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/pfil.h>
88 #include <net/route.h>
89 #include <net/route/nhop.h>
90 #include <net/vnet.h>
91
92 #include <netinet/in.h>
93 #include <netinet/in_fib.h>
94 #include <netinet/in_kdtrace.h>
95 #include <netinet/in_systm.h>
96 #include <netinet/in_var.h>
97 #include <netinet/ip.h>
98 #include <netinet/ip_var.h>
99 #include <netinet/ip_icmp.h>
100 #include <netinet/ip_options.h>
101
102 #include <machine/in_cksum.h>
103
104 #define V_ipsendredirects VNET(ipsendredirects)
105
106 static struct mbuf *
ip_redir_alloc(struct mbuf * m,struct nhop_object * nh,u_short ip_len,struct in_addr * osrc,struct in_addr * newgw)107 ip_redir_alloc(struct mbuf *m, struct nhop_object *nh, u_short ip_len,
108 struct in_addr *osrc, struct in_addr *newgw)
109 {
110 struct in_ifaddr *nh_ia;
111 struct mbuf *mcopy;
112
113 KASSERT(nh != NULL, ("%s: m %p nh is NULL\n", __func__, m));
114
115 /*
116 * Only send a redirect if:
117 * - Redirects are not disabled (must be checked by caller),
118 * - We have not applied NAT (must be checked by caller as possible),
119 * - Neither a MCAST or BCAST packet (must be checked by caller)
120 * [RFC1009 Appendix A.2].
121 * - The packet does not do IP source routing or having any other
122 * IP options (this case was handled already by ip_input() calling
123 * ip_dooptions() [RFC792, p13],
124 * - The packet is being forwarded out the same physical interface
125 * that it was received from [RFC1812, 5.2.7.2].
126 */
127
128 /*
129 * - The forwarding route was not created by a redirect
130 * [RFC1812, 5.2.7.2], or
131 * if it was to follow a default route (see below).
132 * - The next-hop is reachable by us [RFC1009 Appendix A.2].
133 */
134 if ((nh->nh_flags & (NHF_DEFAULT | NHF_REDIRECT |
135 NHF_BLACKHOLE | NHF_REJECT)) != 0)
136 return (NULL);
137
138 /* Get the new gateway. */
139 if ((nh->nh_flags & NHF_GATEWAY) == 0 || nh->gw_sa.sa_family != AF_INET)
140 return (NULL);
141 newgw->s_addr = nh->gw4_sa.sin_addr.s_addr;
142
143 /*
144 * - The resulting forwarding destination is not "This host on this
145 * network" [RFC1122, Section 3.2.1.3] (default route check above).
146 */
147 if (newgw->s_addr == 0)
148 return (NULL);
149
150 /*
151 * - We know how to reach the sender and the source address is
152 * directly connected to us [RFC792, p13].
153 * + The new gateway address and the source address are on the same
154 * subnet [RFC1009 Appendix A.2, RFC1122 3.2.2.2, RFC1812, 5.2.7.2].
155 * NB: if you think multiple logical subnets on the same wire should
156 * receive redirects read [RFC1812, APPENDIX C (14->15)].
157 */
158 nh_ia = (struct in_ifaddr *)nh->nh_ifa;
159 if ((ntohl(osrc->s_addr) & nh_ia->ia_subnetmask) != nh_ia->ia_subnet)
160 return (NULL);
161
162 /* Prepare for sending the redirect. */
163
164 /*
165 * Make a copy of as much as we need of the packet as the original
166 * one will be forwarded but we need (a portion) for icmp_error().
167 */
168 mcopy = m_gethdr(M_NOWAIT, m->m_type);
169 if (mcopy == NULL)
170 return (NULL);
171
172 if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) {
173 /*
174 * It's probably ok if the pkthdr dup fails (because
175 * the deep copy of the tag chain failed), but for now
176 * be conservative and just discard the copy since
177 * code below may some day want the tags.
178 */
179 m_free(mcopy);
180 return (NULL);
181 }
182 mcopy->m_len = min(ip_len, M_TRAILINGSPACE(mcopy));
183 mcopy->m_pkthdr.len = mcopy->m_len;
184 m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t));
185
186 return (mcopy);
187 }
188
189
190 static int
ip_findroute(struct nhop_object ** pnh,struct in_addr dest,struct mbuf * m)191 ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m)
192 {
193 struct nhop_object *nh;
194
195 nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE,
196 m->m_pkthdr.flowid);
197 if (nh == NULL) {
198 IPSTAT_INC(ips_noroute);
199 IPSTAT_INC(ips_cantforward);
200 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
201 return (EHOSTUNREACH);
202 }
203 /*
204 * Drop blackholed traffic and directed broadcasts.
205 */
206 if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) {
207 IPSTAT_INC(ips_cantforward);
208 m_freem(m);
209 return (EHOSTUNREACH);
210 }
211
212 if (nh->nh_flags & NHF_REJECT) {
213 IPSTAT_INC(ips_cantforward);
214 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
215 return (EHOSTUNREACH);
216 }
217
218 *pnh = nh;
219
220 return (0);
221 }
222
223 /*
224 * Try to forward a packet based on the destination address.
225 * This is a fast path optimized for the plain forwarding case.
226 * If the packet is handled (and consumed) here then we return NULL;
227 * otherwise mbuf is returned and the packet should be delivered
228 * to ip_input for full processing.
229 */
230 struct mbuf *
ip_tryforward(struct mbuf * m)231 ip_tryforward(struct mbuf *m)
232 {
233 struct ip *ip;
234 struct mbuf *m0 = NULL;
235 struct nhop_object *nh = NULL;
236 struct route ro;
237 struct sockaddr_in *dst;
238 const struct sockaddr *gw;
239 struct in_addr dest, odest, rtdest, osrc;
240 uint16_t ip_len, ip_off;
241 int error = 0;
242 struct m_tag *fwd_tag = NULL;
243 struct mbuf *mcopy = NULL;
244 struct in_addr redest;
245 /*
246 * Are we active and forwarding packets?
247 */
248
249 M_ASSERTVALID(m);
250 M_ASSERTPKTHDR(m);
251
252 #ifdef ALTQ
253 /*
254 * Is packet dropped by traffic conditioner?
255 */
256 if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0)
257 goto drop;
258 #endif
259
260 /*
261 * Only IP packets without options
262 */
263 ip = mtod(m, struct ip *);
264
265 if (ip->ip_hl != (sizeof(struct ip) >> 2)) {
266 if (V_ip_doopts == 1)
267 return m;
268 else if (V_ip_doopts == 2) {
269 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB,
270 0, 0);
271 return NULL; /* mbuf already free'd */
272 }
273 /* else ignore IP options and continue */
274 }
275
276 /*
277 * Only unicast IP, not from loopback, no L2 or IP broadcast,
278 * no multicast, no INADDR_ANY
279 *
280 * XXX: Probably some of these checks could be direct drop
281 * conditions. However it is not clear whether there are some
282 * hacks or obscure behaviours which make it necessary to
283 * let ip_input handle it. We play safe here and let ip_input
284 * deal with it until it is proven that we can directly drop it.
285 */
286 if ((m->m_flags & (M_BCAST|M_MCAST)) ||
287 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) ||
288 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST ||
289 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST ||
290 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
291 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
292 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) ||
293 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) ||
294 ip->ip_src.s_addr == INADDR_ANY ||
295 ip->ip_dst.s_addr == INADDR_ANY )
296 return m;
297
298 /*
299 * Is it for a local address on this host?
300 */
301 if (in_localip(ip->ip_dst))
302 return m;
303
304 IPSTAT_INC(ips_total);
305
306 /*
307 * Step 3: incoming packet firewall processing
308 */
309
310 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr;
311 osrc.s_addr = ip->ip_src.s_addr;
312
313 /*
314 * Run through list of ipfilter hooks for input packets
315 */
316 if (!PFIL_HOOKED_IN(V_inet_pfil_head))
317 goto passin;
318
319 if (pfil_run_hooks(V_inet_pfil_head, &m, m->m_pkthdr.rcvif, PFIL_IN,
320 NULL) != PFIL_PASS)
321 goto drop;
322
323 M_ASSERTVALID(m);
324 M_ASSERTPKTHDR(m);
325
326 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */
327 dest.s_addr = ip->ip_dst.s_addr;
328
329 /*
330 * Destination address changed?
331 */
332 if (odest.s_addr != dest.s_addr) {
333 /*
334 * Is it now for a local address on this host?
335 */
336 if (in_localip(dest))
337 goto forwardlocal;
338 /*
339 * Go on with new destination address
340 */
341 }
342
343 if (m->m_flags & M_FASTFWD_OURS) {
344 /*
345 * ipfw changed it for a local address on this host.
346 */
347 goto forwardlocal;
348 }
349
350 passin:
351 /*
352 * Step 4: decrement TTL and look up route
353 */
354
355 /*
356 * Check TTL
357 */
358 #ifdef IPSTEALTH
359 if (!V_ipstealth) {
360 #endif
361 if (ip->ip_ttl <= IPTTLDEC) {
362 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0);
363 return NULL; /* mbuf already free'd */
364 }
365
366 /*
367 * Decrement the TTL and incrementally change the IP header checksum.
368 * Don't bother doing this with hw checksum offloading, it's faster
369 * doing it right here.
370 */
371 ip->ip_ttl -= IPTTLDEC;
372 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8))
373 ip->ip_sum -= ~htons(IPTTLDEC << 8);
374 else
375 ip->ip_sum += htons(IPTTLDEC << 8);
376 #ifdef IPSTEALTH
377 }
378 #endif
379
380 /*
381 * Next hop forced by pfil(9) hook?
382 */
383 if ((m->m_flags & M_IP_NEXTHOP) &&
384 ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) {
385 /*
386 * Now we will find route to forced destination.
387 */
388 dest.s_addr = ((struct sockaddr_in *)
389 (fwd_tag + 1))->sin_addr.s_addr;
390 m_tag_delete(m, fwd_tag);
391 m->m_flags &= ~M_IP_NEXTHOP;
392 }
393
394 /*
395 * Find route to destination.
396 */
397 if (ip_findroute(&nh, dest, m) != 0)
398 return (NULL); /* icmp unreach already sent */
399
400 /*
401 * Avoid second route lookup by caching destination.
402 */
403 rtdest.s_addr = dest.s_addr;
404
405 /*
406 * Step 5: outgoing firewall packet processing
407 */
408 if (!PFIL_HOOKED_OUT(V_inet_pfil_head))
409 goto passout;
410
411 if (pfil_run_hooks(V_inet_pfil_head, &m, nh->nh_ifp,
412 PFIL_OUT | PFIL_FWD, NULL) != PFIL_PASS)
413 goto drop;
414
415 M_ASSERTVALID(m);
416 M_ASSERTPKTHDR(m);
417
418 ip = mtod(m, struct ip *);
419 dest.s_addr = ip->ip_dst.s_addr;
420
421 /*
422 * Destination address changed?
423 */
424 if (m->m_flags & M_IP_NEXTHOP)
425 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
426 else
427 fwd_tag = NULL;
428 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) {
429 /*
430 * Is it now for a local address on this host?
431 */
432 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) {
433 forwardlocal:
434 /*
435 * Return packet for processing by ip_input().
436 */
437 m->m_flags |= M_FASTFWD_OURS;
438 return (m);
439 }
440 /*
441 * Redo route lookup with new destination address
442 */
443 if (fwd_tag) {
444 dest.s_addr = ((struct sockaddr_in *)
445 (fwd_tag + 1))->sin_addr.s_addr;
446 m_tag_delete(m, fwd_tag);
447 m->m_flags &= ~M_IP_NEXTHOP;
448 }
449 if (dest.s_addr != rtdest.s_addr &&
450 ip_findroute(&nh, dest, m) != 0)
451 return (NULL); /* icmp unreach already sent */
452 }
453
454 passout:
455 /*
456 * Step 6: send off the packet
457 */
458 ip_len = ntohs(ip->ip_len);
459 ip_off = ntohs(ip->ip_off);
460
461 bzero(&ro, sizeof(ro));
462 dst = (struct sockaddr_in *)&ro.ro_dst;
463 dst->sin_family = AF_INET;
464 dst->sin_len = sizeof(*dst);
465 dst->sin_addr = dest;
466 if (nh->nh_flags & NHF_GATEWAY) {
467 gw = &nh->gw_sa;
468 ro.ro_flags |= RT_HAS_GW;
469 } else
470 gw = (const struct sockaddr *)dst;
471
472 /* Handle redirect case. */
473 redest.s_addr = 0;
474 if (V_ipsendredirects && osrc.s_addr == ip->ip_src.s_addr &&
475 nh->nh_ifp == m->m_pkthdr.rcvif)
476 mcopy = ip_redir_alloc(m, nh, ip_len, &osrc, &redest);
477
478 /*
479 * Check if packet fits MTU or if hardware will fragment for us
480 */
481 if (ip_len <= nh->nh_mtu) {
482 /*
483 * Avoid confusing lower layers.
484 */
485 m_clrprotoflags(m);
486 /*
487 * Send off the packet via outgoing interface
488 */
489 IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL);
490 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro);
491 } else {
492 /*
493 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery
494 */
495 if (ip_off & IP_DF) {
496 IPSTAT_INC(ips_cantfrag);
497 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
498 0, nh->nh_mtu);
499 goto consumed;
500 } else {
501 /*
502 * We have to fragment the packet
503 */
504 m->m_pkthdr.csum_flags |= CSUM_IP;
505 if (ip_fragment(ip, &m, nh->nh_mtu,
506 nh->nh_ifp->if_hwassist) != 0)
507 goto drop;
508 KASSERT(m != NULL, ("null mbuf and no error"));
509 /*
510 * Send off the fragments via outgoing interface
511 */
512 error = 0;
513 do {
514 m0 = m->m_nextpkt;
515 m->m_nextpkt = NULL;
516 /*
517 * Avoid confusing lower layers.
518 */
519 m_clrprotoflags(m);
520
521 IP_PROBE(send, NULL, NULL,
522 mtod(m, struct ip *), nh->nh_ifp,
523 mtod(m, struct ip *), NULL);
524 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m,
525 gw, &ro);
526 if (error)
527 break;
528 } while ((m = m0) != NULL);
529 if (error) {
530 /* Reclaim remaining fragments */
531 for (m = m0; m; m = m0) {
532 m0 = m->m_nextpkt;
533 m_freem(m);
534 }
535 } else
536 IPSTAT_INC(ips_fragmented);
537 }
538 }
539
540 if (error != 0)
541 IPSTAT_INC(ips_odropped);
542 else {
543 IPSTAT_INC(ips_forward);
544 IPSTAT_INC(ips_fastforward);
545 }
546
547 /* Send required redirect */
548 if (mcopy != NULL) {
549 icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0);
550 mcopy = NULL; /* Was consumed by callee. */
551 }
552
553 consumed:
554 if (mcopy != NULL)
555 m_freem(mcopy);
556 return NULL;
557 drop:
558 if (m)
559 m_freem(m);
560 return NULL;
561 }
562