Branch data Line data Source code
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 : :
30 : : int sysctl_tcp_syncookies __read_mostly = 1;
31 : : EXPORT_SYMBOL(sysctl_tcp_syncookies);
32 : :
33 : : int sysctl_tcp_abort_on_overflow __read_mostly;
34 : :
35 : : struct 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 : : };
50 : : EXPORT_SYMBOL_GPL(tcp_death_row);
51 : :
52 : : static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
53 : : {
54 [ - + ][ # # ]: 28 : if (seq == s_win)
55 : : return true;
56 [ # # ][ # # ]: 0 : if (after(end_seq, s_win) && before(seq, e_win))
[ # # ][ # # ]
57 : : return true;
58 : 0 : 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 : : */
91 : : enum tcp_tw_status
92 : 0 : tcp_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 : 0 : tmp_opt.saw_tstamp = 0;
100 [ # # ][ # # ]: 0 : if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
101 : 0 : tcp_parse_options(skb, &tmp_opt, 0, NULL);
102 : :
103 [ # # ]: 0 : if (tmp_opt.saw_tstamp) {
104 : 0 : tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
105 : 0 : tmp_opt.ts_recent = tcptw->tw_ts_recent;
106 : 0 : tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
107 : 0 : paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
108 : : }
109 : : }
110 : :
111 [ # # ]: 0 : 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 [ # # ][ # # ]: 0 : if (paws_reject ||
116 : 0 : !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
117 : : tcptw->tw_rcv_nxt,
118 : 0 : tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
119 : : return TCP_TW_ACK;
120 : :
121 [ # # ]: 0 : if (th->rst)
122 : : goto kill;
123 : :
124 [ # # ][ # # ]: 0 : if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
125 : : goto kill_with_rst;
126 : :
127 : : /* Dup ACK? */
128 [ # # ][ # # ]: 0 : if (!th->ack ||
129 [ # # ]: 0 : !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
130 : : TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
131 : 0 : inet_twsk_put(tw);
132 : 0 : return TCP_TW_SUCCESS;
133 : : }
134 : :
135 : : /* New data or FIN. If new data arrive after half-duplex close,
136 : : * reset.
137 : : */
138 [ # # ][ # # ]: 0 : if (!th->fin ||
139 : 0 : TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) {
140 : : kill_with_rst:
141 : 0 : inet_twsk_deschedule(tw, &tcp_death_row);
142 : 0 : inet_twsk_put(tw);
143 : 0 : return TCP_TW_RST;
144 : : }
145 : :
146 : : /* FIN arrived, enter true time-wait state. */
147 : 0 : tw->tw_substate = TCP_TIME_WAIT;
148 : 0 : tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
149 [ # # ]: 0 : if (tmp_opt.saw_tstamp) {
150 : 0 : tcptw->tw_ts_recent_stamp = get_seconds();
151 : 0 : tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
152 : : }
153 : :
154 [ # # ][ # # ]: 0 : if (tcp_death_row.sysctl_tw_recycle &&
155 [ # # ]: 0 : tcptw->tw_ts_recent_stamp &&
156 : 0 : tcp_tw_remember_stamp(tw))
157 : 0 : inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout,
158 : : TCP_TIMEWAIT_LEN);
159 : : else
160 : 0 : 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 [ # # ][ # # ]: 0 : if (!paws_reject &&
183 [ # # ]: 0 : (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
184 [ # # ]: 0 : (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 [ # # ]: 0 : 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 [ # # ]: 0 : if (sysctl_tcp_rfc1337 == 0) {
193 : : kill:
194 : 0 : inet_twsk_deschedule(tw, &tcp_death_row);
195 : 0 : inet_twsk_put(tw);
196 : 0 : return TCP_TW_SUCCESS;
197 : : }
198 : : }
199 : 0 : inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
200 : : TCP_TIMEWAIT_LEN);
201 : :
202 [ # # ]: 0 : if (tmp_opt.saw_tstamp) {
203 : 0 : tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
204 : 0 : tcptw->tw_ts_recent_stamp = get_seconds();
205 : : }
206 : :
207 : 0 : inet_twsk_put(tw);
208 : 0 : 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 [ # # ][ # # ]: 0 : if (th->syn && !th->rst && !th->ack && !paws_reject &&
[ # # ]
229 [ # # ]: 0 : (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
230 [ # # ]: 0 : (tmp_opt.saw_tstamp &&
231 : 0 : (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
232 : 0 : u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
233 [ # # ]: 0 : if (isn == 0)
234 : 0 : isn++;
235 : 0 : TCP_SKB_CB(skb)->when = isn;
236 : 0 : return TCP_TW_SYN;
237 : : }
238 : :
239 [ # # ]: 0 : if (paws_reject)
240 : 0 : NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
241 : :
242 [ # # ]: 0 : 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 [ # # ][ # # ]: 0 : if (paws_reject || th->ack)
250 : 0 : 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 : 0 : inet_twsk_put(tw);
259 : 0 : return TCP_TW_SUCCESS;
260 : : }
261 : : EXPORT_SYMBOL(tcp_timewait_state_process);
262 : :
263 : : /*
264 : : * Move a socket to time-wait or dead fin-wait-2 state.
265 : : */
266 : 0 : void 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 [ - + ][ # # ]: 16 : if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
274 : 0 : recycle_ok = tcp_remember_stamp(sk);
275 : :
276 [ + - ]: 32 : if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
277 : 16 : tw = inet_twsk_alloc(sk, state);
278 : :
279 [ + - ]: 16 : if (tw != NULL) {
280 : : struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
281 : 16 : const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
282 : : struct inet_sock *inet = inet_sk(sk);
283 : :
284 : 16 : tw->tw_transparent = inet->transparent;
285 : 16 : tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
286 : 16 : tcptw->tw_rcv_nxt = tp->rcv_nxt;
287 : 16 : tcptw->tw_snd_nxt = tp->snd_nxt;
288 : 16 : tcptw->tw_rcv_wnd = tcp_receive_window(tp);
289 : 16 : tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
290 : 16 : tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
291 : 16 : tcptw->tw_ts_offset = tp->tsoffset;
292 : :
293 : : #if IS_ENABLED(CONFIG_IPV6)
294 [ - + ]: 16 : if (tw->tw_family == PF_INET6) {
295 : : struct ipv6_pinfo *np = inet6_sk(sk);
296 : :
297 : 0 : tw->tw_v6_daddr = sk->sk_v6_daddr;
298 : 0 : tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
299 : 0 : tw->tw_tclass = np->tclass;
300 : 0 : tw->tw_ipv6only = np->ipv6only;
301 : : }
302 : : #endif
303 : :
304 : : #ifdef CONFIG_TCP_MD5SIG
305 : : /*
306 : : * The timewait bucket does not have the key DB from the
307 : : * sock structure. We just make a quick copy of the
308 : : * md5 key being used (if indeed we are using one)
309 : : * so the timewait ack generating code has the key.
310 : : */
311 : : do {
312 : : struct tcp_md5sig_key *key;
313 : : tcptw->tw_md5_key = NULL;
314 : : key = tp->af_specific->md5_lookup(sk, sk);
315 : : if (key != NULL) {
316 : : tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
317 : : if (tcptw->tw_md5_key && !tcp_alloc_md5sig_pool())
318 : : BUG();
319 : : }
320 : : } while (0);
321 : : #endif
322 : :
323 : : /* Linkage updates. */
324 : 16 : __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
325 : :
326 : : /* Get the TIME_WAIT timeout firing. */
327 [ + - ]: 16 : if (timeo < rto)
328 : : timeo = rto;
329 : :
330 [ - + ]: 16 : if (recycle_ok) {
331 : 0 : tw->tw_timeout = rto;
332 : : } else {
333 : 16 : tw->tw_timeout = TCP_TIMEWAIT_LEN;
334 [ + - ]: 16 : if (state == TCP_TIME_WAIT)
335 : : timeo = TCP_TIMEWAIT_LEN;
336 : : }
337 : :
338 : 16 : inet_twsk_schedule(tw, &tcp_death_row, timeo,
339 : : TCP_TIMEWAIT_LEN);
340 : 16 : inet_twsk_put(tw);
341 : : } else {
342 : : /* Sorry, if we're out of memory, just CLOSE this
343 : : * socket up. We've got bigger problems than
344 : : * non-graceful socket closings.
345 : : */
346 : 0 : NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
347 : : }
348 : :
349 : 16 : tcp_update_metrics(sk);
350 : 16 : tcp_done(sk);
351 : 16 : }
352 : :
353 : 0 : void tcp_twsk_destructor(struct sock *sk)
354 : : {
355 : : #ifdef CONFIG_TCP_MD5SIG
356 : : struct tcp_timewait_sock *twsk = tcp_twsk(sk);
357 : :
358 : : if (twsk->tw_md5_key)
359 : : kfree_rcu(twsk->tw_md5_key, rcu);
360 : : #endif
361 : 16 : }
362 : : EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
363 : :
364 : : static inline void TCP_ECN_openreq_child(struct tcp_sock *tp,
365 : : struct request_sock *req)
366 : : {
367 : 28 : tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
368 : : }
369 : :
370 : : /* This is not only more efficient than what we used to do, it eliminates
371 : : * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
372 : : *
373 : : * Actually, we could lots of memory writes here. tp of listening
374 : : * socket contains all necessary default parameters.
375 : : */
376 : 0 : struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
377 : : {
378 : 28 : struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
379 : :
380 [ + - ]: 28 : if (newsk != NULL) {
381 : : const struct inet_request_sock *ireq = inet_rsk(req);
382 : : struct tcp_request_sock *treq = tcp_rsk(req);
383 : : struct inet_connection_sock *newicsk = inet_csk(newsk);
384 : : struct tcp_sock *newtp = tcp_sk(newsk);
385 : :
386 : : /* Now setup tcp_sock */
387 : 28 : newtp->pred_flags = 0;
388 : :
389 : 28 : newtp->rcv_wup = newtp->copied_seq =
390 : 28 : newtp->rcv_nxt = treq->rcv_isn + 1;
391 : :
392 : 28 : newtp->snd_sml = newtp->snd_una =
393 : 28 : newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
394 : :
395 : : tcp_prequeue_init(newtp);
396 : 28 : INIT_LIST_HEAD(&newtp->tsq_node);
397 : :
398 : 28 : tcp_init_wl(newtp, treq->rcv_isn);
399 : :
400 : 28 : newtp->srtt = 0;
401 : 28 : newtp->mdev = TCP_TIMEOUT_INIT;
402 : 28 : newicsk->icsk_rto = TCP_TIMEOUT_INIT;
403 : :
404 : 28 : newtp->packets_out = 0;
405 : 28 : newtp->retrans_out = 0;
406 : 28 : newtp->sacked_out = 0;
407 : 28 : newtp->fackets_out = 0;
408 : 28 : newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
409 : : tcp_enable_early_retrans(newtp);
410 : 28 : newtp->tlp_high_seq = 0;
411 : 28 : newtp->lsndtime = treq->snt_synack;
412 : 28 : newtp->total_retrans = req->num_retrans;
413 : :
414 : : /* So many TCP implementations out there (incorrectly) count the
415 : : * initial SYN frame in their delayed-ACK and congestion control
416 : : * algorithms that we must have the following bandaid to talk
417 : : * efficiently to them. -DaveM
418 : : */
419 : 28 : newtp->snd_cwnd = TCP_INIT_CWND;
420 : 28 : newtp->snd_cwnd_cnt = 0;
421 : :
422 [ - + # # ]: 28 : if (newicsk->icsk_ca_ops != &tcp_init_congestion_ops &&
423 : 0 : !try_module_get(newicsk->icsk_ca_ops->owner))
424 : 0 : newicsk->icsk_ca_ops = &tcp_init_congestion_ops;
425 : :
426 : : tcp_set_ca_state(newsk, TCP_CA_Open);
427 : 28 : tcp_init_xmit_timers(newsk);
428 : 28 : skb_queue_head_init(&newtp->out_of_order_queue);
429 : 28 : newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
430 : :
431 : 28 : newtp->rx_opt.saw_tstamp = 0;
432 : :
433 : 28 : newtp->rx_opt.dsack = 0;
434 : 28 : newtp->rx_opt.num_sacks = 0;
435 : :
436 : 28 : newtp->urg_data = 0;
437 : :
438 [ - + ]: 28 : if (sock_flag(newsk, SOCK_KEEPOPEN))
439 : 0 : inet_csk_reset_keepalive_timer(newsk,
440 : : keepalive_time_when(newtp));
441 : :
442 : 28 : newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
443 [ + - ]: 56 : if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
444 [ + - ]: 28 : if (sysctl_tcp_fack)
445 : : tcp_enable_fack(newtp);
446 : : }
447 : 28 : newtp->window_clamp = req->window_clamp;
448 : 28 : newtp->rcv_ssthresh = req->rcv_wnd;
449 : 28 : newtp->rcv_wnd = req->rcv_wnd;
450 : 28 : newtp->rx_opt.wscale_ok = ireq->wscale_ok;
451 [ + - ]: 28 : if (newtp->rx_opt.wscale_ok) {
452 : 28 : newtp->rx_opt.snd_wscale = ireq->snd_wscale;
453 : 28 : newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
454 : : } else {
455 : 0 : newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
456 : 0 : newtp->window_clamp = min(newtp->window_clamp, 65535U);
457 : : }
458 : 84 : newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) <<
459 : 28 : newtp->rx_opt.snd_wscale);
460 : 28 : newtp->max_window = newtp->snd_wnd;
461 : :
462 [ + - ]: 28 : if (newtp->rx_opt.tstamp_ok) {
463 : 28 : newtp->rx_opt.ts_recent = req->ts_recent;
464 : 28 : newtp->rx_opt.ts_recent_stamp = get_seconds();
465 : 28 : newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
466 : : } else {
467 : 0 : newtp->rx_opt.ts_recent_stamp = 0;
468 : 0 : newtp->tcp_header_len = sizeof(struct tcphdr);
469 : : }
470 : 28 : newtp->tsoffset = 0;
471 : : #ifdef CONFIG_TCP_MD5SIG
472 : : newtp->md5sig_info = NULL; /*XXX*/
473 : : if (newtp->af_specific->md5_lookup(sk, newsk))
474 : : newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
475 : : #endif
476 [ - + ]: 28 : if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
477 : 0 : newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
478 : 28 : newtp->rx_opt.mss_clamp = req->mss;
479 : : TCP_ECN_openreq_child(newtp, req);
480 : 28 : newtp->fastopen_rsk = NULL;
481 : 28 : newtp->syn_data_acked = 0;
482 : :
483 : 28 : TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
484 : : }
485 : 28 : return newsk;
486 : : }
487 : : EXPORT_SYMBOL(tcp_create_openreq_child);
488 : :
489 : : /*
490 : : * Process an incoming packet for SYN_RECV sockets represented as a
491 : : * request_sock. Normally sk is the listener socket but for TFO it
492 : : * points to the child socket.
493 : : *
494 : : * XXX (TFO) - The current impl contains a special check for ack
495 : : * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
496 : : *
497 : : * We don't need to initialize tmp_opt.sack_ok as we don't use the results
498 : : */
499 : :
500 : 0 : struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
501 : : struct request_sock *req,
502 : : struct request_sock **prev,
503 : : bool fastopen)
504 : : {
505 : : struct tcp_options_received tmp_opt;
506 : : struct sock *child;
507 : : const struct tcphdr *th = tcp_hdr(skb);
508 : 28 : __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
509 : : bool paws_reject = false;
510 : :
511 [ - + ]: 28 : BUG_ON(fastopen == (sk->sk_state == TCP_LISTEN));
512 : :
513 : 28 : tmp_opt.saw_tstamp = 0;
514 [ + - ]: 28 : if (th->doff > (sizeof(struct tcphdr)>>2)) {
515 : 28 : tcp_parse_options(skb, &tmp_opt, 0, NULL);
516 : :
517 [ + - ]: 28 : if (tmp_opt.saw_tstamp) {
518 : 28 : tmp_opt.ts_recent = req->ts_recent;
519 : : /* We do not store true stamp, but it is not required,
520 : : * it can be estimated (approximately)
521 : : * from another data.
522 : : */
523 : 28 : tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
524 : 28 : paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
525 : : }
526 : : }
527 : :
528 : : /* Check for pure retransmitted SYN. */
529 [ - + ]: 28 : if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
530 [ # # ]: 0 : flg == TCP_FLAG_SYN &&
531 : 0 : !paws_reject) {
532 : : /*
533 : : * RFC793 draws (Incorrectly! It was fixed in RFC1122)
534 : : * this case on figure 6 and figure 8, but formal
535 : : * protocol description says NOTHING.
536 : : * To be more exact, it says that we should send ACK,
537 : : * because this segment (at least, if it has no data)
538 : : * is out of window.
539 : : *
540 : : * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
541 : : * describe SYN-RECV state. All the description
542 : : * is wrong, we cannot believe to it and should
543 : : * rely only on common sense and implementation
544 : : * experience.
545 : : *
546 : : * Enforce "SYN-ACK" according to figure 8, figure 6
547 : : * of RFC793, fixed by RFC1122.
548 : : *
549 : : * Note that even if there is new data in the SYN packet
550 : : * they will be thrown away too.
551 : : *
552 : : * Reset timer after retransmitting SYNACK, similar to
553 : : * the idea of fast retransmit in recovery.
554 : : */
555 [ # # ]: 0 : if (!inet_rtx_syn_ack(sk, req))
556 : 0 : req->expires = min(TCP_TIMEOUT_INIT << req->num_timeout,
557 : 0 : TCP_RTO_MAX) + jiffies;
558 : : return NULL;
559 : : }
560 : :
561 : : /* Further reproduces section "SEGMENT ARRIVES"
562 : : for state SYN-RECEIVED of RFC793.
563 : : It is broken, however, it does not work only
564 : : when SYNs are crossed.
565 : :
566 : : You would think that SYN crossing is impossible here, since
567 : : we should have a SYN_SENT socket (from connect()) on our end,
568 : : but this is not true if the crossed SYNs were sent to both
569 : : ends by a malicious third party. We must defend against this,
570 : : and to do that we first verify the ACK (as per RFC793, page
571 : : 36) and reset if it is invalid. Is this a true full defense?
572 : : To convince ourselves, let us consider a way in which the ACK
573 : : test can still pass in this 'malicious crossed SYNs' case.
574 : : Malicious sender sends identical SYNs (and thus identical sequence
575 : : numbers) to both A and B:
576 : :
577 : : A: gets SYN, seq=7
578 : : B: gets SYN, seq=7
579 : :
580 : : By our good fortune, both A and B select the same initial
581 : : send sequence number of seven :-)
582 : :
583 : : A: sends SYN|ACK, seq=7, ack_seq=8
584 : : B: sends SYN|ACK, seq=7, ack_seq=8
585 : :
586 : : So we are now A eating this SYN|ACK, ACK test passes. So
587 : : does sequence test, SYN is truncated, and thus we consider
588 : : it a bare ACK.
589 : :
590 : : If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
591 : : bare ACK. Otherwise, we create an established connection. Both
592 : : ends (listening sockets) accept the new incoming connection and try
593 : : to talk to each other. 8-)
594 : :
595 : : Note: This case is both harmless, and rare. Possibility is about the
596 : : same as us discovering intelligent life on another plant tomorrow.
597 : :
598 : : But generally, we should (RFC lies!) to accept ACK
599 : : from SYNACK both here and in tcp_rcv_state_process().
600 : : tcp_rcv_state_process() does not, hence, we do not too.
601 : :
602 : : Note that the case is absolutely generic:
603 : : we cannot optimize anything here without
604 : : violating protocol. All the checks must be made
605 : : before attempt to create socket.
606 : : */
607 : :
608 : : /* RFC793 page 36: "If the connection is in any non-synchronized state ...
609 : : * and the incoming segment acknowledges something not yet
610 : : * sent (the segment carries an unacceptable ACK) ...
611 : : * a reset is sent."
612 : : *
613 : : * Invalid ACK: reset will be sent by listening socket.
614 : : * Note that the ACK validity check for a Fast Open socket is done
615 : : * elsewhere and is checked directly against the child socket rather
616 : : * than req because user data may have been sent out.
617 : : */
618 [ + - ][ + - ]: 28 : if ((flg & TCP_FLAG_ACK) && !fastopen &&
[ + ]
619 : 28 : (TCP_SKB_CB(skb)->ack_seq !=
620 : 28 : tcp_rsk(req)->snt_isn + 1))
621 : : return sk;
622 : :
623 : : /* Also, it would be not so bad idea to check rcv_tsecr, which
624 : : * is essentially ACK extension and too early or too late values
625 : : * should cause reset in unsynchronized states.
626 : : */
627 : :
628 : : /* RFC793: "first check sequence number". */
629 : :
630 [ + - ][ - + ]: 84 : if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
631 : 28 : tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rcv_wnd)) {
632 : : /* Out of window: send ACK and drop. */
633 [ # # ]: 0 : if (!(flg & TCP_FLAG_RST))
634 : 0 : req->rsk_ops->send_ack(sk, skb, req);
635 [ # # ]: 0 : if (paws_reject)
636 : 0 : NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
637 : : return NULL;
638 : : }
639 : :
640 : : /* In sequence, PAWS is OK. */
641 : :
642 [ + - ][ + - ]: 28 : if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
643 : 28 : req->ts_recent = tmp_opt.rcv_tsval;
644 : :
645 [ - + ]: 28 : if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
646 : : /* Truncate SYN, it is out of window starting
647 : : at tcp_rsk(req)->rcv_isn + 1. */
648 : 0 : flg &= ~TCP_FLAG_SYN;
649 : : }
650 : :
651 : : /* RFC793: "second check the RST bit" and
652 : : * "fourth, check the SYN bit"
653 : : */
654 [ - + ]: 28 : if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
655 : 0 : TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
656 : : goto embryonic_reset;
657 : : }
658 : :
659 : : /* ACK sequence verified above, just make sure ACK is
660 : : * set. If ACK not set, just silently drop the packet.
661 : : *
662 : : * XXX (TFO) - if we ever allow "data after SYN", the
663 : : * following check needs to be removed.
664 : : */
665 [ + - ]: 28 : if (!(flg & TCP_FLAG_ACK))
666 : : return NULL;
667 : :
668 : : /* For Fast Open no more processing is needed (sk is the
669 : : * child socket).
670 : : */
671 [ + - ]: 28 : if (fastopen)
672 : : return sk;
673 : :
674 : : /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
675 [ - + ][ # # ]: 28 : if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
676 : 0 : TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
677 : 0 : inet_rsk(req)->acked = 1;
678 : 0 : NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
679 : 0 : return NULL;
680 : : }
681 : :
682 : : /* OK, ACK is valid, create big socket and
683 : : * feed this segment to it. It will repeat all
684 : : * the tests. THIS SEGMENT MUST MOVE SOCKET TO
685 : : * ESTABLISHED STATE. If it will be dropped after
686 : : * socket is created, wait for troubles.
687 : : */
688 : 28 : child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
689 [ + - ]: 28 : if (child == NULL)
690 : : goto listen_overflow;
691 : :
692 : : inet_csk_reqsk_queue_unlink(sk, req, prev);
693 : : inet_csk_reqsk_queue_removed(sk, req);
694 : :
695 : : inet_csk_reqsk_queue_add(sk, req, child);
696 : 28 : return child;
697 : :
698 : : listen_overflow:
699 [ # # ]: 0 : if (!sysctl_tcp_abort_on_overflow) {
700 : 0 : inet_rsk(req)->acked = 1;
701 : 0 : return NULL;
702 : : }
703 : :
704 : : embryonic_reset:
705 [ # # ]: 0 : if (!(flg & TCP_FLAG_RST)) {
706 : : /* Received a bad SYN pkt - for TFO We try not to reset
707 : : * the local connection unless it's really necessary to
708 : : * avoid becoming vulnerable to outside attack aiming at
709 : : * resetting legit local connections.
710 : : */
711 : 0 : req->rsk_ops->send_reset(sk, skb);
712 [ # # ]: 0 : } else if (fastopen) { /* received a valid RST pkt */
713 : 0 : reqsk_fastopen_remove(sk, req, true);
714 : 0 : tcp_reset(sk);
715 : : }
716 [ # # ]: 0 : if (!fastopen) {
717 : : inet_csk_reqsk_queue_drop(sk, req, prev);
718 : 0 : NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
719 : : }
720 : : return NULL;
721 : : }
722 : : EXPORT_SYMBOL(tcp_check_req);
723 : :
724 : : /*
725 : : * Queue segment on the new socket if the new socket is active,
726 : : * otherwise we just shortcircuit this and continue with
727 : : * the new socket.
728 : : *
729 : : * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
730 : : * when entering. But other states are possible due to a race condition
731 : : * where after __inet_lookup_established() fails but before the listener
732 : : * locked is obtained, other packets cause the same connection to
733 : : * be created.
734 : : */
735 : :
736 : 0 : int tcp_child_process(struct sock *parent, struct sock *child,
737 : : struct sk_buff *skb)
738 : : {
739 : : int ret = 0;
740 : 28 : int state = child->sk_state;
741 : :
742 [ + - ]: 28 : if (!sock_owned_by_user(child)) {
743 : 28 : ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
744 : : skb->len);
745 : : /* Wakeup parent, send SIGIO */
746 [ + - ][ + - ]: 28 : if (state == TCP_SYN_RECV && child->sk_state != state)
747 : 28 : parent->sk_data_ready(parent, 0);
748 : : } else {
749 : : /* Alas, it is possible again, because we do lookup
750 : : * in main socket hash table and lock on listening
751 : : * socket does not protect us more.
752 : : */
753 : : __sk_add_backlog(child, skb);
754 : : }
755 : :
756 : : bh_unlock_sock(child);
757 : : sock_put(child);
758 : 28 : return ret;
759 : : }
760 : : EXPORT_SYMBOL(tcp_child_process);
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