common/bpf.c

   1 /* bpf.c
   2
   3    BPF socket interface code, originally contributed by Archie Cobbs. */
   4
   5 /*
   6  * Copyright (c) 1996-1999 Internet Software Consortium.
   7  * Use is subject to license terms which appear in the file named
   8  * ISC-LICENSE that should have accompanied this file when you
   9  * received it.   If a file named ISC-LICENSE did not accompany this
  10  * file, or you are not sure the one you have is correct, you may
  11  * obtain an applicable copy of the license at:
  12  *
  13  *             http://www.isc.org/isc-license-1.0.html.
  14  *
  15  * This file is part of the ISC DHCP distribution.   The documentation
  16  * associated with this file is listed in the file DOCUMENTATION,
  17  * included in the top-level directory of this release.
  18  *
  19  * Support and other services are available for ISC products - see
  20  * http://www.isc.org for more information.
  21  */
  22
  23 #ifndef lint
  24 static char copyright[] =
  25 "$Id: bpf.c,v 1.25 1999/03/16 05:50:31 mellon Exp $ Copyright (c) 1995, 1996 The Internet Software Consortium.  All rights reserved.\n";
  26 #endif /* not lint */
  27
  28 #include "dhcpd.h"
  29 #if defined (USE_BPF_SEND) || defined (USE_BPF_RECEIVE) \
  30                                 || defined (USE_LPF_RECEIVE)
  31 # if defined (USE_LPF_RECEIVE)
  32 #  include <asm/types.h>
  33 #  include <linux/filter.h>
  34 #  define bpf_insn sock_filter /* Linux: dare to be gratuitously different. */
  35 # else
  36 #  include <sys/ioctl.h>
  37 #  include <sys/uio.h>
  38 #  include <net/bpf.h>
  39 #  if defined (NEED_OSF_PFILT_HACKS)
  40 #   include <net/pfilt.h>
  41 #  endif
  42 # endif
  43
  44 #include <netinet/in_systm.h>
  45 #include "includes/netinet/ip.h"
  46 #include "includes/netinet/udp.h"
  47 #include "includes/netinet/if_ether.h"
  48 #endif
  49
  50 /* Reinitializes the specified interface after an address change.   This
  51    is not required for packet-filter APIs. */
  52
  53 #ifdef USE_BPF_SEND
  54 void if_reinitialize_send (info)
  55         struct interface_info *info;
  56 {
  57 }
  58 #endif
  59
  60 #ifdef USE_BPF_RECEIVE
  61 void if_reinitialize_receive (info)
  62         struct interface_info *info;
  63 {
  64 }
  65 #endif
  66
  67 /* Called by get_interface_list for each interface that's discovered.
  68    Opens a packet filter for each interface and adds it to the select
  69    mask. */
  70
  71 #if defined (USE_BPF_SEND) || defined (USE_BPF_RECEIVE)
  72 int if_register_bpf (info)
  73         struct interface_info *info;
  74 {
  75         int sock;
  76         char filename[50];
  77         int b;
  78
  79         /* Open a BPF device */
  80         for (b = 0; 1; b++) {
  81 #ifndef NO_SNPRINTF
  82                 snprintf(filename, sizeof(filename), BPF_FORMAT, b);
  83 #else
  84                 sprintf(filename, BPF_FORMAT, b);
  85 #endif
  86                 sock = open (filename, O_RDWR, 0);
  87                 if (sock < 0) {
  88                         if (errno == EBUSY) {
  89                                 continue;
  90                         } else {
  91                                 if (!b)
  92                                         log_fatal ("No bpf devices.%s%s%s",
  93                                                "   Please read the README",
  94                                                " section for your operating",
  95                                                " system.");
  96                                 log_fatal ("Can't find free bpf: %m");
  97                         }
  98                 } else {
  99                         break;
 100                 }
 101         }
 102
 103         /* Set the BPF device to point at this interface. */
 104         if (ioctl (sock, BIOCSETIF, info -> ifp) < 0)
 105                 log_fatal ("Can't attach interface %s to bpf device %s: %m",
 106                        info -> name, filename);
 107
 108         return sock;
 109 }
 110 #endif /* USE_BPF_SEND || USE_BPF_RECEIVE */
 111
 112 #ifdef USE_BPF_SEND
 113 void if_register_send (info)
 114         struct interface_info *info;
 115 {
 116         /* If we're using the bpf API for sending and receiving,
 117            we don't need to register this interface twice. */
 118 #ifndef USE_BPF_RECEIVE
 119         info -> wfdesc = if_register_bpf (info, interface);
 120 #else
 121         info -> wfdesc = info -> rfdesc;
 122 #endif
 123         if (!quiet_interface_discovery)
 124                 log_info ("Sending on   BPF/%s/%s%s%s",
 125                       info -> name,
 126                       print_hw_addr (info -> hw_address.htype,
 127                                      info -> hw_address.hlen,
 128                                      info -> hw_address.haddr),
 129                       (info -> shared_network ? "/" : ""),
 130                       (info -> shared_network ?
 131                        info -> shared_network -> name : ""));
 132 }
 133 #endif /* USE_BPF_SEND */
 134
 135 #if defined (USE_BPF_RECEIVE) || defined (USE_LPF_RECEIVE)
 136 /* Packet filter program...
 137    XXX Changes to the filter program may require changes to the constant
 138    offsets used in if_register_send to patch the BPF program! XXX */
 139
 140 struct bpf_insn dhcp_bpf_filter [] = {
 141         /* Make sure this is an IP packet... */
 142         BPF_STMT (BPF_LD + BPF_H + BPF_ABS, 12),
 143         BPF_JUMP (BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
 144
 145         /* Make sure it's a UDP packet... */
 146         BPF_STMT (BPF_LD + BPF_B + BPF_ABS, 23),
 147         BPF_JUMP (BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
 148
 149         /* Make sure this isn't a fragment... */
 150         BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20),
 151         BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
 152
 153         /* Get the IP header length... */
 154         BPF_STMT (BPF_LDX + BPF_B + BPF_MSH, 14),
 155
 156         /* Make sure it's to the right port... */
 157         BPF_STMT (BPF_LD + BPF_H + BPF_IND, 16),
 158         BPF_JUMP (BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1),             /* patch */
 159
 160         /* If we passed all the tests, ask for the whole packet. */
 161         BPF_STMT(BPF_RET+BPF_K, (u_int)-1),
 162
 163         /* Otherwise, drop it. */
 164         BPF_STMT(BPF_RET+BPF_K, 0),
 165 };
 166
 167 int dhcp_bpf_filter_len = sizeof dhcp_bpf_filter / sizeof (struct bpf_insn);
 168 #endif
 169
 170 #if defined (USE_BPF_RECEIVE)
 171 void if_register_receive (info)
 172         struct interface_info *info;
 173 {
 174         int flag = 1;
 175         struct bpf_version v;
 176         u_int32_t addr;
 177         struct bpf_program p;
 178         u_int32_t bits;
 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) < 0)
 185                 log_fatal ("Can't get BPF version: %m");
 186
 187         if (v.bv_major != BPF_MAJOR_VERSION ||
 188             v.bv_minor < BPF_MINOR_VERSION)
 189                 log_fatal ("Kernel BPF version out of range - recompile dhcpd!");
 190
 191         /* Set immediate mode so that reads return as soon as a packet
 192            comes in, rather than waiting for the input buffer to fill with
 193            packets. */
 194         if (ioctl (info -> rfdesc, BIOCIMMEDIATE, &flag) < 0)
 195                 log_fatal ("Can't set immediate mode on bpf device: %m");
 196
 197 #ifdef NEED_OSF_PFILT_HACKS
 198         /* Allow the copyall flag to be set... */
 199         if (ioctl(info -> rfdesc, EIOCALLOWCOPYALL, &flag) < 0)
 200                 log_fatal ("Can't set ALLOWCOPYALL: %m");
 201
 202         /* Clear all the packet filter mode bits first... */
 203         bits = 0;
 204         if (ioctl (info -> rfdesc, EIOCMBIS, &bits) < 0)
 205                 log_fatal ("Can't clear pfilt bits: %m");
 206
 207         /* Set the ENBATCH, ENCOPYALL, ENBPFHDR bits... */
 208         bits = ENBATCH | ENCOPYALL | ENBPFHDR;
 209         if (ioctl (info -> rfdesc, EIOCMBIS, &bits) < 0)
 210                 log_fatal ("Can't set ENBATCH|ENCOPYALL|ENBPFHDR: %m");
 211 #endif
 212         /* Get the required BPF buffer length from the kernel. */
 213         if (ioctl (info -> rfdesc, BIOCGBLEN, &info -> rbuf_max) < 0)
 214                 log_fatal ("Can't get bpf buffer length: %m");
 215         info -> rbuf = malloc (info -> rbuf_max);
 216         if (!info -> rbuf)
 217                 log_fatal ("Can't allocate %d bytes for bpf input buffer.");
 218         info -> rbuf_offset = 0;
 219         info -> rbuf_len = 0;
 220
 221         /* Set up the bpf filter program structure. */
 222         p.bf_len = dhcp_bpf_filter_len;
 223         p.bf_insns = dhcp_bpf_filter;
 224
 225         /* Patch the server port into the BPF  program...
 226            XXX changes to filter program may require changes
 227            to the insn number(s) used below! XXX */
 228         dhcp_bpf_filter [8].k = ntohs (local_port);
 229
 230         if (ioctl (info -> rfdesc, BIOCSETF, &p) < 0)
 231                 log_fatal ("Can't install packet filter program: %m");
 232         if (!quiet_interface_discovery)
 233                 log_info ("Listening on BPF/%s/%s%s%s",
 234                       info -> name,
 235                       print_hw_addr (info -> hw_address.htype,
 236                                      info -> hw_address.hlen,
 237                                      info -> hw_address.haddr),
 238                       (info -> shared_network ? "/" : ""),
 239                       (info -> shared_network ?
 240                        info -> shared_network -> name : ""));
 241 }
 242 #endif /* USE_BPF_RECEIVE */
 243
 244 #ifdef USE_BPF_SEND
 245 ssize_t send_packet (interface, packet, raw, len, from, to, hto)
 246         struct interface_info *interface;
 247         struct packet *packet;
 248         struct dhcp_packet *raw;
 249         size_t len;
 250         struct in_addr from;
 251         struct sockaddr_in *to;
 252         struct hardware *hto;
 253 {
 254         int bufp = 0;
 255         unsigned char buf [256];
 256         struct iovec iov [2];
 257         int result;
 258
 259         if (!strcmp (interface -> name, "fallback"))
 260                 return send_fallback (interface, packet, raw,
 261                                       len, from, to, hto);
 262
 263         /* Assemble the headers... */
 264         assemble_hw_header (interface, buf, &bufp, hto);
 265         assemble_udp_ip_header (interface, buf, &bufp, from.s_addr,
 266                                 to -> sin_addr.s_addr, to -> sin_port,
 267                                 (unsigned char *)raw, len);
 268
 269         /* Fire it off */
 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;
 274
 275         result = writev(interface -> wfdesc, iov, 2);
 276         if (result < 0)
 277                 warn ("send_packet: %m");
 278         return result;
 279 }
 280 #endif /* USE_BPF_SEND */
 281
 282 #ifdef USE_BPF_RECEIVE
 283 ssize_t receive_packet (interface, buf, len, from, hfrom)
 284         struct interface_info *interface;
 285         unsigned char *buf;
 286         size_t len;
 287         struct sockaddr_in *from;
 288         struct hardware *hfrom;
 289 {
 290         int length = 0;
 291         int offset = 0;
 292         struct bpf_hdr hdr;
 293
 294         /* All this complexity is because BPF doesn't guarantee
 295            that only one packet will be returned at a time.   We're
 296            getting what we deserve, though - this is a terrible abuse
 297            of the BPF interface.   Sigh. */
 298
 299         /* Process packets until we get one we can return or until we've
 300            done a read and gotten nothing we can return... */
 301
 302         do {
 303                 /* If the buffer is empty, fill it. */
 304                 if (interface -> rbuf_offset == interface -> rbuf_len) {
 305                         length = read (interface -> rfdesc,
 306                                        interface -> rbuf,
 307                                        interface -> rbuf_max);
 308                         if (length <= 0)
 309                                 return length;
 310                         interface -> rbuf_offset = 0;
 311                         interface -> rbuf_len = length;
 312                 }
 313
 314                 /* If there isn't room for a whole bpf header, something went
 315                    wrong, but we'll ignore it and hope it goes away... XXX */
 316                 if (interface -> rbuf_len -
 317                     interface -> rbuf_offset < sizeof hdr) {
 318                         interface -> rbuf_offset = interface -> rbuf_len;
 319                         continue;
 320                 }
 321
 322                 /* Copy out a bpf header... */
 323                 memcpy (&hdr, &interface -> rbuf [interface -> rbuf_offset],
 324                         sizeof hdr);
 325
 326                 /* If the bpf header plus data doesn't fit in what's left
 327                    of the buffer, stick head in sand yet again... */
 328                 if (interface -> rbuf_offset +
 329                     hdr.bh_hdrlen + hdr.bh_caplen > interface -> rbuf_len) {
 330                         interface -> rbuf_offset = interface -> rbuf_len;
 331                         continue;
 332                 }
 333
 334                 /* If the captured data wasn't the whole packet, or if
 335                    the packet won't fit in the input buffer, all we
 336                    can do is drop it. */
 337                 if (hdr.bh_caplen != hdr.bh_datalen) {
 338                         interface -> rbuf_offset +=
 339                                 hdr.bh_hdrlen = hdr.bh_caplen;
 340                         continue;
 341                 }
 342
 343                 /* Skip over the BPF header... */
 344                 interface -> rbuf_offset += hdr.bh_hdrlen;
 345
 346                 /* Decode the physical header... */
 347                 offset = decode_hw_header (interface,
 348                                            interface -> rbuf,
 349                                            interface -> rbuf_offset,
 350                                            hfrom);
 351
 352                 /* If a physical layer checksum failed (dunno of any
 353                    physical layer that supports this, but WTH), skip this
 354                    packet. */
 355                 if (offset < 0) {
 356                         interface -> rbuf_offset += hdr.bh_caplen;
 357                         continue;
 358                 }
 359                 interface -> rbuf_offset += offset;
 360                 hdr.bh_caplen -= offset;
 361
 362                 /* Decode the IP and UDP headers... */
 363                 offset = decode_udp_ip_header (interface,
 364                                                interface -> rbuf,
 365                                                interface -> rbuf_offset,
 366                                                from,
 367                                                (unsigned char *)0,
 368                                                hdr.bh_caplen);
 369
 370                 /* If the IP or UDP checksum was bad, skip the packet... */
 371                 if (offset < 0) {
 372                         interface -> rbuf_offset += hdr.bh_caplen;
 373                         continue;
 374                 }
 375                 interface -> rbuf_offset += offset;
 376                 hdr.bh_caplen -= offset;
 377
 378                 /* If there's not enough room to stash the packet data,
 379                    we have to skip it (this shouldn't happen in real
 380                    life, though). */
 381                 if (hdr.bh_caplen > len) {
 382                         interface -> rbuf_offset += hdr.bh_caplen;
 383                         continue;
 384                 }
 385
 386                 /* Copy out the data in the packet... */
 387                 memcpy (buf, interface -> rbuf + interface -> rbuf_offset,
 388                         hdr.bh_caplen);
 389                 interface -> rbuf_offset += hdr.bh_caplen;
 390                 return hdr.bh_caplen;
 391         } while (!length);
 392         return 0;
 393 }
 394
 395 int can_unicast_without_arp (ip)
 396         struct interface_info *ip;
 397 {
 398         return 1;
 399 }
 400
 401 int can_receive_unicast_unconfigured (ip)
 402         struct interface_info *ip;
 403 {
 404         return 1;
 405 }
 406
 407 void maybe_setup_fallback ()
 408 {
 409         struct interface_info *fbi;
 410         fbi = setup_fallback ();
 411         if (fbi) {
 412                 if_register_fallback (fbi);
 413                 add_protocol ("fallback", fallback_interface -> wfdesc,
 414                               fallback_discard, fallback_interface);
 415         }
 416 }
 417 #endif