1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. The name of the author may not be used to endorse or promote 16 * products derived from this software without specific prior written 17 * permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 */ 31 32 /* 33 * ip_fastforward gets its speed from processing the forwarded packet to 34 * completion (if_output on the other side) without any queues or netisr's. 35 * The receiving interface DMAs the packet into memory, the upper half of 36 * driver calls ip_fastforward, we do our routing table lookup and directly 37 * send it off to the outgoing interface, which DMAs the packet to the 38 * network card. The only part of the packet we touch with the CPU is the 39 * IP header (unless there are complex firewall rules touching other parts 40 * of the packet, but that is up to you). We are essentially limited by bus 41 * bandwidth and how fast the network card/driver can set up receives and 42 * transmits. 43 * 44 * We handle basic errors, IP header errors, checksum errors, 45 * destination unreachable, fragmentation and fragmentation needed and 46 * report them via ICMP to the sender. 47 * 48 * Else if something is not pure IPv4 unicast forwarding we fall back to 49 * the normal ip_input processing path. We should only be called from 50 * interfaces connected to the outside world. 51 * 52 * Firewalling is fully supported including divert, ipfw fwd and ipfilter 53 * ipnat and address rewrite. 54 * 55 * IPSEC is not supported if this host is a tunnel broker. IPSEC is 56 * supported for connections to/from local host. 57 * 58 * We try to do the least expensive (in CPU ops) checks and operations 59 * first to catch junk with as little overhead as possible. 60 * 61 * We take full advantage of hardware support for IP checksum and 62 * fragmentation offloading. 63 */ 64 65 /* 66 * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which 67 * is being followed here. 68 */ 69 70 #include <sys/cdefs.h> 71 #include "opt_ipstealth.h" 72 73 #include <sys/param.h> 74 #include <sys/systm.h> 75 #include <sys/kernel.h> 76 #include <sys/malloc.h> 77 #include <sys/mbuf.h> 78 #include <sys/protosw.h> 79 #include <sys/sdt.h> 80 #include <sys/socket.h> 81 #include <sys/sysctl.h> 82 83 #include <net/if.h> 84 #include <net/if_types.h> 85 #include <net/if_var.h> 86 #include <net/if_dl.h> 87 #include <net/if_private.h> 88 #include <net/pfil.h> 89 #include <net/route.h> 90 #include <net/route/nhop.h> 91 #include <net/vnet.h> 92 93 #include <netinet/in.h> 94 #include <netinet/in_fib.h> 95 #include <netinet/in_kdtrace.h> 96 #include <netinet/in_systm.h> 97 #include <netinet/in_var.h> 98 #include <netinet/ip.h> 99 #include <netinet/ip_var.h> 100 #include <netinet/ip_icmp.h> 101 #include <netinet/ip_options.h> 102 103 #include <machine/in_cksum.h> 104 105 #define V_ipsendredirects VNET(ipsendredirects) 106 107 static struct mbuf * 108 ip_redir_alloc(struct mbuf *m, struct nhop_object *nh, u_short ip_len, 109 struct in_addr *osrc, struct in_addr *newgw) 110 { 111 struct in_ifaddr *nh_ia; 112 struct mbuf *mcopy; 113 114 KASSERT(nh != NULL, ("%s: m %p nh is NULL\n", __func__, m)); 115 116 /* 117 * Only send a redirect if: 118 * - Redirects are not disabled (must be checked by caller), 119 * - We have not applied NAT (must be checked by caller as possible), 120 * - Neither a MCAST or BCAST packet (must be checked by caller) 121 * [RFC1009 Appendix A.2]. 122 * - The packet does not do IP source routing or having any other 123 * IP options (this case was handled already by ip_input() calling 124 * ip_dooptions() [RFC792, p13], 125 * - The packet is being forwarded out the same physical interface 126 * that it was received from [RFC1812, 5.2.7.2]. 127 */ 128 129 /* 130 * - The forwarding route was not created by a redirect 131 * [RFC1812, 5.2.7.2], or 132 * if it was to follow a default route (see below). 133 * - The next-hop is reachable by us [RFC1009 Appendix A.2]. 134 */ 135 if ((nh->nh_flags & (NHF_DEFAULT | NHF_REDIRECT | 136 NHF_BLACKHOLE | NHF_REJECT)) != 0) 137 return (NULL); 138 139 /* Get the new gateway. */ 140 if ((nh->nh_flags & NHF_GATEWAY) == 0 || nh->gw_sa.sa_family != AF_INET) 141 return (NULL); 142 newgw->s_addr = nh->gw4_sa.sin_addr.s_addr; 143 144 /* 145 * - The resulting forwarding destination is not "This host on this 146 * network" [RFC1122, Section 3.2.1.3] (default route check above). 147 */ 148 if (newgw->s_addr == 0) 149 return (NULL); 150 151 /* 152 * - We know how to reach the sender and the source address is 153 * directly connected to us [RFC792, p13]. 154 * + The new gateway address and the source address are on the same 155 * subnet [RFC1009 Appendix A.2, RFC1122 3.2.2.2, RFC1812, 5.2.7.2]. 156 * NB: if you think multiple logical subnets on the same wire should 157 * receive redirects read [RFC1812, APPENDIX C (14->15)]. 158 */ 159 nh_ia = (struct in_ifaddr *)nh->nh_ifa; 160 if ((ntohl(osrc->s_addr) & nh_ia->ia_subnetmask) != nh_ia->ia_subnet) 161 return (NULL); 162 163 /* Prepare for sending the redirect. */ 164 165 /* 166 * Make a copy of as much as we need of the packet as the original 167 * one will be forwarded but we need (a portion) for icmp_error(). 168 */ 169 mcopy = m_gethdr(M_NOWAIT, m->m_type); 170 if (mcopy == NULL) 171 return (NULL); 172 173 if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) { 174 /* 175 * It's probably ok if the pkthdr dup fails (because 176 * the deep copy of the tag chain failed), but for now 177 * be conservative and just discard the copy since 178 * code below may some day want the tags. 179 */ 180 m_free(mcopy); 181 return (NULL); 182 } 183 mcopy->m_len = min(ip_len, M_TRAILINGSPACE(mcopy)); 184 mcopy->m_pkthdr.len = mcopy->m_len; 185 m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t)); 186 187 return (mcopy); 188 } 189 190 191 static int 192 ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m) 193 { 194 struct nhop_object *nh; 195 196 nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE, 197 m->m_pkthdr.flowid); 198 if (nh == NULL) { 199 IPSTAT_INC(ips_noroute); 200 IPSTAT_INC(ips_cantforward); 201 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 202 return (EHOSTUNREACH); 203 } 204 /* 205 * Drop blackholed traffic and directed broadcasts. 206 */ 207 if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) { 208 IPSTAT_INC(ips_cantforward); 209 m_freem(m); 210 return (EHOSTUNREACH); 211 } 212 213 if (nh->nh_flags & NHF_REJECT) { 214 IPSTAT_INC(ips_cantforward); 215 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 216 return (EHOSTUNREACH); 217 } 218 219 *pnh = nh; 220 221 return (0); 222 } 223 224 /* 225 * Try to forward a packet based on the destination address. 226 * This is a fast path optimized for the plain forwarding case. 227 * If the packet is handled (and consumed) here then we return NULL; 228 * otherwise mbuf is returned and the packet should be delivered 229 * to ip_input for full processing. 230 */ 231 struct mbuf * 232 ip_tryforward(struct mbuf *m) 233 { 234 struct ip *ip; 235 struct mbuf *m0 = NULL; 236 struct nhop_object *nh = NULL; 237 struct route ro; 238 struct sockaddr_in *dst; 239 const struct sockaddr *gw; 240 struct in_addr dest, odest, rtdest, osrc; 241 uint16_t ip_len, ip_off; 242 int error = 0; 243 struct m_tag *fwd_tag = NULL; 244 struct mbuf *mcopy = NULL; 245 struct in_addr redest; 246 /* 247 * Are we active and forwarding packets? 248 */ 249 250 M_ASSERTVALID(m); 251 M_ASSERTPKTHDR(m); 252 253 /* 254 * Only IP packets without options 255 */ 256 ip = mtod(m, struct ip *); 257 258 if (ip->ip_hl != (sizeof(struct ip) >> 2)) { 259 if (V_ip_doopts == 1) 260 return m; 261 else if (V_ip_doopts == 2) { 262 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB, 263 0, 0); 264 return NULL; /* mbuf already free'd */ 265 } 266 /* else ignore IP options and continue */ 267 } 268 269 /* 270 * Only unicast IP, not from loopback, no L2 or IP broadcast, 271 * no multicast, no INADDR_ANY 272 * 273 * XXX: Probably some of these checks could be direct drop 274 * conditions. However it is not clear whether there are some 275 * hacks or obscure behaviours which make it necessary to 276 * let ip_input handle it. We play safe here and let ip_input 277 * deal with it until it is proven that we can directly drop it. 278 */ 279 if ((m->m_flags & (M_BCAST|M_MCAST)) || 280 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) || 281 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST || 282 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST || 283 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 284 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 285 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) || 286 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) || 287 ip->ip_src.s_addr == INADDR_ANY || 288 ip->ip_dst.s_addr == INADDR_ANY ) 289 return m; 290 291 /* 292 * Is it for a local address on this host? 293 */ 294 if (in_localip(ip->ip_dst)) 295 return m; 296 297 IPSTAT_INC(ips_total); 298 299 /* 300 * Step 3: incoming packet firewall processing 301 */ 302 303 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr; 304 osrc.s_addr = ip->ip_src.s_addr; 305 306 /* 307 * Run through list of ipfilter hooks for input packets 308 */ 309 if (!PFIL_HOOKED_IN(V_inet_pfil_head)) 310 goto passin; 311 312 if (pfil_mbuf_in(V_inet_pfil_head, &m, m->m_pkthdr.rcvif, 313 NULL) != PFIL_PASS) 314 goto drop; 315 316 M_ASSERTVALID(m); 317 M_ASSERTPKTHDR(m); 318 319 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */ 320 dest.s_addr = ip->ip_dst.s_addr; 321 322 /* 323 * Destination address changed? 324 */ 325 if (odest.s_addr != dest.s_addr) { 326 /* 327 * Is it now for a local address on this host? 328 */ 329 if (in_localip(dest)) 330 goto forwardlocal; 331 /* 332 * Go on with new destination address 333 */ 334 } 335 336 if (m->m_flags & M_FASTFWD_OURS) { 337 /* 338 * ipfw changed it for a local address on this host. 339 */ 340 goto forwardlocal; 341 } 342 343 passin: 344 /* 345 * Step 4: decrement TTL and look up route 346 */ 347 348 /* 349 * Check TTL 350 */ 351 #ifdef IPSTEALTH 352 if (!V_ipstealth) { 353 #endif 354 if (ip->ip_ttl <= IPTTLDEC) { 355 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0); 356 return NULL; /* mbuf already free'd */ 357 } 358 359 /* 360 * Decrement the TTL and incrementally change the IP header checksum. 361 * Don't bother doing this with hw checksum offloading, it's faster 362 * doing it right here. 363 */ 364 ip->ip_ttl -= IPTTLDEC; 365 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8)) 366 ip->ip_sum -= ~htons(IPTTLDEC << 8); 367 else 368 ip->ip_sum += htons(IPTTLDEC << 8); 369 #ifdef IPSTEALTH 370 } 371 #endif 372 373 /* 374 * Next hop forced by pfil(9) hook? 375 */ 376 if ((m->m_flags & M_IP_NEXTHOP) && 377 ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) { 378 /* 379 * Now we will find route to forced destination. 380 */ 381 dest.s_addr = ((struct sockaddr_in *) 382 (fwd_tag + 1))->sin_addr.s_addr; 383 m_tag_delete(m, fwd_tag); 384 m->m_flags &= ~M_IP_NEXTHOP; 385 } 386 387 /* 388 * Find route to destination. 389 */ 390 if (ip_findroute(&nh, dest, m) != 0) 391 return (NULL); /* icmp unreach already sent */ 392 393 /* 394 * Avoid second route lookup by caching destination. 395 */ 396 rtdest.s_addr = dest.s_addr; 397 398 /* 399 * Step 5: outgoing firewall packet processing 400 */ 401 if (!PFIL_HOOKED_OUT(V_inet_pfil_head)) 402 goto passout; 403 404 if (pfil_mbuf_out(V_inet_pfil_head, &m, nh->nh_ifp, 405 NULL) != PFIL_PASS) 406 goto drop; 407 408 M_ASSERTVALID(m); 409 M_ASSERTPKTHDR(m); 410 411 ip = mtod(m, struct ip *); 412 dest.s_addr = ip->ip_dst.s_addr; 413 414 /* 415 * Destination address changed? 416 */ 417 if (m->m_flags & M_IP_NEXTHOP) 418 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); 419 else 420 fwd_tag = NULL; 421 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) { 422 /* 423 * Is it now for a local address on this host? 424 */ 425 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) { 426 forwardlocal: 427 /* 428 * Return packet for processing by ip_input(). 429 */ 430 m->m_flags |= M_FASTFWD_OURS; 431 return (m); 432 } 433 /* 434 * Redo route lookup with new destination address 435 */ 436 if (fwd_tag) { 437 dest.s_addr = ((struct sockaddr_in *) 438 (fwd_tag + 1))->sin_addr.s_addr; 439 m_tag_delete(m, fwd_tag); 440 m->m_flags &= ~M_IP_NEXTHOP; 441 } 442 if (dest.s_addr != rtdest.s_addr && 443 ip_findroute(&nh, dest, m) != 0) 444 return (NULL); /* icmp unreach already sent */ 445 } 446 447 passout: 448 /* 449 * Step 6: send off the packet 450 */ 451 ip_len = ntohs(ip->ip_len); 452 ip_off = ntohs(ip->ip_off); 453 454 bzero(&ro, sizeof(ro)); 455 dst = (struct sockaddr_in *)&ro.ro_dst; 456 dst->sin_family = AF_INET; 457 dst->sin_len = sizeof(*dst); 458 dst->sin_addr = dest; 459 if (nh->nh_flags & NHF_GATEWAY) { 460 gw = &nh->gw_sa; 461 ro.ro_flags |= RT_HAS_GW; 462 } else 463 gw = (const struct sockaddr *)dst; 464 465 /* Handle redirect case. */ 466 redest.s_addr = 0; 467 if (V_ipsendredirects && osrc.s_addr == ip->ip_src.s_addr && 468 nh->nh_ifp == m->m_pkthdr.rcvif) 469 mcopy = ip_redir_alloc(m, nh, ip_len, &osrc, &redest); 470 471 /* 472 * Check if packet fits MTU or if hardware will fragment for us 473 */ 474 if (ip_len <= nh->nh_mtu) { 475 /* 476 * Avoid confusing lower layers. 477 */ 478 m_clrprotoflags(m); 479 /* 480 * Send off the packet via outgoing interface 481 */ 482 IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL); 483 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro); 484 } else { 485 /* 486 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery 487 */ 488 if (ip_off & IP_DF) { 489 IPSTAT_INC(ips_cantfrag); 490 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG, 491 0, nh->nh_mtu); 492 goto consumed; 493 } else { 494 /* 495 * We have to fragment the packet 496 */ 497 m->m_pkthdr.csum_flags |= CSUM_IP; 498 if (ip_fragment(ip, &m, nh->nh_mtu, 499 nh->nh_ifp->if_hwassist) != 0) 500 goto drop; 501 KASSERT(m != NULL, ("null mbuf and no error")); 502 /* 503 * Send off the fragments via outgoing interface 504 */ 505 error = 0; 506 do { 507 m0 = m->m_nextpkt; 508 m->m_nextpkt = NULL; 509 /* 510 * Avoid confusing lower layers. 511 */ 512 m_clrprotoflags(m); 513 514 IP_PROBE(send, NULL, NULL, 515 mtod(m, struct ip *), nh->nh_ifp, 516 mtod(m, struct ip *), NULL); 517 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, 518 gw, &ro); 519 if (error) 520 break; 521 } while ((m = m0) != NULL); 522 if (error) { 523 /* Reclaim remaining fragments */ 524 for (m = m0; m; m = m0) { 525 m0 = m->m_nextpkt; 526 m_freem(m); 527 } 528 } else 529 IPSTAT_INC(ips_fragmented); 530 } 531 } 532 533 if (error != 0) 534 IPSTAT_INC(ips_odropped); 535 else { 536 IPSTAT_INC(ips_forward); 537 IPSTAT_INC(ips_fastforward); 538 } 539 540 /* Send required redirect */ 541 if (mcopy != NULL) { 542 icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0); 543 mcopy = NULL; /* Was consumed by callee. */ 544 } 545 546 consumed: 547 if (mcopy != NULL) 548 m_freem(mcopy); 549 return NULL; 550 drop: 551 if (m) 552 m_freem(m); 553 return NULL; 554 } 555