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