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 "opt_ipstealth.h"
71 #include "opt_sctp.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 #if defined(SCTP) || defined(SCTP_SUPPORT)
106 #include <netinet/sctp_crc32.h>
107 #endif
108
109 #define V_ipsendredirects VNET(ipsendredirects)
110
111 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)112 ip_redir_alloc(struct mbuf *m, struct nhop_object *nh, u_short ip_len,
113 struct in_addr *osrc, struct in_addr *newgw)
114 {
115 struct in_ifaddr *nh_ia;
116 struct mbuf *mcopy;
117
118 KASSERT(nh != NULL, ("%s: m %p nh is NULL\n", __func__, m));
119
120 /*
121 * Only send a redirect if:
122 * - Redirects are not disabled (must be checked by caller),
123 * - We have not applied NAT (must be checked by caller as possible),
124 * - Neither a MCAST or BCAST packet (must be checked by caller)
125 * [RFC1009 Appendix A.2].
126 * - The packet does not do IP source routing or having any other
127 * IP options (this case was handled already by ip_input() calling
128 * ip_dooptions() [RFC792, p13],
129 * - The packet is being forwarded out the same physical interface
130 * that it was received from [RFC1812, 5.2.7.2].
131 */
132
133 /*
134 * - The forwarding route was not created by a redirect
135 * [RFC1812, 5.2.7.2], or
136 * if it was to follow a default route (see below).
137 * - The next-hop is reachable by us [RFC1009 Appendix A.2].
138 */
139 if ((nh->nh_flags & (NHF_DEFAULT | NHF_REDIRECT |
140 NHF_BLACKHOLE | NHF_REJECT)) != 0)
141 return (NULL);
142
143 /* Get the new gateway. */
144 if ((nh->nh_flags & NHF_GATEWAY) == 0 || nh->gw_sa.sa_family != AF_INET)
145 return (NULL);
146 newgw->s_addr = nh->gw4_sa.sin_addr.s_addr;
147
148 /*
149 * - The resulting forwarding destination is not "This host on this
150 * network" [RFC1122, Section 3.2.1.3] (default route check above).
151 */
152 if (newgw->s_addr == 0)
153 return (NULL);
154
155 /*
156 * - We know how to reach the sender and the source address is
157 * directly connected to us [RFC792, p13].
158 * + The new gateway address and the source address are on the same
159 * subnet [RFC1009 Appendix A.2, RFC1122 3.2.2.2, RFC1812, 5.2.7.2].
160 * NB: if you think multiple logical subnets on the same wire should
161 * receive redirects read [RFC1812, APPENDIX C (14->15)].
162 */
163 nh_ia = (struct in_ifaddr *)nh->nh_ifa;
164 if ((ntohl(osrc->s_addr) & nh_ia->ia_subnetmask) != nh_ia->ia_subnet)
165 return (NULL);
166
167 /* Prepare for sending the redirect. */
168
169 /*
170 * Make a copy of as much as we need of the packet as the original
171 * one will be forwarded but we need (a portion) for icmp_error().
172 */
173 mcopy = m_gethdr(M_NOWAIT, m->m_type);
174 if (mcopy == NULL)
175 return (NULL);
176
177 if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) {
178 /*
179 * It's probably ok if the pkthdr dup fails (because
180 * the deep copy of the tag chain failed), but for now
181 * be conservative and just discard the copy since
182 * code below may some day want the tags.
183 */
184 m_free(mcopy);
185 return (NULL);
186 }
187 mcopy->m_len = min(ip_len, M_TRAILINGSPACE(mcopy));
188 mcopy->m_pkthdr.len = mcopy->m_len;
189 m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t));
190
191 return (mcopy);
192 }
193
194
195 static int
ip_findroute(struct nhop_object ** pnh,struct in_addr dest,struct mbuf * m)196 ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m)
197 {
198 struct nhop_object *nh;
199
200 nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE,
201 m->m_pkthdr.flowid);
202 if (nh == NULL) {
203 IPSTAT_INC(ips_noroute);
204 IPSTAT_INC(ips_cantforward);
205 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
206 return (EHOSTUNREACH);
207 }
208 /*
209 * Drop blackholed traffic and directed broadcasts.
210 */
211 if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) {
212 IPSTAT_INC(ips_cantforward);
213 m_freem(m);
214 return (EHOSTUNREACH);
215 }
216
217 if (nh->nh_flags & NHF_REJECT) {
218 IPSTAT_INC(ips_cantforward);
219 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
220 return (EHOSTUNREACH);
221 }
222
223 *pnh = nh;
224
225 return (0);
226 }
227
228 /*
229 * Try to forward a packet based on the destination address.
230 * This is a fast path optimized for the plain forwarding case.
231 * If the packet is handled (and consumed) here then we return NULL;
232 * otherwise mbuf is returned and the packet should be delivered
233 * to ip_input for full processing.
234 */
235 struct mbuf *
ip_tryforward(struct mbuf * m)236 ip_tryforward(struct mbuf *m)
237 {
238 struct ip *ip;
239 struct mbuf *m0 = NULL;
240 struct nhop_object *nh = NULL;
241 struct route ro;
242 struct sockaddr_in *dst;
243 const struct sockaddr *gw;
244 struct in_addr dest, odest, rtdest, osrc;
245 uint16_t ip_len, ip_off;
246 int error = 0;
247 struct m_tag *fwd_tag = NULL;
248 struct mbuf *mcopy = NULL;
249 struct in_addr redest;
250 /*
251 * Are we active and forwarding packets?
252 */
253
254 M_ASSERTVALID(m);
255 M_ASSERTPKTHDR(m);
256
257 /*
258 * Only IP packets without options
259 */
260 ip = mtod(m, struct ip *);
261
262 if (ip->ip_hl != (sizeof(struct ip) >> 2)) {
263 if (V_ip_doopts == 1)
264 return m;
265 else if (V_ip_doopts == 2) {
266 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB,
267 0, 0);
268 return NULL; /* mbuf already free'd */
269 }
270 /* else ignore IP options and continue */
271 }
272
273 /*
274 * Only unicast IP, not from loopback, no L2 or IP broadcast,
275 * no multicast, no INADDR_ANY
276 *
277 * XXX: Probably some of these checks could be direct drop
278 * conditions. However it is not clear whether there are some
279 * hacks or obscure behaviours which make it necessary to
280 * let ip_input handle it. We play safe here and let ip_input
281 * deal with it until it is proven that we can directly drop it.
282 */
283 if ((m->m_flags & (M_BCAST|M_MCAST)) ||
284 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) ||
285 in_broadcast(ip->ip_src) ||
286 in_broadcast(ip->ip_dst) ||
287 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
288 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
289 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) ||
290 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) )
291 return m;
292
293 /*
294 * Is it for a local address on this host?
295 */
296 if (in_localip(ip->ip_dst))
297 return m;
298
299 IPSTAT_INC(ips_total);
300
301 /*
302 * Step 3: incoming packet firewall processing
303 */
304
305 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr;
306 osrc.s_addr = ip->ip_src.s_addr;
307
308 /*
309 * Run through list of ipfilter hooks for input packets
310 */
311 if (!PFIL_HOOKED_IN(V_inet_pfil_head))
312 goto passin;
313
314 if (pfil_mbuf_in(V_inet_pfil_head, &m, m->m_pkthdr.rcvif,
315 NULL) != PFIL_PASS)
316 goto drop;
317
318 M_ASSERTVALID(m);
319 M_ASSERTPKTHDR(m);
320
321 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */
322 dest.s_addr = ip->ip_dst.s_addr;
323
324 /*
325 * Destination address changed?
326 */
327 if (odest.s_addr != dest.s_addr) {
328 /*
329 * Is it now for a local address on this host?
330 */
331 if (in_localip(dest))
332 goto forwardlocal;
333 /*
334 * Go on with new destination address
335 */
336 }
337
338 if (m->m_flags & M_FASTFWD_OURS) {
339 /*
340 * ipfw changed it for a local address on this host.
341 */
342 goto forwardlocal;
343 }
344
345 passin:
346 /*
347 * Step 4: decrement TTL and look up route
348 */
349
350 /*
351 * Check TTL
352 */
353 #ifdef IPSTEALTH
354 if (!V_ipstealth) {
355 #endif
356 if (ip->ip_ttl <= IPTTLDEC) {
357 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0);
358 return NULL; /* mbuf already free'd */
359 }
360
361 /*
362 * Decrement the TTL and incrementally change the IP header checksum.
363 * Don't bother doing this with hw checksum offloading, it's faster
364 * doing it right here.
365 */
366 ip->ip_ttl -= IPTTLDEC;
367 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8))
368 ip->ip_sum -= ~htons(IPTTLDEC << 8);
369 else
370 ip->ip_sum += htons(IPTTLDEC << 8);
371 #ifdef IPSTEALTH
372 }
373 #endif
374
375 /*
376 * Next hop forced by pfil(9) hook?
377 */
378 if ((m->m_flags & M_IP_NEXTHOP) &&
379 ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) {
380 /*
381 * Now we will find route to forced destination.
382 */
383 dest.s_addr = ((struct sockaddr_in *)
384 (fwd_tag + 1))->sin_addr.s_addr;
385 m_tag_delete(m, fwd_tag);
386 m->m_flags &= ~M_IP_NEXTHOP;
387 }
388
389 /*
390 * Find route to destination.
391 */
392 if (ip_findroute(&nh, dest, m) != 0)
393 return (NULL); /* icmp unreach already sent */
394
395 /*
396 * Avoid second route lookup by caching destination.
397 */
398 rtdest.s_addr = dest.s_addr;
399
400 /*
401 * Step 5: outgoing firewall packet processing
402 */
403 if (!PFIL_HOOKED_OUT(V_inet_pfil_head))
404 goto passout;
405
406 if (pfil_mbuf_fwd(V_inet_pfil_head, &m, nh->nh_ifp,
407 NULL) != PFIL_PASS)
408 goto drop;
409
410 M_ASSERTVALID(m);
411 M_ASSERTPKTHDR(m);
412
413 ip = mtod(m, struct ip *);
414 dest.s_addr = ip->ip_dst.s_addr;
415
416 /*
417 * Destination address changed?
418 */
419 if (m->m_flags & M_IP_NEXTHOP)
420 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
421 else
422 fwd_tag = NULL;
423 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) {
424 /*
425 * Is it now for a local address on this host?
426 */
427 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) {
428 forwardlocal:
429 /*
430 * Return packet for processing by ip_input().
431 */
432 m->m_flags |= M_FASTFWD_OURS;
433 return (m);
434 }
435 /*
436 * Redo route lookup with new destination address
437 */
438 if (fwd_tag) {
439 dest.s_addr = ((struct sockaddr_in *)
440 (fwd_tag + 1))->sin_addr.s_addr;
441 m_tag_delete(m, fwd_tag);
442 m->m_flags &= ~M_IP_NEXTHOP;
443 }
444 if (dest.s_addr != rtdest.s_addr &&
445 ip_findroute(&nh, dest, m) != 0)
446 return (NULL); /* icmp unreach already sent */
447 }
448
449 passout:
450 /*
451 * Step 6: send off the packet
452 */
453 ip_len = ntohs(ip->ip_len);
454 ip_off = ntohs(ip->ip_off);
455
456 bzero(&ro, sizeof(ro));
457 dst = (struct sockaddr_in *)&ro.ro_dst;
458 dst->sin_family = AF_INET;
459 dst->sin_len = sizeof(*dst);
460 dst->sin_addr = dest;
461 if (nh->nh_flags & NHF_GATEWAY) {
462 gw = &nh->gw_sa;
463 ro.ro_flags |= RT_HAS_GW;
464 } else
465 gw = (const struct sockaddr *)dst;
466
467 /*
468 * If TCP/UDP header still needs a valid checksum and interface will not
469 * calculate it for us, do it here.
470 */
471 if (__predict_false(m->m_pkthdr.csum_flags & CSUM_DELAY_DATA &
472 ~nh->nh_ifp->if_hwassist)) {
473 in_delayed_cksum(m);
474 m->m_pkthdr.csum_flags &= ~CSUM_DELAY_DATA;
475 }
476 #if defined(SCTP) || defined(SCTP_SUPPORT)
477 if (__predict_false(m->m_pkthdr.csum_flags & CSUM_IP_SCTP &
478 ~nh->nh_ifp->if_hwassist)) {
479 sctp_delayed_cksum(m, (uint32_t)(ip->ip_hl << 2));
480 m->m_pkthdr.csum_flags &= ~CSUM_IP_SCTP;
481 }
482 #endif
483
484 /* Handle redirect case. */
485 redest.s_addr = 0;
486 if (V_ipsendredirects && osrc.s_addr == ip->ip_src.s_addr &&
487 nh->nh_ifp == m->m_pkthdr.rcvif)
488 mcopy = ip_redir_alloc(m, nh, ip_len, &osrc, &redest);
489
490 /*
491 * Check if packet fits MTU or if hardware will fragment for us
492 */
493 if (ip_len <= nh->nh_mtu) {
494 /*
495 * Avoid confusing lower layers.
496 */
497 m_clrprotoflags(m);
498 /*
499 * Send off the packet via outgoing interface
500 */
501 IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL);
502 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro);
503 } else {
504 /*
505 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery
506 */
507 if (ip_off & IP_DF) {
508 IPSTAT_INC(ips_cantfrag);
509 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
510 0, nh->nh_mtu);
511 goto consumed;
512 } else {
513 /*
514 * We have to fragment the packet
515 */
516 m->m_pkthdr.csum_flags |= CSUM_IP;
517 if (ip_fragment(ip, &m, nh->nh_mtu,
518 nh->nh_ifp->if_hwassist) != 0)
519 goto drop;
520 KASSERT(m != NULL, ("null mbuf and no error"));
521 /*
522 * Send off the fragments via outgoing interface
523 */
524 error = 0;
525 do {
526 m0 = m->m_nextpkt;
527 m->m_nextpkt = NULL;
528 /*
529 * Avoid confusing lower layers.
530 */
531 m_clrprotoflags(m);
532
533 IP_PROBE(send, NULL, NULL,
534 mtod(m, struct ip *), nh->nh_ifp,
535 mtod(m, struct ip *), NULL);
536 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m,
537 gw, &ro);
538 if (error)
539 break;
540 } while ((m = m0) != NULL);
541 if (error) {
542 /* Reclaim remaining fragments */
543 for (m = m0; m; m = m0) {
544 m0 = m->m_nextpkt;
545 m_freem(m);
546 }
547 } else
548 IPSTAT_INC(ips_fragmented);
549 }
550 }
551
552 if (error != 0)
553 IPSTAT_INC(ips_odropped);
554 else {
555 IPSTAT_INC(ips_forward);
556 IPSTAT_INC(ips_fastforward);
557 }
558
559 /* Send required redirect */
560 if (mcopy != NULL) {
561 icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0);
562 mcopy = NULL; /* Was consumed by callee. */
563 }
564
565 consumed:
566 if (mcopy != NULL)
567 m_freem(mcopy);
568 return NULL;
569 drop:
570 if (m)
571 m_freem(m);
572 return NULL;
573 }
574