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 #define BPF_FORMAT "/dev/bpf%d"
  56
  57 /*
  58  * Called by get_interface_list for each interface that's discovered.
  59  * Opens a packet filter for each interface and adds it to the select
  60  * mask.
  61  */
  62 int
  63 if_register_bpf(void)
  64 {
  65         char filename[50];
  66         int sock, b;
  67
  68         /* Open a BPF device */
  69         for (b = 0; 1; b++) {
  70                 snprintf(filename, sizeof(filename), BPF_FORMAT, b);
  71                 sock = open(filename, O_RDWR, 0);
  72                 if (sock < 0) {
  73                         if (errno == EBUSY)
  74                                 continue;
  75                         else
  76                                 error("Can't find free bpf: %m");
  77                 } else
  78                         break;
  79         }
  80
  81         /* Set the BPF device to point at this interface. */
  82         if (ioctl(sock, BIOCSETIF, ifi->ifp) < 0)
  83                 error("Can't attach interface %s to bpf device %s: %m",
  84                     ifi->name, filename);
  85
  86         return (sock);
  87 }
  88
  89 void
  90 if_register_send(void)
  91 {
  92         int sock, on = 1;
  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         ifi->wfdesc = ifi->rfdesc;
  99
 100         /*
 101          * Use raw socket for unicast send.
 102          */
 103         if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1)
 104                 error("socket(SOCK_RAW): %m");
 105         if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on,
 106             sizeof(on)) == -1)
 107                 error("setsockopt(IP_HDRINCL): %m");
 108         ifi->ufdesc = sock;
 109 }
 110
 111 /*
 112  * Packet filter program...
 113  *
 114  * XXX: Changes to the filter program may require changes to the
 115  * constant offsets used in if_register_send to patch the BPF program!
 116  */
 117 struct bpf_insn dhcp_bpf_filter[] = {
 118         /* Make sure this is an IP packet... */
 119         BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
 120         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
 121
 122         /* Make sure it's a UDP packet... */
 123         BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
 124         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
 125
 126         /* Make sure this isn't a fragment... */
 127         BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
 128         BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
 129
 130         /* Get the IP header length... */
 131         BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
 132
 133         /* Make sure it's to the right port... */
 134         BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
 135         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),          /* patch */
 136
 137         /* If we passed all the tests, ask for the whole packet. */
 138         BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
 139
 140         /* Otherwise, drop it. */
 141         BPF_STMT(BPF_RET+BPF_K, 0),
 142 };
 143
 144 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn);
 145
 146 /*
 147  * Packet write filter program:
 148  * 'ip and udp and src port bootps and dst port (bootps or bootpc)'
 149  */
 150 struct bpf_insn dhcp_bpf_wfilter[] = {
 151         BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14),
 152         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12),
 153
 154         /* Make sure this is an IP packet... */
 155         BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
 156         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10),
 157
 158         /* Make sure it's a UDP packet... */
 159         BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23),
 160         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8),
 161
 162         /* Make sure this isn't a fragment... */
 163         BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
 164         BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0),     /* patched */
 165
 166         /* Get the IP header length... */
 167         BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14),
 168
 169         /* Make sure it's from the right port... */
 170         BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14),
 171         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3),
 172
 173         /* Make sure it is to the right ports ... */
 174         BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16),
 175         BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),
 176
 177         /* If we passed all the tests, ask for the whole packet. */
 178         BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
 179
 180         /* Otherwise, drop it. */
 181         BPF_STMT(BPF_RET+BPF_K, 0),
 182 };
 183
 184 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn);
 185
 186 void
 187 if_register_receive(void)
 188 {
 189         struct bpf_version v;
 190         struct bpf_program p;
 191         int flag = 1, sz;
 192
 193         /* Open a BPF device and hang it on this interface... */
 194         ifi->rfdesc = if_register_bpf();
 195
 196         /* Make sure the BPF version is in range... */
 197         if (ioctl(ifi->rfdesc, BIOCVERSION, &v) < 0)
 198                 error("Can't get BPF version: %m");
 199
 200         if (v.bv_major != BPF_MAJOR_VERSION ||
 201             v.bv_minor < BPF_MINOR_VERSION)
 202                 error("Kernel BPF version out of range - recompile dhcpd!");
 203
 204         /*
 205          * Set immediate mode so that reads return as soon as a packet
 206          * comes in, rather than waiting for the input buffer to fill
 207          * with packets.
 208          */
 209         if (ioctl(ifi->rfdesc, BIOCIMMEDIATE, &flag) < 0)
 210                 error("Can't set immediate mode on bpf device: %m");
 211
 212         /*if (ioctl(ifi->rfdesc, BIOCSFILDROP, &flag) < 0)
 213                 error("Can't set filter-drop mode on bpf device: %m");*/
 214
 215         /* Get the required BPF buffer length from the kernel. */
 216         if (ioctl(ifi->rfdesc, BIOCGBLEN, &sz) < 0)
 217                 error("Can't get bpf buffer length: %m");
 218         ifi->rbuf_max = sz;
 219         ifi->rbuf = malloc(ifi->rbuf_max);
 220         if (!ifi->rbuf)
 221                 error("Can't allocate %lu bytes for bpf input buffer.",
 222                     (unsigned long)ifi->rbuf_max);
 223         ifi->rbuf_offset = 0;
 224         ifi->rbuf_len = 0;
 225
 226         /* Set up the bpf filter program structure. */
 227         p.bf_len = dhcp_bpf_filter_len;
 228         p.bf_insns = dhcp_bpf_filter;
 229
 230         /* Patch the server port into the BPF program...
 231          *
 232          * XXX: changes to filter program may require changes to the
 233          * insn number(s) used below!
 234          */
 235         dhcp_bpf_filter[8].k = LOCAL_PORT;
 236
 237         if (ioctl(ifi->rfdesc, BIOCSETF, &p) < 0)
 238                 error("Can't install packet filter program: %m");
 239
 240         /* Set up the bpf write filter program structure. */
 241         p.bf_len = dhcp_bpf_wfilter_len;
 242         p.bf_insns = dhcp_bpf_wfilter;
 243
 244         if (dhcp_bpf_wfilter[7].k == 0x1fff)
 245                 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK);
 246
 247         if (ioctl(ifi->rfdesc, BIOCSETWF, &p) < 0)
 248                 error("Can't install write filter program: %m");
 249
 250         if (ioctl(ifi->rfdesc, BIOCLOCK, NULL) < 0)
 251                 error("Cannot lock bpf");
 252 }
 253
 254 ssize_t
 255 send_packet(struct in_addr from, struct sockaddr_in *to,
 256     struct hardware *hto)
 257 {
 258 #define IOVCNT          2
 259         unsigned char buf[256];
 260         struct iovec iov[IOVCNT];
 261         struct msghdr msg;
 262         int result, bufp = 0;
 263
 264         if (to->sin_addr.s_addr == INADDR_BROADCAST) {
 265                 assemble_hw_header(buf, &bufp, hto);
 266         }
 267
 268         assemble_udp_ip_header(buf, &bufp, from.s_addr,
 269             to->sin_addr.s_addr, to->sin_port,
 270             (unsigned char *)&client->packet,
 271             client->packet_length);
 272
 273         iov[0].iov_base = (char *)buf;
 274         iov[0].iov_len = bufp;
 275         iov[1].iov_base = (char *)&client->packet;
 276         iov[1].iov_len = client->packet_length;
 277
 278         if (to->sin_addr.s_addr == INADDR_BROADCAST) {
 279                 result = writev(ifi->wfdesc, iov, IOVCNT);
 280         } else {
 281                 struct ip *ip = (struct ip *)buf;
 282
 283                 /*
 284                  * DragonFly's raw socket expects ip_len/ip_off
 285                  * in host byte order.
 286                  */
 287                 ip->ip_len = ntohs(ip->ip_len);
 288                 ip->ip_off = ntohs(ip->ip_off);
 289
 290                 memset(&msg, 0, sizeof(msg));
 291                 msg.msg_name = (struct sockaddr *)to;
 292                 msg.msg_namelen = sizeof(*to);
 293                 msg.msg_iov = iov;
 294                 msg.msg_iovlen = IOVCNT;
 295                 result = sendmsg(ifi->ufdesc, &msg, 0);
 296         }
 297
 298         if (result == -1)
 299                 warning("send_packet: %m");
 300         return (result);
 301 }
 302
 303 ssize_t
 304 receive_packet(struct sockaddr_in *from, struct hardware *hfrom)
 305 {
 306         int length = 0, offset = 0;
 307         struct bpf_hdr hdr;
 308
 309         /*
 310          * All this complexity is because BPF doesn't guarantee that
 311          * only one packet will be returned at a time.  We're getting
 312          * what we deserve, though - this is a terrible abuse of the BPF
 313          * interface.  Sigh.
 314          */
 315
 316         /* Process packets until we get one we can return or until we've
 317          * done a read and gotten nothing we can return...
 318          */
 319         do {
 320                 /* If the buffer is empty, fill it. */
 321                 if (ifi->rbuf_offset == ifi->rbuf_len) {
 322                         length = read(ifi->rfdesc, ifi->rbuf, ifi->rbuf_max);
 323                         if (length <= 0)
 324                                 return (length);
 325                         ifi->rbuf_offset = 0;
 326                         ifi->rbuf_len = BPF_WORDALIGN(length);
 327                 }
 328
 329                 /*
 330                  * If there isn't room for a whole bpf header, something
 331                  * went wrong, but we'll ignore it and hope it goes
 332                  * away... XXX
 333                  */
 334                 if (ifi->rbuf_len - ifi->rbuf_offset < sizeof(hdr)) {
 335                         ifi->rbuf_offset = ifi->rbuf_len;
 336                         continue;
 337                 }
 338
 339                 /* Copy out a bpf header... */
 340                 memcpy(&hdr, &ifi->rbuf[ifi->rbuf_offset], sizeof(hdr));
 341
 342                 /*
 343                  * If the bpf header plus data doesn't fit in what's
 344                  * left of the buffer, stick head in sand yet again...
 345                  */
 346                 if (ifi->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen >
 347                     ifi->rbuf_len) {
 348                         ifi->rbuf_offset = ifi->rbuf_len;
 349                         continue;
 350                 }
 351
 352                 /*
 353                  * If the captured data wasn't the whole packet, or if
 354                  * the packet won't fit in the input buffer, all we can
 355                  * do is drop it.
 356                  */
 357                 if (hdr.bh_caplen != hdr.bh_datalen) {
 358                         ifi->rbuf_offset = BPF_WORDALIGN(
 359                             ifi->rbuf_offset + hdr.bh_hdrlen +
 360                             hdr.bh_caplen);
 361                         continue;
 362                 }
 363
 364                 /* Skip over the BPF header... */
 365                 ifi->rbuf_offset += hdr.bh_hdrlen;
 366
 367                 /* Decode the physical header... */
 368                 offset = decode_hw_header(ifi->rbuf, ifi->rbuf_offset, hfrom);
 369
 370                 /*
 371                  * If a physical layer checksum failed (dunno of any
 372                  * physical layer that supports this, but WTH), skip
 373                  * this packet.
 374                  */
 375                 if (offset < 0) {
 376                         ifi->rbuf_offset = BPF_WORDALIGN(
 377                             ifi->rbuf_offset + hdr.bh_caplen);
 378                         continue;
 379                 }
 380                 ifi->rbuf_offset += offset;
 381                 hdr.bh_caplen -= offset;
 382
 383                 /* Decode the IP and UDP headers... */
 384                 offset = decode_udp_ip_header(ifi->rbuf,
 385                     ifi->rbuf_offset, from, NULL, hdr.bh_caplen);
 386
 387                 /* If the IP or UDP checksum was bad, skip the packet... */
 388                 if (offset < 0) {
 389                         ifi->rbuf_offset = BPF_WORDALIGN(
 390                             ifi->rbuf_offset + hdr.bh_caplen);
 391                         continue;
 392                 }
 393                 ifi->rbuf_offset += offset;
 394                 hdr.bh_caplen -= offset;
 395
 396                 /*
 397                  * If there's not enough room to stash the packet data,
 398                  * we have to skip it (this shouldn't happen in real
 399                  * life, though).
 400                  */
 401                 if (hdr.bh_caplen > sizeof(client->packet)) {
 402                         ifi->rbuf_offset = BPF_WORDALIGN(
 403                             ifi->rbuf_offset + hdr.bh_caplen);
 404                         continue;
 405                 }
 406
 407                 /* Copy out the data in the packet... */
 408                 memset(&client->packet, DHO_END, sizeof(client->packet));
 409                 memcpy(&client->packet, ifi->rbuf + ifi->rbuf_offset,
 410                     hdr.bh_caplen);
 411                 ifi->rbuf_offset = BPF_WORDALIGN(ifi->rbuf_offset +
 412                     hdr.bh_caplen);
 413                 return (hdr.bh_caplen);
 414         } while (!length);
 415         return (0);
 416 }