Commit | Line | Data |
---|---|---|
1da177e4 LT |
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 | * Version: $Id: tcp_minisocks.c,v 1.15 2002/02/01 22:01:04 davem Exp $ | |
9 | * | |
02c30a84 | 10 | * Authors: Ross Biro |
1da177e4 LT |
11 | * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> |
12 | * Mark Evans, <evansmp@uhura.aston.ac.uk> | |
13 | * Corey Minyard <wf-rch!minyard@relay.EU.net> | |
14 | * Florian La Roche, <flla@stud.uni-sb.de> | |
15 | * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> | |
16 | * Linus Torvalds, <torvalds@cs.helsinki.fi> | |
17 | * Alan Cox, <gw4pts@gw4pts.ampr.org> | |
18 | * Matthew Dillon, <dillon@apollo.west.oic.com> | |
19 | * Arnt Gulbrandsen, <agulbra@nvg.unit.no> | |
20 | * Jorge Cwik, <jorge@laser.satlink.net> | |
21 | */ | |
22 | ||
23 | #include <linux/config.h> | |
24 | #include <linux/mm.h> | |
25 | #include <linux/module.h> | |
26 | #include <linux/sysctl.h> | |
27 | #include <linux/workqueue.h> | |
28 | #include <net/tcp.h> | |
29 | #include <net/inet_common.h> | |
30 | #include <net/xfrm.h> | |
31 | ||
32 | #ifdef CONFIG_SYSCTL | |
33 | #define SYNC_INIT 0 /* let the user enable it */ | |
34 | #else | |
35 | #define SYNC_INIT 1 | |
36 | #endif | |
37 | ||
1da177e4 LT |
38 | int sysctl_tcp_syncookies = SYNC_INIT; |
39 | int sysctl_tcp_abort_on_overflow; | |
40 | ||
295ff7ed ACM |
41 | struct inet_timewait_death_row tcp_death_row = { |
42 | .sysctl_max_tw_buckets = NR_FILE * 2, | |
43 | .period = TCP_TIMEWAIT_LEN / INET_TWDR_TWKILL_SLOTS, | |
44 | .death_lock = SPIN_LOCK_UNLOCKED, | |
45 | .hashinfo = &tcp_hashinfo, | |
46 | .tw_timer = TIMER_INITIALIZER(inet_twdr_hangman, 0, | |
47 | (unsigned long)&tcp_death_row), | |
48 | .twkill_work = __WORK_INITIALIZER(tcp_death_row.twkill_work, | |
49 | inet_twdr_twkill_work, | |
50 | &tcp_death_row), | |
51 | /* Short-time timewait calendar */ | |
52 | ||
53 | .twcal_hand = -1, | |
54 | .twcal_timer = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0, | |
55 | (unsigned long)&tcp_death_row), | |
56 | }; | |
57 | ||
58 | EXPORT_SYMBOL_GPL(tcp_death_row); | |
59 | ||
1da177e4 LT |
60 | static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) |
61 | { | |
62 | if (seq == s_win) | |
63 | return 1; | |
64 | if (after(end_seq, s_win) && before(seq, e_win)) | |
65 | return 1; | |
66 | return (seq == e_win && seq == end_seq); | |
67 | } | |
68 | ||
1da177e4 LT |
69 | /* |
70 | * * Main purpose of TIME-WAIT state is to close connection gracefully, | |
71 | * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN | |
72 | * (and, probably, tail of data) and one or more our ACKs are lost. | |
73 | * * What is TIME-WAIT timeout? It is associated with maximal packet | |
74 | * lifetime in the internet, which results in wrong conclusion, that | |
75 | * it is set to catch "old duplicate segments" wandering out of their path. | |
76 | * It is not quite correct. This timeout is calculated so that it exceeds | |
77 | * maximal retransmission timeout enough to allow to lose one (or more) | |
78 | * segments sent by peer and our ACKs. This time may be calculated from RTO. | |
79 | * * When TIME-WAIT socket receives RST, it means that another end | |
80 | * finally closed and we are allowed to kill TIME-WAIT too. | |
81 | * * Second purpose of TIME-WAIT is catching old duplicate segments. | |
82 | * Well, certainly it is pure paranoia, but if we load TIME-WAIT | |
83 | * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. | |
84 | * * If we invented some more clever way to catch duplicates | |
85 | * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. | |
86 | * | |
87 | * The algorithm below is based on FORMAL INTERPRETATION of RFCs. | |
88 | * When you compare it to RFCs, please, read section SEGMENT ARRIVES | |
89 | * from the very beginning. | |
90 | * | |
91 | * NOTE. With recycling (and later with fin-wait-2) TW bucket | |
92 | * is _not_ stateless. It means, that strictly speaking we must | |
93 | * spinlock it. I do not want! Well, probability of misbehaviour | |
94 | * is ridiculously low and, seems, we could use some mb() tricks | |
95 | * to avoid misread sequence numbers, states etc. --ANK | |
96 | */ | |
97 | enum tcp_tw_status | |
8feaf0c0 ACM |
98 | tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, |
99 | const struct tcphdr *th) | |
1da177e4 | 100 | { |
8feaf0c0 | 101 | struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); |
1da177e4 LT |
102 | struct tcp_options_received tmp_opt; |
103 | int paws_reject = 0; | |
104 | ||
105 | tmp_opt.saw_tstamp = 0; | |
8feaf0c0 | 106 | if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { |
1da177e4 LT |
107 | tcp_parse_options(skb, &tmp_opt, 0); |
108 | ||
109 | if (tmp_opt.saw_tstamp) { | |
8feaf0c0 ACM |
110 | tmp_opt.ts_recent = tcptw->tw_ts_recent; |
111 | tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; | |
1da177e4 LT |
112 | paws_reject = tcp_paws_check(&tmp_opt, th->rst); |
113 | } | |
114 | } | |
115 | ||
116 | if (tw->tw_substate == TCP_FIN_WAIT2) { | |
117 | /* Just repeat all the checks of tcp_rcv_state_process() */ | |
118 | ||
119 | /* Out of window, send ACK */ | |
120 | if (paws_reject || | |
121 | !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, | |
8feaf0c0 ACM |
122 | tcptw->tw_rcv_nxt, |
123 | tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) | |
1da177e4 LT |
124 | return TCP_TW_ACK; |
125 | ||
126 | if (th->rst) | |
127 | goto kill; | |
128 | ||
8feaf0c0 | 129 | if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) |
1da177e4 LT |
130 | goto kill_with_rst; |
131 | ||
132 | /* Dup ACK? */ | |
8feaf0c0 | 133 | if (!after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || |
1da177e4 | 134 | TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { |
8feaf0c0 | 135 | inet_twsk_put(tw); |
1da177e4 LT |
136 | return TCP_TW_SUCCESS; |
137 | } | |
138 | ||
139 | /* New data or FIN. If new data arrive after half-duplex close, | |
140 | * reset. | |
141 | */ | |
142 | if (!th->fin || | |
8feaf0c0 | 143 | TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) { |
1da177e4 | 144 | kill_with_rst: |
295ff7ed | 145 | inet_twsk_deschedule(tw, &tcp_death_row); |
8feaf0c0 | 146 | inet_twsk_put(tw); |
1da177e4 LT |
147 | return TCP_TW_RST; |
148 | } | |
149 | ||
150 | /* FIN arrived, enter true time-wait state. */ | |
8feaf0c0 ACM |
151 | tw->tw_substate = TCP_TIME_WAIT; |
152 | tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq; | |
1da177e4 | 153 | if (tmp_opt.saw_tstamp) { |
8feaf0c0 ACM |
154 | tcptw->tw_ts_recent_stamp = xtime.tv_sec; |
155 | tcptw->tw_ts_recent = tmp_opt.rcv_tsval; | |
1da177e4 LT |
156 | } |
157 | ||
158 | /* I am shamed, but failed to make it more elegant. | |
159 | * Yes, it is direct reference to IP, which is impossible | |
160 | * to generalize to IPv6. Taking into account that IPv6 | |
161 | * do not undertsnad recycling in any case, it not | |
162 | * a big problem in practice. --ANK */ | |
163 | if (tw->tw_family == AF_INET && | |
295ff7ed | 164 | tcp_death_row.sysctl_tw_recycle && tcptw->tw_ts_recent_stamp && |
1da177e4 | 165 | tcp_v4_tw_remember_stamp(tw)) |
696ab2d3 ACM |
166 | inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout, |
167 | TCP_TIMEWAIT_LEN); | |
1da177e4 | 168 | else |
696ab2d3 ACM |
169 | inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN, |
170 | TCP_TIMEWAIT_LEN); | |
1da177e4 LT |
171 | return TCP_TW_ACK; |
172 | } | |
173 | ||
174 | /* | |
175 | * Now real TIME-WAIT state. | |
176 | * | |
177 | * RFC 1122: | |
178 | * "When a connection is [...] on TIME-WAIT state [...] | |
179 | * [a TCP] MAY accept a new SYN from the remote TCP to | |
180 | * reopen the connection directly, if it: | |
181 | * | |
182 | * (1) assigns its initial sequence number for the new | |
183 | * connection to be larger than the largest sequence | |
184 | * number it used on the previous connection incarnation, | |
185 | * and | |
186 | * | |
187 | * (2) returns to TIME-WAIT state if the SYN turns out | |
188 | * to be an old duplicate". | |
189 | */ | |
190 | ||
191 | if (!paws_reject && | |
8feaf0c0 | 192 | (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && |
1da177e4 LT |
193 | (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { |
194 | /* In window segment, it may be only reset or bare ack. */ | |
195 | ||
196 | if (th->rst) { | |
197 | /* This is TIME_WAIT assasination, in two flavors. | |
198 | * Oh well... nobody has a sufficient solution to this | |
199 | * protocol bug yet. | |
200 | */ | |
201 | if (sysctl_tcp_rfc1337 == 0) { | |
202 | kill: | |
295ff7ed | 203 | inet_twsk_deschedule(tw, &tcp_death_row); |
8feaf0c0 | 204 | inet_twsk_put(tw); |
1da177e4 LT |
205 | return TCP_TW_SUCCESS; |
206 | } | |
207 | } | |
696ab2d3 ACM |
208 | inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN, |
209 | TCP_TIMEWAIT_LEN); | |
1da177e4 LT |
210 | |
211 | if (tmp_opt.saw_tstamp) { | |
8feaf0c0 ACM |
212 | tcptw->tw_ts_recent = tmp_opt.rcv_tsval; |
213 | tcptw->tw_ts_recent_stamp = xtime.tv_sec; | |
1da177e4 LT |
214 | } |
215 | ||
8feaf0c0 | 216 | inet_twsk_put(tw); |
1da177e4 LT |
217 | return TCP_TW_SUCCESS; |
218 | } | |
219 | ||
220 | /* Out of window segment. | |
221 | ||
222 | All the segments are ACKed immediately. | |
223 | ||
224 | The only exception is new SYN. We accept it, if it is | |
225 | not old duplicate and we are not in danger to be killed | |
226 | by delayed old duplicates. RFC check is that it has | |
227 | newer sequence number works at rates <40Mbit/sec. | |
228 | However, if paws works, it is reliable AND even more, | |
229 | we even may relax silly seq space cutoff. | |
230 | ||
231 | RED-PEN: we violate main RFC requirement, if this SYN will appear | |
232 | old duplicate (i.e. we receive RST in reply to SYN-ACK), | |
233 | we must return socket to time-wait state. It is not good, | |
234 | but not fatal yet. | |
235 | */ | |
236 | ||
237 | if (th->syn && !th->rst && !th->ack && !paws_reject && | |
8feaf0c0 ACM |
238 | (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || |
239 | (tmp_opt.saw_tstamp && | |
240 | (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { | |
241 | u32 isn = tcptw->tw_snd_nxt + 65535 + 2; | |
1da177e4 LT |
242 | if (isn == 0) |
243 | isn++; | |
244 | TCP_SKB_CB(skb)->when = isn; | |
245 | return TCP_TW_SYN; | |
246 | } | |
247 | ||
248 | if (paws_reject) | |
249 | NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED); | |
250 | ||
251 | if(!th->rst) { | |
252 | /* In this case we must reset the TIMEWAIT timer. | |
253 | * | |
254 | * If it is ACKless SYN it may be both old duplicate | |
255 | * and new good SYN with random sequence number <rcv_nxt. | |
256 | * Do not reschedule in the last case. | |
257 | */ | |
258 | if (paws_reject || th->ack) | |
696ab2d3 ACM |
259 | inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN, |
260 | TCP_TIMEWAIT_LEN); | |
1da177e4 LT |
261 | |
262 | /* Send ACK. Note, we do not put the bucket, | |
263 | * it will be released by caller. | |
264 | */ | |
265 | return TCP_TW_ACK; | |
266 | } | |
8feaf0c0 | 267 | inet_twsk_put(tw); |
1da177e4 LT |
268 | return TCP_TW_SUCCESS; |
269 | } | |
270 | ||
1da177e4 LT |
271 | /* |
272 | * Move a socket to time-wait or dead fin-wait-2 state. | |
273 | */ | |
274 | void tcp_time_wait(struct sock *sk, int state, int timeo) | |
275 | { | |
8feaf0c0 ACM |
276 | struct inet_timewait_sock *tw = NULL; |
277 | const struct tcp_sock *tp = tcp_sk(sk); | |
1da177e4 LT |
278 | int recycle_ok = 0; |
279 | ||
295ff7ed | 280 | if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp) |
1da177e4 LT |
281 | recycle_ok = tp->af_specific->remember_stamp(sk); |
282 | ||
295ff7ed | 283 | if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets) |
c676270b | 284 | tw = inet_twsk_alloc(sk, state); |
1da177e4 | 285 | |
8feaf0c0 ACM |
286 | if (tw != NULL) { |
287 | struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); | |
463c84b9 ACM |
288 | const struct inet_connection_sock *icsk = inet_csk(sk); |
289 | const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); | |
8feaf0c0 | 290 | |
1da177e4 | 291 | tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; |
8feaf0c0 ACM |
292 | tcptw->tw_rcv_nxt = tp->rcv_nxt; |
293 | tcptw->tw_snd_nxt = tp->snd_nxt; | |
294 | tcptw->tw_rcv_wnd = tcp_receive_window(tp); | |
295 | tcptw->tw_ts_recent = tp->rx_opt.ts_recent; | |
296 | tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; | |
1da177e4 LT |
297 | |
298 | #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) | |
299 | if (tw->tw_family == PF_INET6) { | |
300 | struct ipv6_pinfo *np = inet6_sk(sk); | |
8feaf0c0 | 301 | struct tcp6_timewait_sock *tcp6tw = tcp6_twsk((struct sock *)tw); |
1da177e4 | 302 | |
8feaf0c0 ACM |
303 | ipv6_addr_copy(&tcp6tw->tw_v6_daddr, &np->daddr); |
304 | ipv6_addr_copy(&tcp6tw->tw_v6_rcv_saddr, &np->rcv_saddr); | |
305 | tw->tw_ipv6only = np->ipv6only; | |
c676270b | 306 | } |
1da177e4 LT |
307 | #endif |
308 | /* Linkage updates. */ | |
e48c414e | 309 | __inet_twsk_hashdance(tw, sk, &tcp_hashinfo); |
1da177e4 LT |
310 | |
311 | /* Get the TIME_WAIT timeout firing. */ | |
312 | if (timeo < rto) | |
313 | timeo = rto; | |
314 | ||
315 | if (recycle_ok) { | |
316 | tw->tw_timeout = rto; | |
317 | } else { | |
318 | tw->tw_timeout = TCP_TIMEWAIT_LEN; | |
319 | if (state == TCP_TIME_WAIT) | |
320 | timeo = TCP_TIMEWAIT_LEN; | |
321 | } | |
322 | ||
696ab2d3 ACM |
323 | inet_twsk_schedule(tw, &tcp_death_row, timeo, |
324 | TCP_TIMEWAIT_LEN); | |
8feaf0c0 | 325 | inet_twsk_put(tw); |
1da177e4 LT |
326 | } else { |
327 | /* Sorry, if we're out of memory, just CLOSE this | |
328 | * socket up. We've got bigger problems than | |
329 | * non-graceful socket closings. | |
330 | */ | |
331 | if (net_ratelimit()) | |
332 | printk(KERN_INFO "TCP: time wait bucket table overflow\n"); | |
333 | } | |
334 | ||
335 | tcp_update_metrics(sk); | |
336 | tcp_done(sk); | |
337 | } | |
338 | ||
1da177e4 LT |
339 | /* This is not only more efficient than what we used to do, it eliminates |
340 | * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM | |
341 | * | |
342 | * Actually, we could lots of memory writes here. tp of listening | |
343 | * socket contains all necessary default parameters. | |
344 | */ | |
60236fdd | 345 | struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb) |
1da177e4 | 346 | { |
9f1d2604 | 347 | struct sock *newsk = inet_csk_clone(sk, req, GFP_ATOMIC); |
1da177e4 | 348 | |
87d11ceb | 349 | if (newsk != NULL) { |
9f1d2604 | 350 | const struct inet_request_sock *ireq = inet_rsk(req); |
2e6599cb | 351 | struct tcp_request_sock *treq = tcp_rsk(req); |
9f1d2604 | 352 | struct inet_connection_sock *newicsk = inet_csk(sk); |
1da177e4 | 353 | struct tcp_sock *newtp; |
1da177e4 | 354 | |
1da177e4 LT |
355 | /* Now setup tcp_sock */ |
356 | newtp = tcp_sk(newsk); | |
357 | newtp->pred_flags = 0; | |
2e6599cb | 358 | newtp->rcv_nxt = treq->rcv_isn + 1; |
87d11ceb | 359 | newtp->snd_nxt = newtp->snd_una = newtp->snd_sml = treq->snt_isn + 1; |
1da177e4 LT |
360 | |
361 | tcp_prequeue_init(newtp); | |
362 | ||
2e6599cb | 363 | tcp_init_wl(newtp, treq->snt_isn, treq->rcv_isn); |
1da177e4 | 364 | |
1da177e4 LT |
365 | newtp->srtt = 0; |
366 | newtp->mdev = TCP_TIMEOUT_INIT; | |
463c84b9 | 367 | newicsk->icsk_rto = TCP_TIMEOUT_INIT; |
1da177e4 LT |
368 | |
369 | newtp->packets_out = 0; | |
370 | newtp->left_out = 0; | |
371 | newtp->retrans_out = 0; | |
372 | newtp->sacked_out = 0; | |
373 | newtp->fackets_out = 0; | |
374 | newtp->snd_ssthresh = 0x7fffffff; | |
375 | ||
376 | /* So many TCP implementations out there (incorrectly) count the | |
377 | * initial SYN frame in their delayed-ACK and congestion control | |
378 | * algorithms that we must have the following bandaid to talk | |
379 | * efficiently to them. -DaveM | |
380 | */ | |
381 | newtp->snd_cwnd = 2; | |
382 | newtp->snd_cwnd_cnt = 0; | |
9772efb9 | 383 | newtp->bytes_acked = 0; |
1da177e4 LT |
384 | |
385 | newtp->frto_counter = 0; | |
386 | newtp->frto_highmark = 0; | |
387 | ||
7957aed7 | 388 | newicsk->icsk_ca_ops = &tcp_init_congestion_ops; |
317a76f9 | 389 | |
6687e988 | 390 | tcp_set_ca_state(newsk, TCP_CA_Open); |
1da177e4 LT |
391 | tcp_init_xmit_timers(newsk); |
392 | skb_queue_head_init(&newtp->out_of_order_queue); | |
2e6599cb ACM |
393 | newtp->rcv_wup = treq->rcv_isn + 1; |
394 | newtp->write_seq = treq->snt_isn + 1; | |
1da177e4 | 395 | newtp->pushed_seq = newtp->write_seq; |
2e6599cb | 396 | newtp->copied_seq = treq->rcv_isn + 1; |
1da177e4 LT |
397 | |
398 | newtp->rx_opt.saw_tstamp = 0; | |
399 | ||
400 | newtp->rx_opt.dsack = 0; | |
401 | newtp->rx_opt.eff_sacks = 0; | |
402 | ||
1da177e4 LT |
403 | newtp->rx_opt.num_sacks = 0; |
404 | newtp->urg_data = 0; | |
1da177e4 | 405 | |
1da177e4 | 406 | if (sock_flag(newsk, SOCK_KEEPOPEN)) |
463c84b9 ACM |
407 | inet_csk_reset_keepalive_timer(newsk, |
408 | keepalive_time_when(newtp)); | |
1da177e4 | 409 | |
2e6599cb ACM |
410 | newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; |
411 | if((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) { | |
1da177e4 LT |
412 | if (sysctl_tcp_fack) |
413 | newtp->rx_opt.sack_ok |= 2; | |
414 | } | |
415 | newtp->window_clamp = req->window_clamp; | |
416 | newtp->rcv_ssthresh = req->rcv_wnd; | |
417 | newtp->rcv_wnd = req->rcv_wnd; | |
2e6599cb | 418 | newtp->rx_opt.wscale_ok = ireq->wscale_ok; |
1da177e4 | 419 | if (newtp->rx_opt.wscale_ok) { |
2e6599cb ACM |
420 | newtp->rx_opt.snd_wscale = ireq->snd_wscale; |
421 | newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; | |
1da177e4 LT |
422 | } else { |
423 | newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; | |
424 | newtp->window_clamp = min(newtp->window_clamp, 65535U); | |
425 | } | |
426 | newtp->snd_wnd = ntohs(skb->h.th->window) << newtp->rx_opt.snd_wscale; | |
427 | newtp->max_window = newtp->snd_wnd; | |
428 | ||
429 | if (newtp->rx_opt.tstamp_ok) { | |
430 | newtp->rx_opt.ts_recent = req->ts_recent; | |
431 | newtp->rx_opt.ts_recent_stamp = xtime.tv_sec; | |
432 | newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; | |
433 | } else { | |
434 | newtp->rx_opt.ts_recent_stamp = 0; | |
435 | newtp->tcp_header_len = sizeof(struct tcphdr); | |
436 | } | |
437 | if (skb->len >= TCP_MIN_RCVMSS+newtp->tcp_header_len) | |
463c84b9 | 438 | newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; |
1da177e4 LT |
439 | newtp->rx_opt.mss_clamp = req->mss; |
440 | TCP_ECN_openreq_child(newtp, req); | |
441 | if (newtp->ecn_flags&TCP_ECN_OK) | |
442 | sock_set_flag(newsk, SOCK_NO_LARGESEND); | |
443 | ||
1da177e4 LT |
444 | TCP_INC_STATS_BH(TCP_MIB_PASSIVEOPENS); |
445 | } | |
446 | return newsk; | |
447 | } | |
448 | ||
449 | /* | |
450 | * Process an incoming packet for SYN_RECV sockets represented | |
60236fdd | 451 | * as a request_sock. |
1da177e4 LT |
452 | */ |
453 | ||
454 | struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb, | |
60236fdd ACM |
455 | struct request_sock *req, |
456 | struct request_sock **prev) | |
1da177e4 LT |
457 | { |
458 | struct tcphdr *th = skb->h.th; | |
459 | struct tcp_sock *tp = tcp_sk(sk); | |
460 | u32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); | |
461 | int paws_reject = 0; | |
462 | struct tcp_options_received tmp_opt; | |
463 | struct sock *child; | |
464 | ||
465 | tmp_opt.saw_tstamp = 0; | |
466 | if (th->doff > (sizeof(struct tcphdr)>>2)) { | |
467 | tcp_parse_options(skb, &tmp_opt, 0); | |
468 | ||
469 | if (tmp_opt.saw_tstamp) { | |
470 | tmp_opt.ts_recent = req->ts_recent; | |
471 | /* We do not store true stamp, but it is not required, | |
472 | * it can be estimated (approximately) | |
473 | * from another data. | |
474 | */ | |
475 | tmp_opt.ts_recent_stamp = xtime.tv_sec - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans); | |
476 | paws_reject = tcp_paws_check(&tmp_opt, th->rst); | |
477 | } | |
478 | } | |
479 | ||
480 | /* Check for pure retransmitted SYN. */ | |
2e6599cb | 481 | if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && |
1da177e4 LT |
482 | flg == TCP_FLAG_SYN && |
483 | !paws_reject) { | |
484 | /* | |
485 | * RFC793 draws (Incorrectly! It was fixed in RFC1122) | |
486 | * this case on figure 6 and figure 8, but formal | |
487 | * protocol description says NOTHING. | |
488 | * To be more exact, it says that we should send ACK, | |
489 | * because this segment (at least, if it has no data) | |
490 | * is out of window. | |
491 | * | |
492 | * CONCLUSION: RFC793 (even with RFC1122) DOES NOT | |
493 | * describe SYN-RECV state. All the description | |
494 | * is wrong, we cannot believe to it and should | |
495 | * rely only on common sense and implementation | |
496 | * experience. | |
497 | * | |
498 | * Enforce "SYN-ACK" according to figure 8, figure 6 | |
499 | * of RFC793, fixed by RFC1122. | |
500 | */ | |
60236fdd | 501 | req->rsk_ops->rtx_syn_ack(sk, req, NULL); |
1da177e4 LT |
502 | return NULL; |
503 | } | |
504 | ||
505 | /* Further reproduces section "SEGMENT ARRIVES" | |
506 | for state SYN-RECEIVED of RFC793. | |
507 | It is broken, however, it does not work only | |
508 | when SYNs are crossed. | |
509 | ||
510 | You would think that SYN crossing is impossible here, since | |
511 | we should have a SYN_SENT socket (from connect()) on our end, | |
512 | but this is not true if the crossed SYNs were sent to both | |
513 | ends by a malicious third party. We must defend against this, | |
514 | and to do that we first verify the ACK (as per RFC793, page | |
515 | 36) and reset if it is invalid. Is this a true full defense? | |
516 | To convince ourselves, let us consider a way in which the ACK | |
517 | test can still pass in this 'malicious crossed SYNs' case. | |
518 | Malicious sender sends identical SYNs (and thus identical sequence | |
519 | numbers) to both A and B: | |
520 | ||
521 | A: gets SYN, seq=7 | |
522 | B: gets SYN, seq=7 | |
523 | ||
524 | By our good fortune, both A and B select the same initial | |
525 | send sequence number of seven :-) | |
526 | ||
527 | A: sends SYN|ACK, seq=7, ack_seq=8 | |
528 | B: sends SYN|ACK, seq=7, ack_seq=8 | |
529 | ||
530 | So we are now A eating this SYN|ACK, ACK test passes. So | |
531 | does sequence test, SYN is truncated, and thus we consider | |
532 | it a bare ACK. | |
533 | ||
295f7324 ACM |
534 | If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this |
535 | bare ACK. Otherwise, we create an established connection. Both | |
536 | ends (listening sockets) accept the new incoming connection and try | |
537 | to talk to each other. 8-) | |
1da177e4 LT |
538 | |
539 | Note: This case is both harmless, and rare. Possibility is about the | |
540 | same as us discovering intelligent life on another plant tomorrow. | |
541 | ||
542 | But generally, we should (RFC lies!) to accept ACK | |
543 | from SYNACK both here and in tcp_rcv_state_process(). | |
544 | tcp_rcv_state_process() does not, hence, we do not too. | |
545 | ||
546 | Note that the case is absolutely generic: | |
547 | we cannot optimize anything here without | |
548 | violating protocol. All the checks must be made | |
549 | before attempt to create socket. | |
550 | */ | |
551 | ||
552 | /* RFC793 page 36: "If the connection is in any non-synchronized state ... | |
553 | * and the incoming segment acknowledges something not yet | |
554 | * sent (the segment carries an unaccaptable ACK) ... | |
555 | * a reset is sent." | |
556 | * | |
557 | * Invalid ACK: reset will be sent by listening socket | |
558 | */ | |
559 | if ((flg & TCP_FLAG_ACK) && | |
2e6599cb | 560 | (TCP_SKB_CB(skb)->ack_seq != tcp_rsk(req)->snt_isn + 1)) |
1da177e4 LT |
561 | return sk; |
562 | ||
563 | /* Also, it would be not so bad idea to check rcv_tsecr, which | |
564 | * is essentially ACK extension and too early or too late values | |
565 | * should cause reset in unsynchronized states. | |
566 | */ | |
567 | ||
568 | /* RFC793: "first check sequence number". */ | |
569 | ||
570 | if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, | |
2e6599cb | 571 | tcp_rsk(req)->rcv_isn + 1, tcp_rsk(req)->rcv_isn + 1 + req->rcv_wnd)) { |
1da177e4 LT |
572 | /* Out of window: send ACK and drop. */ |
573 | if (!(flg & TCP_FLAG_RST)) | |
60236fdd | 574 | req->rsk_ops->send_ack(skb, req); |
1da177e4 LT |
575 | if (paws_reject) |
576 | NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED); | |
577 | return NULL; | |
578 | } | |
579 | ||
580 | /* In sequence, PAWS is OK. */ | |
581 | ||
2e6599cb | 582 | if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_isn + 1)) |
1da177e4 LT |
583 | req->ts_recent = tmp_opt.rcv_tsval; |
584 | ||
2e6599cb | 585 | if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { |
1da177e4 | 586 | /* Truncate SYN, it is out of window starting |
2e6599cb | 587 | at tcp_rsk(req)->rcv_isn + 1. */ |
1da177e4 LT |
588 | flg &= ~TCP_FLAG_SYN; |
589 | } | |
590 | ||
591 | /* RFC793: "second check the RST bit" and | |
592 | * "fourth, check the SYN bit" | |
593 | */ | |
594 | if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) | |
595 | goto embryonic_reset; | |
596 | ||
597 | /* ACK sequence verified above, just make sure ACK is | |
598 | * set. If ACK not set, just silently drop the packet. | |
599 | */ | |
600 | if (!(flg & TCP_FLAG_ACK)) | |
601 | return NULL; | |
602 | ||
603 | /* If TCP_DEFER_ACCEPT is set, drop bare ACK. */ | |
295f7324 ACM |
604 | if (inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && |
605 | TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { | |
2e6599cb | 606 | inet_rsk(req)->acked = 1; |
1da177e4 LT |
607 | return NULL; |
608 | } | |
609 | ||
610 | /* OK, ACK is valid, create big socket and | |
611 | * feed this segment to it. It will repeat all | |
612 | * the tests. THIS SEGMENT MUST MOVE SOCKET TO | |
613 | * ESTABLISHED STATE. If it will be dropped after | |
614 | * socket is created, wait for troubles. | |
615 | */ | |
616 | child = tp->af_specific->syn_recv_sock(sk, skb, req, NULL); | |
617 | if (child == NULL) | |
618 | goto listen_overflow; | |
619 | ||
463c84b9 ACM |
620 | inet_csk_reqsk_queue_unlink(sk, req, prev); |
621 | inet_csk_reqsk_queue_removed(sk, req); | |
1da177e4 | 622 | |
463c84b9 | 623 | inet_csk_reqsk_queue_add(sk, req, child); |
1da177e4 LT |
624 | return child; |
625 | ||
626 | listen_overflow: | |
627 | if (!sysctl_tcp_abort_on_overflow) { | |
2e6599cb | 628 | inet_rsk(req)->acked = 1; |
1da177e4 LT |
629 | return NULL; |
630 | } | |
631 | ||
632 | embryonic_reset: | |
633 | NET_INC_STATS_BH(LINUX_MIB_EMBRYONICRSTS); | |
634 | if (!(flg & TCP_FLAG_RST)) | |
60236fdd | 635 | req->rsk_ops->send_reset(skb); |
1da177e4 | 636 | |
463c84b9 | 637 | inet_csk_reqsk_queue_drop(sk, req, prev); |
1da177e4 LT |
638 | return NULL; |
639 | } | |
640 | ||
641 | /* | |
642 | * Queue segment on the new socket if the new socket is active, | |
643 | * otherwise we just shortcircuit this and continue with | |
644 | * the new socket. | |
645 | */ | |
646 | ||
647 | int tcp_child_process(struct sock *parent, struct sock *child, | |
648 | struct sk_buff *skb) | |
649 | { | |
650 | int ret = 0; | |
651 | int state = child->sk_state; | |
652 | ||
653 | if (!sock_owned_by_user(child)) { | |
654 | ret = tcp_rcv_state_process(child, skb, skb->h.th, skb->len); | |
655 | ||
656 | /* Wakeup parent, send SIGIO */ | |
657 | if (state == TCP_SYN_RECV && child->sk_state != state) | |
658 | parent->sk_data_ready(parent, 0); | |
659 | } else { | |
660 | /* Alas, it is possible again, because we do lookup | |
661 | * in main socket hash table and lock on listening | |
662 | * socket does not protect us more. | |
663 | */ | |
664 | sk_add_backlog(child, skb); | |
665 | } | |
666 | ||
667 | bh_unlock_sock(child); | |
668 | sock_put(child); | |
669 | return ret; | |
670 | } | |
671 | ||
672 | EXPORT_SYMBOL(tcp_check_req); | |
673 | EXPORT_SYMBOL(tcp_child_process); | |
674 | EXPORT_SYMBOL(tcp_create_openreq_child); | |
675 | EXPORT_SYMBOL(tcp_timewait_state_process); |