1 /* $OpenBSD: bpf.c,v 1.13 2004/05/05 14:28:58 deraadt Exp $ */
3 /* BPF socket interface code, originally contributed by Archie Cobbs. */
6 * Copyright (c) 1995, 1996, 1998, 1999
7 * The Internet Software Consortium. All rights reserved.
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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
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33 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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''.
43 #include <sys/cdefs.h>
44 __FBSDID("$FreeBSD$");
47 #include <sys/ioctl.h>
51 #include <netinet/in_systm.h>
52 #include <netinet/ip.h>
53 #include <netinet/udp.h>
54 #include <netinet/if_ether.h>
56 #define BPF_FORMAT "/dev/bpf%d"
59 * Called by get_interface_list for each interface that's discovered.
60 * Opens a packet filter for each interface and adds it to the select
64 if_register_bpf(struct interface_info *info)
69 /* Open a BPF device */
71 snprintf(filename, sizeof(filename), BPF_FORMAT, b);
72 sock = open(filename, O_RDWR, 0);
77 error("Can't find free bpf: %m");
82 /* Set the BPF device to point at this interface. */
83 if (ioctl(sock, BIOCSETIF, info->ifp) < 0)
84 error("Can't attach interface %s to bpf device %s: %m",
85 info->name, filename);
91 if_register_send(struct interface_info *info)
94 * If we're using the bpf API for sending and receiving, we
95 * don't need to register this interface twice.
97 info->wfdesc = info->rfdesc;
101 * Packet filter program...
103 * XXX: Changes to the filter program may require changes to the
104 * constant offsets used in if_register_send to patch the BPF program!
106 struct bpf_insn dhcp_bpf_filter[] = {
107 /* Make sure this is an IP packet... */
108 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
109 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
111 /* Make sure it's a UDP packet... */
112 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
113 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
115 /* Make sure this isn't a fragment... */
116 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
117 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
119 /* Get the IP header length... */
120 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
122 /* Make sure it's to the right port... */
123 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
124 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */
126 /* If we passed all the tests, ask for the whole packet. */
127 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
129 /* Otherwise, drop it. */
130 BPF_STMT(BPF_RET+BPF_K, 0),
133 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
136 * Packet write filter program:
137 * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
139 struct bpf_insn dhcp_bpf_wfilter[] = {
140 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
141 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
143 /* Make sure this is an IP packet... */
144 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
145 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10),
147 /* Make sure it's a UDP packet... */
148 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
149 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
151 /* Make sure this isn't a fragment... */
152 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
153 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */
155 /* Get the IP header length... */
156 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
158 /* Make sure it's from the right port... */
159 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
160 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3),
162 /* Make sure it is to the right ports ... */
163 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
164 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),
166 /* If we passed all the tests, ask for the whole packet. */
167 BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
169 /* Otherwise, drop it. */
170 BPF_STMT(BPF_RET+BPF_K, 0),
173 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
176 if_register_receive(struct interface_info *info)
178 struct bpf_version v;
179 struct bpf_program p;
182 /* Open a BPF device and hang it on this interface... */
183 info->rfdesc = if_register_bpf(info);
185 /* Make sure the BPF version is in range... */
186 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0)
187 error("Can't get BPF version: %m");
189 if (v.bv_major != BPF_MAJOR_VERSION ||
190 v.bv_minor < BPF_MINOR_VERSION)
191 error("Kernel BPF version out of range - recompile dhcpd!");
194 * Set immediate mode so that reads return as soon as a packet
195 * comes in, rather than waiting for the input buffer to fill
198 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0)
199 error("Can't set immediate mode on bpf device: %m");
201 /* Get the required BPF buffer length from the kernel. */
202 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0)
203 error("Can't get bpf buffer length: %m");
205 info->rbuf = malloc(info->rbuf_max);
207 error("Can't allocate %lu bytes for bpf input buffer.",
208 (unsigned long)info->rbuf_max);
209 info->rbuf_offset = 0;
212 /* Set up the bpf filter program structure. */
213 p.bf_len = dhcp_bpf_filter_len;
214 p.bf_insns = dhcp_bpf_filter;
216 /* Patch the server port into the BPF program...
218 * XXX: changes to filter program may require changes to the
219 * insn number(s) used below!
221 dhcp_bpf_filter[8].k = LOCAL_PORT;
223 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0)
224 error("Can't install packet filter program: %m");
226 /* Set up the bpf write filter program structure. */
227 p.bf_len = dhcp_bpf_wfilter_len;
228 p.bf_insns = dhcp_bpf_wfilter;
230 if (dhcp_bpf_wfilter[7].k == 0x1fff)
231 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK);
233 if (ioctl(info->rfdesc, BIOCSETWF, &p) < 0)
234 error("Can't install write filter program: %m");
236 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0)
237 error("Cannot lock bpf");
241 send_packet(struct interface_info *interface, struct dhcp_packet *raw,
242 size_t len, struct in_addr from, struct sockaddr_in *to,
243 struct hardware *hto)
245 unsigned char buf[256];
247 int result, bufp = 0;
250 if (to->sin_addr.s_addr != INADDR_BROADCAST) {
251 note("SENDING DIRECT");
252 /* We know who the server is, send the packet via
253 normal socket interface */
255 if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) >= 0) {
256 result = sendto (sock, (char *)raw, len, 0,
257 (struct sockaddr *)to, sizeof *to);
264 /* Assemble the headers... */
265 assemble_hw_header(interface, buf, &bufp, hto);
266 assemble_udp_ip_header(buf, &bufp, from.s_addr,
267 to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len);
270 iov[0].iov_base = (char *)buf;
271 iov[0].iov_len = bufp;
272 iov[1].iov_base = (char *)raw;
273 iov[1].iov_len = len;
275 result = writev(interface->wfdesc, iov, 2);
277 warning("send_packet: %m");
282 receive_packet(struct interface_info *interface, unsigned char *buf,
283 size_t len, struct sockaddr_in *from, struct hardware *hfrom)
285 int length = 0, offset = 0;
289 * All this complexity is because BPF doesn't guarantee that
290 * only one packet will be returned at a time. We're getting
291 * what we deserve, though - this is a terrible abuse of the BPF
295 /* Process packets until we get one we can return or until we've
296 * done a read and gotten nothing we can return...
299 /* If the buffer is empty, fill it. */
300 if (interface->rbuf_offset >= interface->rbuf_len) {
301 length = read(interface->rfdesc, interface->rbuf,
302 interface->rbuf_max);
305 interface->rbuf_offset = 0;
306 interface->rbuf_len = length;
310 * If there isn't room for a whole bpf header, something
311 * went wrong, but we'll ignore it and hope it goes
314 if (interface->rbuf_len - interface->rbuf_offset <
316 interface->rbuf_offset = interface->rbuf_len;
320 /* Copy out a bpf header... */
321 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset],
325 * If the bpf header plus data doesn't fit in what's
326 * left of the buffer, stick head in sand yet again...
328 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
329 interface->rbuf_len) {
330 interface->rbuf_offset = interface->rbuf_len;
334 /* Skip over the BPF header... */
335 interface->rbuf_offset += hdr.bh_hdrlen;
338 * If the captured data wasn't the whole packet, or if
339 * the packet won't fit in the input buffer, all we can
342 if (hdr.bh_caplen != hdr.bh_datalen) {
343 interface->rbuf_offset =
344 BPF_WORDALIGN(interface->rbuf_offset +
349 /* Decode the physical header... */
350 offset = decode_hw_header(interface->rbuf,
351 interface->rbuf_offset, hfrom);
354 * If a physical layer checksum failed (dunno of any
355 * physical layer that supports this, but WTH), skip
359 interface->rbuf_offset =
360 BPF_WORDALIGN(interface->rbuf_offset +
364 interface->rbuf_offset += offset;
365 hdr.bh_caplen -= offset;
367 /* Decode the IP and UDP headers... */
368 offset = decode_udp_ip_header(interface->rbuf,
369 interface->rbuf_offset, from, NULL, hdr.bh_caplen);
371 /* If the IP or UDP checksum was bad, skip the packet... */
373 interface->rbuf_offset =
374 BPF_WORDALIGN(interface->rbuf_offset +
378 interface->rbuf_offset += offset;
379 hdr.bh_caplen -= offset;
382 * If there's not enough room to stash the packet data,
383 * we have to skip it (this shouldn't happen in real
386 if (hdr.bh_caplen > len) {
387 interface->rbuf_offset =
388 BPF_WORDALIGN(interface->rbuf_offset +
393 /* Copy out the data in the packet... */
394 memcpy(buf, interface->rbuf + interface->rbuf_offset,
396 interface->rbuf_offset =
397 BPF_WORDALIGN(interface->rbuf_offset +
399 return (hdr.bh_caplen);