1 /* $OpenBSD: bpf.c,v 1.13 2004/05/05 14:28:58 deraadt Exp $ */
2
3 /* BPF socket interface code, originally contributed by Archie Cobbs. */
4
5 /*-
6 * SPDX-License-Identifier: BSD-3-Clause
7 *
8 * Copyright (c) 2021 Franco Fichtner <franco@opnsense.org>
9 * Copyright (c) 1995, 1996, 1998, 1999
10 * The Internet Software Consortium. All rights reserved.
11 *
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
14 * are met:
15 *
16 * 1. Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution.
21 * 3. Neither the name of The Internet Software Consortium nor the names
22 * of its contributors may be used to endorse or promote products derived
23 * from this software without specific prior written permission.
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
26 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
27 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
28 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
29 * DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
30 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
31 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
32 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
33 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
34 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
35 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
36 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37 * SUCH DAMAGE.
38 *
39 * This software has been written for the Internet Software Consortium
40 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
41 * Enterprises. To learn more about the Internet Software Consortium,
42 * see ``http://www.vix.com/isc''. To learn more about Vixie
43 * Enterprises, see ``http://www.vix.com''.
44 */
45
46 #include <sys/cdefs.h>
47 #include "dhcpd.h"
48 #include "privsep.h"
49 #include <sys/capsicum.h>
50 #include <sys/ioctl.h>
51 #include <sys/uio.h>
52
53 #include <net/bpf.h>
54 #include <netinet/in_systm.h>
55 #include <netinet/ip.h>
56 #include <netinet/udp.h>
57 #include <netinet/if_ether.h>
58
59 #include <capsicum_helpers.h>
60
61 #define BPF_FORMAT "/dev/bpf%d"
62
63 /*
64 * Called by get_interface_list for each interface that's discovered.
65 * Opens a packet filter for each interface and adds it to the select
66 * mask.
67 */
68 int
if_register_bpf(struct interface_info * info,int flags)69 if_register_bpf(struct interface_info *info, int flags)
70 {
71 char filename[50];
72 int sock, b;
73
74 /* Open a BPF device */
75 for (b = 0;; b++) {
76 snprintf(filename, sizeof(filename), BPF_FORMAT, b);
77 sock = open(filename, flags);
78 if (sock < 0) {
79 if (errno == EBUSY)
80 continue;
81 else
82 error("Can't find free bpf: %m");
83 } else
84 break;
85 }
86
87 /* Set the BPF device to point at this interface. */
88 if (ioctl(sock, BIOCSETIF, info->ifp) < 0)
89 error("Can't attach interface %s to bpf device %s: %m",
90 info->name, filename);
91
92 /* Tag the packets with the proper VLAN PCP setting. */
93 if (info->client->config->vlan_pcp != 0) {
94 if (ioctl(sock, BIOCSETVLANPCP,
95 &info->client->config->vlan_pcp) < 0)
96 error( "Can't set the VLAN PCP tag on interface %s: %m",
97 info->name);
98 }
99
100 return (sock);
101 }
102
103 /*
104 * Packet write filter program:
105 * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
106 */
107 static const struct bpf_insn dhcp_bpf_wfilter[] = {
108 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
109 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
110
111 /* Make sure this is an IP packet... */
112 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
113 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10),
114
115 /* Make sure it's a UDP packet... */
116 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
117 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
118
119 /* Make sure this isn't a fragment... */
120 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
121 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, IP_MF|IP_OFFMASK, 6, 0),
122
123 /* Get the IP header length... */
124 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
125
126 /* Make sure it's from the right port... */
127 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
128 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, LOCAL_PORT, 0, 3),
129
130 /* Make sure it is to the right ports ... */
131 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
132 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, REMOTE_PORT, 0, 1),
133
134 /* If we passed all the tests, ask for the whole packet. */
135 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
136
137 /* Otherwise, drop it. */
138 BPF_STMT(BPF_RET+BPF_K, 0),
139 };
140
141 void
if_register_send(struct interface_info * info)142 if_register_send(struct interface_info *info)
143 {
144 cap_rights_t rights;
145 struct bpf_version v;
146 struct bpf_program p;
147 int sock, on = 1;
148
149 /* Open a BPF device and hang it on this interface... */
150 info->wfdesc = if_register_bpf(info, O_WRONLY);
151
152 /* Make sure the BPF version is in range... */
153 if (ioctl(info->wfdesc, BIOCVERSION, &v) < 0)
154 error("Can't get BPF version: %m");
155
156 if (v.bv_major != BPF_MAJOR_VERSION ||
157 v.bv_minor < BPF_MINOR_VERSION)
158 error("Kernel BPF version out of range - recompile dhcpd!");
159
160 /* Set up the bpf write filter program structure. */
161 p.bf_insns = __DECONST(struct bpf_insn *, dhcp_bpf_wfilter);
162 p.bf_len = nitems(dhcp_bpf_wfilter);
163
164 if (ioctl(info->wfdesc, BIOCSETWF, &p) < 0)
165 error("Can't install write filter program: %m");
166
167 if (ioctl(info->wfdesc, BIOCLOCK, NULL) < 0)
168 error("Cannot lock bpf");
169
170 cap_rights_init(&rights, CAP_WRITE);
171 if (caph_rights_limit(info->wfdesc, &rights) < 0)
172 error("Can't limit bpf descriptor: %m");
173
174 /*
175 * Use raw socket for unicast send.
176 */
177 if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1)
178 error("socket(SOCK_RAW): %m");
179 if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on,
180 sizeof(on)) == -1)
181 error("setsockopt(IP_HDRINCL): %m");
182 info->ufdesc = sock;
183 }
184
185 /*
186 * Packet filter program...
187 */
188 static const struct bpf_insn dhcp_bpf_filter[] = {
189 /* Use relative index (0) for IP packet... */
190 BPF_STMT(BPF_LDX + BPF_W + BPF_IMM, 0),
191
192 /*
193 * Test whether this is a VLAN packet...
194 *
195 * In case the server packet is using a VLAN ID
196 * of 0, meaning an untagged priority was set, the
197 * response shall be read and replied to.
198 */
199 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 12),
200 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_VLAN, 0, 4),
201
202 /* Test whether it has a VID of 0 */
203 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
204 BPF_STMT(BPF_ALU + BPF_AND + BPF_K, EVL_VLID_MASK),
205 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 17),
206
207 /* Correct the relative index for VLAN packet (4)... */
208 BPF_STMT(BPF_LDX + BPF_W + BPF_IMM, 4),
209
210 /* Make sure this is an IP packet... */
211 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 12),
212 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 14),
213
214 /* Make sure it's a UDP packet... */
215 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 23),
216 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 12),
217
218 /* Make sure this isn't a fragment... */
219 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 20),
220 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, IP_MF|IP_OFFMASK, 10, 0),
221
222 /*
223 * Get the IP header length...
224 *
225 * To find the correct position of the IP header
226 * length field store the index (0 or 4) in the
227 * accumulator and compare it with 0.
228 */
229 BPF_STMT(BPF_MISC + BPF_TXA, 0),
230 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 2),
231 /* Store IP header length of IP packet in index. */
232 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
233 /* Skip over following VLAN handling instruction. */
234 BPF_JUMP(BPF_JMP + BPF_JA, 1, 0, 0),
235 /* Store IP header length of VLAN packet in index. */
236 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 18),
237 /* Add IP header length to previous relative index. */
238 BPF_STMT(BPF_ALU + BPF_ADD + BPF_X, 0),
239 /* Move result back to index to reach UDP header below. */
240 BPF_STMT(BPF_MISC + BPF_TAX, 0),
241
242 /* Make sure it's to the right port... */
243 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
244 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, LOCAL_PORT, 0, 1),
245
246 /* If we passed all the tests, ask for the whole packet. */
247 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
248
249 /* Otherwise, drop it. */
250 BPF_STMT(BPF_RET+BPF_K, 0),
251 };
252
253 void
if_register_receive(struct interface_info * info)254 if_register_receive(struct interface_info *info)
255 {
256 static const unsigned long cmds[2] = { SIOCGIFFLAGS, SIOCGIFMEDIA };
257 cap_rights_t rights;
258 struct bpf_version v;
259 struct bpf_program p;
260 int flag = 1, sz;
261
262 /* Open a BPF device and hang it on this interface... */
263 info->rfdesc = if_register_bpf(info, O_RDONLY);
264
265 /* Make sure the BPF version is in range... */
266 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0)
267 error("Can't get BPF version: %m");
268
269 if (v.bv_major != BPF_MAJOR_VERSION ||
270 v.bv_minor < BPF_MINOR_VERSION)
271 error("Kernel BPF version out of range - recompile dhcpd!");
272
273 /*
274 * Set immediate mode so that reads return as soon as a packet
275 * comes in, rather than waiting for the input buffer to fill
276 * with packets.
277 */
278 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0)
279 error("Can't set immediate mode on bpf device: %m");
280
281 /* Get the required BPF buffer length from the kernel. */
282 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0)
283 error("Can't get bpf buffer length: %m");
284 info->rbuf_max = sz;
285 info->rbuf = malloc(info->rbuf_max);
286 if (!info->rbuf)
287 error("Can't allocate %lu bytes for bpf input buffer.",
288 (unsigned long)info->rbuf_max);
289 info->rbuf_offset = 0;
290 info->rbuf_len = 0;
291
292 /* Set up the bpf filter program structure. */
293 p.bf_insns = __DECONST(struct bpf_insn *, dhcp_bpf_filter);
294 p.bf_len = nitems(dhcp_bpf_filter);
295
296 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0)
297 error("Can't install packet filter program: %m");
298
299 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0)
300 error("Cannot lock bpf");
301
302 cap_rights_init(&rights, CAP_IOCTL, CAP_EVENT, CAP_READ);
303 if (caph_rights_limit(info->rfdesc, &rights) < 0)
304 error("Can't limit bpf descriptor: %m");
305 if (caph_ioctls_limit(info->rfdesc, cmds, 2) < 0)
306 error("Can't limit ioctls for bpf descriptor: %m");
307 }
308
309 void
send_packet_unpriv(int privfd,struct dhcp_packet * raw,size_t len,struct in_addr from,struct in_addr to)310 send_packet_unpriv(int privfd, struct dhcp_packet *raw, size_t len,
311 struct in_addr from, struct in_addr to)
312 {
313 struct imsg_hdr hdr;
314 struct buf *buf;
315 int errs;
316
317 hdr.code = IMSG_SEND_PACKET;
318 hdr.len = sizeof(hdr) +
319 sizeof(size_t) + len +
320 sizeof(from) + sizeof(to);
321
322 if ((buf = buf_open(hdr.len)) == NULL)
323 error("buf_open: %m");
324
325 errs = 0;
326 errs += buf_add(buf, &hdr, sizeof(hdr));
327 errs += buf_add(buf, &len, sizeof(len));
328 errs += buf_add(buf, raw, len);
329 errs += buf_add(buf, &from, sizeof(from));
330 errs += buf_add(buf, &to, sizeof(to));
331 if (errs)
332 error("buf_add: %m");
333
334 if (buf_close(privfd, buf) == -1)
335 error("buf_close: %m");
336 }
337
338 void
send_packet_priv(struct interface_info * interface,struct imsg_hdr * hdr,int fd)339 send_packet_priv(struct interface_info *interface, struct imsg_hdr *hdr, int fd)
340 {
341 unsigned char buf[256];
342 struct iovec iov[2];
343 struct msghdr msg;
344 struct dhcp_packet raw;
345 size_t len;
346 struct in_addr from, to;
347 int result, bufp = 0;
348
349 if (hdr->len < sizeof(*hdr) + sizeof(size_t))
350 error("corrupted message received");
351 buf_read(fd, &len, sizeof(len));
352 if (hdr->len != sizeof(*hdr) + sizeof(size_t) + len +
353 sizeof(from) + sizeof(to)) {
354 error("corrupted message received");
355 }
356 if (len > sizeof(raw))
357 error("corrupted message received");
358 buf_read(fd, &raw, len);
359 buf_read(fd, &from, sizeof(from));
360 buf_read(fd, &to, sizeof(to));
361
362 /* Assemble the headers... */
363 if (to.s_addr == INADDR_BROADCAST)
364 assemble_hw_header(interface, buf, &bufp);
365 assemble_udp_ip_header(buf, &bufp, from.s_addr, to.s_addr,
366 htons(REMOTE_PORT), (unsigned char *)&raw, len);
367
368 iov[0].iov_base = buf;
369 iov[0].iov_len = bufp;
370 iov[1].iov_base = &raw;
371 iov[1].iov_len = len;
372
373 /* Fire it off */
374 if (to.s_addr == INADDR_BROADCAST)
375 result = writev(interface->wfdesc, iov, 2);
376 else {
377 struct sockaddr_in sato;
378
379 sato.sin_addr = to;
380 sato.sin_port = htons(REMOTE_PORT);
381 sato.sin_family = AF_INET;
382 sato.sin_len = sizeof(sato);
383
384 memset(&msg, 0, sizeof(msg));
385 msg.msg_name = (struct sockaddr *)&sato;
386 msg.msg_namelen = sizeof(sato);
387 msg.msg_iov = iov;
388 msg.msg_iovlen = 2;
389 result = sendmsg(interface->ufdesc, &msg, 0);
390 }
391
392 if (result < 0)
393 warning("send_packet: %m");
394 }
395
396 ssize_t
receive_packet(struct interface_info * interface,unsigned char * buf,size_t len,struct sockaddr_in * from,struct hardware * hfrom)397 receive_packet(struct interface_info *interface, unsigned char *buf,
398 size_t len, struct sockaddr_in *from, struct hardware *hfrom)
399 {
400 int length = 0, offset = 0;
401 struct bpf_hdr hdr;
402
403 /*
404 * All this complexity is because BPF doesn't guarantee that
405 * only one packet will be returned at a time. We're getting
406 * what we deserve, though - this is a terrible abuse of the BPF
407 * interface. Sigh.
408 */
409
410 /* Process packets until we get one we can return or until we've
411 * done a read and gotten nothing we can return...
412 */
413 do {
414 /* If the buffer is empty, fill it. */
415 if (interface->rbuf_offset >= interface->rbuf_len) {
416 length = read(interface->rfdesc, interface->rbuf,
417 interface->rbuf_max);
418 if (length <= 0)
419 return (length);
420 interface->rbuf_offset = 0;
421 interface->rbuf_len = length;
422 }
423
424 /*
425 * If there isn't room for a whole bpf header, something
426 * went wrong, but we'll ignore it and hope it goes
427 * away... XXX
428 */
429 if (interface->rbuf_len - interface->rbuf_offset <
430 sizeof(hdr)) {
431 interface->rbuf_offset = interface->rbuf_len;
432 continue;
433 }
434
435 /* Copy out a bpf header... */
436 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
437 sizeof(hdr));
438
439 /*
440 * If the bpf header plus data doesn't fit in what's
441 * left of the buffer, stick head in sand yet again...
442 */
443 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
444 interface->rbuf_len) {
445 interface->rbuf_offset = interface->rbuf_len;
446 continue;
447 }
448
449 /* Skip over the BPF header... */
450 interface->rbuf_offset += hdr.bh_hdrlen;
451
452 /*
453 * If the captured data wasn't the whole packet, or if
454 * the packet won't fit in the input buffer, all we can
455 * do is drop it.
456 */
457 if (hdr.bh_caplen != hdr.bh_datalen) {
458 interface->rbuf_offset =
459 BPF_WORDALIGN(interface->rbuf_offset +
460 hdr.bh_caplen);
461 continue;
462 }
463
464 /* Decode the physical header... */
465 offset = decode_hw_header(interface->rbuf,
466 interface->rbuf_offset, hfrom);
467
468 /*
469 * If a physical layer checksum failed (dunno of any
470 * physical layer that supports this, but WTH), skip
471 * this packet.
472 */
473 if (offset < 0) {
474 interface->rbuf_offset =
475 BPF_WORDALIGN(interface->rbuf_offset +
476 hdr.bh_caplen);
477 continue;
478 }
479 interface->rbuf_offset += offset;
480 hdr.bh_caplen -= offset;
481
482 /* Decode the IP and UDP headers... */
483 offset = decode_udp_ip_header(interface->rbuf,
484 interface->rbuf_offset, from, NULL, hdr.bh_caplen);
485
486 /* If the IP or UDP checksum was bad, skip the packet... */
487 if (offset < 0) {
488 interface->rbuf_offset =
489 BPF_WORDALIGN(interface->rbuf_offset +
490 hdr.bh_caplen);
491 continue;
492 }
493 interface->rbuf_offset += offset;
494 hdr.bh_caplen -= offset;
495
496 /*
497 * If there's not enough room to stash the packet data,
498 * we have to skip it (this shouldn't happen in real
499 * life, though).
500 */
501 if (hdr.bh_caplen > len) {
502 interface->rbuf_offset =
503 BPF_WORDALIGN(interface->rbuf_offset +
504 hdr.bh_caplen);
505 continue;
506 }
507
508 /* Copy out the data in the packet... */
509 memcpy(buf, interface->rbuf + interface->rbuf_offset,
510 hdr.bh_caplen);
511 interface->rbuf_offset =
512 BPF_WORDALIGN(interface->rbuf_offset +
513 hdr.bh_caplen);
514 return (hdr.bh_caplen);
515 } while (!length);
516 return (0);
517 }
518