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: src/sys/netinet/tcp_syncache.c,v 1.5.2.14 2003/02/24 04:02:27 silby Exp $ 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 #ifdef FAST_IPSEC 86 #include <netipsec/ipsec.h> 87 #ifdef INET6 88 #include <netipsec/ipsec6.h> 89 #endif 90 #include <netipsec/key.h> 91 #define IPSEC 92 #endif /*FAST_IPSEC*/ 93 94 #include <machine/in_cksum.h> 95 #include <vm/vm_zone.h> 96 97 static int tcp_syncookies = 1; 98 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 99 &tcp_syncookies, 0, 100 "Use TCP SYN cookies if the syncache overflows"); 101 102 static void syncache_drop(struct syncache *, struct syncache_head *); 103 static void syncache_free(struct syncache *); 104 static void syncache_insert(struct syncache *, struct syncache_head *); 105 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 106 static int syncache_respond(struct syncache *, struct mbuf *); 107 static struct socket *syncache_socket(struct syncache *, struct socket *); 108 static void syncache_timer(void *); 109 static u_int32_t syncookie_generate(struct syncache *); 110 static struct syncache *syncookie_lookup(struct in_conninfo *, 111 struct tcphdr *, struct socket *); 112 113 /* 114 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 115 * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds, 116 * the odds are that the user has given up attempting to connect by then. 117 */ 118 #define SYNCACHE_MAXREXMTS 3 119 120 /* Arbitrary values */ 121 #define TCP_SYNCACHE_HASHSIZE 512 122 #define TCP_SYNCACHE_BUCKETLIMIT 30 123 124 struct tcp_syncache { 125 struct syncache_head *hashbase; 126 struct vm_zone *zone; 127 u_int hashsize; 128 u_int hashmask; 129 u_int bucket_limit; 130 u_int cache_count; 131 u_int cache_limit; 132 u_int rexmt_limit; 133 u_int hash_secret; 134 u_int next_reseed; 135 TAILQ_HEAD(, syncache) timerq[SYNCACHE_MAXREXMTS + 1]; 136 struct callout tt_timerq[SYNCACHE_MAXREXMTS + 1]; 137 }; 138 static struct tcp_syncache tcp_syncache; 139 140 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); 141 142 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RD, 143 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); 144 145 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RD, 146 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); 147 148 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, 149 &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); 150 151 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RD, 152 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); 153 154 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 155 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); 156 157 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 158 159 #define SYNCACHE_HASH(inc, mask) \ 160 ((tcp_syncache.hash_secret ^ \ 161 (inc)->inc_faddr.s_addr ^ \ 162 ((inc)->inc_faddr.s_addr >> 16) ^ \ 163 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 164 165 #define SYNCACHE_HASH6(inc, mask) \ 166 ((tcp_syncache.hash_secret ^ \ 167 (inc)->inc6_faddr.s6_addr32[0] ^ \ 168 (inc)->inc6_faddr.s6_addr32[3] ^ \ 169 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 170 171 #define ENDPTS_EQ(a, b) ( \ 172 (a)->ie_fport == (b)->ie_fport && \ 173 (a)->ie_lport == (b)->ie_lport && \ 174 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 175 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 176 ) 177 178 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 179 180 #define SYNCACHE_TIMEOUT(sc, slot) do { \ 181 sc->sc_rxtslot = slot; \ 182 sc->sc_rxttime = ticks + TCPTV_RTOBASE * tcp_backoff[slot]; \ 183 TAILQ_INSERT_TAIL(&tcp_syncache.timerq[slot], sc, sc_timerq); \ 184 if (!callout_active(&tcp_syncache.tt_timerq[slot])) \ 185 callout_reset(&tcp_syncache.tt_timerq[slot], \ 186 TCPTV_RTOBASE * tcp_backoff[slot], \ 187 syncache_timer, (void *)((intptr_t)slot)); \ 188 } while (0) 189 190 static void 191 syncache_free(struct syncache *sc) 192 { 193 struct rtentry *rt; 194 195 if (sc->sc_ipopts) 196 (void) m_free(sc->sc_ipopts); 197 #ifdef INET6 198 if (sc->sc_inc.inc_isipv6) 199 rt = sc->sc_route6.ro_rt; 200 else 201 #endif 202 rt = sc->sc_route.ro_rt; 203 if (rt != NULL) { 204 /* 205 * If this is the only reference to a protocol cloned 206 * route, remove it immediately. 207 */ 208 if (rt->rt_flags & RTF_WASCLONED && 209 (sc->sc_flags & SCF_KEEPROUTE) == 0 && 210 rt->rt_refcnt == 1) 211 rtrequest(RTM_DELETE, rt_key(rt), 212 rt->rt_gateway, rt_mask(rt), 213 rt->rt_flags, NULL); 214 RTFREE(rt); 215 } 216 zfree(tcp_syncache.zone, sc); 217 } 218 219 void 220 syncache_init(void) 221 { 222 int i; 223 224 tcp_syncache.cache_count = 0; 225 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 226 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 227 tcp_syncache.cache_limit = 228 tcp_syncache.hashsize * tcp_syncache.bucket_limit; 229 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 230 tcp_syncache.next_reseed = 0; 231 tcp_syncache.hash_secret = arc4random(); 232 233 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 234 &tcp_syncache.hashsize); 235 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 236 &tcp_syncache.cache_limit); 237 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 238 &tcp_syncache.bucket_limit); 239 if (!powerof2(tcp_syncache.hashsize)) { 240 printf("WARNING: syncache hash size is not a power of 2.\n"); 241 tcp_syncache.hashsize = 512; /* safe default */ 242 } 243 tcp_syncache.hashmask = tcp_syncache.hashsize - 1; 244 245 /* Allocate the hash table. */ 246 MALLOC(tcp_syncache.hashbase, struct syncache_head *, 247 tcp_syncache.hashsize * sizeof(struct syncache_head), 248 M_SYNCACHE, M_WAITOK); 249 250 /* Initialize the hash buckets. */ 251 for (i = 0; i < tcp_syncache.hashsize; i++) { 252 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); 253 tcp_syncache.hashbase[i].sch_length = 0; 254 } 255 256 /* Initialize the timer queues. */ 257 for (i = 0; i <= SYNCACHE_MAXREXMTS; i++) { 258 TAILQ_INIT(&tcp_syncache.timerq[i]); 259 callout_init(&tcp_syncache.tt_timerq[i]); 260 } 261 262 /* 263 * Allocate the syncache entries. Allow the zone to allocate one 264 * more entry than cache limit, so a new entry can bump out an 265 * older one. 266 */ 267 tcp_syncache.cache_limit -= 1; 268 tcp_syncache.zone = zinit("syncache", sizeof(struct syncache), 269 tcp_syncache.cache_limit, ZONE_INTERRUPT, 0); 270 } 271 272 static void 273 syncache_insert(sc, sch) 274 struct syncache *sc; 275 struct syncache_head *sch; 276 { 277 struct syncache *sc2; 278 int s, i; 279 280 /* 281 * Make sure that we don't overflow the per-bucket 282 * limit or the total cache size limit. 283 */ 284 s = splnet(); 285 if (sch->sch_length >= tcp_syncache.bucket_limit) { 286 /* 287 * The bucket is full, toss the oldest element. 288 */ 289 sc2 = TAILQ_FIRST(&sch->sch_bucket); 290 sc2->sc_tp->ts_recent = ticks; 291 syncache_drop(sc2, sch); 292 tcpstat.tcps_sc_bucketoverflow++; 293 } else if (tcp_syncache.cache_count >= tcp_syncache.cache_limit) { 294 /* 295 * The cache is full. Toss the oldest entry in the 296 * entire cache. This is the front entry in the 297 * first non-empty timer queue with the largest 298 * timeout value. 299 */ 300 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) { 301 sc2 = TAILQ_FIRST(&tcp_syncache.timerq[i]); 302 if (sc2 != NULL) 303 break; 304 } 305 sc2->sc_tp->ts_recent = ticks; 306 syncache_drop(sc2, NULL); 307 tcpstat.tcps_sc_cacheoverflow++; 308 } 309 310 /* Initialize the entry's timer. */ 311 SYNCACHE_TIMEOUT(sc, 0); 312 313 /* Put it into the bucket. */ 314 TAILQ_INSERT_TAIL(&sch->sch_bucket, sc, sc_hash); 315 sch->sch_length++; 316 tcp_syncache.cache_count++; 317 tcpstat.tcps_sc_added++; 318 splx(s); 319 } 320 321 static void 322 syncache_drop(sc, sch) 323 struct syncache *sc; 324 struct syncache_head *sch; 325 { 326 int s; 327 328 if (sch == NULL) { 329 #ifdef INET6 330 if (sc->sc_inc.inc_isipv6) { 331 sch = &tcp_syncache.hashbase[ 332 SYNCACHE_HASH6(&sc->sc_inc, tcp_syncache.hashmask)]; 333 } else 334 #endif 335 { 336 sch = &tcp_syncache.hashbase[ 337 SYNCACHE_HASH(&sc->sc_inc, tcp_syncache.hashmask)]; 338 } 339 } 340 341 s = splnet(); 342 343 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 344 sch->sch_length--; 345 tcp_syncache.cache_count--; 346 347 TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], sc, sc_timerq); 348 if (TAILQ_EMPTY(&tcp_syncache.timerq[sc->sc_rxtslot])) 349 callout_stop(&tcp_syncache.tt_timerq[sc->sc_rxtslot]); 350 splx(s); 351 352 syncache_free(sc); 353 } 354 355 /* 356 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 357 * If we have retransmitted an entry the maximum number of times, expire it. 358 */ 359 static void 360 syncache_timer(xslot) 361 void *xslot; 362 { 363 intptr_t slot = (intptr_t)xslot; 364 struct syncache *sc, *nsc; 365 struct inpcb *inp; 366 int s; 367 368 s = splnet(); 369 if (callout_pending(&tcp_syncache.tt_timerq[slot]) || 370 !callout_active(&tcp_syncache.tt_timerq[slot])) { 371 splx(s); 372 return; 373 } 374 callout_deactivate(&tcp_syncache.tt_timerq[slot]); 375 376 nsc = TAILQ_FIRST(&tcp_syncache.timerq[slot]); 377 while (nsc != NULL) { 378 if (ticks < nsc->sc_rxttime) 379 break; 380 sc = nsc; 381 inp = sc->sc_tp->t_inpcb; 382 if (slot == SYNCACHE_MAXREXMTS || 383 slot >= tcp_syncache.rexmt_limit || 384 inp->inp_gencnt != sc->sc_inp_gencnt) { 385 nsc = TAILQ_NEXT(sc, sc_timerq); 386 syncache_drop(sc, NULL); 387 tcpstat.tcps_sc_stale++; 388 continue; 389 } 390 /* 391 * syncache_respond() may call back into the syncache to 392 * to modify another entry, so do not obtain the next 393 * entry on the timer chain until it has completed. 394 */ 395 (void) syncache_respond(sc, NULL); 396 nsc = TAILQ_NEXT(sc, sc_timerq); 397 tcpstat.tcps_sc_retransmitted++; 398 TAILQ_REMOVE(&tcp_syncache.timerq[slot], sc, sc_timerq); 399 SYNCACHE_TIMEOUT(sc, slot + 1); 400 } 401 if (nsc != NULL) 402 callout_reset(&tcp_syncache.tt_timerq[slot], 403 nsc->sc_rxttime - ticks, syncache_timer, (void *)(slot)); 404 splx(s); 405 } 406 407 /* 408 * Find an entry in the syncache. 409 */ 410 struct syncache * 411 syncache_lookup(inc, schp) 412 struct in_conninfo *inc; 413 struct syncache_head **schp; 414 { 415 struct syncache *sc; 416 struct syncache_head *sch; 417 int s; 418 419 #ifdef INET6 420 if (inc->inc_isipv6) { 421 sch = &tcp_syncache.hashbase[ 422 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; 423 *schp = sch; 424 s = splnet(); 425 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 426 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) { 427 splx(s); 428 return (sc); 429 } 430 } 431 splx(s); 432 } else 433 #endif 434 { 435 sch = &tcp_syncache.hashbase[ 436 SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; 437 *schp = sch; 438 s = splnet(); 439 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 440 #ifdef INET6 441 if (sc->sc_inc.inc_isipv6) 442 continue; 443 #endif 444 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) { 445 splx(s); 446 return (sc); 447 } 448 } 449 splx(s); 450 } 451 return (NULL); 452 } 453 454 /* 455 * This function is called when we get a RST for a 456 * non-existent connection, so that we can see if the 457 * connection is in the syn cache. If it is, zap it. 458 */ 459 void 460 syncache_chkrst(inc, th) 461 struct in_conninfo *inc; 462 struct tcphdr *th; 463 { 464 struct syncache *sc; 465 struct syncache_head *sch; 466 467 sc = syncache_lookup(inc, &sch); 468 if (sc == NULL) 469 return; 470 /* 471 * If the RST bit is set, check the sequence number to see 472 * if this is a valid reset segment. 473 * RFC 793 page 37: 474 * In all states except SYN-SENT, all reset (RST) segments 475 * are validated by checking their SEQ-fields. A reset is 476 * valid if its sequence number is in the window. 477 * 478 * The sequence number in the reset segment is normally an 479 * echo of our outgoing acknowlegement numbers, but some hosts 480 * send a reset with the sequence number at the rightmost edge 481 * of our receive window, and we have to handle this case. 482 */ 483 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 484 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 485 syncache_drop(sc, sch); 486 tcpstat.tcps_sc_reset++; 487 } 488 } 489 490 void 491 syncache_badack(inc) 492 struct in_conninfo *inc; 493 { 494 struct syncache *sc; 495 struct syncache_head *sch; 496 497 sc = syncache_lookup(inc, &sch); 498 if (sc != NULL) { 499 syncache_drop(sc, sch); 500 tcpstat.tcps_sc_badack++; 501 } 502 } 503 504 void 505 syncache_unreach(inc, th) 506 struct in_conninfo *inc; 507 struct tcphdr *th; 508 { 509 struct syncache *sc; 510 struct syncache_head *sch; 511 512 /* we are called at splnet() here */ 513 sc = syncache_lookup(inc, &sch); 514 if (sc == NULL) 515 return; 516 517 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 518 if (ntohl(th->th_seq) != sc->sc_iss) 519 return; 520 521 /* 522 * If we've rertransmitted 3 times and this is our second error, 523 * we remove the entry. Otherwise, we allow it to continue on. 524 * This prevents us from incorrectly nuking an entry during a 525 * spurious network outage. 526 * 527 * See tcp_notify(). 528 */ 529 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtslot < 3) { 530 sc->sc_flags |= SCF_UNREACH; 531 return; 532 } 533 syncache_drop(sc, sch); 534 tcpstat.tcps_sc_unreach++; 535 } 536 537 /* 538 * Build a new TCP socket structure from a syncache entry. 539 */ 540 static struct socket * 541 syncache_socket(sc, lso) 542 struct syncache *sc; 543 struct socket *lso; 544 { 545 struct inpcb *inp = NULL; 546 struct socket *so; 547 struct tcpcb *tp; 548 549 /* 550 * Ok, create the full blown connection, and set things up 551 * as they would have been set up if we had created the 552 * connection when the SYN arrived. If we can't create 553 * the connection, abort it. 554 */ 555 so = sonewconn(lso, SS_ISCONNECTED); 556 if (so == NULL) { 557 /* 558 * Drop the connection; we will send a RST if the peer 559 * retransmits the ACK, 560 */ 561 tcpstat.tcps_listendrop++; 562 goto abort; 563 } 564 565 inp = sotoinpcb(so); 566 567 /* 568 * Insert new socket into hash list. 569 */ 570 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; 571 #ifdef INET6 572 if (sc->sc_inc.inc_isipv6) { 573 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 574 } else { 575 inp->inp_vflag &= ~INP_IPV6; 576 inp->inp_vflag |= INP_IPV4; 577 #endif 578 inp->inp_laddr = sc->sc_inc.inc_laddr; 579 #ifdef INET6 580 } 581 #endif 582 inp->inp_lport = sc->sc_inc.inc_lport; 583 if (in_pcbinshash(inp) != 0) { 584 /* 585 * Undo the assignments above if we failed to 586 * put the PCB on the hash lists. 587 */ 588 #ifdef INET6 589 if (sc->sc_inc.inc_isipv6) 590 inp->in6p_laddr = in6addr_any; 591 else 592 #endif 593 inp->inp_laddr.s_addr = INADDR_ANY; 594 inp->inp_lport = 0; 595 goto abort; 596 } 597 #ifdef IPSEC 598 /* copy old policy into new socket's */ 599 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 600 printf("syncache_expand: could not copy policy\n"); 601 #endif 602 #ifdef INET6 603 if (sc->sc_inc.inc_isipv6) { 604 struct inpcb *oinp = sotoinpcb(lso); 605 struct in6_addr laddr6; 606 struct sockaddr_in6 *sin6; 607 /* 608 * Inherit socket options from the listening socket. 609 * Note that in6p_inputopts are not (and should not be) 610 * copied, since it stores previously received options and is 611 * used to detect if each new option is different than the 612 * previous one and hence should be passed to a user. 613 * If we copied in6p_inputopts, a user would not be able to 614 * receive options just after calling the accept system call. 615 */ 616 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 617 if (oinp->in6p_outputopts) 618 inp->in6p_outputopts = 619 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 620 inp->in6p_route = sc->sc_route6; 621 sc->sc_route6.ro_rt = NULL; 622 623 MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6, 624 M_SONAME, M_NOWAIT | M_ZERO); 625 if (sin6 == NULL) 626 goto abort; 627 sin6->sin6_family = AF_INET6; 628 sin6->sin6_len = sizeof(*sin6); 629 sin6->sin6_addr = sc->sc_inc.inc6_faddr; 630 sin6->sin6_port = sc->sc_inc.inc_fport; 631 laddr6 = inp->in6p_laddr; 632 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 633 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 634 if (in6_pcbconnect(inp, (struct sockaddr *)sin6, &proc0)) { 635 inp->in6p_laddr = laddr6; 636 FREE(sin6, M_SONAME); 637 goto abort; 638 } 639 FREE(sin6, M_SONAME); 640 } else 641 #endif 642 { 643 struct in_addr laddr; 644 struct sockaddr_in *sin; 645 646 inp->inp_options = ip_srcroute(); 647 if (inp->inp_options == NULL) { 648 inp->inp_options = sc->sc_ipopts; 649 sc->sc_ipopts = NULL; 650 } 651 inp->inp_route = sc->sc_route; 652 sc->sc_route.ro_rt = NULL; 653 654 MALLOC(sin, struct sockaddr_in *, sizeof *sin, 655 M_SONAME, M_NOWAIT | M_ZERO); 656 if (sin == NULL) 657 goto abort; 658 sin->sin_family = AF_INET; 659 sin->sin_len = sizeof(*sin); 660 sin->sin_addr = sc->sc_inc.inc_faddr; 661 sin->sin_port = sc->sc_inc.inc_fport; 662 bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero)); 663 laddr = inp->inp_laddr; 664 if (inp->inp_laddr.s_addr == INADDR_ANY) 665 inp->inp_laddr = sc->sc_inc.inc_laddr; 666 if (in_pcbconnect(inp, (struct sockaddr *)sin, &proc0)) { 667 inp->inp_laddr = laddr; 668 FREE(sin, M_SONAME); 669 goto abort; 670 } 671 FREE(sin, M_SONAME); 672 } 673 674 tp = intotcpcb(inp); 675 tp->t_state = TCPS_SYN_RECEIVED; 676 tp->iss = sc->sc_iss; 677 tp->irs = sc->sc_irs; 678 tcp_rcvseqinit(tp); 679 tcp_sendseqinit(tp); 680 tp->snd_wl1 = sc->sc_irs; 681 tp->rcv_up = sc->sc_irs + 1; 682 tp->rcv_wnd = sc->sc_wnd; 683 tp->rcv_adv += tp->rcv_wnd; 684 685 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 686 if (sc->sc_flags & SCF_NOOPT) 687 tp->t_flags |= TF_NOOPT; 688 if (sc->sc_flags & SCF_WINSCALE) { 689 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 690 tp->requested_s_scale = sc->sc_requested_s_scale; 691 tp->request_r_scale = sc->sc_request_r_scale; 692 } 693 if (sc->sc_flags & SCF_TIMESTAMP) { 694 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 695 tp->ts_recent = sc->sc_tsrecent; 696 tp->ts_recent_age = ticks; 697 } 698 if (sc->sc_flags & SCF_CC) { 699 /* 700 * Initialization of the tcpcb for transaction; 701 * set SND.WND = SEG.WND, 702 * initialize CCsend and CCrecv. 703 */ 704 tp->t_flags |= TF_REQ_CC|TF_RCVD_CC; 705 tp->cc_send = sc->sc_cc_send; 706 tp->cc_recv = sc->sc_cc_recv; 707 } 708 709 tcp_mss(tp, sc->sc_peer_mss); 710 711 /* 712 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. 713 */ 714 if (sc->sc_rxtslot != 0) 715 tp->snd_cwnd = tp->t_maxseg; 716 callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp); 717 718 tcpstat.tcps_accepts++; 719 return (so); 720 721 abort: 722 if (so != NULL) 723 (void) soabort(so); 724 return (NULL); 725 } 726 727 /* 728 * This function gets called when we receive an ACK for a 729 * socket in the LISTEN state. We look up the connection 730 * in the syncache, and if its there, we pull it out of 731 * the cache and turn it into a full-blown connection in 732 * the SYN-RECEIVED state. 733 */ 734 int 735 syncache_expand(inc, th, sop, m) 736 struct in_conninfo *inc; 737 struct tcphdr *th; 738 struct socket **sop; 739 struct mbuf *m; 740 { 741 struct syncache *sc; 742 struct syncache_head *sch; 743 struct socket *so; 744 745 sc = syncache_lookup(inc, &sch); 746 if (sc == NULL) { 747 /* 748 * There is no syncache entry, so see if this ACK is 749 * a returning syncookie. To do this, first: 750 * A. See if this socket has had a syncache entry dropped in 751 * the past. We don't want to accept a bogus syncookie 752 * if we've never received a SYN. 753 * B. check that the syncookie is valid. If it is, then 754 * cobble up a fake syncache entry, and return. 755 */ 756 if (!tcp_syncookies) 757 return (0); 758 sc = syncookie_lookup(inc, th, *sop); 759 if (sc == NULL) 760 return (0); 761 sch = NULL; 762 tcpstat.tcps_sc_recvcookie++; 763 } 764 765 /* 766 * If seg contains an ACK, but not for our SYN/ACK, send a RST. 767 */ 768 if (th->th_ack != sc->sc_iss + 1) 769 return (0); 770 771 so = syncache_socket(sc, *sop); 772 if (so == NULL) { 773 #if 0 774 resetandabort: 775 /* XXXjlemon check this - is this correct? */ 776 (void) tcp_respond(NULL, m, m, th, 777 th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK); 778 #endif 779 m_freem(m); /* XXX only needed for above */ 780 tcpstat.tcps_sc_aborted++; 781 } else { 782 sc->sc_flags |= SCF_KEEPROUTE; 783 tcpstat.tcps_sc_completed++; 784 } 785 if (sch == NULL) 786 syncache_free(sc); 787 else 788 syncache_drop(sc, sch); 789 *sop = so; 790 return (1); 791 } 792 793 /* 794 * Given a LISTEN socket and an inbound SYN request, add 795 * this to the syn cache, and send back a segment: 796 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 797 * to the source. 798 * 799 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 800 * Doing so would require that we hold onto the data and deliver it 801 * to the application. However, if we are the target of a SYN-flood 802 * DoS attack, an attacker could send data which would eventually 803 * consume all available buffer space if it were ACKed. By not ACKing 804 * the data, we avoid this DoS scenario. 805 */ 806 int 807 syncache_add(inc, to, th, sop, m) 808 struct in_conninfo *inc; 809 struct tcpopt *to; 810 struct tcphdr *th; 811 struct socket **sop; 812 struct mbuf *m; 813 { 814 struct tcpcb *tp; 815 struct socket *so; 816 struct syncache *sc = NULL; 817 struct syncache_head *sch; 818 struct mbuf *ipopts = NULL; 819 struct rmxp_tao *taop; 820 int i, s, win; 821 822 so = *sop; 823 tp = sototcpcb(so); 824 825 /* 826 * Remember the IP options, if any. 827 */ 828 #ifdef INET6 829 if (!inc->inc_isipv6) 830 #endif 831 ipopts = ip_srcroute(); 832 833 /* 834 * See if we already have an entry for this connection. 835 * If we do, resend the SYN,ACK, and reset the retransmit timer. 836 * 837 * XXX 838 * should the syncache be re-initialized with the contents 839 * of the new SYN here (which may have different options?) 840 */ 841 sc = syncache_lookup(inc, &sch); 842 if (sc != NULL) { 843 tcpstat.tcps_sc_dupsyn++; 844 if (ipopts) { 845 /* 846 * If we were remembering a previous source route, 847 * forget it and use the new one we've been given. 848 */ 849 if (sc->sc_ipopts) 850 (void) m_free(sc->sc_ipopts); 851 sc->sc_ipopts = ipopts; 852 } 853 /* 854 * Update timestamp if present. 855 */ 856 if (sc->sc_flags & SCF_TIMESTAMP) 857 sc->sc_tsrecent = to->to_tsval; 858 /* 859 * PCB may have changed, pick up new values. 860 */ 861 sc->sc_tp = tp; 862 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt; 863 if (syncache_respond(sc, m) == 0) { 864 s = splnet(); 865 TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], 866 sc, sc_timerq); 867 SYNCACHE_TIMEOUT(sc, sc->sc_rxtslot); 868 splx(s); 869 tcpstat.tcps_sndacks++; 870 tcpstat.tcps_sndtotal++; 871 } 872 *sop = NULL; 873 return (1); 874 } 875 876 sc = zalloc(tcp_syncache.zone); 877 if (sc == NULL) { 878 /* 879 * The zone allocator couldn't provide more entries. 880 * Treat this as if the cache was full; drop the oldest 881 * entry and insert the new one. 882 */ 883 s = splnet(); 884 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) { 885 sc = TAILQ_FIRST(&tcp_syncache.timerq[i]); 886 if (sc != NULL) 887 break; 888 } 889 sc->sc_tp->ts_recent = ticks; 890 syncache_drop(sc, NULL); 891 splx(s); 892 tcpstat.tcps_sc_zonefail++; 893 sc = zalloc(tcp_syncache.zone); 894 if (sc == NULL) { 895 if (ipopts) 896 (void) m_free(ipopts); 897 return (0); 898 } 899 } 900 901 /* 902 * Fill in the syncache values. 903 */ 904 bzero(sc, sizeof(*sc)); 905 sc->sc_tp = tp; 906 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt; 907 sc->sc_ipopts = ipopts; 908 sc->sc_inc.inc_fport = inc->inc_fport; 909 sc->sc_inc.inc_lport = inc->inc_lport; 910 #ifdef INET6 911 sc->sc_inc.inc_isipv6 = inc->inc_isipv6; 912 if (inc->inc_isipv6) { 913 sc->sc_inc.inc6_faddr = inc->inc6_faddr; 914 sc->sc_inc.inc6_laddr = inc->inc6_laddr; 915 sc->sc_route6.ro_rt = NULL; 916 } else 917 #endif 918 { 919 sc->sc_inc.inc_faddr = inc->inc_faddr; 920 sc->sc_inc.inc_laddr = inc->inc_laddr; 921 sc->sc_route.ro_rt = NULL; 922 } 923 sc->sc_irs = th->th_seq; 924 sc->sc_flags = 0; 925 sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0; 926 if (tcp_syncookies) 927 sc->sc_iss = syncookie_generate(sc); 928 else 929 sc->sc_iss = arc4random(); 930 931 /* Initial receive window: clip sbspace to [0 .. TCP_MAXWIN] */ 932 win = sbspace(&so->so_rcv); 933 win = imax(win, 0); 934 win = imin(win, TCP_MAXWIN); 935 sc->sc_wnd = win; 936 937 if (tcp_do_rfc1323) { 938 /* 939 * A timestamp received in a SYN makes 940 * it ok to send timestamp requests and replies. 941 */ 942 if (to->to_flags & TOF_TS) { 943 sc->sc_tsrecent = to->to_tsval; 944 sc->sc_flags |= SCF_TIMESTAMP; 945 } 946 if (to->to_flags & TOF_SCALE) { 947 int wscale = 0; 948 949 /* Compute proper scaling value from buffer space */ 950 while (wscale < TCP_MAX_WINSHIFT && 951 (TCP_MAXWIN << wscale) < so->so_rcv.sb_hiwat) 952 wscale++; 953 sc->sc_request_r_scale = wscale; 954 sc->sc_requested_s_scale = to->to_requested_s_scale; 955 sc->sc_flags |= SCF_WINSCALE; 956 } 957 } 958 if (tcp_do_rfc1644) { 959 /* 960 * A CC or CC.new option received in a SYN makes 961 * it ok to send CC in subsequent segments. 962 */ 963 if (to->to_flags & (TOF_CC|TOF_CCNEW)) { 964 sc->sc_cc_recv = to->to_cc; 965 sc->sc_cc_send = CC_INC(tcp_ccgen); 966 sc->sc_flags |= SCF_CC; 967 } 968 } 969 if (tp->t_flags & TF_NOOPT) 970 sc->sc_flags = SCF_NOOPT; 971 972 /* 973 * XXX 974 * We have the option here of not doing TAO (even if the segment 975 * qualifies) and instead fall back to a normal 3WHS via the syncache. 976 * This allows us to apply synflood protection to TAO-qualifying SYNs 977 * also. However, there should be a hueristic to determine when to 978 * do this, and is not present at the moment. 979 */ 980 981 /* 982 * Perform TAO test on incoming CC (SEG.CC) option, if any. 983 * - compare SEG.CC against cached CC from the same host, if any. 984 * - if SEG.CC > chached value, SYN must be new and is accepted 985 * immediately: save new CC in the cache, mark the socket 986 * connected, enter ESTABLISHED state, turn on flag to 987 * send a SYN in the next segment. 988 * A virtual advertised window is set in rcv_adv to 989 * initialize SWS prevention. Then enter normal segment 990 * processing: drop SYN, process data and FIN. 991 * - otherwise do a normal 3-way handshake. 992 */ 993 taop = tcp_gettaocache(&sc->sc_inc); 994 if ((to->to_flags & TOF_CC) != 0) { 995 if (((tp->t_flags & TF_NOPUSH) != 0) && 996 sc->sc_flags & SCF_CC && 997 taop != NULL && taop->tao_cc != 0 && 998 CC_GT(to->to_cc, taop->tao_cc)) { 999 sc->sc_rxtslot = 0; 1000 so = syncache_socket(sc, *sop); 1001 if (so != NULL) { 1002 sc->sc_flags |= SCF_KEEPROUTE; 1003 taop->tao_cc = to->to_cc; 1004 *sop = so; 1005 } 1006 syncache_free(sc); 1007 return (so != NULL); 1008 } 1009 } else { 1010 /* 1011 * No CC option, but maybe CC.NEW: invalidate cached value. 1012 */ 1013 if (taop != NULL) 1014 taop->tao_cc = 0; 1015 } 1016 /* 1017 * TAO test failed or there was no CC option, 1018 * do a standard 3-way handshake. 1019 */ 1020 if (syncache_respond(sc, m) == 0) { 1021 syncache_insert(sc, sch); 1022 tcpstat.tcps_sndacks++; 1023 tcpstat.tcps_sndtotal++; 1024 } else { 1025 syncache_free(sc); 1026 tcpstat.tcps_sc_dropped++; 1027 } 1028 *sop = NULL; 1029 return (1); 1030 } 1031 1032 static int 1033 syncache_respond(sc, m) 1034 struct syncache *sc; 1035 struct mbuf *m; 1036 { 1037 u_int8_t *optp; 1038 int optlen, error; 1039 u_int16_t tlen, hlen, mssopt; 1040 struct ip *ip = NULL; 1041 struct rtentry *rt; 1042 struct tcphdr *th; 1043 #ifdef INET6 1044 struct ip6_hdr *ip6 = NULL; 1045 #endif 1046 1047 #ifdef INET6 1048 if (sc->sc_inc.inc_isipv6) { 1049 rt = tcp_rtlookup6(&sc->sc_inc); 1050 if (rt != NULL) 1051 mssopt = rt->rt_ifp->if_mtu - 1052 (sizeof(struct ip6_hdr) + sizeof(struct tcphdr)); 1053 else 1054 mssopt = tcp_v6mssdflt; 1055 hlen = sizeof(struct ip6_hdr); 1056 } else 1057 #endif 1058 { 1059 rt = tcp_rtlookup(&sc->sc_inc); 1060 if (rt != NULL) 1061 mssopt = rt->rt_ifp->if_mtu - 1062 (sizeof(struct ip) + sizeof(struct tcphdr)); 1063 else 1064 mssopt = tcp_mssdflt; 1065 hlen = sizeof(struct ip); 1066 } 1067 1068 /* Compute the size of the TCP options. */ 1069 if (sc->sc_flags & SCF_NOOPT) { 1070 optlen = 0; 1071 } else { 1072 optlen = TCPOLEN_MAXSEG + 1073 ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) + 1074 ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0) + 1075 ((sc->sc_flags & SCF_CC) ? TCPOLEN_CC_APPA * 2 : 0); 1076 } 1077 tlen = hlen + sizeof(struct tcphdr) + optlen; 1078 1079 /* 1080 * XXX 1081 * assume that the entire packet will fit in a header mbuf 1082 */ 1083 KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small")); 1084 1085 /* 1086 * XXX shouldn't this reuse the mbuf if possible ? 1087 * Create the IP+TCP header from scratch. 1088 */ 1089 if (m) 1090 m_freem(m); 1091 1092 m = m_gethdr(M_DONTWAIT, MT_HEADER); 1093 if (m == NULL) 1094 return (ENOBUFS); 1095 m->m_data += max_linkhdr; 1096 m->m_len = tlen; 1097 m->m_pkthdr.len = tlen; 1098 m->m_pkthdr.rcvif = NULL; 1099 1100 #ifdef INET6 1101 if (sc->sc_inc.inc_isipv6) { 1102 ip6 = mtod(m, struct ip6_hdr *); 1103 ip6->ip6_vfc = IPV6_VERSION; 1104 ip6->ip6_nxt = IPPROTO_TCP; 1105 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1106 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1107 ip6->ip6_plen = htons(tlen - hlen); 1108 /* ip6_hlim is set after checksum */ 1109 /* ip6_flow = ??? */ 1110 1111 th = (struct tcphdr *)(ip6 + 1); 1112 } else 1113 #endif 1114 { 1115 ip = mtod(m, struct ip *); 1116 ip->ip_v = IPVERSION; 1117 ip->ip_hl = sizeof(struct ip) >> 2; 1118 ip->ip_len = tlen; 1119 ip->ip_id = 0; 1120 ip->ip_off = 0; 1121 ip->ip_sum = 0; 1122 ip->ip_p = IPPROTO_TCP; 1123 ip->ip_src = sc->sc_inc.inc_laddr; 1124 ip->ip_dst = sc->sc_inc.inc_faddr; 1125 ip->ip_ttl = sc->sc_tp->t_inpcb->inp_ip_ttl; /* XXX */ 1126 ip->ip_tos = sc->sc_tp->t_inpcb->inp_ip_tos; /* XXX */ 1127 1128 /* 1129 * See if we should do MTU discovery. Route lookups are expensive, 1130 * so we will only unset the DF bit if: 1131 * 1132 * 1) path_mtu_discovery is disabled 1133 * 2) the SCF_UNREACH flag has been set 1134 */ 1135 if (path_mtu_discovery 1136 && ((sc->sc_flags & SCF_UNREACH) == 0)) { 1137 ip->ip_off |= IP_DF; 1138 } 1139 1140 th = (struct tcphdr *)(ip + 1); 1141 } 1142 th->th_sport = sc->sc_inc.inc_lport; 1143 th->th_dport = sc->sc_inc.inc_fport; 1144 1145 th->th_seq = htonl(sc->sc_iss); 1146 th->th_ack = htonl(sc->sc_irs + 1); 1147 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1148 th->th_x2 = 0; 1149 th->th_flags = TH_SYN|TH_ACK; 1150 th->th_win = htons(sc->sc_wnd); 1151 th->th_urp = 0; 1152 1153 /* Tack on the TCP options. */ 1154 if (optlen == 0) 1155 goto no_options; 1156 optp = (u_int8_t *)(th + 1); 1157 *optp++ = TCPOPT_MAXSEG; 1158 *optp++ = TCPOLEN_MAXSEG; 1159 *optp++ = (mssopt >> 8) & 0xff; 1160 *optp++ = mssopt & 0xff; 1161 1162 if (sc->sc_flags & SCF_WINSCALE) { 1163 *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 | 1164 TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 | 1165 sc->sc_request_r_scale); 1166 optp += 4; 1167 } 1168 1169 if (sc->sc_flags & SCF_TIMESTAMP) { 1170 u_int32_t *lp = (u_int32_t *)(optp); 1171 1172 /* Form timestamp option as shown in appendix A of RFC 1323. */ 1173 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 1174 *lp++ = htonl(ticks); 1175 *lp = htonl(sc->sc_tsrecent); 1176 optp += TCPOLEN_TSTAMP_APPA; 1177 } 1178 1179 /* 1180 * Send CC and CC.echo if we received CC from our peer. 1181 */ 1182 if (sc->sc_flags & SCF_CC) { 1183 u_int32_t *lp = (u_int32_t *)(optp); 1184 1185 *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CC)); 1186 *lp++ = htonl(sc->sc_cc_send); 1187 *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CCECHO)); 1188 *lp = htonl(sc->sc_cc_recv); 1189 optp += TCPOLEN_CC_APPA * 2; 1190 } 1191 no_options: 1192 1193 #ifdef INET6 1194 if (sc->sc_inc.inc_isipv6) { 1195 struct route_in6 *ro6 = &sc->sc_route6; 1196 1197 th->th_sum = 0; 1198 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen); 1199 ip6->ip6_hlim = in6_selecthlim(NULL, 1200 ro6->ro_rt ? ro6->ro_rt->rt_ifp : NULL); 1201 error = ip6_output(m, NULL, ro6, 0, NULL, NULL, 1202 sc->sc_tp->t_inpcb); 1203 } else 1204 #endif 1205 { 1206 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1207 htons(tlen - hlen + IPPROTO_TCP)); 1208 m->m_pkthdr.csum_flags = CSUM_TCP; 1209 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1210 error = ip_output(m, sc->sc_ipopts, &sc->sc_route, 0, NULL, 1211 sc->sc_tp->t_inpcb); 1212 } 1213 return (error); 1214 } 1215 1216 /* 1217 * cookie layers: 1218 * 1219 * |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .| 1220 * | peer iss | 1221 * | MD5(laddr,faddr,secret,lport,fport) |. . . . . . .| 1222 * | 0 |(A)| | 1223 * (A): peer mss index 1224 */ 1225 1226 /* 1227 * The values below are chosen to minimize the size of the tcp_secret 1228 * table, as well as providing roughly a 16 second lifetime for the cookie. 1229 */ 1230 1231 #define SYNCOOKIE_WNDBITS 5 /* exposed bits for window indexing */ 1232 #define SYNCOOKIE_TIMESHIFT 1 /* scale ticks to window time units */ 1233 1234 #define SYNCOOKIE_WNDMASK ((1 << SYNCOOKIE_WNDBITS) - 1) 1235 #define SYNCOOKIE_NSECRETS (1 << SYNCOOKIE_WNDBITS) 1236 #define SYNCOOKIE_TIMEOUT \ 1237 (hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT)) 1238 #define SYNCOOKIE_DATAMASK ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK) 1239 1240 static struct { 1241 u_int32_t ts_secbits[4]; 1242 u_int ts_expire; 1243 } tcp_secret[SYNCOOKIE_NSECRETS]; 1244 1245 static int tcp_msstab[] = { 0, 536, 1460, 8960 }; 1246 1247 static MD5_CTX syn_ctx; 1248 1249 #define MD5Add(v) MD5Update(&syn_ctx, (u_char *)&v, sizeof(v)) 1250 1251 struct md5_add { 1252 u_int32_t laddr, faddr; 1253 u_int32_t secbits[4]; 1254 u_int16_t lport, fport; 1255 }; 1256 1257 #ifdef CTASSERT 1258 CTASSERT(sizeof(struct md5_add) == 28); 1259 #endif 1260 1261 /* 1262 * Consider the problem of a recreated (and retransmitted) cookie. If the 1263 * original SYN was accepted, the connection is established. The second 1264 * SYN is inflight, and if it arrives with an ISN that falls within the 1265 * receive window, the connection is killed. 1266 * 1267 * However, since cookies have other problems, this may not be worth 1268 * worrying about. 1269 */ 1270 1271 static u_int32_t 1272 syncookie_generate(struct syncache *sc) 1273 { 1274 u_int32_t md5_buffer[4]; 1275 u_int32_t data; 1276 int idx, i; 1277 struct md5_add add; 1278 1279 idx = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK; 1280 if (tcp_secret[idx].ts_expire < ticks) { 1281 for (i = 0; i < 4; i++) 1282 tcp_secret[idx].ts_secbits[i] = arc4random(); 1283 tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT; 1284 } 1285 for (data = sizeof(tcp_msstab) / sizeof(int) - 1; data > 0; data--) 1286 if (tcp_msstab[data] <= sc->sc_peer_mss) 1287 break; 1288 data = (data << SYNCOOKIE_WNDBITS) | idx; 1289 data ^= sc->sc_irs; /* peer's iss */ 1290 MD5Init(&syn_ctx); 1291 #ifdef INET6 1292 if (sc->sc_inc.inc_isipv6) { 1293 MD5Add(sc->sc_inc.inc6_laddr); 1294 MD5Add(sc->sc_inc.inc6_faddr); 1295 add.laddr = 0; 1296 add.faddr = 0; 1297 } else 1298 #endif 1299 { 1300 add.laddr = sc->sc_inc.inc_laddr.s_addr; 1301 add.faddr = sc->sc_inc.inc_faddr.s_addr; 1302 } 1303 add.lport = sc->sc_inc.inc_lport; 1304 add.fport = sc->sc_inc.inc_fport; 1305 add.secbits[0] = tcp_secret[idx].ts_secbits[0]; 1306 add.secbits[1] = tcp_secret[idx].ts_secbits[1]; 1307 add.secbits[2] = tcp_secret[idx].ts_secbits[2]; 1308 add.secbits[3] = tcp_secret[idx].ts_secbits[3]; 1309 MD5Add(add); 1310 MD5Final((u_char *)&md5_buffer, &syn_ctx); 1311 data ^= (md5_buffer[0] & ~SYNCOOKIE_WNDMASK); 1312 return (data); 1313 } 1314 1315 static struct syncache * 1316 syncookie_lookup(inc, th, so) 1317 struct in_conninfo *inc; 1318 struct tcphdr *th; 1319 struct socket *so; 1320 { 1321 u_int32_t md5_buffer[4]; 1322 struct syncache *sc; 1323 u_int32_t data; 1324 int wnd, idx; 1325 struct md5_add add; 1326 1327 data = (th->th_ack - 1) ^ (th->th_seq - 1); /* remove ISS */ 1328 idx = data & SYNCOOKIE_WNDMASK; 1329 if (tcp_secret[idx].ts_expire < ticks || 1330 sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks) 1331 return (NULL); 1332 MD5Init(&syn_ctx); 1333 #ifdef INET6 1334 if (inc->inc_isipv6) { 1335 MD5Add(inc->inc6_laddr); 1336 MD5Add(inc->inc6_faddr); 1337 add.laddr = 0; 1338 add.faddr = 0; 1339 } else 1340 #endif 1341 { 1342 add.laddr = inc->inc_laddr.s_addr; 1343 add.faddr = inc->inc_faddr.s_addr; 1344 } 1345 add.lport = inc->inc_lport; 1346 add.fport = inc->inc_fport; 1347 add.secbits[0] = tcp_secret[idx].ts_secbits[0]; 1348 add.secbits[1] = tcp_secret[idx].ts_secbits[1]; 1349 add.secbits[2] = tcp_secret[idx].ts_secbits[2]; 1350 add.secbits[3] = tcp_secret[idx].ts_secbits[3]; 1351 MD5Add(add); 1352 MD5Final((u_char *)&md5_buffer, &syn_ctx); 1353 data ^= md5_buffer[0]; 1354 if ((data & ~SYNCOOKIE_DATAMASK) != 0) 1355 return (NULL); 1356 data = data >> SYNCOOKIE_WNDBITS; 1357 1358 sc = zalloc(tcp_syncache.zone); 1359 if (sc == NULL) 1360 return (NULL); 1361 /* 1362 * Fill in the syncache values. 1363 * XXX duplicate code from syncache_add 1364 */ 1365 sc->sc_ipopts = NULL; 1366 sc->sc_inc.inc_fport = inc->inc_fport; 1367 sc->sc_inc.inc_lport = inc->inc_lport; 1368 #ifdef INET6 1369 sc->sc_inc.inc_isipv6 = inc->inc_isipv6; 1370 if (inc->inc_isipv6) { 1371 sc->sc_inc.inc6_faddr = inc->inc6_faddr; 1372 sc->sc_inc.inc6_laddr = inc->inc6_laddr; 1373 sc->sc_route6.ro_rt = NULL; 1374 } else 1375 #endif 1376 { 1377 sc->sc_inc.inc_faddr = inc->inc_faddr; 1378 sc->sc_inc.inc_laddr = inc->inc_laddr; 1379 sc->sc_route.ro_rt = NULL; 1380 } 1381 sc->sc_irs = th->th_seq - 1; 1382 sc->sc_iss = th->th_ack - 1; 1383 wnd = sbspace(&so->so_rcv); 1384 wnd = imax(wnd, 0); 1385 wnd = imin(wnd, TCP_MAXWIN); 1386 sc->sc_wnd = wnd; 1387 sc->sc_flags = 0; 1388 sc->sc_rxtslot = 0; 1389 sc->sc_peer_mss = tcp_msstab[data]; 1390 return (sc); 1391 } 1392