1 /* $OpenBSD: bpf.c,v 1.20 2019/03/18 00:00:59 dlg 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/ioctl.h>
44 #include <sys/types.h>
45 #include <sys/socket.h>
46
47 #include <arpa/inet.h>
48
49 #include <net/bpf.h>
50 #include <net/if.h>
51
52 #include <netinet/if_ether.h>
53 #include <netinet/in.h>
54
55 #include <errno.h>
56 #include <fcntl.h>
57 #include <stdio.h>
58 #include <stdlib.h>
59 #include <string.h>
60 #include <unistd.h>
61
62 #include "dhcp.h"
63 #include "tree.h"
64 #include "dhcpd.h"
65 #include "log.h"
66
67 ssize_t send_packet (struct interface_info *, struct dhcp_packet *,
68 size_t, struct in_addr, struct sockaddr_in *, struct hardware *);
69
70 /*
71 * Called by get_interface_list for each interface that's discovered.
72 * Opens a packet filter for each interface and adds it to the select
73 * mask.
74 */
75 int
if_register_bpf(struct interface_info * info)76 if_register_bpf(struct interface_info *info)
77 {
78 int sock;
79
80 if ((sock = open("/dev/bpf", O_RDWR)) == -1)
81 fatal("Can't open bpf device");
82
83 /* Set the BPF device to point at this interface. */
84 if (ioctl(sock, BIOCSETIF, info->ifp) == -1)
85 fatal("Can't attach interface %s to bpf device", info->name);
86
87 info->send_packet = send_packet;
88 return (sock);
89 }
90
91 void
if_register_send(struct interface_info * info)92 if_register_send(struct interface_info *info)
93 {
94 /*
95 * If we're using the bpf API for sending and receiving, we
96 * don't need to register this interface twice.
97 */
98 info->wfdesc = info->rfdesc;
99 }
100
101 /*
102 * Packet read filter program: 'ip and udp and dst port bootps'
103 */
104 struct bpf_insn dhcp_bpf_filter[] = {
105 /* Make sure this is an IP packet... */
106 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
107 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
108
109 /* Make sure it's a UDP packet... */
110 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
111 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
112
113 /* Make sure this isn't a fragment... */
114 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
115 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
116
117 /* Get the IP header length... */
118 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
119
120 /* Make sure it's to the right port... */
121 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
122 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1),
123
124 /* If we passed all the tests, ask for the whole packet. */
125 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
126
127 /* Otherwise, drop it. */
128 BPF_STMT(BPF_RET+BPF_K, 0),
129 };
130
131 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
132
133
134 /*
135 * Packet write filter program:
136 * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
137 */
138 struct bpf_insn dhcp_bpf_wfilter[] = {
139 /* Make sure this is an IP packet... */
140 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
141 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 11),
142
143 /* Make sure it's a UDP packet... */
144 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
145 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 9),
146
147 /* Make sure this isn't a fragment... */
148 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
149 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 7, 0),
150
151 /* Get the IP header length... */
152 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
153
154 /* Make sure it's from the right port... */
155 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
156 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 4),
157
158 /* Make sure it is to the right ports ... */
159 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
160 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, CLIENT_PORT, 1, 0),
161 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1),
162
163 /* If we passed all the tests, ask for the whole packet. */
164 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
165
166 /* Otherwise, drop it. */
167 BPF_STMT(BPF_RET+BPF_K, 0),
168 };
169
170 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
171
172 void
if_register_receive(struct interface_info * info)173 if_register_receive(struct interface_info *info)
174 {
175 struct bpf_version v;
176 struct bpf_program p;
177 int flag = 1, sz, cmplt = 0;
178 int fildrop = BPF_FILDROP_CAPTURE;
179
180 /* Open a BPF device and hang it on this interface... */
181 info->rfdesc = if_register_bpf(info);
182
183 /* Make sure the BPF version is in range... */
184 if (ioctl(info->rfdesc, BIOCVERSION, &v) == -1)
185 fatal("Can't get BPF version");
186
187 if (v.bv_major != BPF_MAJOR_VERSION ||
188 v.bv_minor < BPF_MINOR_VERSION)
189 fatalx("Kernel BPF version out of range - recompile dhcpd!");
190
191 /*
192 * Set immediate mode so that reads return as soon as a packet
193 * comes in, rather than waiting for the input buffer to fill
194 * with packets.
195 */
196 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) == -1)
197 fatal("Can't set immediate mode on bpf device");
198
199 if (ioctl(info->rfdesc, BIOCSFILDROP, &fildrop) == -1)
200 fatal("Can't set filter-drop mode on bpf device");
201
202 /* make sure kernel fills in the source ethernet address */
203 if (ioctl(info->rfdesc, BIOCSHDRCMPLT, &cmplt) == -1)
204 fatal("Can't set header complete flag on bpf device");
205
206 /* Get the required BPF buffer length from the kernel. */
207 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) == -1)
208 fatal("Can't get bpf buffer length");
209 info->rbuf_max = sz;
210 info->rbuf = malloc(info->rbuf_max);
211 if (!info->rbuf)
212 fatalx("Can't allocate %lu bytes for bpf input buffer.",
213 (unsigned long)info->rbuf_max);
214 info->rbuf_offset = 0;
215 info->rbuf_len = 0;
216
217 /* Set up the bpf filter program structure. */
218 p.bf_len = dhcp_bpf_filter_len;
219 p.bf_insns = dhcp_bpf_filter;
220
221 if (ioctl(info->rfdesc, BIOCSETF, &p) == -1)
222 fatal("Can't install packet filter program");
223
224 /* Set up the bpf write filter program structure. */
225 p.bf_len = dhcp_bpf_wfilter_len;
226 p.bf_insns = dhcp_bpf_wfilter;
227
228 if (ioctl(info->rfdesc, BIOCSETWF, &p) == -1)
229 fatal("Can't install write filter program");
230
231 /* make sure these settings cannot be changed after dropping privs */
232 if (ioctl(info->rfdesc, BIOCLOCK) == -1)
233 fatal("Failed to lock bpf descriptor");
234 }
235
236 ssize_t
send_packet(struct interface_info * interface,struct dhcp_packet * raw,size_t len,struct in_addr from,struct sockaddr_in * to,struct hardware * hto)237 send_packet(struct interface_info *interface, struct dhcp_packet *raw,
238 size_t len, struct in_addr from, struct sockaddr_in *to,
239 struct hardware *hto)
240 {
241 unsigned char buf[256];
242 struct iovec iov[2];
243 ssize_t result;
244 int bufp = 0;
245
246 /* Assemble the headers... */
247 assemble_hw_header(interface, buf, &bufp, hto);
248 assemble_udp_ip_header(interface, buf, &bufp, from.s_addr,
249 to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len);
250
251 /* Fire it off */
252 iov[0].iov_base = (char *)buf;
253 iov[0].iov_len = bufp;
254 iov[1].iov_base = (char *)raw;
255 iov[1].iov_len = len;
256
257 result = writev(interface->wfdesc, iov, 2);
258 if (result == -1)
259 log_warn("send_packet");
260 return (result);
261 }
262
263 ssize_t
receive_packet(struct interface_info * interface,unsigned char * buf,size_t len,struct sockaddr_in * from,struct hardware * hfrom)264 receive_packet(struct interface_info *interface, unsigned char *buf,
265 size_t len, struct sockaddr_in *from, struct hardware *hfrom)
266 {
267 int length = 0, offset = 0;
268 struct bpf_hdr hdr;
269
270 /*
271 * All this complexity is because BPF doesn't guarantee that
272 * only one packet will be returned at a time. We're getting
273 * what we deserve, though - this is a terrible abuse of the BPF
274 * interface. Sigh.
275 */
276
277 /* Process packets until we get one we can return or until we've
278 * done a read and gotten nothing we can return...
279 */
280 do {
281 /* If the buffer is empty, fill it. */
282 if (interface->rbuf_offset >= interface->rbuf_len) {
283 length = read(interface->rfdesc, interface->rbuf,
284 interface->rbuf_max);
285 if (length <= 0)
286 return (length);
287 interface->rbuf_offset = 0;
288 interface->rbuf_len = length;
289 }
290
291 /*
292 * If there isn't room for a whole bpf header, something
293 * went wrong, but we'll ignore it and hope it goes
294 * away... XXX
295 */
296 if (interface->rbuf_len - interface->rbuf_offset <
297 sizeof(hdr)) {
298 interface->rbuf_offset = interface->rbuf_len;
299 continue;
300 }
301
302 /* Copy out a bpf header... */
303 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
304 sizeof(hdr));
305
306 /*
307 * If the bpf header plus data doesn't fit in what's
308 * left of the buffer, stick head in sand yet again...
309 */
310 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
311 interface->rbuf_len) {
312 interface->rbuf_offset = interface->rbuf_len;
313 continue;
314 }
315
316 /*
317 * If the captured data wasn't the whole packet, or if
318 * the packet won't fit in the input buffer, all we can
319 * do is drop it.
320 */
321 if (hdr.bh_caplen != hdr.bh_datalen) {
322 interface->rbuf_offset = BPF_WORDALIGN(
323 interface->rbuf_offset + hdr.bh_hdrlen +
324 hdr.bh_caplen);
325 continue;
326 }
327
328 /* Skip over the BPF header... */
329 interface->rbuf_offset += hdr.bh_hdrlen;
330
331 /* Decode the physical header... */
332 offset = decode_hw_header(interface->rbuf +
333 interface->rbuf_offset, hdr.bh_caplen, hfrom);
334
335 /*
336 * If a physical layer checksum failed (dunno of any
337 * physical layer that supports this, but WTH), skip
338 * this packet.
339 */
340 if (offset < 0) {
341 interface->rbuf_offset = BPF_WORDALIGN(
342 interface->rbuf_offset + hdr.bh_caplen);
343 continue;
344 }
345 interface->rbuf_offset += offset;
346 hdr.bh_caplen -= offset;
347
348 /* Decode the IP and UDP headers... */
349 offset = decode_udp_ip_header(interface->rbuf +
350 interface->rbuf_offset, hdr.bh_caplen, from);
351
352 /* If the IP or UDP checksum was bad, skip the packet... */
353 if (offset < 0) {
354 interface->rbuf_offset = BPF_WORDALIGN(
355 interface->rbuf_offset + hdr.bh_caplen);
356 continue;
357 }
358 interface->rbuf_offset += offset;
359 hdr.bh_caplen -= offset;
360
361 /*
362 * If there's not enough room to stash the packet data,
363 * we have to skip it (this shouldn't happen in real
364 * life, though).
365 */
366 if (hdr.bh_caplen > len) {
367 interface->rbuf_offset = BPF_WORDALIGN(
368 interface->rbuf_offset + hdr.bh_caplen);
369 continue;
370 }
371
372 /* Copy out the data in the packet... */
373 memcpy(buf, interface->rbuf + interface->rbuf_offset,
374 hdr.bh_caplen);
375 interface->rbuf_offset = BPF_WORDALIGN(interface->rbuf_offset +
376 hdr.bh_caplen);
377 return (hdr.bh_caplen);
378 } while (!length);
379 return (0);
380 }
381