sbin/dhclient/bpf.c

   1 /*      $OpenBSD: bpf.c,v 1.20 2007/01/08 02:51:13 krw Exp $    */
   2 /*      $DragonFly: src/sbin/dhclient/bpf.c,v 1.2 2008/11/05 14:08:41 sephe Exp $       */
   3
   4 /* BPF socket interface code, originally contributed by Archie Cobbs. */
   5
   6 /*
   7  * Copyright (c) 1995, 1996, 1998, 1999
   8  * The Internet Software Consortium.    All rights reserved.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  *
  14  * 1. Redistributions of source code must retain the above copyright
  15  *    notice, this list of conditions and the following disclaimer.
  16  * 2. Redistributions in binary form must reproduce the above copyright
  17  *    notice, this list of conditions and the following disclaimer in the
  18  *    documentation and/or other materials provided with the distribution.
  19  * 3. Neither the name of The Internet Software Consortium nor the names
  20  *    of its contributors may be used to endorse or promote products derived
  21  *    from this software without specific prior written permission.
  22  *
  23  * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
  24  * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
  25  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  26  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  27  * DISCLAIMED.  IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
  28  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  29  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  30  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  31  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  32  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  33  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  34  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  35  * SUCH DAMAGE.
  36  *
  37  * This software has been written for the Internet Software Consortium
  38  * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
  39  * Enterprises.  To learn more about the Internet Software Consortium,
  40  * see ``http://www.vix.com/isc''.  To learn more about Vixie
  41  * Enterprises, see ``http://www.vix.com''.
  42  */
  43
  44 #include <sys/ioctl.h>
  45 #include <sys/uio.h>
  46
  47 #include <net/bpf.h>
  48 #include <netinet/if_ether.h>
  49 #include <netinet/in_systm.h>
  50 #include <netinet/ip.h>
  51 #include <netinet/udp.h>
  52
  53 #include "dhcpd.h"
  54
  55 /*
  56  * Called by get_interface_list for each interface that's discovered.
  57  * Opens a packet filter for each interface and adds it to the select
  58  * mask.
  59  */
  60 int
  61 if_register_bpf(void)
  62 {
  63         char filename[50];
  64         int sock, b;
  65
  66         /*
  67          * Open a BPF device.  Try auto-clone first (newer kernels),
  68          * otherwise iterate (older kernels).
  69          */
  70         sock = open("/dev/bpf", O_RDWR, 0);
  71         if (sock < 0) {
  72                 for (b = 0; 1; b++) {
  73                         snprintf(filename, sizeof(filename), "/dev/bpf%d", b);
  74                         sock = open(filename, O_RDWR, 0);
  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         }
  85
  86         /* Set the BPF device to point at this interface. */
  87         if (ioctl(sock, BIOCSETIF, ifi->ifp) < 0)
  88                 error("Can't attach interface %s to bpf device %s: %m",
  89                     ifi->name, filename);
  90
  91         return (sock);
  92 }
  93
  94 void
  95 if_register_send(void)
  96 {
  97         int sock, on = 1;
  98
  99         /*
 100          * If we're using the bpf API for sending and receiving, we
 101          * don't need to register this interface twice.
 102          */
 103         ifi->wfdesc = ifi->rfdesc;
 104
 105         /*
 106          * Use raw socket for unicast send.
 107          */
 108         if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1)
 109                 error("socket(SOCK_RAW): %m");
 110         if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on,
 111             sizeof(on)) == -1)
 112                 error("setsockopt(IP_HDRINCL): %m");
 113         ifi->ufdesc = sock;
 114 }
 115
 116 /*
 117  * Packet filter program...
 118  *
 119  * XXX: Changes to the filter program may require changes to the
 120  * constant offsets used in if_register_send to patch the BPF program!
 121  */
 122 struct bpf_insn dhcp_bpf_filter[] = {
 123         /* Make sure this is an IP packet... */
 124         BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
 125         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
 126
 127         /* Make sure it's a UDP packet... */
 128         BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
 129         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
 130
 131         /* Make sure this isn't a fragment... */
 132         BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
 133         BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
 134
 135         /* Get the IP header length... */
 136         BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
 137
 138         /* Make sure it's to the right port... */
 139         BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
 140         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),          /* patch */
 141
 142         /* If we passed all the tests, ask for the whole packet. */
 143         BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
 144
 145         /* Otherwise, drop it. */
 146         BPF_STMT(BPF_RET+BPF_K, 0),
 147 };
 148
 149 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
 150
 151 /*
 152  * Packet write filter program:
 153  * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
 154  */
 155 struct bpf_insn dhcp_bpf_wfilter[] = {
 156         BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
 157         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
 158
 159         /* Make sure this is an IP packet... */
 160         BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
 161         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10),
 162
 163         /* Make sure it's a UDP packet... */
 164         BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
 165         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
 166
 167         /* Make sure this isn't a fragment... */
 168         BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
 169         BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0),     /* patched */
 170
 171         /* Get the IP header length... */
 172         BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
 173
 174         /* Make sure it's from the right port... */
 175         BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
 176         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3),
 177
 178         /* Make sure it is to the right ports ... */
 179         BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
 180         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),
 181
 182         /* If we passed all the tests, ask for the whole packet. */
 183         BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
 184
 185         /* Otherwise, drop it. */
 186         BPF_STMT(BPF_RET+BPF_K, 0),
 187 };
 188
 189 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
 190
 191 void
 192 if_register_receive(void)
 193 {
 194         struct bpf_version v;
 195         struct bpf_program p;
 196         int flag = 1, sz;
 197
 198         /* Open a BPF device and hang it on this interface... */
 199         ifi->rfdesc = if_register_bpf();
 200
 201         /* Make sure the BPF version is in range... */
 202         if (ioctl(ifi->rfdesc, BIOCVERSION, &v) < 0)
 203                 error("Can't get BPF version: %m");
 204
 205         if (v.bv_major != BPF_MAJOR_VERSION ||
 206             v.bv_minor < BPF_MINOR_VERSION)
 207                 error("Kernel BPF version out of range - recompile dhcpd!");
 208
 209         /*
 210          * Set immediate mode so that reads return as soon as a packet
 211          * comes in, rather than waiting for the input buffer to fill
 212          * with packets.
 213          */
 214         if (ioctl(ifi->rfdesc, BIOCIMMEDIATE, &flag) < 0)
 215                 error("Can't set immediate mode on bpf device: %m");
 216
 217         /*if (ioctl(ifi->rfdesc, BIOCSFILDROP, &flag) < 0)
 218                 error("Can't set filter-drop mode on bpf device: %m");*/
 219
 220         /* Get the required BPF buffer length from the kernel. */
 221         if (ioctl(ifi->rfdesc, BIOCGBLEN, &sz) < 0)
 222                 error("Can't get bpf buffer length: %m");
 223         ifi->rbuf_max = sz;
 224         ifi->rbuf = malloc(ifi->rbuf_max);
 225         if (!ifi->rbuf)
 226                 error("Can't allocate %lu bytes for bpf input buffer.",
 227                     (unsigned long)ifi->rbuf_max);
 228         ifi->rbuf_offset = 0;
 229         ifi->rbuf_len = 0;
 230
 231         /* Set up the bpf filter program structure. */
 232         p.bf_len = dhcp_bpf_filter_len;
 233         p.bf_insns = dhcp_bpf_filter;
 234
 235         /* Patch the server port into the BPF program...
 236          *
 237          * XXX: changes to filter program may require changes to the
 238          * insn number(s) used below!
 239          */
 240         dhcp_bpf_filter[8].k = LOCAL_PORT;
 241
 242         if (ioctl(ifi->rfdesc, BIOCSETF, &p) < 0)
 243                 error("Can't install packet filter program: %m");
 244
 245         /* Set up the bpf write filter program structure. */
 246         p.bf_len = dhcp_bpf_wfilter_len;
 247         p.bf_insns = dhcp_bpf_wfilter;
 248
 249         if (dhcp_bpf_wfilter[7].k == 0x1fff)
 250                 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK);
 251
 252         if (ioctl(ifi->rfdesc, BIOCSETWF, &p) < 0)
 253                 error("Can't install write filter program: %m");
 254
 255         if (ioctl(ifi->rfdesc, BIOCLOCK, NULL) < 0)
 256                 error("Cannot lock bpf");
 257 }
 258
 259 ssize_t
 260 send_packet(struct in_addr from, struct sockaddr_in *to,
 261     struct hardware *hto)
 262 {
 263 #define IOVCNT          2
 264         unsigned char buf[256];
 265         struct iovec iov[IOVCNT];
 266         struct msghdr msg;
 267         int result, bufp = 0;
 268
 269         if (to->sin_addr.s_addr == INADDR_BROADCAST) {
 270                 assemble_hw_header(buf, &bufp, hto);
 271         }
 272
 273         assemble_udp_ip_header(buf, &bufp, from.s_addr,
 274             to->sin_addr.s_addr, to->sin_port,
 275             (unsigned char *)&client->packet,
 276             client->packet_length);
 277
 278         iov[0].iov_base = (char *)buf;
 279         iov[0].iov_len = bufp;
 280         iov[1].iov_base = (char *)&client->packet;
 281         iov[1].iov_len = client->packet_length;
 282
 283         if (to->sin_addr.s_addr == INADDR_BROADCAST) {
 284                 result = writev(ifi->wfdesc, iov, IOVCNT);
 285         } else {
 286                 struct ip *ip = (struct ip *)buf;
 287
 288                 /*
 289                  * DragonFly's raw socket expects ip_len/ip_off
 290                  * in host byte order.
 291                  */
 292                 ip->ip_len = ntohs(ip->ip_len);
 293                 ip->ip_off = ntohs(ip->ip_off);
 294
 295                 memset(&msg, 0, sizeof(msg));
 296                 msg.msg_name = (struct sockaddr *)to;
 297                 msg.msg_namelen = sizeof(*to);
 298                 msg.msg_iov = iov;
 299                 msg.msg_iovlen = IOVCNT;
 300                 result = sendmsg(ifi->ufdesc, &msg, 0);
 301         }
 302
 303         if (result == -1)
 304                 warning("send_packet: %m");
 305         return (result);
 306 }
 307
 308 ssize_t
 309 receive_packet(struct sockaddr_in *from, struct hardware *hfrom)
 310 {
 311         int length = 0, offset = 0;
 312         struct bpf_hdr hdr;
 313
 314         /*
 315          * All this complexity is because BPF doesn't guarantee that
 316          * only one packet will be returned at a time.  We're getting
 317          * what we deserve, though - this is a terrible abuse of the BPF
 318          * interface.  Sigh.
 319          */
 320
 321         /* Process packets until we get one we can return or until we've
 322          * done a read and gotten nothing we can return...
 323          */
 324         do {
 325                 /* If the buffer is empty, fill it. */
 326                 if (ifi->rbuf_offset == ifi->rbuf_len) {
 327                         length = read(ifi->rfdesc, ifi->rbuf, ifi->rbuf_max);
 328                         if (length <= 0)
 329                                 return (length);
 330                         ifi->rbuf_offset = 0;
 331                         ifi->rbuf_len = BPF_WORDALIGN(length);
 332                 }
 333
 334                 /*
 335                  * If there isn't room for a whole bpf header, something
 336                  * went wrong, but we'll ignore it and hope it goes
 337                  * away... XXX
 338                  */
 339                 if (ifi->rbuf_len - ifi->rbuf_offset < sizeof(hdr)) {
 340                         ifi->rbuf_offset = ifi->rbuf_len;
 341                         continue;
 342                 }
 343
 344                 /* Copy out a bpf header... */
 345                 memcpy(&hdr, &ifi->rbuf[ifi->rbuf_offset], sizeof(hdr));
 346
 347                 /*
 348                  * If the bpf header plus data doesn't fit in what's
 349                  * left of the buffer, stick head in sand yet again...
 350                  */
 351                 if (ifi->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
 352                     ifi->rbuf_len) {
 353                         ifi->rbuf_offset = ifi->rbuf_len;
 354                         continue;
 355                 }
 356
 357                 /*
 358                  * If the captured data wasn't the whole packet, or if
 359                  * the packet won't fit in the input buffer, all we can
 360                  * do is drop it.
 361                  */
 362                 if (hdr.bh_caplen != hdr.bh_datalen) {
 363                         ifi->rbuf_offset = BPF_WORDALIGN(
 364                             ifi->rbuf_offset + hdr.bh_hdrlen +
 365                             hdr.bh_caplen);
 366                         continue;
 367                 }
 368
 369                 /* Skip over the BPF header... */
 370                 ifi->rbuf_offset += hdr.bh_hdrlen;
 371
 372                 /* Decode the physical header... */
 373                 offset = decode_hw_header(ifi->rbuf, ifi->rbuf_offset, hfrom);
 374
 375                 /*
 376                  * If a physical layer checksum failed (dunno of any
 377                  * physical layer that supports this, but WTH), skip
 378                  * this packet.
 379                  */
 380                 if (offset < 0) {
 381                         ifi->rbuf_offset = BPF_WORDALIGN(
 382                             ifi->rbuf_offset + hdr.bh_caplen);
 383                         continue;
 384                 }
 385                 ifi->rbuf_offset += offset;
 386                 hdr.bh_caplen -= offset;
 387
 388                 /* Decode the IP and UDP headers... */
 389                 offset = decode_udp_ip_header(ifi->rbuf,
 390                     ifi->rbuf_offset, from, NULL, hdr.bh_caplen);
 391
 392                 /* If the IP or UDP checksum was bad, skip the packet... */
 393                 if (offset < 0) {
 394                         ifi->rbuf_offset = BPF_WORDALIGN(
 395                             ifi->rbuf_offset + hdr.bh_caplen);
 396                         continue;
 397                 }
 398                 ifi->rbuf_offset += offset;
 399                 hdr.bh_caplen -= offset;
 400
 401                 /*
 402                  * If there's not enough room to stash the packet data,
 403                  * we have to skip it (this shouldn't happen in real
 404                  * life, though).
 405                  */
 406                 if (hdr.bh_caplen > sizeof(client->packet)) {
 407                         ifi->rbuf_offset = BPF_WORDALIGN(
 408                             ifi->rbuf_offset + hdr.bh_caplen);
 409                         continue;
 410                 }
 411
 412                 /* Copy out the data in the packet... */
 413                 memset(&client->packet, DHO_END, sizeof(client->packet));
 414                 memcpy(&client->packet, ifi->rbuf + ifi->rbuf_offset,
 415                     hdr.bh_caplen);
 416                 ifi->rbuf_offset = BPF_WORDALIGN(ifi->rbuf_offset +
 417                     hdr.bh_caplen);
 418                 return (hdr.bh_caplen);
 419         } while (!length);
 420         return (0);
 421 }