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 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 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 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 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 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