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 * 10 * Authors: Ross Biro, <bir7@leland.Stanford.Edu> 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 38 int sysctl_tcp_tw_recycle; 39 int sysctl_tcp_max_tw_buckets = NR_FILE*2; 40 41 int sysctl_tcp_syncookies = SYNC_INIT; 42 int sysctl_tcp_abort_on_overflow; 43 44 static void tcp_tw_schedule(struct tcp_tw_bucket *tw, int timeo); 45 46 static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) 47 { 48 if (seq == s_win) 49 return 1; 50 if (after(end_seq, s_win) && before(seq, e_win)) 51 return 1; 52 return (seq == e_win && seq == end_seq); 53 } 54 55 /* New-style handling of TIME_WAIT sockets. */ 56 57 int tcp_tw_count; 58 59 60 /* Must be called with locally disabled BHs. */ 61 static void tcp_timewait_kill(struct tcp_tw_bucket *tw) 62 { 63 struct tcp_ehash_bucket *ehead; 64 struct tcp_bind_hashbucket *bhead; 65 struct tcp_bind_bucket *tb; 66 67 /* Unlink from established hashes. */ 68 ehead = &tcp_ehash[tw->tw_hashent]; 69 write_lock(&ehead->lock); 70 if (hlist_unhashed(&tw->tw_node)) { 71 write_unlock(&ehead->lock); 72 return; 73 } 74 __hlist_del(&tw->tw_node); 75 sk_node_init(&tw->tw_node); 76 write_unlock(&ehead->lock); 77 78 /* Disassociate with bind bucket. */ 79 bhead = &tcp_bhash[tcp_bhashfn(tw->tw_num)]; 80 spin_lock(&bhead->lock); 81 tb = tw->tw_tb; 82 __hlist_del(&tw->tw_bind_node); 83 tw->tw_tb = NULL; 84 tcp_bucket_destroy(tb); 85 spin_unlock(&bhead->lock); 86 87 #ifdef INET_REFCNT_DEBUG 88 if (atomic_read(&tw->tw_refcnt) != 1) { 89 printk(KERN_DEBUG "tw_bucket %p refcnt=%d\n", tw, 90 atomic_read(&tw->tw_refcnt)); 91 } 92 #endif 93 tcp_tw_put(tw); 94 } 95 96 /* 97 * * Main purpose of TIME-WAIT state is to close connection gracefully, 98 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 99 * (and, probably, tail of data) and one or more our ACKs are lost. 100 * * What is TIME-WAIT timeout? It is associated with maximal packet 101 * lifetime in the internet, which results in wrong conclusion, that 102 * it is set to catch "old duplicate segments" wandering out of their path. 103 * It is not quite correct. This timeout is calculated so that it exceeds 104 * maximal retransmission timeout enough to allow to lose one (or more) 105 * segments sent by peer and our ACKs. This time may be calculated from RTO. 106 * * When TIME-WAIT socket receives RST, it means that another end 107 * finally closed and we are allowed to kill TIME-WAIT too. 108 * * Second purpose of TIME-WAIT is catching old duplicate segments. 109 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 110 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 111 * * If we invented some more clever way to catch duplicates 112 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 113 * 114 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 115 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 116 * from the very beginning. 117 * 118 * NOTE. With recycling (and later with fin-wait-2) TW bucket 119 * is _not_ stateless. It means, that strictly speaking we must 120 * spinlock it. I do not want! Well, probability of misbehaviour 121 * is ridiculously low and, seems, we could use some mb() tricks 122 * to avoid misread sequence numbers, states etc. --ANK 123 */ 124 enum tcp_tw_status 125 tcp_timewait_state_process(struct tcp_tw_bucket *tw, struct sk_buff *skb, 126 struct tcphdr *th, unsigned len) 127 { 128 struct tcp_options_received tmp_opt; 129 int paws_reject = 0; 130 131 tmp_opt.saw_tstamp = 0; 132 if (th->doff > (sizeof(struct tcphdr) >> 2) && tw->tw_ts_recent_stamp) { 133 tcp_parse_options(skb, &tmp_opt, 0); 134 135 if (tmp_opt.saw_tstamp) { 136 tmp_opt.ts_recent = tw->tw_ts_recent; 137 tmp_opt.ts_recent_stamp = tw->tw_ts_recent_stamp; 138 paws_reject = tcp_paws_check(&tmp_opt, th->rst); 139 } 140 } 141 142 if (tw->tw_substate == TCP_FIN_WAIT2) { 143 /* Just repeat all the checks of tcp_rcv_state_process() */ 144 145 /* Out of window, send ACK */ 146 if (paws_reject || 147 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 148 tw->tw_rcv_nxt, 149 tw->tw_rcv_nxt + tw->tw_rcv_wnd)) 150 return TCP_TW_ACK; 151 152 if (th->rst) 153 goto kill; 154 155 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tw->tw_rcv_nxt)) 156 goto kill_with_rst; 157 158 /* Dup ACK? */ 159 if (!after(TCP_SKB_CB(skb)->end_seq, tw->tw_rcv_nxt) || 160 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 161 tcp_tw_put(tw); 162 return TCP_TW_SUCCESS; 163 } 164 165 /* New data or FIN. If new data arrive after half-duplex close, 166 * reset. 167 */ 168 if (!th->fin || 169 TCP_SKB_CB(skb)->end_seq != tw->tw_rcv_nxt + 1) { 170 kill_with_rst: 171 tcp_tw_deschedule(tw); 172 tcp_tw_put(tw); 173 return TCP_TW_RST; 174 } 175 176 /* FIN arrived, enter true time-wait state. */ 177 tw->tw_substate = TCP_TIME_WAIT; 178 tw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq; 179 if (tmp_opt.saw_tstamp) { 180 tw->tw_ts_recent_stamp = xtime.tv_sec; 181 tw->tw_ts_recent = tmp_opt.rcv_tsval; 182 } 183 184 /* I am shamed, but failed to make it more elegant. 185 * Yes, it is direct reference to IP, which is impossible 186 * to generalize to IPv6. Taking into account that IPv6 187 * do not undertsnad recycling in any case, it not 188 * a big problem in practice. --ANK */ 189 if (tw->tw_family == AF_INET && 190 sysctl_tcp_tw_recycle && tw->tw_ts_recent_stamp && 191 tcp_v4_tw_remember_stamp(tw)) 192 tcp_tw_schedule(tw, tw->tw_timeout); 193 else 194 tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN); 195 return TCP_TW_ACK; 196 } 197 198 /* 199 * Now real TIME-WAIT state. 200 * 201 * RFC 1122: 202 * "When a connection is [...] on TIME-WAIT state [...] 203 * [a TCP] MAY accept a new SYN from the remote TCP to 204 * reopen the connection directly, if it: 205 * 206 * (1) assigns its initial sequence number for the new 207 * connection to be larger than the largest sequence 208 * number it used on the previous connection incarnation, 209 * and 210 * 211 * (2) returns to TIME-WAIT state if the SYN turns out 212 * to be an old duplicate". 213 */ 214 215 if (!paws_reject && 216 (TCP_SKB_CB(skb)->seq == tw->tw_rcv_nxt && 217 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 218 /* In window segment, it may be only reset or bare ack. */ 219 220 if (th->rst) { 221 /* This is TIME_WAIT assasination, in two flavors. 222 * Oh well... nobody has a sufficient solution to this 223 * protocol bug yet. 224 */ 225 if (sysctl_tcp_rfc1337 == 0) { 226 kill: 227 tcp_tw_deschedule(tw); 228 tcp_tw_put(tw); 229 return TCP_TW_SUCCESS; 230 } 231 } 232 tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN); 233 234 if (tmp_opt.saw_tstamp) { 235 tw->tw_ts_recent = tmp_opt.rcv_tsval; 236 tw->tw_ts_recent_stamp = xtime.tv_sec; 237 } 238 239 tcp_tw_put(tw); 240 return TCP_TW_SUCCESS; 241 } 242 243 /* Out of window segment. 244 245 All the segments are ACKed immediately. 246 247 The only exception is new SYN. We accept it, if it is 248 not old duplicate and we are not in danger to be killed 249 by delayed old duplicates. RFC check is that it has 250 newer sequence number works at rates <40Mbit/sec. 251 However, if paws works, it is reliable AND even more, 252 we even may relax silly seq space cutoff. 253 254 RED-PEN: we violate main RFC requirement, if this SYN will appear 255 old duplicate (i.e. we receive RST in reply to SYN-ACK), 256 we must return socket to time-wait state. It is not good, 257 but not fatal yet. 258 */ 259 260 if (th->syn && !th->rst && !th->ack && !paws_reject && 261 (after(TCP_SKB_CB(skb)->seq, tw->tw_rcv_nxt) || 262 (tmp_opt.saw_tstamp && (s32)(tw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { 263 u32 isn = tw->tw_snd_nxt + 65535 + 2; 264 if (isn == 0) 265 isn++; 266 TCP_SKB_CB(skb)->when = isn; 267 return TCP_TW_SYN; 268 } 269 270 if (paws_reject) 271 NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED); 272 273 if(!th->rst) { 274 /* In this case we must reset the TIMEWAIT timer. 275 * 276 * If it is ACKless SYN it may be both old duplicate 277 * and new good SYN with random sequence number <rcv_nxt. 278 * Do not reschedule in the last case. 279 */ 280 if (paws_reject || th->ack) 281 tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN); 282 283 /* Send ACK. Note, we do not put the bucket, 284 * it will be released by caller. 285 */ 286 return TCP_TW_ACK; 287 } 288 tcp_tw_put(tw); 289 return TCP_TW_SUCCESS; 290 } 291 292 /* Enter the time wait state. This is called with locally disabled BH. 293 * Essentially we whip up a timewait bucket, copy the 294 * relevant info into it from the SK, and mess with hash chains 295 * and list linkage. 296 */ 297 static void __tcp_tw_hashdance(struct sock *sk, struct tcp_tw_bucket *tw) 298 { 299 struct tcp_ehash_bucket *ehead = &tcp_ehash[sk->sk_hashent]; 300 struct tcp_bind_hashbucket *bhead; 301 302 /* Step 1: Put TW into bind hash. Original socket stays there too. 303 Note, that any socket with inet_sk(sk)->num != 0 MUST be bound in 304 binding cache, even if it is closed. 305 */ 306 bhead = &tcp_bhash[tcp_bhashfn(inet_sk(sk)->num)]; 307 spin_lock(&bhead->lock); 308 tw->tw_tb = tcp_sk(sk)->bind_hash; 309 BUG_TRAP(tcp_sk(sk)->bind_hash); 310 tw_add_bind_node(tw, &tw->tw_tb->owners); 311 spin_unlock(&bhead->lock); 312 313 write_lock(&ehead->lock); 314 315 /* Step 2: Remove SK from established hash. */ 316 if (__sk_del_node_init(sk)) 317 sock_prot_dec_use(sk->sk_prot); 318 319 /* Step 3: Hash TW into TIMEWAIT half of established hash table. */ 320 tw_add_node(tw, &(ehead + tcp_ehash_size)->chain); 321 atomic_inc(&tw->tw_refcnt); 322 323 write_unlock(&ehead->lock); 324 } 325 326 /* 327 * Move a socket to time-wait or dead fin-wait-2 state. 328 */ 329 void tcp_time_wait(struct sock *sk, int state, int timeo) 330 { 331 struct tcp_tw_bucket *tw = NULL; 332 struct tcp_sock *tp = tcp_sk(sk); 333 int recycle_ok = 0; 334 335 if (sysctl_tcp_tw_recycle && tp->rx_opt.ts_recent_stamp) 336 recycle_ok = tp->af_specific->remember_stamp(sk); 337 338 if (tcp_tw_count < sysctl_tcp_max_tw_buckets) 339 tw = kmem_cache_alloc(tcp_timewait_cachep, SLAB_ATOMIC); 340 341 if(tw != NULL) { 342 struct inet_sock *inet = inet_sk(sk); 343 int rto = (tp->rto<<2) - (tp->rto>>1); 344 345 /* Give us an identity. */ 346 tw->tw_daddr = inet->daddr; 347 tw->tw_rcv_saddr = inet->rcv_saddr; 348 tw->tw_bound_dev_if = sk->sk_bound_dev_if; 349 tw->tw_num = inet->num; 350 tw->tw_state = TCP_TIME_WAIT; 351 tw->tw_substate = state; 352 tw->tw_sport = inet->sport; 353 tw->tw_dport = inet->dport; 354 tw->tw_family = sk->sk_family; 355 tw->tw_reuse = sk->sk_reuse; 356 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 357 atomic_set(&tw->tw_refcnt, 1); 358 359 tw->tw_hashent = sk->sk_hashent; 360 tw->tw_rcv_nxt = tp->rcv_nxt; 361 tw->tw_snd_nxt = tp->snd_nxt; 362 tw->tw_rcv_wnd = tcp_receive_window(tp); 363 tw->tw_ts_recent = tp->rx_opt.ts_recent; 364 tw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 365 tw_dead_node_init(tw); 366 367 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) 368 if (tw->tw_family == PF_INET6) { 369 struct ipv6_pinfo *np = inet6_sk(sk); 370 371 ipv6_addr_copy(&tw->tw_v6_daddr, &np->daddr); 372 ipv6_addr_copy(&tw->tw_v6_rcv_saddr, &np->rcv_saddr); 373 tw->tw_v6_ipv6only = np->ipv6only; 374 } else { 375 memset(&tw->tw_v6_daddr, 0, sizeof(tw->tw_v6_daddr)); 376 memset(&tw->tw_v6_rcv_saddr, 0, sizeof(tw->tw_v6_rcv_saddr)); 377 tw->tw_v6_ipv6only = 0; 378 } 379 #endif 380 /* Linkage updates. */ 381 __tcp_tw_hashdance(sk, tw); 382 383 /* Get the TIME_WAIT timeout firing. */ 384 if (timeo < rto) 385 timeo = rto; 386 387 if (recycle_ok) { 388 tw->tw_timeout = rto; 389 } else { 390 tw->tw_timeout = TCP_TIMEWAIT_LEN; 391 if (state == TCP_TIME_WAIT) 392 timeo = TCP_TIMEWAIT_LEN; 393 } 394 395 tcp_tw_schedule(tw, timeo); 396 tcp_tw_put(tw); 397 } else { 398 /* Sorry, if we're out of memory, just CLOSE this 399 * socket up. We've got bigger problems than 400 * non-graceful socket closings. 401 */ 402 if (net_ratelimit()) 403 printk(KERN_INFO "TCP: time wait bucket table overflow\n"); 404 } 405 406 tcp_update_metrics(sk); 407 tcp_done(sk); 408 } 409 410 /* Kill off TIME_WAIT sockets once their lifetime has expired. */ 411 static int tcp_tw_death_row_slot; 412 413 static void tcp_twkill(unsigned long); 414 415 /* TIME_WAIT reaping mechanism. */ 416 #define TCP_TWKILL_SLOTS 8 /* Please keep this a power of 2. */ 417 #define TCP_TWKILL_PERIOD (TCP_TIMEWAIT_LEN/TCP_TWKILL_SLOTS) 418 419 #define TCP_TWKILL_QUOTA 100 420 421 static struct hlist_head tcp_tw_death_row[TCP_TWKILL_SLOTS]; 422 static DEFINE_SPINLOCK(tw_death_lock); 423 static struct timer_list tcp_tw_timer = TIMER_INITIALIZER(tcp_twkill, 0, 0); 424 static void twkill_work(void *); 425 static DECLARE_WORK(tcp_twkill_work, twkill_work, NULL); 426 static u32 twkill_thread_slots; 427 428 /* Returns non-zero if quota exceeded. */ 429 static int tcp_do_twkill_work(int slot, unsigned int quota) 430 { 431 struct tcp_tw_bucket *tw; 432 struct hlist_node *node; 433 unsigned int killed; 434 int ret; 435 436 /* NOTE: compare this to previous version where lock 437 * was released after detaching chain. It was racy, 438 * because tw buckets are scheduled in not serialized context 439 * in 2.3 (with netfilter), and with softnet it is common, because 440 * soft irqs are not sequenced. 441 */ 442 killed = 0; 443 ret = 0; 444 rescan: 445 tw_for_each_inmate(tw, node, &tcp_tw_death_row[slot]) { 446 __tw_del_dead_node(tw); 447 spin_unlock(&tw_death_lock); 448 tcp_timewait_kill(tw); 449 tcp_tw_put(tw); 450 killed++; 451 spin_lock(&tw_death_lock); 452 if (killed > quota) { 453 ret = 1; 454 break; 455 } 456 457 /* While we dropped tw_death_lock, another cpu may have 458 * killed off the next TW bucket in the list, therefore 459 * do a fresh re-read of the hlist head node with the 460 * lock reacquired. We still use the hlist traversal 461 * macro in order to get the prefetches. 462 */ 463 goto rescan; 464 } 465 466 tcp_tw_count -= killed; 467 NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITED, killed); 468 469 return ret; 470 } 471 472 static void tcp_twkill(unsigned long dummy) 473 { 474 int need_timer, ret; 475 476 spin_lock(&tw_death_lock); 477 478 if (tcp_tw_count == 0) 479 goto out; 480 481 need_timer = 0; 482 ret = tcp_do_twkill_work(tcp_tw_death_row_slot, TCP_TWKILL_QUOTA); 483 if (ret) { 484 twkill_thread_slots |= (1 << tcp_tw_death_row_slot); 485 mb(); 486 schedule_work(&tcp_twkill_work); 487 need_timer = 1; 488 } else { 489 /* We purged the entire slot, anything left? */ 490 if (tcp_tw_count) 491 need_timer = 1; 492 } 493 tcp_tw_death_row_slot = 494 ((tcp_tw_death_row_slot + 1) & (TCP_TWKILL_SLOTS - 1)); 495 if (need_timer) 496 mod_timer(&tcp_tw_timer, jiffies + TCP_TWKILL_PERIOD); 497 out: 498 spin_unlock(&tw_death_lock); 499 } 500 501 extern void twkill_slots_invalid(void); 502 503 static void twkill_work(void *dummy) 504 { 505 int i; 506 507 if ((TCP_TWKILL_SLOTS - 1) > (sizeof(twkill_thread_slots) * 8)) 508 twkill_slots_invalid(); 509 510 while (twkill_thread_slots) { 511 spin_lock_bh(&tw_death_lock); 512 for (i = 0; i < TCP_TWKILL_SLOTS; i++) { 513 if (!(twkill_thread_slots & (1 << i))) 514 continue; 515 516 while (tcp_do_twkill_work(i, TCP_TWKILL_QUOTA) != 0) { 517 if (need_resched()) { 518 spin_unlock_bh(&tw_death_lock); 519 schedule(); 520 spin_lock_bh(&tw_death_lock); 521 } 522 } 523 524 twkill_thread_slots &= ~(1 << i); 525 } 526 spin_unlock_bh(&tw_death_lock); 527 } 528 } 529 530 /* These are always called from BH context. See callers in 531 * tcp_input.c to verify this. 532 */ 533 534 /* This is for handling early-kills of TIME_WAIT sockets. */ 535 void tcp_tw_deschedule(struct tcp_tw_bucket *tw) 536 { 537 spin_lock(&tw_death_lock); 538 if (tw_del_dead_node(tw)) { 539 tcp_tw_put(tw); 540 if (--tcp_tw_count == 0) 541 del_timer(&tcp_tw_timer); 542 } 543 spin_unlock(&tw_death_lock); 544 tcp_timewait_kill(tw); 545 } 546 547 /* Short-time timewait calendar */ 548 549 static int tcp_twcal_hand = -1; 550 static int tcp_twcal_jiffie; 551 static void tcp_twcal_tick(unsigned long); 552 static struct timer_list tcp_twcal_timer = 553 TIMER_INITIALIZER(tcp_twcal_tick, 0, 0); 554 static struct hlist_head tcp_twcal_row[TCP_TW_RECYCLE_SLOTS]; 555 556 static void tcp_tw_schedule(struct tcp_tw_bucket *tw, int timeo) 557 { 558 struct hlist_head *list; 559 int slot; 560 561 /* timeout := RTO * 3.5 562 * 563 * 3.5 = 1+2+0.5 to wait for two retransmits. 564 * 565 * RATIONALE: if FIN arrived and we entered TIME-WAIT state, 566 * our ACK acking that FIN can be lost. If N subsequent retransmitted 567 * FINs (or previous seqments) are lost (probability of such event 568 * is p^(N+1), where p is probability to lose single packet and 569 * time to detect the loss is about RTO*(2^N - 1) with exponential 570 * backoff). Normal timewait length is calculated so, that we 571 * waited at least for one retransmitted FIN (maximal RTO is 120sec). 572 * [ BTW Linux. following BSD, violates this requirement waiting 573 * only for 60sec, we should wait at least for 240 secs. 574 * Well, 240 consumes too much of resources 8) 575 * ] 576 * This interval is not reduced to catch old duplicate and 577 * responces to our wandering segments living for two MSLs. 578 * However, if we use PAWS to detect 579 * old duplicates, we can reduce the interval to bounds required 580 * by RTO, rather than MSL. So, if peer understands PAWS, we 581 * kill tw bucket after 3.5*RTO (it is important that this number 582 * is greater than TS tick!) and detect old duplicates with help 583 * of PAWS. 584 */ 585 slot = (timeo + (1<<TCP_TW_RECYCLE_TICK) - 1) >> TCP_TW_RECYCLE_TICK; 586 587 spin_lock(&tw_death_lock); 588 589 /* Unlink it, if it was scheduled */ 590 if (tw_del_dead_node(tw)) 591 tcp_tw_count--; 592 else 593 atomic_inc(&tw->tw_refcnt); 594 595 if (slot >= TCP_TW_RECYCLE_SLOTS) { 596 /* Schedule to slow timer */ 597 if (timeo >= TCP_TIMEWAIT_LEN) { 598 slot = TCP_TWKILL_SLOTS-1; 599 } else { 600 slot = (timeo + TCP_TWKILL_PERIOD-1) / TCP_TWKILL_PERIOD; 601 if (slot >= TCP_TWKILL_SLOTS) 602 slot = TCP_TWKILL_SLOTS-1; 603 } 604 tw->tw_ttd = jiffies + timeo; 605 slot = (tcp_tw_death_row_slot + slot) & (TCP_TWKILL_SLOTS - 1); 606 list = &tcp_tw_death_row[slot]; 607 } else { 608 tw->tw_ttd = jiffies + (slot << TCP_TW_RECYCLE_TICK); 609 610 if (tcp_twcal_hand < 0) { 611 tcp_twcal_hand = 0; 612 tcp_twcal_jiffie = jiffies; 613 tcp_twcal_timer.expires = tcp_twcal_jiffie + (slot<<TCP_TW_RECYCLE_TICK); 614 add_timer(&tcp_twcal_timer); 615 } else { 616 if (time_after(tcp_twcal_timer.expires, jiffies + (slot<<TCP_TW_RECYCLE_TICK))) 617 mod_timer(&tcp_twcal_timer, jiffies + (slot<<TCP_TW_RECYCLE_TICK)); 618 slot = (tcp_twcal_hand + slot)&(TCP_TW_RECYCLE_SLOTS-1); 619 } 620 list = &tcp_twcal_row[slot]; 621 } 622 623 hlist_add_head(&tw->tw_death_node, list); 624 625 if (tcp_tw_count++ == 0) 626 mod_timer(&tcp_tw_timer, jiffies+TCP_TWKILL_PERIOD); 627 spin_unlock(&tw_death_lock); 628 } 629 630 void tcp_twcal_tick(unsigned long dummy) 631 { 632 int n, slot; 633 unsigned long j; 634 unsigned long now = jiffies; 635 int killed = 0; 636 int adv = 0; 637 638 spin_lock(&tw_death_lock); 639 if (tcp_twcal_hand < 0) 640 goto out; 641 642 slot = tcp_twcal_hand; 643 j = tcp_twcal_jiffie; 644 645 for (n=0; n<TCP_TW_RECYCLE_SLOTS; n++) { 646 if (time_before_eq(j, now)) { 647 struct hlist_node *node, *safe; 648 struct tcp_tw_bucket *tw; 649 650 tw_for_each_inmate_safe(tw, node, safe, 651 &tcp_twcal_row[slot]) { 652 __tw_del_dead_node(tw); 653 tcp_timewait_kill(tw); 654 tcp_tw_put(tw); 655 killed++; 656 } 657 } else { 658 if (!adv) { 659 adv = 1; 660 tcp_twcal_jiffie = j; 661 tcp_twcal_hand = slot; 662 } 663 664 if (!hlist_empty(&tcp_twcal_row[slot])) { 665 mod_timer(&tcp_twcal_timer, j); 666 goto out; 667 } 668 } 669 j += (1<<TCP_TW_RECYCLE_TICK); 670 slot = (slot+1)&(TCP_TW_RECYCLE_SLOTS-1); 671 } 672 tcp_twcal_hand = -1; 673 674 out: 675 if ((tcp_tw_count -= killed) == 0) 676 del_timer(&tcp_tw_timer); 677 NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITKILLED, killed); 678 spin_unlock(&tw_death_lock); 679 } 680 681 /* This is not only more efficient than what we used to do, it eliminates 682 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 683 * 684 * Actually, we could lots of memory writes here. tp of listening 685 * socket contains all necessary default parameters. 686 */ 687 struct sock *tcp_create_openreq_child(struct sock *sk, struct open_request *req, struct sk_buff *skb) 688 { 689 /* allocate the newsk from the same slab of the master sock, 690 * if not, at sk_free time we'll try to free it from the wrong 691 * slabcache (i.e. is it TCPv4 or v6?), this is handled thru sk->sk_prot -acme */ 692 struct sock *newsk = sk_alloc(PF_INET, GFP_ATOMIC, sk->sk_prot, 0); 693 694 if(newsk != NULL) { 695 struct tcp_sock *newtp; 696 struct sk_filter *filter; 697 698 memcpy(newsk, sk, sizeof(struct tcp_sock)); 699 newsk->sk_state = TCP_SYN_RECV; 700 701 /* SANITY */ 702 sk_node_init(&newsk->sk_node); 703 tcp_sk(newsk)->bind_hash = NULL; 704 705 /* Clone the TCP header template */ 706 inet_sk(newsk)->dport = req->rmt_port; 707 708 sock_lock_init(newsk); 709 bh_lock_sock(newsk); 710 711 rwlock_init(&newsk->sk_dst_lock); 712 atomic_set(&newsk->sk_rmem_alloc, 0); 713 skb_queue_head_init(&newsk->sk_receive_queue); 714 atomic_set(&newsk->sk_wmem_alloc, 0); 715 skb_queue_head_init(&newsk->sk_write_queue); 716 atomic_set(&newsk->sk_omem_alloc, 0); 717 newsk->sk_wmem_queued = 0; 718 newsk->sk_forward_alloc = 0; 719 720 sock_reset_flag(newsk, SOCK_DONE); 721 newsk->sk_userlocks = sk->sk_userlocks & ~SOCK_BINDPORT_LOCK; 722 newsk->sk_backlog.head = newsk->sk_backlog.tail = NULL; 723 newsk->sk_send_head = NULL; 724 rwlock_init(&newsk->sk_callback_lock); 725 skb_queue_head_init(&newsk->sk_error_queue); 726 newsk->sk_write_space = sk_stream_write_space; 727 728 if ((filter = newsk->sk_filter) != NULL) 729 sk_filter_charge(newsk, filter); 730 731 if (unlikely(xfrm_sk_clone_policy(newsk))) { 732 /* It is still raw copy of parent, so invalidate 733 * destructor and make plain sk_free() */ 734 newsk->sk_destruct = NULL; 735 sk_free(newsk); 736 return NULL; 737 } 738 739 /* Now setup tcp_sock */ 740 newtp = tcp_sk(newsk); 741 newtp->pred_flags = 0; 742 newtp->rcv_nxt = req->rcv_isn + 1; 743 newtp->snd_nxt = req->snt_isn + 1; 744 newtp->snd_una = req->snt_isn + 1; 745 newtp->snd_sml = req->snt_isn + 1; 746 747 tcp_prequeue_init(newtp); 748 749 tcp_init_wl(newtp, req->snt_isn, req->rcv_isn); 750 751 newtp->retransmits = 0; 752 newtp->backoff = 0; 753 newtp->srtt = 0; 754 newtp->mdev = TCP_TIMEOUT_INIT; 755 newtp->rto = TCP_TIMEOUT_INIT; 756 757 newtp->packets_out = 0; 758 newtp->left_out = 0; 759 newtp->retrans_out = 0; 760 newtp->sacked_out = 0; 761 newtp->fackets_out = 0; 762 newtp->snd_ssthresh = 0x7fffffff; 763 764 /* So many TCP implementations out there (incorrectly) count the 765 * initial SYN frame in their delayed-ACK and congestion control 766 * algorithms that we must have the following bandaid to talk 767 * efficiently to them. -DaveM 768 */ 769 newtp->snd_cwnd = 2; 770 newtp->snd_cwnd_cnt = 0; 771 772 newtp->frto_counter = 0; 773 newtp->frto_highmark = 0; 774 775 tcp_set_ca_state(newtp, TCP_CA_Open); 776 tcp_init_xmit_timers(newsk); 777 skb_queue_head_init(&newtp->out_of_order_queue); 778 newtp->rcv_wup = req->rcv_isn + 1; 779 newtp->write_seq = req->snt_isn + 1; 780 newtp->pushed_seq = newtp->write_seq; 781 newtp->copied_seq = req->rcv_isn + 1; 782 783 newtp->rx_opt.saw_tstamp = 0; 784 785 newtp->rx_opt.dsack = 0; 786 newtp->rx_opt.eff_sacks = 0; 787 788 newtp->probes_out = 0; 789 newtp->rx_opt.num_sacks = 0; 790 newtp->urg_data = 0; 791 newtp->listen_opt = NULL; 792 newtp->accept_queue = newtp->accept_queue_tail = NULL; 793 /* Deinitialize syn_wait_lock to trap illegal accesses. */ 794 memset(&newtp->syn_wait_lock, 0, sizeof(newtp->syn_wait_lock)); 795 796 /* Back to base struct sock members. */ 797 newsk->sk_err = 0; 798 newsk->sk_priority = 0; 799 atomic_set(&newsk->sk_refcnt, 2); 800 #ifdef INET_REFCNT_DEBUG 801 atomic_inc(&inet_sock_nr); 802 #endif 803 atomic_inc(&tcp_sockets_allocated); 804 805 if (sock_flag(newsk, SOCK_KEEPOPEN)) 806 tcp_reset_keepalive_timer(newsk, 807 keepalive_time_when(newtp)); 808 newsk->sk_socket = NULL; 809 newsk->sk_sleep = NULL; 810 811 newtp->rx_opt.tstamp_ok = req->tstamp_ok; 812 if((newtp->rx_opt.sack_ok = req->sack_ok) != 0) { 813 if (sysctl_tcp_fack) 814 newtp->rx_opt.sack_ok |= 2; 815 } 816 newtp->window_clamp = req->window_clamp; 817 newtp->rcv_ssthresh = req->rcv_wnd; 818 newtp->rcv_wnd = req->rcv_wnd; 819 newtp->rx_opt.wscale_ok = req->wscale_ok; 820 if (newtp->rx_opt.wscale_ok) { 821 newtp->rx_opt.snd_wscale = req->snd_wscale; 822 newtp->rx_opt.rcv_wscale = req->rcv_wscale; 823 } else { 824 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 825 newtp->window_clamp = min(newtp->window_clamp, 65535U); 826 } 827 newtp->snd_wnd = ntohs(skb->h.th->window) << newtp->rx_opt.snd_wscale; 828 newtp->max_window = newtp->snd_wnd; 829 830 if (newtp->rx_opt.tstamp_ok) { 831 newtp->rx_opt.ts_recent = req->ts_recent; 832 newtp->rx_opt.ts_recent_stamp = xtime.tv_sec; 833 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 834 } else { 835 newtp->rx_opt.ts_recent_stamp = 0; 836 newtp->tcp_header_len = sizeof(struct tcphdr); 837 } 838 if (skb->len >= TCP_MIN_RCVMSS+newtp->tcp_header_len) 839 newtp->ack.last_seg_size = skb->len-newtp->tcp_header_len; 840 newtp->rx_opt.mss_clamp = req->mss; 841 TCP_ECN_openreq_child(newtp, req); 842 if (newtp->ecn_flags&TCP_ECN_OK) 843 sock_set_flag(newsk, SOCK_NO_LARGESEND); 844 845 tcp_ca_init(newtp); 846 847 TCP_INC_STATS_BH(TCP_MIB_PASSIVEOPENS); 848 } 849 return newsk; 850 } 851 852 /* 853 * Process an incoming packet for SYN_RECV sockets represented 854 * as an open_request. 855 */ 856 857 struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb, 858 struct open_request *req, 859 struct open_request **prev) 860 { 861 struct tcphdr *th = skb->h.th; 862 struct tcp_sock *tp = tcp_sk(sk); 863 u32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 864 int paws_reject = 0; 865 struct tcp_options_received tmp_opt; 866 struct sock *child; 867 868 tmp_opt.saw_tstamp = 0; 869 if (th->doff > (sizeof(struct tcphdr)>>2)) { 870 tcp_parse_options(skb, &tmp_opt, 0); 871 872 if (tmp_opt.saw_tstamp) { 873 tmp_opt.ts_recent = req->ts_recent; 874 /* We do not store true stamp, but it is not required, 875 * it can be estimated (approximately) 876 * from another data. 877 */ 878 tmp_opt.ts_recent_stamp = xtime.tv_sec - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans); 879 paws_reject = tcp_paws_check(&tmp_opt, th->rst); 880 } 881 } 882 883 /* Check for pure retransmitted SYN. */ 884 if (TCP_SKB_CB(skb)->seq == req->rcv_isn && 885 flg == TCP_FLAG_SYN && 886 !paws_reject) { 887 /* 888 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 889 * this case on figure 6 and figure 8, but formal 890 * protocol description says NOTHING. 891 * To be more exact, it says that we should send ACK, 892 * because this segment (at least, if it has no data) 893 * is out of window. 894 * 895 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 896 * describe SYN-RECV state. All the description 897 * is wrong, we cannot believe to it and should 898 * rely only on common sense and implementation 899 * experience. 900 * 901 * Enforce "SYN-ACK" according to figure 8, figure 6 902 * of RFC793, fixed by RFC1122. 903 */ 904 req->class->rtx_syn_ack(sk, req, NULL); 905 return NULL; 906 } 907 908 /* Further reproduces section "SEGMENT ARRIVES" 909 for state SYN-RECEIVED of RFC793. 910 It is broken, however, it does not work only 911 when SYNs are crossed. 912 913 You would think that SYN crossing is impossible here, since 914 we should have a SYN_SENT socket (from connect()) on our end, 915 but this is not true if the crossed SYNs were sent to both 916 ends by a malicious third party. We must defend against this, 917 and to do that we first verify the ACK (as per RFC793, page 918 36) and reset if it is invalid. Is this a true full defense? 919 To convince ourselves, let us consider a way in which the ACK 920 test can still pass in this 'malicious crossed SYNs' case. 921 Malicious sender sends identical SYNs (and thus identical sequence 922 numbers) to both A and B: 923 924 A: gets SYN, seq=7 925 B: gets SYN, seq=7 926 927 By our good fortune, both A and B select the same initial 928 send sequence number of seven :-) 929 930 A: sends SYN|ACK, seq=7, ack_seq=8 931 B: sends SYN|ACK, seq=7, ack_seq=8 932 933 So we are now A eating this SYN|ACK, ACK test passes. So 934 does sequence test, SYN is truncated, and thus we consider 935 it a bare ACK. 936 937 If tp->defer_accept, we silently drop this bare ACK. Otherwise, 938 we create an established connection. Both ends (listening sockets) 939 accept the new incoming connection and try to talk to each other. 8-) 940 941 Note: This case is both harmless, and rare. Possibility is about the 942 same as us discovering intelligent life on another plant tomorrow. 943 944 But generally, we should (RFC lies!) to accept ACK 945 from SYNACK both here and in tcp_rcv_state_process(). 946 tcp_rcv_state_process() does not, hence, we do not too. 947 948 Note that the case is absolutely generic: 949 we cannot optimize anything here without 950 violating protocol. All the checks must be made 951 before attempt to create socket. 952 */ 953 954 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 955 * and the incoming segment acknowledges something not yet 956 * sent (the segment carries an unaccaptable ACK) ... 957 * a reset is sent." 958 * 959 * Invalid ACK: reset will be sent by listening socket 960 */ 961 if ((flg & TCP_FLAG_ACK) && 962 (TCP_SKB_CB(skb)->ack_seq != req->snt_isn+1)) 963 return sk; 964 965 /* Also, it would be not so bad idea to check rcv_tsecr, which 966 * is essentially ACK extension and too early or too late values 967 * should cause reset in unsynchronized states. 968 */ 969 970 /* RFC793: "first check sequence number". */ 971 972 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 973 req->rcv_isn+1, req->rcv_isn+1+req->rcv_wnd)) { 974 /* Out of window: send ACK and drop. */ 975 if (!(flg & TCP_FLAG_RST)) 976 req->class->send_ack(skb, req); 977 if (paws_reject) 978 NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED); 979 return NULL; 980 } 981 982 /* In sequence, PAWS is OK. */ 983 984 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, req->rcv_isn+1)) 985 req->ts_recent = tmp_opt.rcv_tsval; 986 987 if (TCP_SKB_CB(skb)->seq == req->rcv_isn) { 988 /* Truncate SYN, it is out of window starting 989 at req->rcv_isn+1. */ 990 flg &= ~TCP_FLAG_SYN; 991 } 992 993 /* RFC793: "second check the RST bit" and 994 * "fourth, check the SYN bit" 995 */ 996 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) 997 goto embryonic_reset; 998 999 /* ACK sequence verified above, just make sure ACK is 1000 * set. If ACK not set, just silently drop the packet. 1001 */ 1002 if (!(flg & TCP_FLAG_ACK)) 1003 return NULL; 1004 1005 /* If TCP_DEFER_ACCEPT is set, drop bare ACK. */ 1006 if (tp->defer_accept && TCP_SKB_CB(skb)->end_seq == req->rcv_isn+1) { 1007 req->acked = 1; 1008 return NULL; 1009 } 1010 1011 /* OK, ACK is valid, create big socket and 1012 * feed this segment to it. It will repeat all 1013 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 1014 * ESTABLISHED STATE. If it will be dropped after 1015 * socket is created, wait for troubles. 1016 */ 1017 child = tp->af_specific->syn_recv_sock(sk, skb, req, NULL); 1018 if (child == NULL) 1019 goto listen_overflow; 1020 1021 tcp_synq_unlink(tp, req, prev); 1022 tcp_synq_removed(sk, req); 1023 1024 tcp_acceptq_queue(sk, req, child); 1025 return child; 1026 1027 listen_overflow: 1028 if (!sysctl_tcp_abort_on_overflow) { 1029 req->acked = 1; 1030 return NULL; 1031 } 1032 1033 embryonic_reset: 1034 NET_INC_STATS_BH(LINUX_MIB_EMBRYONICRSTS); 1035 if (!(flg & TCP_FLAG_RST)) 1036 req->class->send_reset(skb); 1037 1038 tcp_synq_drop(sk, req, prev); 1039 return NULL; 1040 } 1041 1042 /* 1043 * Queue segment on the new socket if the new socket is active, 1044 * otherwise we just shortcircuit this and continue with 1045 * the new socket. 1046 */ 1047 1048 int tcp_child_process(struct sock *parent, struct sock *child, 1049 struct sk_buff *skb) 1050 { 1051 int ret = 0; 1052 int state = child->sk_state; 1053 1054 if (!sock_owned_by_user(child)) { 1055 ret = tcp_rcv_state_process(child, skb, skb->h.th, skb->len); 1056 1057 /* Wakeup parent, send SIGIO */ 1058 if (state == TCP_SYN_RECV && child->sk_state != state) 1059 parent->sk_data_ready(parent, 0); 1060 } else { 1061 /* Alas, it is possible again, because we do lookup 1062 * in main socket hash table and lock on listening 1063 * socket does not protect us more. 1064 */ 1065 sk_add_backlog(child, skb); 1066 } 1067 1068 bh_unlock_sock(child); 1069 sock_put(child); 1070 return ret; 1071 } 1072 1073 EXPORT_SYMBOL(tcp_check_req); 1074 EXPORT_SYMBOL(tcp_child_process); 1075 EXPORT_SYMBOL(tcp_create_openreq_child); 1076 EXPORT_SYMBOL(tcp_timewait_state_process); 1077 EXPORT_SYMBOL(tcp_tw_deschedule); 1078