tcp_syncache.c revision 98108
1/*- 2 * Copyright (c) 2001 Networks Associates Technology, Inc. 3 * All rights reserved. 4 * 5 * This software was developed for the FreeBSD Project by Jonathan Lemon 6 * and NAI Labs, the Security Research Division of Network Associates, Inc. 7 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 8 * DARPA CHATS research program. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. The name of the author may not be used to endorse or promote 19 * products derived from this software without specific prior written 20 * permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 * 34 * $FreeBSD: head/sys/netinet/tcp_syncache.c 98108 2002-06-10 23:48:37Z hsu $ 35 */ 36 37#include "opt_inet6.h" 38#include "opt_ipsec.h" 39 40#include <sys/param.h> 41#include <sys/systm.h> 42#include <sys/kernel.h> 43#include <sys/sysctl.h> 44#include <sys/malloc.h> 45#include <sys/mbuf.h> 46#include <sys/md5.h> 47#include <sys/proc.h> /* for proc0 declaration */ 48#include <sys/random.h> 49#include <sys/socket.h> 50#include <sys/socketvar.h> 51 52#include <net/if.h> 53#include <net/route.h> 54 55#include <netinet/in.h> 56#include <netinet/in_systm.h> 57#include <netinet/ip.h> 58#include <netinet/in_var.h> 59#include <netinet/in_pcb.h> 60#include <netinet/ip_var.h> 61#ifdef INET6 62#include <netinet/ip6.h> 63#include <netinet/icmp6.h> 64#include <netinet6/nd6.h> 65#include <netinet6/ip6_var.h> 66#include <netinet6/in6_pcb.h> 67#endif 68#include <netinet/tcp.h> 69#include <netinet/tcp_fsm.h> 70#include <netinet/tcp_seq.h> 71#include <netinet/tcp_timer.h> 72#include <netinet/tcp_var.h> 73#ifdef INET6 74#include <netinet6/tcp6_var.h> 75#endif 76 77#ifdef IPSEC 78#include <netinet6/ipsec.h> 79#ifdef INET6 80#include <netinet6/ipsec6.h> 81#endif 82#include <netkey/key.h> 83#endif /*IPSEC*/ 84 85#include <machine/in_cksum.h> 86#include <vm/uma.h> 87 88static int tcp_syncookies = 1; 89SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 90 &tcp_syncookies, 0, 91 "Use TCP SYN cookies if the syncache overflows"); 92 93static void syncache_drop(struct syncache *, struct syncache_head *); 94static void syncache_free(struct syncache *); 95static void syncache_insert(struct syncache *, struct syncache_head *); 96struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 97static int syncache_respond(struct syncache *, struct mbuf *); 98static struct socket *syncache_socket(struct syncache *, struct socket *, 99 struct mbuf *m); 100static void syncache_timer(void *); 101static u_int32_t syncookie_generate(struct syncache *); 102static struct syncache *syncookie_lookup(struct in_conninfo *, 103 struct tcphdr *, struct socket *); 104 105/* 106 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 107 * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds, 108 * the odds are that the user has given up attempting to connect by then. 109 */ 110#define SYNCACHE_MAXREXMTS 3 111 112/* Arbitrary values */ 113#define TCP_SYNCACHE_HASHSIZE 512 114#define TCP_SYNCACHE_BUCKETLIMIT 30 115 116struct tcp_syncache { 117 struct syncache_head *hashbase; 118 uma_zone_t zone; 119 u_int hashsize; 120 u_int hashmask; 121 u_int bucket_limit; 122 u_int cache_count; 123 u_int cache_limit; 124 u_int rexmt_limit; 125 u_int hash_secret; 126 u_int next_reseed; 127 TAILQ_HEAD(, syncache) timerq[SYNCACHE_MAXREXMTS + 1]; 128 struct callout tt_timerq[SYNCACHE_MAXREXMTS + 1]; 129}; 130static struct tcp_syncache tcp_syncache; 131 132SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); 133 134SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RD, 135 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); 136 137SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RD, 138 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); 139 140SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, 141 &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); 142 143SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RD, 144 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); 145 146SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 147 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); 148 149static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 150 151#define SYNCACHE_HASH(inc, mask) \ 152 ((tcp_syncache.hash_secret ^ \ 153 (inc)->inc_faddr.s_addr ^ \ 154 ((inc)->inc_faddr.s_addr >> 16) ^ \ 155 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 156 157#define SYNCACHE_HASH6(inc, mask) \ 158 ((tcp_syncache.hash_secret ^ \ 159 (inc)->inc6_faddr.s6_addr32[0] ^ \ 160 (inc)->inc6_faddr.s6_addr32[3] ^ \ 161 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 162 163#define ENDPTS_EQ(a, b) ( \ 164 (a)->ie_fport == (b)->ie_fport && \ 165 (a)->ie_lport == (b)->ie_lport && \ 166 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 167 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 168) 169 170#define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 171 172#define SYNCACHE_TIMEOUT(sc, slot) do { \ 173 sc->sc_rxtslot = slot; \ 174 sc->sc_rxttime = ticks + TCPTV_RTOBASE * tcp_backoff[slot]; \ 175 TAILQ_INSERT_TAIL(&tcp_syncache.timerq[slot], sc, sc_timerq); \ 176 if (!callout_active(&tcp_syncache.tt_timerq[slot])) \ 177 callout_reset(&tcp_syncache.tt_timerq[slot], \ 178 TCPTV_RTOBASE * tcp_backoff[slot], \ 179 syncache_timer, (void *)((intptr_t)slot)); \ 180} while (0) 181 182static void 183syncache_free(struct syncache *sc) 184{ 185 struct rtentry *rt; 186 187 if (sc->sc_ipopts) 188 (void) m_free(sc->sc_ipopts); 189#ifdef INET6 190 if (sc->sc_inc.inc_isipv6) 191 rt = sc->sc_route6.ro_rt; 192 else 193#endif 194 rt = sc->sc_route.ro_rt; 195 if (rt != NULL) { 196 /* 197 * If this is the only reference to a protocol cloned 198 * route, remove it immediately. 199 */ 200 if (rt->rt_flags & RTF_WASCLONED && 201 (sc->sc_flags & SCF_KEEPROUTE) == 0 && 202 rt->rt_refcnt == 1) 203 rtrequest(RTM_DELETE, rt_key(rt), 204 rt->rt_gateway, rt_mask(rt), 205 rt->rt_flags, NULL); 206 RTFREE(rt); 207 } 208 uma_zfree(tcp_syncache.zone, sc); 209} 210 211void 212syncache_init(void) 213{ 214 int i; 215 216 tcp_syncache.cache_count = 0; 217 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 218 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 219 tcp_syncache.cache_limit = 220 tcp_syncache.hashsize * tcp_syncache.bucket_limit; 221 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 222 tcp_syncache.next_reseed = 0; 223 tcp_syncache.hash_secret = arc4random(); 224 225 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 226 &tcp_syncache.hashsize); 227 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 228 &tcp_syncache.cache_limit); 229 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 230 &tcp_syncache.bucket_limit); 231 if (!powerof2(tcp_syncache.hashsize)) { 232 printf("WARNING: syncache hash size is not a power of 2.\n"); 233 tcp_syncache.hashsize = 512; /* safe default */ 234 } 235 tcp_syncache.hashmask = tcp_syncache.hashsize - 1; 236 237 /* Allocate the hash table. */ 238 MALLOC(tcp_syncache.hashbase, struct syncache_head *, 239 tcp_syncache.hashsize * sizeof(struct syncache_head), 240 M_SYNCACHE, M_WAITOK); 241 242 /* Initialize the hash buckets. */ 243 for (i = 0; i < tcp_syncache.hashsize; i++) { 244 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); 245 tcp_syncache.hashbase[i].sch_length = 0; 246 } 247 248 /* Initialize the timer queues. */ 249 for (i = 0; i <= SYNCACHE_MAXREXMTS; i++) { 250 TAILQ_INIT(&tcp_syncache.timerq[i]); 251 callout_init(&tcp_syncache.tt_timerq[i], 0); 252 } 253 254 /* 255 * Allocate the syncache entries. Allow the zone to allocate one 256 * more entry than cache limit, so a new entry can bump out an 257 * older one. 258 */ 259 tcp_syncache.cache_limit -= 1; 260 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 261 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE); 262 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit); 263} 264 265static void 266syncache_insert(sc, sch) 267 struct syncache *sc; 268 struct syncache_head *sch; 269{ 270 struct syncache *sc2; 271 int s, i; 272 273 /* 274 * Make sure that we don't overflow the per-bucket 275 * limit or the total cache size limit. 276 */ 277 s = splnet(); 278 if (sch->sch_length >= tcp_syncache.bucket_limit) { 279 /* 280 * The bucket is full, toss the oldest element. 281 */ 282 sc2 = TAILQ_FIRST(&sch->sch_bucket); 283 sc2->sc_tp->ts_recent = ticks; 284 syncache_drop(sc2, sch); 285 tcpstat.tcps_sc_bucketoverflow++; 286 } else if (tcp_syncache.cache_count >= tcp_syncache.cache_limit) { 287 /* 288 * The cache is full. Toss the oldest entry in the 289 * entire cache. This is the front entry in the 290 * first non-empty timer queue with the largest 291 * timeout value. 292 */ 293 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) { 294 sc2 = TAILQ_FIRST(&tcp_syncache.timerq[i]); 295 if (sc2 != NULL) 296 break; 297 } 298 sc2->sc_tp->ts_recent = ticks; 299 syncache_drop(sc2, NULL); 300 tcpstat.tcps_sc_cacheoverflow++; 301 } 302 303 /* Initialize the entry's timer. */ 304 SYNCACHE_TIMEOUT(sc, 0); 305 306 /* Put it into the bucket. */ 307 TAILQ_INSERT_TAIL(&sch->sch_bucket, sc, sc_hash); 308 sch->sch_length++; 309 tcp_syncache.cache_count++; 310 tcpstat.tcps_sc_added++; 311 splx(s); 312} 313 314static void 315syncache_drop(sc, sch) 316 struct syncache *sc; 317 struct syncache_head *sch; 318{ 319 int s; 320 321 if (sch == NULL) { 322#ifdef INET6 323 if (sc->sc_inc.inc_isipv6) { 324 sch = &tcp_syncache.hashbase[ 325 SYNCACHE_HASH6(&sc->sc_inc, tcp_syncache.hashmask)]; 326 } else 327#endif 328 { 329 sch = &tcp_syncache.hashbase[ 330 SYNCACHE_HASH(&sc->sc_inc, tcp_syncache.hashmask)]; 331 } 332 } 333 334 s = splnet(); 335 336 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 337 sch->sch_length--; 338 tcp_syncache.cache_count--; 339 340 TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], sc, sc_timerq); 341 if (TAILQ_EMPTY(&tcp_syncache.timerq[sc->sc_rxtslot])) 342 callout_stop(&tcp_syncache.tt_timerq[sc->sc_rxtslot]); 343 splx(s); 344 345 syncache_free(sc); 346} 347 348/* 349 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 350 * If we have retransmitted an entry the maximum number of times, expire it. 351 */ 352static void 353syncache_timer(xslot) 354 void *xslot; 355{ 356 intptr_t slot = (intptr_t)xslot; 357 struct syncache *sc, *nsc; 358 struct inpcb *inp; 359 int s; 360 361 s = splnet(); 362 if (callout_pending(&tcp_syncache.tt_timerq[slot]) || 363 !callout_active(&tcp_syncache.tt_timerq[slot])) { 364 splx(s); 365 return; 366 } 367 callout_deactivate(&tcp_syncache.tt_timerq[slot]); 368 369 nsc = TAILQ_FIRST(&tcp_syncache.timerq[slot]); 370 INP_INFO_RLOCK(&tcbinfo); 371 while (nsc != NULL) { 372 if (ticks < nsc->sc_rxttime) 373 break; 374 sc = nsc; 375 nsc = TAILQ_NEXT(sc, sc_timerq); 376 inp = sc->sc_tp->t_inpcb; 377 INP_LOCK(inp); 378 if (slot == SYNCACHE_MAXREXMTS || 379 slot >= tcp_syncache.rexmt_limit || 380 inp->inp_gencnt != sc->sc_inp_gencnt) { 381 syncache_drop(sc, NULL); 382 tcpstat.tcps_sc_stale++; 383 INP_UNLOCK(inp); 384 continue; 385 } 386 (void) syncache_respond(sc, NULL); 387 INP_UNLOCK(inp); 388 tcpstat.tcps_sc_retransmitted++; 389 TAILQ_REMOVE(&tcp_syncache.timerq[slot], sc, sc_timerq); 390 SYNCACHE_TIMEOUT(sc, slot + 1); 391 } 392 INP_INFO_RUNLOCK(&tcbinfo); 393 if (nsc != NULL) 394 callout_reset(&tcp_syncache.tt_timerq[slot], 395 nsc->sc_rxttime - ticks, syncache_timer, (void *)(slot)); 396 splx(s); 397} 398 399/* 400 * Find an entry in the syncache. 401 */ 402struct syncache * 403syncache_lookup(inc, schp) 404 struct in_conninfo *inc; 405 struct syncache_head **schp; 406{ 407 struct syncache *sc; 408 struct syncache_head *sch; 409 int s; 410 411#ifdef INET6 412 if (inc->inc_isipv6) { 413 sch = &tcp_syncache.hashbase[ 414 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; 415 *schp = sch; 416 s = splnet(); 417 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 418 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) { 419 splx(s); 420 return (sc); 421 } 422 } 423 splx(s); 424 } else 425#endif 426 { 427 sch = &tcp_syncache.hashbase[ 428 SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; 429 *schp = sch; 430 s = splnet(); 431 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 432#ifdef INET6 433 if (sc->sc_inc.inc_isipv6) 434 continue; 435#endif 436 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) { 437 splx(s); 438 return (sc); 439 } 440 } 441 splx(s); 442 } 443 return (NULL); 444} 445 446/* 447 * This function is called when we get a RST for a 448 * non-existent connection, so that we can see if the 449 * connection is in the syn cache. If it is, zap it. 450 */ 451void 452syncache_chkrst(inc, th) 453 struct in_conninfo *inc; 454 struct tcphdr *th; 455{ 456 struct syncache *sc; 457 struct syncache_head *sch; 458 459 sc = syncache_lookup(inc, &sch); 460 if (sc == NULL) 461 return; 462 /* 463 * If the RST bit is set, check the sequence number to see 464 * if this is a valid reset segment. 465 * RFC 793 page 37: 466 * In all states except SYN-SENT, all reset (RST) segments 467 * are validated by checking their SEQ-fields. A reset is 468 * valid if its sequence number is in the window. 469 * 470 * The sequence number in the reset segment is normally an 471 * echo of our outgoing acknowlegement numbers, but some hosts 472 * send a reset with the sequence number at the rightmost edge 473 * of our receive window, and we have to handle this case. 474 */ 475 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 476 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 477 syncache_drop(sc, sch); 478 tcpstat.tcps_sc_reset++; 479 } 480} 481 482void 483syncache_badack(inc) 484 struct in_conninfo *inc; 485{ 486 struct syncache *sc; 487 struct syncache_head *sch; 488 489 sc = syncache_lookup(inc, &sch); 490 if (sc != NULL) { 491 syncache_drop(sc, sch); 492 tcpstat.tcps_sc_badack++; 493 } 494} 495 496void 497syncache_unreach(inc, th) 498 struct in_conninfo *inc; 499 struct tcphdr *th; 500{ 501 struct syncache *sc; 502 struct syncache_head *sch; 503 504 /* we are called at splnet() here */ 505 sc = syncache_lookup(inc, &sch); 506 if (sc == NULL) 507 return; 508 509 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 510 if (ntohl(th->th_seq) != sc->sc_iss) 511 return; 512 513 /* 514 * If we've rertransmitted 3 times and this is our second error, 515 * we remove the entry. Otherwise, we allow it to continue on. 516 * This prevents us from incorrectly nuking an entry during a 517 * spurious network outage. 518 * 519 * See tcp_notify(). 520 */ 521 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtslot < 3) { 522 sc->sc_flags |= SCF_UNREACH; 523 return; 524 } 525 syncache_drop(sc, sch); 526 tcpstat.tcps_sc_unreach++; 527} 528 529/* 530 * Build a new TCP socket structure from a syncache entry. 531 */ 532static struct socket * 533syncache_socket(sc, lso, m) 534 struct syncache *sc; 535 struct socket *lso; 536 struct mbuf *m; 537{ 538 struct inpcb *inp = NULL; 539 struct socket *so; 540 struct tcpcb *tp; 541 542 /* 543 * Ok, create the full blown connection, and set things up 544 * as they would have been set up if we had created the 545 * connection when the SYN arrived. If we can't create 546 * the connection, abort it. 547 */ 548 so = sonewconn(lso, SS_ISCONNECTED); 549 if (so == NULL) { 550 /* 551 * Drop the connection; we will send a RST if the peer 552 * retransmits the ACK, 553 */ 554 tcpstat.tcps_listendrop++; 555 goto abort; 556 } 557 558 inp = sotoinpcb(so); 559 560 /* 561 * Insert new socket into hash list. 562 */ 563 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; 564#ifdef INET6 565 if (sc->sc_inc.inc_isipv6) { 566 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 567 } else { 568 inp->inp_vflag &= ~INP_IPV6; 569 inp->inp_vflag |= INP_IPV4; 570#endif 571 inp->inp_laddr = sc->sc_inc.inc_laddr; 572#ifdef INET6 573 } 574#endif 575 inp->inp_lport = sc->sc_inc.inc_lport; 576 if (in_pcbinshash(inp) != 0) { 577 /* 578 * Undo the assignments above if we failed to 579 * put the PCB on the hash lists. 580 */ 581#ifdef INET6 582 if (sc->sc_inc.inc_isipv6) 583 inp->in6p_laddr = in6addr_any; 584 else 585#endif 586 inp->inp_laddr.s_addr = INADDR_ANY; 587 inp->inp_lport = 0; 588 goto abort; 589 } 590#ifdef IPSEC 591 /* copy old policy into new socket's */ 592 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 593 printf("syncache_expand: could not copy policy\n"); 594#endif 595#ifdef INET6 596 if (sc->sc_inc.inc_isipv6) { 597 struct inpcb *oinp = sotoinpcb(lso); 598 struct in6_addr laddr6; 599 struct sockaddr_in6 *sin6; 600 /* 601 * Inherit socket options from the listening socket. 602 * Note that in6p_inputopts are not (and should not be) 603 * copied, since it stores previously received options and is 604 * used to detect if each new option is different than the 605 * previous one and hence should be passed to a user. 606 * If we copied in6p_inputopts, a user would not be able to 607 * receive options just after calling the accept system call. 608 */ 609 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 610 if (oinp->in6p_outputopts) 611 inp->in6p_outputopts = 612 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 613 inp->in6p_route = sc->sc_route6; 614 sc->sc_route6.ro_rt = NULL; 615 616 MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6, 617 M_SONAME, M_NOWAIT | M_ZERO); 618 if (sin6 == NULL) 619 goto abort; 620 sin6->sin6_family = AF_INET6; 621 sin6->sin6_len = sizeof(*sin6); 622 sin6->sin6_addr = sc->sc_inc.inc6_faddr; 623 sin6->sin6_port = sc->sc_inc.inc_fport; 624 laddr6 = inp->in6p_laddr; 625 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 626 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 627 if (in6_pcbconnect(inp, (struct sockaddr *)sin6, &thread0)) { 628 inp->in6p_laddr = laddr6; 629 FREE(sin6, M_SONAME); 630 goto abort; 631 } 632 FREE(sin6, M_SONAME); 633 } else 634#endif 635 { 636 struct in_addr laddr; 637 struct sockaddr_in *sin; 638 639 inp->inp_options = ip_srcroute(); 640 if (inp->inp_options == NULL) { 641 inp->inp_options = sc->sc_ipopts; 642 sc->sc_ipopts = NULL; 643 } 644 inp->inp_route = sc->sc_route; 645 sc->sc_route.ro_rt = NULL; 646 647 MALLOC(sin, struct sockaddr_in *, sizeof *sin, 648 M_SONAME, M_NOWAIT | M_ZERO); 649 if (sin == NULL) 650 goto abort; 651 sin->sin_family = AF_INET; 652 sin->sin_len = sizeof(*sin); 653 sin->sin_addr = sc->sc_inc.inc_faddr; 654 sin->sin_port = sc->sc_inc.inc_fport; 655 bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero)); 656 laddr = inp->inp_laddr; 657 if (inp->inp_laddr.s_addr == INADDR_ANY) 658 inp->inp_laddr = sc->sc_inc.inc_laddr; 659 if (in_pcbconnect(inp, (struct sockaddr *)sin, &thread0)) { 660 inp->inp_laddr = laddr; 661 FREE(sin, M_SONAME); 662 goto abort; 663 } 664 FREE(sin, M_SONAME); 665 } 666 667 tp = intotcpcb(inp); 668 tp->t_state = TCPS_SYN_RECEIVED; 669 tp->iss = sc->sc_iss; 670 tp->irs = sc->sc_irs; 671 tcp_rcvseqinit(tp); 672 tcp_sendseqinit(tp); 673 tp->snd_wl1 = sc->sc_irs; 674 tp->rcv_up = sc->sc_irs + 1; 675 tp->rcv_wnd = sc->sc_wnd; 676 tp->rcv_adv += tp->rcv_wnd; 677 678 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 679 if (sc->sc_flags & SCF_NOOPT) 680 tp->t_flags |= TF_NOOPT; 681 if (sc->sc_flags & SCF_WINSCALE) { 682 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 683 tp->requested_s_scale = sc->sc_requested_s_scale; 684 tp->request_r_scale = sc->sc_request_r_scale; 685 } 686 if (sc->sc_flags & SCF_TIMESTAMP) { 687 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 688 tp->ts_recent = sc->sc_tsrecent; 689 tp->ts_recent_age = ticks; 690 } 691 if (sc->sc_flags & SCF_CC) { 692 /* 693 * Initialization of the tcpcb for transaction; 694 * set SND.WND = SEG.WND, 695 * initialize CCsend and CCrecv. 696 */ 697 tp->t_flags |= TF_REQ_CC|TF_RCVD_CC; 698 tp->cc_send = sc->sc_cc_send; 699 tp->cc_recv = sc->sc_cc_recv; 700 } 701 702 tcp_mss(tp, sc->sc_peer_mss); 703 704 /* 705 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. 706 */ 707 if (sc->sc_rxtslot != 0) 708 tp->snd_cwnd = tp->t_maxseg; 709 callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp); 710 711 tcpstat.tcps_accepts++; 712 return (so); 713 714abort: 715 if (so != NULL) 716 (void) soabort(so); 717 return (NULL); 718} 719 720/* 721 * This function gets called when we receive an ACK for a 722 * socket in the LISTEN state. We look up the connection 723 * in the syncache, and if its there, we pull it out of 724 * the cache and turn it into a full-blown connection in 725 * the SYN-RECEIVED state. 726 */ 727int 728syncache_expand(inc, th, sop, m) 729 struct in_conninfo *inc; 730 struct tcphdr *th; 731 struct socket **sop; 732 struct mbuf *m; 733{ 734 struct syncache *sc; 735 struct syncache_head *sch; 736 struct socket *so; 737 738 sc = syncache_lookup(inc, &sch); 739 if (sc == NULL) { 740 /* 741 * There is no syncache entry, so see if this ACK is 742 * a returning syncookie. To do this, first: 743 * A. See if this socket has had a syncache entry dropped in 744 * the past. We don't want to accept a bogus syncookie 745 * if we've never received a SYN. 746 * B. check that the syncookie is valid. If it is, then 747 * cobble up a fake syncache entry, and return. 748 */ 749 if (!tcp_syncookies) 750 return (0); 751 sc = syncookie_lookup(inc, th, *sop); 752 if (sc == NULL) 753 return (0); 754 sch = NULL; 755 tcpstat.tcps_sc_recvcookie++; 756 } 757 758 /* 759 * If seg contains an ACK, but not for our SYN/ACK, send a RST. 760 */ 761 if (th->th_ack != sc->sc_iss + 1) 762 return (0); 763 764 so = syncache_socket(sc, *sop, m); 765 if (so == NULL) { 766#if 0 767resetandabort: 768 /* XXXjlemon check this - is this correct? */ 769 (void) tcp_respond(NULL, m, m, th, 770 th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK); 771#endif 772 m_freem(m); /* XXX only needed for above */ 773 tcpstat.tcps_sc_aborted++; 774 } else { 775 sc->sc_flags |= SCF_KEEPROUTE; 776 tcpstat.tcps_sc_completed++; 777 } 778 if (sch == NULL) 779 syncache_free(sc); 780 else 781 syncache_drop(sc, sch); 782 *sop = so; 783 return (1); 784} 785 786/* 787 * Given a LISTEN socket and an inbound SYN request, add 788 * this to the syn cache, and send back a segment: 789 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 790 * to the source. 791 * 792 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 793 * Doing so would require that we hold onto the data and deliver it 794 * to the application. However, if we are the target of a SYN-flood 795 * DoS attack, an attacker could send data which would eventually 796 * consume all available buffer space if it were ACKed. By not ACKing 797 * the data, we avoid this DoS scenario. 798 */ 799int 800syncache_add(inc, to, th, sop, m) 801 struct in_conninfo *inc; 802 struct tcpopt *to; 803 struct tcphdr *th; 804 struct socket **sop; 805 struct mbuf *m; 806{ 807 struct tcpcb *tp; 808 struct socket *so; 809 struct syncache *sc = NULL; 810 struct syncache_head *sch; 811 struct mbuf *ipopts = NULL; 812 struct rmxp_tao *taop; 813 int i, s, win; 814 815 so = *sop; 816 tp = sototcpcb(so); 817 818 /* 819 * Remember the IP options, if any. 820 */ 821#ifdef INET6 822 if (!inc->inc_isipv6) 823#endif 824 ipopts = ip_srcroute(); 825 826 /* 827 * See if we already have an entry for this connection. 828 * If we do, resend the SYN,ACK, and reset the retransmit timer. 829 * 830 * XXX 831 * should the syncache be re-initialized with the contents 832 * of the new SYN here (which may have different options?) 833 */ 834 sc = syncache_lookup(inc, &sch); 835 if (sc != NULL) { 836 tcpstat.tcps_sc_dupsyn++; 837 if (ipopts) { 838 /* 839 * If we were remembering a previous source route, 840 * forget it and use the new one we've been given. 841 */ 842 if (sc->sc_ipopts) 843 (void) m_free(sc->sc_ipopts); 844 sc->sc_ipopts = ipopts; 845 } 846 /* 847 * Update timestamp if present. 848 */ 849 if (sc->sc_flags & SCF_TIMESTAMP) 850 sc->sc_tsrecent = to->to_tsval; 851 /* 852 * PCB may have changed, pick up new values. 853 */ 854 sc->sc_tp = tp; 855 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt; 856 if (syncache_respond(sc, m) == 0) { 857 s = splnet(); 858 TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], 859 sc, sc_timerq); 860 SYNCACHE_TIMEOUT(sc, sc->sc_rxtslot); 861 splx(s); 862 tcpstat.tcps_sndacks++; 863 tcpstat.tcps_sndtotal++; 864 } 865 *sop = NULL; 866 return (1); 867 } 868 869 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT); 870 if (sc == NULL) { 871 /* 872 * The zone allocator couldn't provide more entries. 873 * Treat this as if the cache was full; drop the oldest 874 * entry and insert the new one. 875 */ 876 s = splnet(); 877 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) { 878 sc = TAILQ_FIRST(&tcp_syncache.timerq[i]); 879 if (sc != NULL) 880 break; 881 } 882 sc->sc_tp->ts_recent = ticks; 883 syncache_drop(sc, NULL); 884 splx(s); 885 tcpstat.tcps_sc_zonefail++; 886 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT); 887 if (sc == NULL) { 888 if (ipopts) 889 (void) m_free(ipopts); 890 return (0); 891 } 892 } 893 894 /* 895 * Fill in the syncache values. 896 */ 897 bzero(sc, sizeof(*sc)); 898 sc->sc_tp = tp; 899 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt; 900 sc->sc_ipopts = ipopts; 901 sc->sc_inc.inc_fport = inc->inc_fport; 902 sc->sc_inc.inc_lport = inc->inc_lport; 903#ifdef INET6 904 sc->sc_inc.inc_isipv6 = inc->inc_isipv6; 905 if (inc->inc_isipv6) { 906 sc->sc_inc.inc6_faddr = inc->inc6_faddr; 907 sc->sc_inc.inc6_laddr = inc->inc6_laddr; 908 sc->sc_route6.ro_rt = NULL; 909 } else 910#endif 911 { 912 sc->sc_inc.inc_faddr = inc->inc_faddr; 913 sc->sc_inc.inc_laddr = inc->inc_laddr; 914 sc->sc_route.ro_rt = NULL; 915 } 916 sc->sc_irs = th->th_seq; 917 if (tcp_syncookies) 918 sc->sc_iss = syncookie_generate(sc); 919 else 920 sc->sc_iss = arc4random(); 921 922 /* Initial receive window: clip sbspace to [0 .. TCP_MAXWIN] */ 923 win = sbspace(&so->so_rcv); 924 win = imax(win, 0); 925 win = imin(win, TCP_MAXWIN); 926 sc->sc_wnd = win; 927 928 sc->sc_flags = 0; 929 sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0; 930 if (tcp_do_rfc1323) { 931 /* 932 * A timestamp received in a SYN makes 933 * it ok to send timestamp requests and replies. 934 */ 935 if (to->to_flags & TOF_TS) { 936 sc->sc_tsrecent = to->to_tsval; 937 sc->sc_flags |= SCF_TIMESTAMP; 938 } 939 if (to->to_flags & TOF_SCALE) { 940 int wscale = 0; 941 942 /* Compute proper scaling value from buffer space */ 943 while (wscale < TCP_MAX_WINSHIFT && 944 (TCP_MAXWIN << wscale) < so->so_rcv.sb_hiwat) 945 wscale++; 946 sc->sc_request_r_scale = wscale; 947 sc->sc_requested_s_scale = to->to_requested_s_scale; 948 sc->sc_flags |= SCF_WINSCALE; 949 } 950 } 951 if (tcp_do_rfc1644) { 952 /* 953 * A CC or CC.new option received in a SYN makes 954 * it ok to send CC in subsequent segments. 955 */ 956 if (to->to_flags & (TOF_CC|TOF_CCNEW)) { 957 sc->sc_cc_recv = to->to_cc; 958 sc->sc_cc_send = CC_INC(tcp_ccgen); 959 sc->sc_flags |= SCF_CC; 960 } 961 } 962 if (tp->t_flags & TF_NOOPT) 963 sc->sc_flags = SCF_NOOPT; 964 965 /* 966 * XXX 967 * We have the option here of not doing TAO (even if the segment 968 * qualifies) and instead fall back to a normal 3WHS via the syncache. 969 * This allows us to apply synflood protection to TAO-qualifying SYNs 970 * also. However, there should be a hueristic to determine when to 971 * do this, and is not present at the moment. 972 */ 973 974 /* 975 * Perform TAO test on incoming CC (SEG.CC) option, if any. 976 * - compare SEG.CC against cached CC from the same host, if any. 977 * - if SEG.CC > chached value, SYN must be new and is accepted 978 * immediately: save new CC in the cache, mark the socket 979 * connected, enter ESTABLISHED state, turn on flag to 980 * send a SYN in the next segment. 981 * A virtual advertised window is set in rcv_adv to 982 * initialize SWS prevention. Then enter normal segment 983 * processing: drop SYN, process data and FIN. 984 * - otherwise do a normal 3-way handshake. 985 */ 986 taop = tcp_gettaocache(&sc->sc_inc); 987 if ((to->to_flags & TOF_CC) != 0) { 988 if (((tp->t_flags & TF_NOPUSH) != 0) && 989 sc->sc_flags & SCF_CC && 990 taop != NULL && taop->tao_cc != 0 && 991 CC_GT(to->to_cc, taop->tao_cc)) { 992 sc->sc_rxtslot = 0; 993 so = syncache_socket(sc, *sop, m); 994 if (so != NULL) { 995 sc->sc_flags |= SCF_KEEPROUTE; 996 taop->tao_cc = to->to_cc; 997 *sop = so; 998 } 999 syncache_free(sc); 1000 return (so != NULL); 1001 } 1002 } else { 1003 /* 1004 * No CC option, but maybe CC.NEW: invalidate cached value. 1005 */ 1006 if (taop != NULL) 1007 taop->tao_cc = 0; 1008 } 1009 /* 1010 * TAO test failed or there was no CC option, 1011 * do a standard 3-way handshake. 1012 */ 1013 if (syncache_respond(sc, m) == 0) { 1014 syncache_insert(sc, sch); 1015 tcpstat.tcps_sndacks++; 1016 tcpstat.tcps_sndtotal++; 1017 } else { 1018 syncache_free(sc); 1019 tcpstat.tcps_sc_dropped++; 1020 } 1021 *sop = NULL; 1022 return (1); 1023} 1024 1025static int 1026syncache_respond(sc, m) 1027 struct syncache *sc; 1028 struct mbuf *m; 1029{ 1030 u_int8_t *optp; 1031 int optlen, error; 1032 u_int16_t tlen, hlen, mssopt; 1033 struct ip *ip = NULL; 1034 struct rtentry *rt; 1035 struct tcphdr *th; 1036#ifdef INET6 1037 struct ip6_hdr *ip6 = NULL; 1038#endif 1039 1040#ifdef INET6 1041 if (sc->sc_inc.inc_isipv6) { 1042 rt = tcp_rtlookup6(&sc->sc_inc); 1043 if (rt != NULL) 1044 mssopt = rt->rt_ifp->if_mtu - 1045 (sizeof(struct ip6_hdr) + sizeof(struct tcphdr)); 1046 else 1047 mssopt = tcp_v6mssdflt; 1048 hlen = sizeof(struct ip6_hdr); 1049 } else 1050#endif 1051 { 1052 rt = tcp_rtlookup(&sc->sc_inc); 1053 if (rt != NULL) 1054 mssopt = rt->rt_ifp->if_mtu - 1055 (sizeof(struct ip) + sizeof(struct tcphdr)); 1056 else 1057 mssopt = tcp_mssdflt; 1058 hlen = sizeof(struct ip); 1059 } 1060 1061 /* Compute the size of the TCP options. */ 1062 if (sc->sc_flags & SCF_NOOPT) { 1063 optlen = 0; 1064 } else { 1065 optlen = TCPOLEN_MAXSEG + 1066 ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) + 1067 ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0) + 1068 ((sc->sc_flags & SCF_CC) ? TCPOLEN_CC_APPA * 2 : 0); 1069 } 1070 tlen = hlen + sizeof(struct tcphdr) + optlen; 1071 1072 /* 1073 * XXX 1074 * assume that the entire packet will fit in a header mbuf 1075 */ 1076 KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small")); 1077 1078 /* 1079 * XXX shouldn't this reuse the mbuf if possible ? 1080 * Create the IP+TCP header from scratch. 1081 */ 1082 if (m) 1083 m_freem(m); 1084 1085 m = m_gethdr(M_DONTWAIT, MT_HEADER); 1086 if (m == NULL) 1087 return (ENOBUFS); 1088 m->m_data += max_linkhdr; 1089 m->m_len = tlen; 1090 m->m_pkthdr.len = tlen; 1091 m->m_pkthdr.rcvif = NULL; 1092 1093#ifdef IPSEC 1094 /* use IPsec policy on listening socket to send SYN,ACK */ 1095 if (ipsec_setsocket(m, sc->sc_tp->t_inpcb->inp_socket) != 0) { 1096 m_freem(m); 1097 return (ENOBUFS); 1098 } 1099#endif 1100 1101#ifdef INET6 1102 if (sc->sc_inc.inc_isipv6) { 1103 ip6 = mtod(m, struct ip6_hdr *); 1104 ip6->ip6_vfc = IPV6_VERSION; 1105 ip6->ip6_nxt = IPPROTO_TCP; 1106 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1107 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1108 ip6->ip6_plen = htons(tlen - hlen); 1109 /* ip6_hlim is set after checksum */ 1110 /* ip6_flow = ??? */ 1111 1112 th = (struct tcphdr *)(ip6 + 1); 1113 } else 1114#endif 1115 { 1116 ip = mtod(m, struct ip *); 1117 ip->ip_v = IPVERSION; 1118 ip->ip_hl = sizeof(struct ip) >> 2; 1119 ip->ip_tos = 0; 1120 ip->ip_len = tlen; 1121 ip->ip_id = 0; 1122 ip->ip_off = 0; 1123 ip->ip_ttl = ip_defttl; 1124 ip->ip_sum = 0; 1125 ip->ip_p = IPPROTO_TCP; 1126 ip->ip_src = sc->sc_inc.inc_laddr; 1127 ip->ip_dst = sc->sc_inc.inc_faddr; 1128 1129 th = (struct tcphdr *)(ip + 1); 1130 } 1131 th->th_sport = sc->sc_inc.inc_lport; 1132 th->th_dport = sc->sc_inc.inc_fport; 1133 1134 th->th_seq = htonl(sc->sc_iss); 1135 th->th_ack = htonl(sc->sc_irs + 1); 1136 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1137 th->th_x2 = 0; 1138 th->th_flags = TH_SYN|TH_ACK; 1139 th->th_win = htons(sc->sc_wnd); 1140 th->th_urp = 0; 1141 1142 /* Tack on the TCP options. */ 1143 if (optlen == 0) 1144 goto no_options; 1145 optp = (u_int8_t *)(th + 1); 1146 *optp++ = TCPOPT_MAXSEG; 1147 *optp++ = TCPOLEN_MAXSEG; 1148 *optp++ = (mssopt >> 8) & 0xff; 1149 *optp++ = mssopt & 0xff; 1150 1151 if (sc->sc_flags & SCF_WINSCALE) { 1152 *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 | 1153 TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 | 1154 sc->sc_request_r_scale); 1155 optp += 4; 1156 } 1157 1158 if (sc->sc_flags & SCF_TIMESTAMP) { 1159 u_int32_t *lp = (u_int32_t *)(optp); 1160 1161 /* Form timestamp option as shown in appendix A of RFC 1323. */ 1162 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 1163 *lp++ = htonl(ticks); 1164 *lp = htonl(sc->sc_tsrecent); 1165 optp += TCPOLEN_TSTAMP_APPA; 1166 } 1167 1168 /* 1169 * Send CC and CC.echo if we received CC from our peer. 1170 */ 1171 if (sc->sc_flags & SCF_CC) { 1172 u_int32_t *lp = (u_int32_t *)(optp); 1173 1174 *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CC)); 1175 *lp++ = htonl(sc->sc_cc_send); 1176 *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CCECHO)); 1177 *lp = htonl(sc->sc_cc_recv); 1178 optp += TCPOLEN_CC_APPA * 2; 1179 } 1180no_options: 1181 1182#ifdef INET6 1183 if (sc->sc_inc.inc_isipv6) { 1184 struct route_in6 *ro6 = &sc->sc_route6; 1185 1186 th->th_sum = 0; 1187 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen); 1188 ip6->ip6_hlim = in6_selecthlim(NULL, 1189 ro6->ro_rt ? ro6->ro_rt->rt_ifp : NULL); 1190 error = ip6_output(m, NULL, ro6, 0, NULL, NULL); 1191 } else 1192#endif 1193 { 1194 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1195 htons(tlen - hlen + IPPROTO_TCP)); 1196 m->m_pkthdr.csum_flags = CSUM_TCP; 1197 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1198 error = ip_output(m, sc->sc_ipopts, &sc->sc_route, 0, NULL); 1199 } 1200 return (error); 1201} 1202 1203/* 1204 * cookie layers: 1205 * 1206 * |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .| 1207 * | peer iss | 1208 * | MD5(laddr,faddr,lport,fport,secret) |. . . . . . .| 1209 * | 0 |(A)| | 1210 * (A): peer mss index 1211 */ 1212 1213/* 1214 * The values below are chosen to minimize the size of the tcp_secret 1215 * table, as well as providing roughly a 4 second lifetime for the cookie. 1216 */ 1217 1218#define SYNCOOKIE_HASHSHIFT 2 /* log2(# of 32bit words from hash) */ 1219#define SYNCOOKIE_WNDBITS 7 /* exposed bits for window indexing */ 1220#define SYNCOOKIE_TIMESHIFT 5 /* scale ticks to window time units */ 1221 1222#define SYNCOOKIE_HASHMASK ((1 << SYNCOOKIE_HASHSHIFT) - 1) 1223#define SYNCOOKIE_WNDMASK ((1 << SYNCOOKIE_WNDBITS) - 1) 1224#define SYNCOOKIE_NSECRETS (1 << (SYNCOOKIE_WNDBITS - SYNCOOKIE_HASHSHIFT)) 1225#define SYNCOOKIE_TIMEOUT \ 1226 (hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT)) 1227#define SYNCOOKIE_DATAMASK ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK) 1228 1229static struct { 1230 u_int32_t ts_secbits; 1231 u_int ts_expire; 1232} tcp_secret[SYNCOOKIE_NSECRETS]; 1233 1234static int tcp_msstab[] = { 0, 536, 1460, 8960 }; 1235 1236static MD5_CTX syn_ctx; 1237 1238#define MD5Add(v) MD5Update(&syn_ctx, (u_char *)&v, sizeof(v)) 1239 1240/* 1241 * Consider the problem of a recreated (and retransmitted) cookie. If the 1242 * original SYN was accepted, the connection is established. The second 1243 * SYN is inflight, and if it arrives with an ISN that falls within the 1244 * receive window, the connection is killed. 1245 * 1246 * However, since cookies have other problems, this may not be worth 1247 * worrying about. 1248 */ 1249 1250static u_int32_t 1251syncookie_generate(struct syncache *sc) 1252{ 1253 u_int32_t md5_buffer[4]; 1254 u_int32_t data; 1255 int wnd, idx; 1256 1257 wnd = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK; 1258 idx = wnd >> SYNCOOKIE_HASHSHIFT; 1259 if (tcp_secret[idx].ts_expire < ticks) { 1260 tcp_secret[idx].ts_secbits = arc4random(); 1261 tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT; 1262 } 1263 for (data = sizeof(tcp_msstab) / sizeof(int) - 1; data > 0; data--) 1264 if (tcp_msstab[data] <= sc->sc_peer_mss) 1265 break; 1266 data = (data << SYNCOOKIE_WNDBITS) | wnd; 1267 data ^= sc->sc_irs; /* peer's iss */ 1268 MD5Init(&syn_ctx); 1269#ifdef INET6 1270 if (sc->sc_inc.inc_isipv6) { 1271 MD5Add(sc->sc_inc.inc6_laddr); 1272 MD5Add(sc->sc_inc.inc6_faddr); 1273 } else 1274#endif 1275 { 1276 MD5Add(sc->sc_inc.inc_laddr); 1277 MD5Add(sc->sc_inc.inc_faddr); 1278 } 1279 MD5Add(sc->sc_inc.inc_lport); 1280 MD5Add(sc->sc_inc.inc_fport); 1281 MD5Add(tcp_secret[idx].ts_secbits); 1282 MD5Final((u_char *)&md5_buffer, &syn_ctx); 1283 data ^= (md5_buffer[wnd & SYNCOOKIE_HASHMASK] & ~SYNCOOKIE_WNDMASK); 1284 return (data); 1285} 1286 1287static struct syncache * 1288syncookie_lookup(inc, th, so) 1289 struct in_conninfo *inc; 1290 struct tcphdr *th; 1291 struct socket *so; 1292{ 1293 u_int32_t md5_buffer[4]; 1294 struct syncache *sc; 1295 u_int32_t data; 1296 int wnd, idx; 1297 1298 data = (th->th_ack - 1) ^ (th->th_seq - 1); /* remove ISS */ 1299 wnd = data & SYNCOOKIE_WNDMASK; 1300 idx = wnd >> SYNCOOKIE_HASHSHIFT; 1301 if (tcp_secret[idx].ts_expire < ticks || 1302 sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks) 1303 return (NULL); 1304 MD5Init(&syn_ctx); 1305#ifdef INET6 1306 if (inc->inc_isipv6) { 1307 MD5Add(inc->inc6_laddr); 1308 MD5Add(inc->inc6_faddr); 1309 } else 1310#endif 1311 { 1312 MD5Add(inc->inc_laddr); 1313 MD5Add(inc->inc_faddr); 1314 } 1315 MD5Add(inc->inc_lport); 1316 MD5Add(inc->inc_fport); 1317 MD5Add(tcp_secret[idx].ts_secbits); 1318 MD5Final((u_char *)&md5_buffer, &syn_ctx); 1319 data ^= md5_buffer[wnd & SYNCOOKIE_HASHMASK]; 1320 if ((data & ~SYNCOOKIE_DATAMASK) != 0) 1321 return (NULL); 1322 data = data >> SYNCOOKIE_WNDBITS; 1323 1324 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT); 1325 if (sc == NULL) 1326 return (NULL); 1327 /* 1328 * Fill in the syncache values. 1329 * XXX duplicate code from syncache_add 1330 */ 1331 sc->sc_ipopts = NULL; 1332 sc->sc_inc.inc_fport = inc->inc_fport; 1333 sc->sc_inc.inc_lport = inc->inc_lport; 1334#ifdef INET6 1335 sc->sc_inc.inc_isipv6 = inc->inc_isipv6; 1336 if (inc->inc_isipv6) { 1337 sc->sc_inc.inc6_faddr = inc->inc6_faddr; 1338 sc->sc_inc.inc6_laddr = inc->inc6_laddr; 1339 sc->sc_route6.ro_rt = NULL; 1340 } else 1341#endif 1342 { 1343 sc->sc_inc.inc_faddr = inc->inc_faddr; 1344 sc->sc_inc.inc_laddr = inc->inc_laddr; 1345 sc->sc_route.ro_rt = NULL; 1346 } 1347 sc->sc_irs = th->th_seq - 1; 1348 sc->sc_iss = th->th_ack - 1; 1349 wnd = sbspace(&so->so_rcv); 1350 wnd = imax(wnd, 0); 1351 wnd = imin(wnd, TCP_MAXWIN); 1352 sc->sc_wnd = wnd; 1353 sc->sc_flags = 0; 1354 sc->sc_rxtslot = 0; 1355 sc->sc_peer_mss = tcp_msstab[data]; 1356 return (sc); 1357} 1358