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 * Copyright (c) 1995, 1996, 1998, 1999
7 * The Internet Software Consortium. All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 *
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. Neither the name of The Internet Software Consortium nor the names
19 * of its contributors may be used to endorse or promote products derived
20 * from this software without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
23 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
24 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
25 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
26 * DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
27 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
28 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
29 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
30 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
31 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
32 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
33 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 *
36 * This software has been written for the Internet Software Consortium
37 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
38 * Enterprises. To learn more about the Internet Software Consortium,
39 * see ``http://www.vix.com/isc''. To learn more about Vixie
40 * Enterprises, see ``http://www.vix.com''.
41 */
42
43 #include <sys/cdefs.h>
44 __FBSDID("$FreeBSD$");
45
46 #include "dhcpd.h"
47 #include "privsep.h"
48 #include <sys/capsicum.h>
49 #include <sys/ioctl.h>
50 #include <sys/uio.h>
51
52 #include <net/bpf.h>
53 #include <netinet/in_systm.h>
54 #include <netinet/ip.h>
55 #include <netinet/udp.h>
56 #include <netinet/if_ether.h>
57
58 #define BPF_FORMAT "/dev/bpf%d"
59
60 /*
61 * Called by get_interface_list for each interface that's discovered.
62 * Opens a packet filter for each interface and adds it to the select
63 * mask.
64 */
65 int
if_register_bpf(struct interface_info * info,int flags)66 if_register_bpf(struct interface_info *info, int flags)
67 {
68 char filename[50];
69 int sock, b;
70
71 /* Open a BPF device */
72 for (b = 0;; b++) {
73 snprintf(filename, sizeof(filename), BPF_FORMAT, b);
74 sock = open(filename, flags);
75 if (sock < 0) {
76 if (errno == EBUSY)
77 continue;
78 else
79 error("Can't find free bpf: %m");
80 } else
81 break;
82 }
83
84 /* Set the BPF device to point at this interface. */
85 if (ioctl(sock, BIOCSETIF, info->ifp) < 0)
86 error("Can't attach interface %s to bpf device %s: %m",
87 info->name, filename);
88
89 return (sock);
90 }
91
92 /*
93 * Packet write filter program:
94 * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
95 */
96 struct bpf_insn dhcp_bpf_wfilter[] = {
97 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
98 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
99
100 /* Make sure this is an IP packet... */
101 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
102 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10),
103
104 /* Make sure it's a UDP packet... */
105 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
106 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
107
108 /* Make sure this isn't a fragment... */
109 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
110 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */
111
112 /* Get the IP header length... */
113 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
114
115 /* Make sure it's from the right port... */
116 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
117 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3),
118
119 /* Make sure it is to the right ports ... */
120 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
121 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),
122
123 /* If we passed all the tests, ask for the whole packet. */
124 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
125
126 /* Otherwise, drop it. */
127 BPF_STMT(BPF_RET+BPF_K, 0),
128 };
129
130 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
131
132 void
if_register_send(struct interface_info * info)133 if_register_send(struct interface_info *info)
134 {
135 cap_rights_t rights;
136 struct bpf_version v;
137 struct bpf_program p;
138 int sock, on = 1;
139
140 /* Open a BPF device and hang it on this interface... */
141 info->wfdesc = if_register_bpf(info, O_WRONLY);
142
143 /* Make sure the BPF version is in range... */
144 if (ioctl(info->wfdesc, BIOCVERSION, &v) < 0)
145 error("Can't get BPF version: %m");
146
147 if (v.bv_major != BPF_MAJOR_VERSION ||
148 v.bv_minor < BPF_MINOR_VERSION)
149 error("Kernel BPF version out of range - recompile dhcpd!");
150
151 /* Set up the bpf write filter program structure. */
152 p.bf_len = dhcp_bpf_wfilter_len;
153 p.bf_insns = dhcp_bpf_wfilter;
154
155 if (dhcp_bpf_wfilter[7].k == 0x1fff)
156 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK);
157
158 if (ioctl(info->wfdesc, BIOCSETWF, &p) < 0)
159 error("Can't install write filter program: %m");
160
161 if (ioctl(info->wfdesc, BIOCLOCK, NULL) < 0)
162 error("Cannot lock bpf");
163
164 cap_rights_init(&rights, CAP_WRITE);
165 if (cap_rights_limit(info->wfdesc, &rights) < 0 && errno != ENOSYS)
166 error("Can't limit bpf descriptor: %m");
167
168 /*
169 * Use raw socket for unicast send.
170 */
171 if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1)
172 error("socket(SOCK_RAW): %m");
173 if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on,
174 sizeof(on)) == -1)
175 error("setsockopt(IP_HDRINCL): %m");
176 info->ufdesc = sock;
177 }
178
179 /*
180 * Packet filter program...
181 *
182 * XXX: Changes to the filter program may require changes to the
183 * constant offsets used in if_register_send to patch the BPF program!
184 */
185 struct bpf_insn dhcp_bpf_filter[] = {
186 /* Make sure this is an IP packet... */
187 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
188 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
189
190 /* Make sure it's a UDP packet... */
191 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
192 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
193
194 /* Make sure this isn't a fragment... */
195 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
196 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
197
198 /* Get the IP header length... */
199 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
200
201 /* Make sure it's to the right port... */
202 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
203 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */
204
205 /* If we passed all the tests, ask for the whole packet. */
206 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
207
208 /* Otherwise, drop it. */
209 BPF_STMT(BPF_RET+BPF_K, 0),
210 };
211
212 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
213
214 void
if_register_receive(struct interface_info * info)215 if_register_receive(struct interface_info *info)
216 {
217 static const unsigned long cmds[2] = { SIOCGIFFLAGS, SIOCGIFMEDIA };
218 cap_rights_t rights;
219 struct bpf_version v;
220 struct bpf_program p;
221 int flag = 1, sz;
222
223 /* Open a BPF device and hang it on this interface... */
224 info->rfdesc = if_register_bpf(info, O_RDONLY);
225
226 /* Make sure the BPF version is in range... */
227 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0)
228 error("Can't get BPF version: %m");
229
230 if (v.bv_major != BPF_MAJOR_VERSION ||
231 v.bv_minor < BPF_MINOR_VERSION)
232 error("Kernel BPF version out of range - recompile dhcpd!");
233
234 /*
235 * Set immediate mode so that reads return as soon as a packet
236 * comes in, rather than waiting for the input buffer to fill
237 * with packets.
238 */
239 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0)
240 error("Can't set immediate mode on bpf device: %m");
241
242 /* Get the required BPF buffer length from the kernel. */
243 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0)
244 error("Can't get bpf buffer length: %m");
245 info->rbuf_max = sz;
246 info->rbuf = malloc(info->rbuf_max);
247 if (!info->rbuf)
248 error("Can't allocate %lu bytes for bpf input buffer.",
249 (unsigned long)info->rbuf_max);
250 info->rbuf_offset = 0;
251 info->rbuf_len = 0;
252
253 /* Set up the bpf filter program structure. */
254 p.bf_len = dhcp_bpf_filter_len;
255 p.bf_insns = dhcp_bpf_filter;
256
257 /* Patch the server port into the BPF program...
258 *
259 * XXX: changes to filter program may require changes to the
260 * insn number(s) used below!
261 */
262 dhcp_bpf_filter[8].k = LOCAL_PORT;
263
264 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0)
265 error("Can't install packet filter program: %m");
266
267 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0)
268 error("Cannot lock bpf");
269
270 cap_rights_init(&rights, CAP_IOCTL, CAP_EVENT, CAP_READ);
271 if (cap_rights_limit(info->rfdesc, &rights) < 0 && errno != ENOSYS)
272 error("Can't limit bpf descriptor: %m");
273 if (cap_ioctls_limit(info->rfdesc, cmds, 2) < 0 && errno != ENOSYS)
274 error("Can't limit ioctls for bpf descriptor: %m");
275 }
276
277 void
send_packet_unpriv(int privfd,struct dhcp_packet * raw,size_t len,struct in_addr from,struct in_addr to)278 send_packet_unpriv(int privfd, struct dhcp_packet *raw, size_t len,
279 struct in_addr from, struct in_addr to)
280 {
281 struct imsg_hdr hdr;
282 struct buf *buf;
283 int errs;
284
285 hdr.code = IMSG_SEND_PACKET;
286 hdr.len = sizeof(hdr) +
287 sizeof(size_t) + len +
288 sizeof(from) + sizeof(to);
289
290 if ((buf = buf_open(hdr.len)) == NULL)
291 error("buf_open: %m");
292
293 errs = 0;
294 errs += buf_add(buf, &hdr, sizeof(hdr));
295 errs += buf_add(buf, &len, sizeof(len));
296 errs += buf_add(buf, raw, len);
297 errs += buf_add(buf, &from, sizeof(from));
298 errs += buf_add(buf, &to, sizeof(to));
299 if (errs)
300 error("buf_add: %m");
301
302 if (buf_close(privfd, buf) == -1)
303 error("buf_close: %m");
304 }
305
306 void
send_packet_priv(struct interface_info * interface,struct imsg_hdr * hdr,int fd)307 send_packet_priv(struct interface_info *interface, struct imsg_hdr *hdr, int fd)
308 {
309 unsigned char buf[256];
310 struct iovec iov[2];
311 struct msghdr msg;
312 struct dhcp_packet raw;
313 size_t len;
314 struct in_addr from, to;
315 int result, bufp = 0;
316
317 if (hdr->len < sizeof(*hdr) + sizeof(size_t))
318 error("corrupted message received");
319 buf_read(fd, &len, sizeof(len));
320 if (hdr->len != sizeof(*hdr) + sizeof(size_t) + len +
321 sizeof(from) + sizeof(to)) {
322 error("corrupted message received");
323 }
324 if (len > sizeof(raw))
325 error("corrupted message received");
326 buf_read(fd, &raw, len);
327 buf_read(fd, &from, sizeof(from));
328 buf_read(fd, &to, sizeof(to));
329
330 /* Assemble the headers... */
331 if (to.s_addr == INADDR_BROADCAST)
332 assemble_hw_header(interface, buf, &bufp);
333 assemble_udp_ip_header(buf, &bufp, from.s_addr, to.s_addr,
334 htons(REMOTE_PORT), (unsigned char *)&raw, len);
335
336 iov[0].iov_base = buf;
337 iov[0].iov_len = bufp;
338 iov[1].iov_base = &raw;
339 iov[1].iov_len = len;
340
341 /* Fire it off */
342 if (to.s_addr == INADDR_BROADCAST)
343 result = writev(interface->wfdesc, iov, 2);
344 else {
345 struct sockaddr_in sato;
346
347 sato.sin_addr = to;
348 sato.sin_port = htons(REMOTE_PORT);
349 sato.sin_family = AF_INET;
350 sato.sin_len = sizeof(sato);
351
352 memset(&msg, 0, sizeof(msg));
353 msg.msg_name = (struct sockaddr *)&sato;
354 msg.msg_namelen = sizeof(sato);
355 msg.msg_iov = iov;
356 msg.msg_iovlen = 2;
357 result = sendmsg(interface->ufdesc, &msg, 0);
358 }
359
360 if (result < 0)
361 warning("send_packet: %m");
362 }
363
364 ssize_t
receive_packet(struct interface_info * interface,unsigned char * buf,size_t len,struct sockaddr_in * from,struct hardware * hfrom)365 receive_packet(struct interface_info *interface, unsigned char *buf,
366 size_t len, struct sockaddr_in *from, struct hardware *hfrom)
367 {
368 int length = 0, offset = 0;
369 struct bpf_hdr hdr;
370
371 /*
372 * All this complexity is because BPF doesn't guarantee that
373 * only one packet will be returned at a time. We're getting
374 * what we deserve, though - this is a terrible abuse of the BPF
375 * interface. Sigh.
376 */
377
378 /* Process packets until we get one we can return or until we've
379 * done a read and gotten nothing we can return...
380 */
381 do {
382 /* If the buffer is empty, fill it. */
383 if (interface->rbuf_offset >= interface->rbuf_len) {
384 length = read(interface->rfdesc, interface->rbuf,
385 interface->rbuf_max);
386 if (length <= 0)
387 return (length);
388 interface->rbuf_offset = 0;
389 interface->rbuf_len = length;
390 }
391
392 /*
393 * If there isn't room for a whole bpf header, something
394 * went wrong, but we'll ignore it and hope it goes
395 * away... XXX
396 */
397 if (interface->rbuf_len - interface->rbuf_offset <
398 sizeof(hdr)) {
399 interface->rbuf_offset = interface->rbuf_len;
400 continue;
401 }
402
403 /* Copy out a bpf header... */
404 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
405 sizeof(hdr));
406
407 /*
408 * If the bpf header plus data doesn't fit in what's
409 * left of the buffer, stick head in sand yet again...
410 */
411 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
412 interface->rbuf_len) {
413 interface->rbuf_offset = interface->rbuf_len;
414 continue;
415 }
416
417 /* Skip over the BPF header... */
418 interface->rbuf_offset += hdr.bh_hdrlen;
419
420 /*
421 * If the captured data wasn't the whole packet, or if
422 * the packet won't fit in the input buffer, all we can
423 * do is drop it.
424 */
425 if (hdr.bh_caplen != hdr.bh_datalen) {
426 interface->rbuf_offset =
427 BPF_WORDALIGN(interface->rbuf_offset +
428 hdr.bh_caplen);
429 continue;
430 }
431
432 /* Decode the physical header... */
433 offset = decode_hw_header(interface->rbuf,
434 interface->rbuf_offset, hfrom);
435
436 /*
437 * If a physical layer checksum failed (dunno of any
438 * physical layer that supports this, but WTH), skip
439 * this packet.
440 */
441 if (offset < 0) {
442 interface->rbuf_offset =
443 BPF_WORDALIGN(interface->rbuf_offset +
444 hdr.bh_caplen);
445 continue;
446 }
447 interface->rbuf_offset += offset;
448 hdr.bh_caplen -= offset;
449
450 /* Decode the IP and UDP headers... */
451 offset = decode_udp_ip_header(interface->rbuf,
452 interface->rbuf_offset, from, NULL, hdr.bh_caplen);
453
454 /* If the IP or UDP checksum was bad, skip the packet... */
455 if (offset < 0) {
456 interface->rbuf_offset =
457 BPF_WORDALIGN(interface->rbuf_offset +
458 hdr.bh_caplen);
459 continue;
460 }
461 interface->rbuf_offset += offset;
462 hdr.bh_caplen -= offset;
463
464 /*
465 * If there's not enough room to stash the packet data,
466 * we have to skip it (this shouldn't happen in real
467 * life, though).
468 */
469 if (hdr.bh_caplen > len) {
470 interface->rbuf_offset =
471 BPF_WORDALIGN(interface->rbuf_offset +
472 hdr.bh_caplen);
473 continue;
474 }
475
476 /* Copy out the data in the packet... */
477 memcpy(buf, interface->rbuf + interface->rbuf_offset,
478 hdr.bh_caplen);
479 interface->rbuf_offset =
480 BPF_WORDALIGN(interface->rbuf_offset +
481 hdr.bh_caplen);
482 return (hdr.bh_caplen);
483 } while (!length);
484 return (0);
485 }
486