           ends (listening sockets) accept the new incoming connection and try
626           to talk to each other. 8-)
627
628           Note: This case is both harmless, and rare.  Possibility is about the
629           same as us discovering intelligent life on another plant tomorrow.
630
631           But generally, we should (RFC lies!) to accept ACK
632           from SYNACK both here and in tcp_rcv_state_process().
633           tcp_rcv_state_process() does not, hence, we do not too.
634
635           Note that the case is absolutely generic:
636           we cannot optimize anything here without
637           violating protocol. All the checks must be made
638           before attempt to create socket.
639         */
640
641        /* RFC793 page 36: "If the connection is in any non-synchronized state ...
642         *                  and the incoming segment acknowledges something not yet
643         *                  sent (the segment carries an unacceptable ACK) ...
644         *                  a reset is sent."
645         *
646         * Invalid ACK: reset will be sent by listening socket.
647         * Note that the ACK validity check for a Fast Open socket is done
648         * elsewhere and is checked directly against the child socket rather
649         * than req because user data may have been sent out.
650         */
651        if ((flg & TCP_FLAG_ACK) && !fastopen &&
652            (TCP_SKB_CB(skb)->ack_seq !=
653             tcp_rsk(req)->snt_isn + 1))
654                return sk;
655
656        /* Also, it would be not so bad idea to check rcv_tsecr, which
657         * is essentially ACK extension and too early or too late values
658         * should cause reset in unsynchronized states.
659         */
660
661        /* RFC793: "first check sequence number". */
662
663        if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
664                                          tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rcv_wnd)) {
665                /* Out of window: send ACK and drop. */
666                if (!(flg & TCP_FLAG_RST))
667                        req->rsk_ops->send_ack(sk, skb, req);
668                if (paws_reject)
669                        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
670                return NULL;
671        }
672
673        /* In sequence, PAWS is OK. */
674
675        if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
676                req->ts_recent = tmp_opt.rcv_tsval;
677
678        if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
679                /* Truncate SYN, it is out of window starting
680                   at tcp_rsk(req)->rcv_isn + 1. */
681                flg &= ~TCP_FLAG_SYN;
682        }
683
684        /* RFC793: "second check the RST bit" and
685         *         "fourth, check the SYN bit"
686         */
687        if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
688                TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
689                goto embryonic_reset;
690        }
691
692        /* ACK sequence verified above, just make sure ACK is
693         * set.  If ACK not set, just silently drop the packet.
694         *
695         * XXX (TFO) - if we ever allow "data after SYN", the
696         * following check needs to be removed.
697         */
698        if (!(flg & TCP_FLAG_ACK))
699                return NULL;
700
701        /* For Fast Open no more processing is needed (sk is the
702         * child socket).
703         */
704        if (fastopen)
705                return sk;
706
707        /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
708        if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
709            TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
710                inet_rsk(req)->acked = 1;
711                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
712                return NULL;
713        }
714
715        /* OK, ACK is valid, create big socket and
716         * feed this segment to it. It will repeat all
717         * the tests. THIS SEGMENT MUST MOVE SOCKET TO
718         * ESTABLISHED STATE. If it will be dropped after
719         * socket is created, wait for troubles.
720         */
721        child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
722        if (child == NULL)
723                goto listen_overflow;
724
725        inet_csk_reqsk_queue_unlink(sk, req, prev);
726        inet_csk_reqsk_queue_removed(sk, req);
727
728        inet_csk_reqsk_queue_add(sk, req, child);
729        return child;
730
731listen_overflow:
732        if (!sysctl_tcp_abort_on_overflow) {
733                inet_rsk(req)->acked = 1;
734                return NULL;
735        }
736
737embryonic_reset:
738        if (!(flg & TCP_FLAG_RST)) {
739                /* Received a bad SYN pkt - for TFO We try not to reset
740                 * the local connection unless it's really necessary to
741                 * avoid becoming vulnerable to outside attack aiming at
742                 * resetting legit local connections.
743                 */
744                req->rsk_ops->send_reset(sk, skb);
745        } else if (fastopen) { /* received a valid RST pkt */
746                reqsk_fastopen_remove(sk, req, true);
747                tcp_reset(sk);
748        }
749        if (!fastopen) {
750                inet_csk_reqsk_queue_drop(sk, req, prev);
751                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
752        }
753        return NULL;
754}
755EXPORT_SYMBOL(tcp_check_req);
756
757/*
758 * Queue segment on the new socket if the new socket is active,
759 * otherwise we just shortcircuit this and continue with
760 * the new socket.
761 *
762 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
763 * when entering. But other states are possible due to a race condition
764 * where after __inet_lookup_established() fails but before the listener
765 * locked is obtained, other packets cause the same connection to
766 * be created.
767 */
768
769int tcp_child_process(struct sock *parent, struct sock *child,
770                      struct sk_buff *skb)
771{
772        int ret = 0;
773        int state = child->sk_state;
774
775        if (!sock_owned_by_user(child)) {
776                ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
777                                            skb->len);
778                /* Wakeup parent, send SIGIO */
779                if (state == TCP_SYN_RECV && child->sk_state != state)
780                        parent->sk_data_ready(parent);
781        } else {
782                /* Alas, it is possible again, because we do lookup
783                 * in main socket hash table and lock on listening
784                 * socket does not protect us more.
785                 */
786                __sk_add_backlog(child, skb);
787        }
788
789        bh_unlock_sock(child);
790        sock_put(child);
791        return ret;
792}
793EXPORT_SYMBOL(tcp_child_process);
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