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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 | |
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 | |
51 | EXPORT_SYMBOL_GPL(tcp_death_row); |
52 | |
53 | static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) |
54 | { |
55 | if (seq == s_win) |
56 | return 1; |
57 | if (after(end_seq, s_win) && before(seq, e_win)) |
58 | return 1; |
59 | return (seq == e_win && seq == end_seq); |
60 | } |
61 | |
62 | /* |
63 | * * Main purpose of TIME-WAIT state is to close connection gracefully, |
64 | * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN |
65 | * (and, probably, tail of data) and one or more our ACKs are lost. |
66 | * * What is TIME-WAIT timeout? It is associated with maximal packet |
67 | * lifetime in the internet, which results in wrong conclusion, that |
68 | * it is set to catch "old duplicate segments" wandering out of their path. |
69 | * It is not quite correct. This timeout is calculated so that it exceeds |
70 | * maximal retransmission timeout enough to allow to lose one (or more) |
71 | * segments sent by peer and our ACKs. This time may be calculated from RTO. |
72 | * * When TIME-WAIT socket receives RST, it means that another end |
73 | * finally closed and we are allowed to kill TIME-WAIT too. |
74 | * * Second purpose of TIME-WAIT is catching old duplicate segments. |
75 | * Well, certainly it is pure paranoia, but if we load TIME-WAIT |
76 | * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. |
77 | * * If we invented some more clever way to catch duplicates |
78 | * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. |
79 | * |
80 | * The algorithm below is based on FORMAL INTERPRETATION of RFCs. |
81 | * When you compare it to RFCs, please, read section SEGMENT ARRIVES |
82 | * from the very beginning. |
83 | * |
84 | * NOTE. With recycling (and later with fin-wait-2) TW bucket |
85 | * is _not_ stateless. It means, that strictly speaking we must |
86 | * spinlock it. I do not want! Well, probability of misbehaviour |
87 | * is ridiculously low and, seems, we could use some mb() tricks |
88 | * to avoid misread sequence numbers, states etc. --ANK |
89 | */ |
90 | enum tcp_tw_status |
91 | tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, |
92 | const struct tcphdr *th) |
93 | { |
94 | struct tcp_options_received tmp_opt; |
95 | u8 *hash_location; |
96 | struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); |
97 | int paws_reject = 0; |
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, &hash_location, 0); |
102 | |
103 | if (tmp_opt.saw_tstamp) { |
104 | tmp_opt.ts_recent = tcptw->tw_ts_recent; |
105 | tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; |
106 | paws_reject = tcp_paws_reject(&tmp_opt, th->rst); |
107 | } |
108 | } |
109 | |
110 | if (tw->tw_substate == TCP_FIN_WAIT2) { |
111 | /* Just repeat all the checks of tcp_rcv_state_process() */ |
112 | |
113 | /* Out of window, send ACK */ |
114 | if (paws_reject || |
115 | !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, |
116 | tcptw->tw_rcv_nxt, |
117 | tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) |
118 | return TCP_TW_ACK; |
119 | |
120 | if (th->rst) |
121 | goto kill; |
122 | |
123 | if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) |
124 | goto kill_with_rst; |
125 | |
126 | /* Dup ACK? */ |
127 | if (!th->ack || |
128 | !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || |
129 | TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { |
130 | inet_twsk_put(tw); |
131 | return TCP_TW_SUCCESS; |
132 | } |
133 | |
134 | /* New data or FIN. If new data arrive after half-duplex close, |
135 | * reset. |
136 | */ |
137 | if (!th->fin || |
138 | TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) { |
139 | kill_with_rst: |
140 | inet_twsk_deschedule(tw, &tcp_death_row); |
141 | inet_twsk_put(tw); |
142 | return TCP_TW_RST; |
143 | } |
144 | |
145 | /* FIN arrived, enter true time-wait state. */ |
146 | tw->tw_substate = TCP_TIME_WAIT; |
147 | tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq; |
148 | if (tmp_opt.saw_tstamp) { |
149 | tcptw->tw_ts_recent_stamp = get_seconds(); |
150 | tcptw->tw_ts_recent = tmp_opt.rcv_tsval; |
151 | } |
152 | |
153 | /* I am shamed, but failed to make it more elegant. |
154 | * Yes, it is direct reference to IP, which is impossible |
155 | * to generalize to IPv6. Taking into account that IPv6 |
156 | * do not understand recycling in any case, it not |
157 | * a big problem in practice. --ANK */ |
158 | if (tw->tw_family == AF_INET && |
159 | tcp_death_row.sysctl_tw_recycle && tcptw->tw_ts_recent_stamp && |
160 | tcp_v4_tw_remember_stamp(tw)) |
161 | inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout, |
162 | TCP_TIMEWAIT_LEN); |
163 | else |
164 | inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN, |
165 | TCP_TIMEWAIT_LEN); |
166 | return TCP_TW_ACK; |
167 | } |
168 | |
169 | /* |
170 | * Now real TIME-WAIT state. |
171 | * |
172 | * RFC 1122: |
173 | * "When a connection is [...] on TIME-WAIT state [...] |
174 | * [a TCP] MAY accept a new SYN from the remote TCP to |
175 | * reopen the connection directly, if it: |
176 | * |
177 | * (1) assigns its initial sequence number for the new |
178 | * connection to be larger than the largest sequence |
179 | * number it used on the previous connection incarnation, |
180 | * and |
181 | * |
182 | * (2) returns to TIME-WAIT state if the SYN turns out |
183 | * to be an old duplicate". |
184 | */ |
185 | |
186 | if (!paws_reject && |
187 | (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && |
188 | (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { |
189 | /* In window segment, it may be only reset or bare ack. */ |
190 | |
191 | if (th->rst) { |
192 | /* This is TIME_WAIT assassination, in two flavors. |
193 | * Oh well... nobody has a sufficient solution to this |
194 | * protocol bug yet. |
195 | */ |
196 | if (sysctl_tcp_rfc1337 == 0) { |
197 | kill: |
198 | inet_twsk_deschedule(tw, &tcp_death_row); |
199 | inet_twsk_put(tw); |
200 | return TCP_TW_SUCCESS; |
201 | } |
202 | } |
203 | inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN, |
204 | TCP_TIMEWAIT_LEN); |
205 | |
206 | if (tmp_opt.saw_tstamp) { |
207 | tcptw->tw_ts_recent = tmp_opt.rcv_tsval; |
208 | tcptw->tw_ts_recent_stamp = get_seconds(); |
209 | } |
210 | |
211 | inet_twsk_put(tw); |
212 | return TCP_TW_SUCCESS; |
213 | } |
214 | |
215 | /* Out of window segment. |
216 | |
217 | All the segments are ACKed immediately. |
218 | |
219 | The only exception is new SYN. We accept it, if it is |
220 | not old duplicate and we are not in danger to be killed |
221 | by delayed old duplicates. RFC check is that it has |
222 | newer sequence number works at rates <40Mbit/sec. |
223 | However, if paws works, it is reliable AND even more, |
224 | we even may relax silly seq space cutoff. |
225 | |
226 | RED-PEN: we violate main RFC requirement, if this SYN will appear |
227 | old duplicate (i.e. we receive RST in reply to SYN-ACK), |
228 | we must return socket to time-wait state. It is not good, |
229 | but not fatal yet. |
230 | */ |
231 | |
232 | if (th->syn && !th->rst && !th->ack && !paws_reject && |
233 | (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || |
234 | (tmp_opt.saw_tstamp && |
235 | (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { |
236 | u32 isn = tcptw->tw_snd_nxt + 65535 + 2; |
237 | if (isn == 0) |
238 | isn++; |
239 | TCP_SKB_CB(skb)->when = isn; |
240 | return TCP_TW_SYN; |
241 | } |
242 | |
243 | if (paws_reject) |
244 | NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); |
245 | |
246 | if (!th->rst) { |
247 | /* In this case we must reset the TIMEWAIT timer. |
248 | * |
249 | * If it is ACKless SYN it may be both old duplicate |
250 | * and new good SYN with random sequence number <rcv_nxt. |
251 | * Do not reschedule in the last case. |
252 | */ |
253 | if (paws_reject || th->ack) |
254 | inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN, |
255 | TCP_TIMEWAIT_LEN); |
256 | |
257 | /* Send ACK. Note, we do not put the bucket, |
258 | * it will be released by caller. |
259 | */ |
260 | return TCP_TW_ACK; |
261 | } |
262 | inet_twsk_put(tw); |
263 | return TCP_TW_SUCCESS; |
264 | } |
265 | |
266 | /* |
267 | * Move a socket to time-wait or dead fin-wait-2 state. |
268 | */ |
269 | void tcp_time_wait(struct sock *sk, int state, int timeo) |
270 | { |
271 | struct inet_timewait_sock *tw = NULL; |
272 | const struct inet_connection_sock *icsk = inet_csk(sk); |
273 | const struct tcp_sock *tp = tcp_sk(sk); |
274 | int recycle_ok = 0; |
275 | |
276 | if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp) |
277 | recycle_ok = icsk->icsk_af_ops->remember_stamp(sk); |
278 | |
279 | if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets) |
280 | tw = inet_twsk_alloc(sk, state); |
281 | |
282 | if (tw != NULL) { |
283 | struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); |
284 | const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); |
285 | |
286 | tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; |
287 | tcptw->tw_rcv_nxt = tp->rcv_nxt; |
288 | tcptw->tw_snd_nxt = tp->snd_nxt; |
289 | tcptw->tw_rcv_wnd = tcp_receive_window(tp); |
290 | tcptw->tw_ts_recent = tp->rx_opt.ts_recent; |
291 | tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; |
292 | |
293 | #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) |
294 | if (tw->tw_family == PF_INET6) { |
295 | struct ipv6_pinfo *np = inet6_sk(sk); |
296 | struct inet6_timewait_sock *tw6; |
297 | |
298 | tw->tw_ipv6_offset = inet6_tw_offset(sk->sk_prot); |
299 | tw6 = inet6_twsk((struct sock *)tw); |
300 | ipv6_addr_copy(&tw6->tw_v6_daddr, &np->daddr); |
301 | ipv6_addr_copy(&tw6->tw_v6_rcv_saddr, &np->rcv_saddr); |
302 | tw->tw_ipv6only = np->ipv6only; |
303 | } |
304 | #endif |
305 | |
306 | #ifdef CONFIG_TCP_MD5SIG |
307 | /* |
308 | * The timewait bucket does not have the key DB from the |
309 | * sock structure. We just make a quick copy of the |
310 | * md5 key being used (if indeed we are using one) |
311 | * so the timewait ack generating code has the key. |
312 | */ |
313 | do { |
314 | struct tcp_md5sig_key *key; |
315 | memset(tcptw->tw_md5_key, 0, sizeof(tcptw->tw_md5_key)); |
316 | tcptw->tw_md5_keylen = 0; |
317 | key = tp->af_specific->md5_lookup(sk, sk); |
318 | if (key != NULL) { |
319 | memcpy(&tcptw->tw_md5_key, key->key, key->keylen); |
320 | tcptw->tw_md5_keylen = key->keylen; |
321 | if (tcp_alloc_md5sig_pool(sk) == NULL) |
322 | BUG(); |
323 | } |
324 | } while (0); |
325 | #endif |
326 | |
327 | /* Linkage updates. */ |
328 | __inet_twsk_hashdance(tw, sk, &tcp_hashinfo); |
329 | |
330 | /* Get the TIME_WAIT timeout firing. */ |
331 | if (timeo < rto) |
332 | timeo = rto; |
333 | |
334 | if (recycle_ok) { |
335 | tw->tw_timeout = rto; |
336 | } else { |
337 | tw->tw_timeout = TCP_TIMEWAIT_LEN; |
338 | if (state == TCP_TIME_WAIT) |
339 | timeo = TCP_TIMEWAIT_LEN; |
340 | } |
341 | |
342 | inet_twsk_schedule(tw, &tcp_death_row, timeo, |
343 | TCP_TIMEWAIT_LEN); |
344 | inet_twsk_put(tw); |
345 | } else { |
346 | /* Sorry, if we're out of memory, just CLOSE this |
347 | * socket up. We've got bigger problems than |
348 | * non-graceful socket closings. |
349 | */ |
350 | LIMIT_NETDEBUG(KERN_INFO "TCP: time wait bucket table overflow\n"); |
351 | } |
352 | |
353 | tcp_update_metrics(sk); |
354 | tcp_done(sk); |
355 | } |
356 | |
357 | void tcp_twsk_destructor(struct sock *sk) |
358 | { |
359 | #ifdef CONFIG_TCP_MD5SIG |
360 | struct tcp_timewait_sock *twsk = tcp_twsk(sk); |
361 | if (twsk->tw_md5_keylen) |
362 | tcp_free_md5sig_pool(); |
363 | #endif |
364 | } |
365 | |
366 | EXPORT_SYMBOL_GPL(tcp_twsk_destructor); |
367 | |
368 | static inline void TCP_ECN_openreq_child(struct tcp_sock *tp, |
369 | struct request_sock *req) |
370 | { |
371 | tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; |
372 | } |
373 | |
374 | /* This is not only more efficient than what we used to do, it eliminates |
375 | * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM |
376 | * |
377 | * Actually, we could lots of memory writes here. tp of listening |
378 | * socket contains all necessary default parameters. |
379 | */ |
380 | struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb) |
381 | { |
382 | struct sock *newsk = inet_csk_clone(sk, req, GFP_ATOMIC); |
383 | |
384 | if (newsk != NULL) { |
385 | const struct inet_request_sock *ireq = inet_rsk(req); |
386 | struct tcp_request_sock *treq = tcp_rsk(req); |
387 | struct inet_connection_sock *newicsk = inet_csk(newsk); |
388 | struct tcp_sock *newtp = tcp_sk(newsk); |
389 | struct tcp_sock *oldtp = tcp_sk(sk); |
390 | struct tcp_cookie_values *oldcvp = oldtp->cookie_values; |
391 | |
392 | /* TCP Cookie Transactions require space for the cookie pair, |
393 | * as it differs for each connection. There is no need to |
394 | * copy any s_data_payload stored at the original socket. |
395 | * Failure will prevent resuming the connection. |
396 | * |
397 | * Presumed copied, in order of appearance: |
398 | * cookie_in_always, cookie_out_never |
399 | */ |
400 | if (oldcvp != NULL) { |
401 | struct tcp_cookie_values *newcvp = |
402 | kzalloc(sizeof(*newtp->cookie_values), |
403 | GFP_ATOMIC); |
404 | |
405 | if (newcvp != NULL) { |
406 | kref_init(&newcvp->kref); |
407 | newcvp->cookie_desired = |
408 | oldcvp->cookie_desired; |
409 | newtp->cookie_values = newcvp; |
410 | } else { |
411 | /* Not Yet Implemented */ |
412 | newtp->cookie_values = NULL; |
413 | } |
414 | } |
415 | |
416 | /* Now setup tcp_sock */ |
417 | newtp->pred_flags = 0; |
418 | |
419 | newtp->rcv_wup = newtp->copied_seq = |
420 | newtp->rcv_nxt = treq->rcv_isn + 1; |
421 | |
422 | newtp->snd_sml = newtp->snd_una = |
423 | newtp->snd_nxt = newtp->snd_up = |
424 | treq->snt_isn + 1 + tcp_s_data_size(oldtp); |
425 | |
426 | tcp_prequeue_init(newtp); |
427 | |
428 | tcp_init_wl(newtp, treq->rcv_isn); |
429 | |
430 | newtp->srtt = 0; |
431 | newtp->mdev = TCP_TIMEOUT_INIT; |
432 | newicsk->icsk_rto = TCP_TIMEOUT_INIT; |
433 | |
434 | newtp->packets_out = 0; |
435 | newtp->retrans_out = 0; |
436 | newtp->sacked_out = 0; |
437 | newtp->fackets_out = 0; |
438 | newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH; |
439 | |
440 | /* So many TCP implementations out there (incorrectly) count the |
441 | * initial SYN frame in their delayed-ACK and congestion control |
442 | * algorithms that we must have the following bandaid to talk |
443 | * efficiently to them. -DaveM |
444 | */ |
445 | newtp->snd_cwnd = 2; |
446 | newtp->snd_cwnd_cnt = 0; |
447 | newtp->bytes_acked = 0; |
448 | |
449 | newtp->frto_counter = 0; |
450 | newtp->frto_highmark = 0; |
451 | |
452 | newicsk->icsk_ca_ops = &tcp_init_congestion_ops; |
453 | |
454 | tcp_set_ca_state(newsk, TCP_CA_Open); |
455 | tcp_init_xmit_timers(newsk); |
456 | skb_queue_head_init(&newtp->out_of_order_queue); |
457 | newtp->write_seq = newtp->pushed_seq = |
458 | treq->snt_isn + 1 + tcp_s_data_size(oldtp); |
459 | |
460 | newtp->rx_opt.saw_tstamp = 0; |
461 | |
462 | newtp->rx_opt.dsack = 0; |
463 | newtp->rx_opt.num_sacks = 0; |
464 | |
465 | newtp->urg_data = 0; |
466 | |
467 | if (sock_flag(newsk, SOCK_KEEPOPEN)) |
468 | inet_csk_reset_keepalive_timer(newsk, |
469 | keepalive_time_when(newtp)); |
470 | |
471 | newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; |
472 | if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) { |
473 | if (sysctl_tcp_fack) |
474 | tcp_enable_fack(newtp); |
475 | } |
476 | newtp->window_clamp = req->window_clamp; |
477 | newtp->rcv_ssthresh = req->rcv_wnd; |
478 | newtp->rcv_wnd = req->rcv_wnd; |
479 | newtp->rx_opt.wscale_ok = ireq->wscale_ok; |
480 | if (newtp->rx_opt.wscale_ok) { |
481 | newtp->rx_opt.snd_wscale = ireq->snd_wscale; |
482 | newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; |
483 | } else { |
484 | newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; |
485 | newtp->window_clamp = min(newtp->window_clamp, 65535U); |
486 | } |
487 | newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) << |
488 | newtp->rx_opt.snd_wscale); |
489 | newtp->max_window = newtp->snd_wnd; |
490 | |
491 | if (newtp->rx_opt.tstamp_ok) { |
492 | newtp->rx_opt.ts_recent = req->ts_recent; |
493 | newtp->rx_opt.ts_recent_stamp = get_seconds(); |
494 | newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; |
495 | } else { |
496 | newtp->rx_opt.ts_recent_stamp = 0; |
497 | newtp->tcp_header_len = sizeof(struct tcphdr); |
498 | } |
499 | #ifdef CONFIG_TCP_MD5SIG |
500 | newtp->md5sig_info = NULL; /*XXX*/ |
501 | if (newtp->af_specific->md5_lookup(sk, newsk)) |
502 | newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; |
503 | #endif |
504 | if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) |
505 | newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; |
506 | newtp->rx_opt.mss_clamp = req->mss; |
507 | TCP_ECN_openreq_child(newtp, req); |
508 | |
509 | TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS); |
510 | } |
511 | return newsk; |
512 | } |
513 | |
514 | /* |
515 | * Process an incoming packet for SYN_RECV sockets represented |
516 | * as a request_sock. |
517 | */ |
518 | |
519 | struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, |
520 | struct request_sock *req, |
521 | struct request_sock **prev) |
522 | { |
523 | struct tcp_options_received tmp_opt; |
524 | u8 *hash_location; |
525 | struct sock *child; |
526 | const struct tcphdr *th = tcp_hdr(skb); |
527 | __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); |
528 | int paws_reject = 0; |
529 | |
530 | tmp_opt.saw_tstamp = 0; |
531 | if (th->doff > (sizeof(struct tcphdr)>>2)) { |
532 | tcp_parse_options(skb, &tmp_opt, &hash_location, 0); |
533 | |
534 | if (tmp_opt.saw_tstamp) { |
535 | tmp_opt.ts_recent = req->ts_recent; |
536 | /* We do not store true stamp, but it is not required, |
537 | * it can be estimated (approximately) |
538 | * from another data. |
539 | */ |
540 | tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans); |
541 | paws_reject = tcp_paws_reject(&tmp_opt, th->rst); |
542 | } |
543 | } |
544 | |
545 | /* Check for pure retransmitted SYN. */ |
546 | if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && |
547 | flg == TCP_FLAG_SYN && |
548 | !paws_reject) { |
549 | /* |
550 | * RFC793 draws (Incorrectly! It was fixed in RFC1122) |
551 | * this case on figure 6 and figure 8, but formal |
552 | * protocol description says NOTHING. |
553 | * To be more exact, it says that we should send ACK, |
554 | * because this segment (at least, if it has no data) |
555 | * is out of window. |
556 | * |
557 | * CONCLUSION: RFC793 (even with RFC1122) DOES NOT |
558 | * describe SYN-RECV state. All the description |
559 | * is wrong, we cannot believe to it and should |
560 | * rely only on common sense and implementation |
561 | * experience. |
562 | * |
563 | * Enforce "SYN-ACK" according to figure 8, figure 6 |
564 | * of RFC793, fixed by RFC1122. |
565 | */ |
566 | req->rsk_ops->rtx_syn_ack(sk, req, NULL); |
567 | return NULL; |
568 | } |
569 | |
570 | /* Further reproduces section "SEGMENT ARRIVES" |
571 | for state SYN-RECEIVED of RFC793. |
572 | It is broken, however, it does not work only |
573 | when SYNs are crossed. |
574 | |
575 | You would think that SYN crossing is impossible here, since |
576 | we should have a SYN_SENT socket (from connect()) on our end, |
577 | but this is not true if the crossed SYNs were sent to both |
578 | ends by a malicious third party. We must defend against this, |
579 | and to do that we first verify the ACK (as per RFC793, page |
580 | 36) and reset if it is invalid. Is this a true full defense? |
581 | To convince ourselves, let us consider a way in which the ACK |
582 | test can still pass in this 'malicious crossed SYNs' case. |
583 | Malicious sender sends identical SYNs (and thus identical sequence |
584 | numbers) to both A and B: |
585 | |
586 | A: gets SYN, seq=7 |
587 | B: gets SYN, seq=7 |
588 | |
589 | By our good fortune, both A and B select the same initial |
590 | send sequence number of seven :-) |
591 | |
592 | A: sends SYN|ACK, seq=7, ack_seq=8 |
593 | B: sends SYN|ACK, seq=7, ack_seq=8 |
594 | |
595 | So we are now A eating this SYN|ACK, ACK test passes. So |
596 | does sequence test, SYN is truncated, and thus we consider |
597 | it a bare ACK. |
598 | |
599 | If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this |
600 | bare ACK. Otherwise, we create an established connection. Both |
601 | ends (listening sockets) accept the new incoming connection and try |
602 | to talk to each other. 8-) |
603 | |
604 | Note: This case is both harmless, and rare. Possibility is about the |
605 | same as us discovering intelligent life on another plant tomorrow. |
606 | |
607 | But generally, we should (RFC lies!) to accept ACK |
608 | from SYNACK both here and in tcp_rcv_state_process(). |
609 | tcp_rcv_state_process() does not, hence, we do not too. |
610 | |
611 | Note that the case is absolutely generic: |
612 | we cannot optimize anything here without |
613 | violating protocol. All the checks must be made |
614 | before attempt to create socket. |
615 | */ |
616 | |
617 | /* RFC793 page 36: "If the connection is in any non-synchronized state ... |
618 | * and the incoming segment acknowledges something not yet |
619 | * sent (the segment carries an unacceptable ACK) ... |
620 | * a reset is sent." |
621 | * |
622 | * Invalid ACK: reset will be sent by listening socket |
623 | */ |
624 | if ((flg & TCP_FLAG_ACK) && |
625 | (TCP_SKB_CB(skb)->ack_seq != |
626 | tcp_rsk(req)->snt_isn + 1 + tcp_s_data_size(tcp_sk(sk)))) |
627 | return sk; |
628 | |
629 | /* Also, it would be not so bad idea to check rcv_tsecr, which |
630 | * is essentially ACK extension and too early or too late values |
631 | * should cause reset in unsynchronized states. |
632 | */ |
633 | |
634 | /* RFC793: "first check sequence number". */ |
635 | |
636 | if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, |
637 | tcp_rsk(req)->rcv_isn + 1, tcp_rsk(req)->rcv_isn + 1 + req->rcv_wnd)) { |
638 | /* Out of window: send ACK and drop. */ |
639 | if (!(flg & TCP_FLAG_RST)) |
640 | req->rsk_ops->send_ack(sk, skb, req); |
641 | if (paws_reject) |
642 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); |
643 | return NULL; |
644 | } |
645 | |
646 | /* In sequence, PAWS is OK. */ |
647 | |
648 | if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_isn + 1)) |
649 | req->ts_recent = tmp_opt.rcv_tsval; |
650 | |
651 | if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { |
652 | /* Truncate SYN, it is out of window starting |
653 | at tcp_rsk(req)->rcv_isn + 1. */ |
654 | flg &= ~TCP_FLAG_SYN; |
655 | } |
656 | |
657 | /* RFC793: "second check the RST bit" and |
658 | * "fourth, check the SYN bit" |
659 | */ |
660 | if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { |
661 | TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS); |
662 | goto embryonic_reset; |
663 | } |
664 | |
665 | /* ACK sequence verified above, just make sure ACK is |
666 | * set. If ACK not set, just silently drop the packet. |
667 | */ |
668 | if (!(flg & TCP_FLAG_ACK)) |
669 | return NULL; |
670 | |
671 | /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ |
672 | if (req->retrans < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && |
673 | TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { |
674 | inet_rsk(req)->acked = 1; |
675 | return NULL; |
676 | } |
677 | |
678 | /* OK, ACK is valid, create big socket and |
679 | * feed this segment to it. It will repeat all |
680 | * the tests. THIS SEGMENT MUST MOVE SOCKET TO |
681 | * ESTABLISHED STATE. If it will be dropped after |
682 | * socket is created, wait for troubles. |
683 | */ |
684 | child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL); |
685 | if (child == NULL) |
686 | goto listen_overflow; |
687 | |
688 | inet_csk_reqsk_queue_unlink(sk, req, prev); |
689 | inet_csk_reqsk_queue_removed(sk, req); |
690 | |
691 | inet_csk_reqsk_queue_add(sk, req, child); |
692 | return child; |
693 | |
694 | listen_overflow: |
695 | if (!sysctl_tcp_abort_on_overflow) { |
696 | inet_rsk(req)->acked = 1; |
697 | return NULL; |
698 | } |
699 | |
700 | embryonic_reset: |
701 | NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); |
702 | if (!(flg & TCP_FLAG_RST)) |
703 | req->rsk_ops->send_reset(sk, skb); |
704 | |
705 | inet_csk_reqsk_queue_drop(sk, req, prev); |
706 | return NULL; |
707 | } |
708 | |
709 | /* |
710 | * Queue segment on the new socket if the new socket is active, |
711 | * otherwise we just shortcircuit this and continue with |
712 | * the new socket. |
713 | */ |
714 | |
715 | int tcp_child_process(struct sock *parent, struct sock *child, |
716 | struct sk_buff *skb) |
717 | { |
718 | int ret = 0; |
719 | int state = child->sk_state; |
720 | |
721 | if (!sock_owned_by_user(child)) { |
722 | ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb), |
723 | skb->len); |
724 | /* Wakeup parent, send SIGIO */ |
725 | if (state == TCP_SYN_RECV && child->sk_state != state) |
726 | parent->sk_data_ready(parent, 0); |
727 | } else { |
728 | /* Alas, it is possible again, because we do lookup |
729 | * in main socket hash table and lock on listening |
730 | * socket does not protect us more. |
731 | */ |
732 | __sk_add_backlog(child, skb); |
733 | } |
734 | |
735 | bh_unlock_sock(child); |
736 | sock_put(child); |
737 | return ret; |
738 | } |
739 | |
740 | EXPORT_SYMBOL(tcp_check_req); |
741 | EXPORT_SYMBOL(tcp_child_process); |
742 | EXPORT_SYMBOL(tcp_create_openreq_child); |
743 | EXPORT_SYMBOL(tcp_timewait_state_process); |
744 |
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