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pcap-linux.c

/*
 *  pcap-linux.c: Packet capture interface to the Linux kernel
 *
 *  Copyright (c) 2000 Torsten Landschoff <torsten@debian.org>
 *                 Sebastian Krahmer  <krahmer@cs.uni-potsdam.de>
 *
 *  License: BSD
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in
 *     the documentation and/or other materials provided with the
 *     distribution.
 *  3. The names of the authors may not be used to endorse or promote
 *     products derived from this software without specific prior
 *     written permission.
 *
 *  THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 *  IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 *  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#ifndef lint
static const char rcsid[] _U_ =
    "@(#) $Header: /CVS/nmap/libpcap-possiblymodified/pcap-linux.c,v 1.6 2004/08/01 05:34:47 fyodor Exp $ (LBL)";
#endif

/*
 * Known problems with 2.0[.x] kernels:
 *
 *   - The loopback device gives every packet twice; on 2.2[.x] kernels,
 *     if we use PF_PACKET, we can filter out the transmitted version
 *     of the packet by using data in the "sockaddr_ll" returned by
 *     "recvfrom()", but, on 2.0[.x] kernels, we have to use
 *     PF_INET/SOCK_PACKET, which means "recvfrom()" supplies a
 *     "sockaddr_pkt" which doesn't give us enough information to let
 *     us do that.
 *
 *   - We have to set the interface's IFF_PROMISC flag ourselves, if
 *     we're to run in promiscuous mode, which means we have to turn
 *     it off ourselves when we're done; the kernel doesn't keep track
 *     of how many sockets are listening promiscuously, which means
 *     it won't get turned off automatically when no sockets are
 *     listening promiscuously.  We catch "pcap_close()" and, for
 *     interfaces we put into promiscuous mode, take them out of
 *     promiscuous mode - which isn't necessarily the right thing to
 *     do, if another socket also requested promiscuous mode between
 *     the time when we opened the socket and the time when we close
 *     the socket.
 *
 *   - MSG_TRUNC isn't supported, so you can't specify that "recvfrom()"
 *     return the amount of data that you could have read, rather than
 *     the amount that was returned, so we can't just allocate a buffer
 *     whose size is the snapshot length and pass the snapshot length
 *     as the byte count, and also pass MSG_TRUNC, so that the return
 *     value tells us how long the packet was on the wire.
 *
 *     This means that, if we want to get the actual size of the packet,
 *     so we can return it in the "len" field of the packet header,
 *     we have to read the entire packet, not just the part that fits
 *     within the snapshot length, and thus waste CPU time copying data
 *     from the kernel that our caller won't see.
 *
 *     We have to get the actual size, and supply it in "len", because
 *     otherwise, the IP dissector in tcpdump, for example, will complain
 *     about "truncated-ip", as the packet will appear to have been
 *     shorter, on the wire, than the IP header said it should have been.
 */


#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "pcap-int.h"
#include "sll.h"

#ifdef HAVE_DAG_API
#include "pcap-dag.h"
#endif /* HAVE_DAG_API */
        
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/utsname.h>
#include <net/if.h>
#include <netinet/in.h>
#include <linux/if_ether.h>
#include <net/if_arp.h>
#include <assert.h>

/*
 * If PF_PACKET is defined, we can use {SOCK_RAW,SOCK_DGRAM}/PF_PACKET
 * sockets rather than SOCK_PACKET sockets.
 *
 * To use them, we include <linux/if_packet.h> rather than
 * <netpacket/packet.h>; we do so because
 *
 *    some Linux distributions (e.g., Slackware 4.0) have 2.2 or
 *    later kernels and libc5, and don't provide a <netpacket/packet.h>
 *    file;
 *
 *    not all versions of glibc2 have a <netpacket/packet.h> file
 *    that defines stuff needed for some of the 2.4-or-later-kernel
 *    features, so if the system has a 2.4 or later kernel, we
 *    still can't use those features.
 *
 * We're already including a number of other <linux/XXX.h> headers, and
 * this code is Linux-specific (no other OS has PF_PACKET sockets as
 * a raw packet capture mechanism), so it's not as if you gain any
 * useful portability by using <netpacket/packet.h>
 *
 * XXX - should we just include <linux/if_packet.h> even if PF_PACKET
 * isn't defined?  It only defines one data structure in 2.0.x, so
 * it shouldn't cause any problems.
 */
#ifdef PF_PACKET
# include <linux/if_packet.h>

 /*
  * On at least some Linux distributions (for example, Red Hat 5.2),
  * there's no <netpacket/packet.h> file, but PF_PACKET is defined if
  * you include <sys/socket.h>, but <linux/if_packet.h> doesn't define
  * any of the PF_PACKET stuff such as "struct sockaddr_ll" or any of
  * the PACKET_xxx stuff.
  *
  * So we check whether PACKET_HOST is defined, and assume that we have
  * PF_PACKET sockets only if it is defined.
  */
# ifdef PACKET_HOST
#  define HAVE_PF_PACKET_SOCKETS
# endif /* PACKET_HOST */
#endif /* PF_PACKET */

#ifdef SO_ATTACH_FILTER
#include <linux/types.h>
#include <linux/filter.h>
#endif

#ifndef __GLIBC__
typedef int       socklen_t;
#endif

#ifndef MSG_TRUNC
/*
 * This is being compiled on a system that lacks MSG_TRUNC; define it
 * with the value it has in the 2.2 and later kernels, so that, on
 * those kernels, when we pass it in the flags argument to "recvfrom()"
 * we're passing the right value and thus get the MSG_TRUNC behavior
 * we want.  (We don't get that behavior on 2.0[.x] kernels, because
 * they didn't support MSG_TRUNC.)
 */
#define MSG_TRUNC 0x20
#endif

#ifndef SOL_PACKET
/*
 * This is being compiled on a system that lacks SOL_PACKET; define it
 * with the value it has in the 2.2 and later kernels, so that we can
 * set promiscuous mode in the good modern way rather than the old
 * 2.0-kernel crappy way.
 */
#define SOL_PACKET      263
#endif

#define MAX_LINKHEADER_SIZE   256

/*
 * When capturing on all interfaces we use this as the buffer size.
 * Should be bigger then all MTUs that occur in real life.
 * 64kB should be enough for now.
 */
#define BIGGER_THAN_ALL_MTUS  (64*1024)

/*
 * Prototypes for internal functions
 */
static void map_arphrd_to_dlt(pcap_t *, int, int);
static int live_open_old(pcap_t *, const char *, int, int, char *);
static int live_open_new(pcap_t *, const char *, int, int, char *);
static int pcap_read_linux(pcap_t *, int, pcap_handler, u_char *);
static int pcap_read_packet(pcap_t *, pcap_handler, u_char *);
static int pcap_stats_linux(pcap_t *, struct pcap_stat *);
static int pcap_setfilter_linux(pcap_t *, struct bpf_program *);
static void pcap_close_linux(pcap_t *);

/*
 * Wrap some ioctl calls
 */
#ifdef HAVE_PF_PACKET_SOCKETS
static int  iface_get_id(int fd, const char *device, char *ebuf);
#endif
static int  iface_get_mtu(int fd, const char *device, char *ebuf);
static int  iface_get_arptype(int fd, const char *device, char *ebuf);
#ifdef HAVE_PF_PACKET_SOCKETS
static int  iface_bind(int fd, int ifindex, char *ebuf);
#endif
static int  iface_bind_old(int fd, const char *device, char *ebuf);

#ifdef SO_ATTACH_FILTER
static int  fix_program(pcap_t *handle, struct sock_fprog *fcode);
static int  fix_offset(struct bpf_insn *p);
static int  set_kernel_filter(pcap_t *handle, struct sock_fprog *fcode);
static int  reset_kernel_filter(pcap_t *handle);

static struct sock_filter     total_insn
      = BPF_STMT(BPF_RET | BPF_K, 0);
static struct sock_fprog      total_fcode
      = { 1, &total_insn };
#endif

/*
 *  Get a handle for a live capture from the given device. You can
 *  pass NULL as device to get all packages (without link level
 *  information of course). If you pass 1 as promisc the interface
 *  will be set to promiscous mode (XXX: I think this usage should
 *  be deprecated and functions be added to select that later allow
 *  modification of that values -- Torsten).
 *
 *  See also pcap(3).
 */
pcap_t *
pcap_open_live(const char *device, int snaplen, int promisc, int to_ms,
    char *ebuf)
{
      pcap_t            *handle;
      int         mtu;
      int         err;
      int         live_open_ok = 0;
      struct utsname    utsname;

#ifdef HAVE_DAG_API
      if (strstr(device, "dag")) {
            return dag_open_live(device, snaplen, promisc, to_ms, ebuf);
      }
#endif /* HAVE_DAG_API */

        /* Allocate a handle for this session. */

      handle = malloc(sizeof(*handle));
      if (handle == NULL) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE, "malloc: %s",
                   pcap_strerror(errno));
            return NULL;
      }

      /* Initialize some components of the pcap structure. */

      memset(handle, 0, sizeof(*handle));
      handle->snapshot  = snaplen;
      handle->md.timeout      = to_ms;

      /*
       * NULL and "any" are special devices which give us the hint to
       * monitor all devices.
       */
      if (!device || strcmp(device, "any") == 0) {
            device                  = NULL;
            handle->md.device = strdup("any");
            if (promisc) {
                  promisc = 0;
                  /* Just a warning. */
                  snprintf(ebuf, PCAP_ERRBUF_SIZE,
                      "Promiscuous mode not supported on the \"any\" device");
            }

      } else
            handle->md.device = strdup(device);

      if (handle->md.device == NULL) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE, "strdup: %s",
                   pcap_strerror(errno) );
            free(handle);
            return NULL;
      }

      /*
       * Current Linux kernels use the protocol family PF_PACKET to
       * allow direct access to all packets on the network while
       * older kernels had a special socket type SOCK_PACKET to
       * implement this feature.
       * While this old implementation is kind of obsolete we need
       * to be compatible with older kernels for a while so we are
       * trying both methods with the newer method preferred.
       */

      if ((err = live_open_new(handle, device, promisc, to_ms, ebuf)) == 1)
            live_open_ok = 1;
      else if (err == 0) {
            /* Non-fatal error; try old way */
            if (live_open_old(handle, device, promisc, to_ms, ebuf))
                  live_open_ok = 1;
      }
      if (!live_open_ok) {
            /*
             * Both methods to open the packet socket failed. Tidy
             * up and report our failure (ebuf is expected to be
             * set by the functions above).
             */

            if (handle->md.device != NULL)
                  free(handle->md.device);
            free(handle);
            return NULL;
      }

      /*
       * Compute the buffer size.
       *
       * If we're using SOCK_PACKET, this might be a 2.0[.x] kernel,
       * and might require special handling - check.
       */
      if (handle->md.sock_packet && (uname(&utsname) < 0 ||
          strncmp(utsname.release, "2.0", 3) == 0)) {
            /*
             * We're using a SOCK_PACKET structure, and either
             * we couldn't find out what kernel release this is,
             * or it's a 2.0[.x] kernel.
             *
             * In the 2.0[.x] kernel, a "recvfrom()" on
             * a SOCK_PACKET socket, with MSG_TRUNC set, will
             * return the number of bytes read, so if we pass
             * a length based on the snapshot length, it'll
             * return the number of bytes from the packet
             * copied to userland, not the actual length
             * of the packet.
             *
             * This means that, for example, the IP dissector
             * in tcpdump will get handed a packet length less
             * than the length in the IP header, and will
             * complain about "truncated-ip".
             *
             * So we don't bother trying to copy from the
             * kernel only the bytes in which we're interested,
             * but instead copy them all, just as the older
             * versions of libpcap for Linux did.
             *
             * The buffer therefore needs to be big enough to
             * hold the largest packet we can get from this
             * device.  Unfortunately, we can't get the MRU
             * of the network; we can only get the MTU.  The
             * MTU may be too small, in which case a packet larger
             * than the buffer size will be truncated *and* we
             * won't get the actual packet size.
             *
             * However, if the snapshot length is larger than
             * the buffer size based on the MTU, we use the
             * snapshot length as the buffer size, instead;
             * this means that with a sufficiently large snapshot
             * length we won't artificially truncate packets
             * to the MTU-based size.
             *
             * This mess just one of many problems with packet
             * capture on 2.0[.x] kernels; you really want a
             * 2.2[.x] or later kernel if you want packet capture
             * to work well.
             */
            mtu = iface_get_mtu(handle->fd, device, ebuf);
            if (mtu == -1) {
                  pcap_close_linux(handle);
                  free(handle);
                  return NULL;
            }
            handle->bufsize = MAX_LINKHEADER_SIZE + mtu;
            if (handle->bufsize < handle->snapshot)
                  handle->bufsize = handle->snapshot;
      } else {
            /*
             * This is a 2.2[.x] or later kernel (we know that
             * either because we're not using a SOCK_PACKET
             * socket - PF_PACKET is supported only in 2.2
             * and later kernels - or because we checked the
             * kernel version).
             *
             * We can safely pass "recvfrom()" a byte count
             * based on the snapshot length.
             */
            handle->bufsize = handle->snapshot;
      }

      /* Allocate the buffer */

      handle->buffer     = malloc(handle->bufsize + handle->offset);
      if (!handle->buffer) {
              snprintf(ebuf, PCAP_ERRBUF_SIZE,
                   "malloc: %s", pcap_strerror(errno));
            pcap_close_linux(handle);
            free(handle);
            return NULL;
      }

      /*
       * "handle->fd" is a socket, so "select()" and "poll()"
       * should work on it.
       */
      handle->selectable_fd = handle->fd;

      handle->read_op = pcap_read_linux;
      handle->setfilter_op = pcap_setfilter_linux;
      handle->set_datalink_op = NULL;     /* can't change data link type */
      handle->getnonblock_op = pcap_getnonblock_fd;
      handle->setnonblock_op = pcap_setnonblock_fd;
      handle->stats_op = pcap_stats_linux;
      handle->close_op = pcap_close_linux;

      return handle;
}

/*
 *  Read at most max_packets from the capture stream and call the callback
 *  for each of them. Returns the number of packets handled or -1 if an
 *  error occured.
 */
static int
pcap_read_linux(pcap_t *handle, int max_packets, pcap_handler callback, u_char *user)
{
      /*
       * Currently, on Linux only one packet is delivered per read,
       * so we don't loop.
       */
      return pcap_read_packet(handle, callback, user);
}

/*
 *  Read a packet from the socket calling the handler provided by
 *  the user. Returns the number of packets received or -1 if an
 *  error occured.
 */
static int
pcap_read_packet(pcap_t *handle, pcap_handler callback, u_char *userdata)
{
      u_char                  *bp;
      int               offset;
#ifdef HAVE_PF_PACKET_SOCKETS
      struct sockaddr_ll      from;
      struct sll_header *hdrp;
#else
      struct sockaddr         from;
#endif
      socklen_t         fromlen;
      int               packet_len, caplen;
      struct pcap_pkthdr      pcap_header;

#ifdef HAVE_PF_PACKET_SOCKETS
      /*
       * If this is a cooked device, leave extra room for a
       * fake packet header.
       */
      if (handle->md.cooked)
            offset = SLL_HDR_LEN;
      else
            offset = 0;
#else
      /*
       * This system doesn't have PF_PACKET sockets, so it doesn't
       * support cooked devices.
       */
      offset = 0;
#endif

      /* Receive a single packet from the kernel */

      bp = handle->buffer + handle->offset;
      do {
            /*
             * Has "pcap_breakloop()" been called?
             */
            if (handle->break_loop) {
                  /*
                   * Yes - clear the flag that indicates that it
                   * has, and return -2 as an indication that we
                   * were told to break out of the loop.
                   */
                  handle->break_loop = 0;
                  return -2;
            }
            fromlen = sizeof(from);
            /* If the user specified a timeout in pcap_open_live(),
               we will honor the timeout and return even if no packets
               have arrived */
            if (handle->md.timeout > 0) {
              fd_set readfs;
              struct timeval tv;
                  int res;
              
                  FD_ZERO(&readfs);
                  FD_SET(handle->fd, &readfs);
                  bzero((void *) &tv, sizeof(tv));
                  tv.tv_sec = handle->md.timeout / 1000;
                  tv.tv_usec = (handle->md.timeout % 1000 ) * 1000;
                  do {
                /* since this is in pcap-linux.c, we can assume
                   Linux select() behavior WRT decrementing tv */
                    res = select(handle->fd + 1, &readfs, NULL, NULL, &tv);
                if (res == 1) break;
                if (res == 0) return 0;
                assert(res == -1);
                if (errno == EINTR) continue;
                snprintf(handle->errbuf, sizeof(handle->errbuf), "select: %s", pcap_strerror(errno));
                return -1;
              } while (1);
            }
            
            packet_len = recvfrom(
                  handle->fd, bp + offset,
                  handle->bufsize - offset, MSG_TRUNC,
                  (struct sockaddr *) &from, &fromlen);
      } while (packet_len == -1 && errno == EINTR);

      /* Check if an error occured */

      if (packet_len == -1) {
            if (errno == EAGAIN)
                  return 0;   /* no packet there */
            else {
                  snprintf(handle->errbuf, sizeof(handle->errbuf),
                         "recvfrom: %s", pcap_strerror(errno));
                  return -1;
            }
      }

#ifdef HAVE_PF_PACKET_SOCKETS
      /*
       * If this is from the loopback device, reject outgoing packets;
       * we'll see the packet as an incoming packet as well, and
       * we don't want to see it twice.
       *
       * We can only do this if we're using PF_PACKET; the address
       * returned for SOCK_PACKET is a "sockaddr_pkt" which lacks
       * the relevant packet type information.
       */
      if (!handle->md.sock_packet &&
          from.sll_ifindex == handle->md.lo_ifindex &&
          from.sll_pkttype == PACKET_OUTGOING)
            return 0;
#endif

#ifdef HAVE_PF_PACKET_SOCKETS
      /*
       * If this is a cooked device, fill in the fake packet header.
       */
      if (handle->md.cooked) {
            /*
             * Add the length of the fake header to the length
             * of packet data we read.
             */
            packet_len += SLL_HDR_LEN;

            hdrp = (struct sll_header *)bp;

            /*
             * Map the PACKET_ value to a LINUX_SLL_ value; we
             * want the same numerical value to be used in
             * the link-layer header even if the numerical values
             * for the PACKET_ #defines change, so that programs
             * that look at the packet type field will always be
             * able to handle DLT_LINUX_SLL captures.
             */
            switch (from.sll_pkttype) {

            case PACKET_HOST:
                  hdrp->sll_pkttype = htons(LINUX_SLL_HOST);
                  break;

            case PACKET_BROADCAST:
                  hdrp->sll_pkttype = htons(LINUX_SLL_BROADCAST);
                  break;

            case PACKET_MULTICAST:
                  hdrp->sll_pkttype = htons(LINUX_SLL_MULTICAST);
                  break;

            case PACKET_OTHERHOST:
                  hdrp->sll_pkttype = htons(LINUX_SLL_OTHERHOST);
                  break;

            case PACKET_OUTGOING:
                  hdrp->sll_pkttype = htons(LINUX_SLL_OUTGOING);
                  break;

            default:
                  hdrp->sll_pkttype = -1;
                  break;
            }

            hdrp->sll_hatype = htons(from.sll_hatype);
            hdrp->sll_halen = htons(from.sll_halen);
            memcpy(hdrp->sll_addr, from.sll_addr,
                (from.sll_halen > SLL_ADDRLEN) ?
                  SLL_ADDRLEN :
                  from.sll_halen);
            hdrp->sll_protocol = from.sll_protocol;
      }
#endif

      /*
       * XXX: According to the kernel source we should get the real
       * packet len if calling recvfrom with MSG_TRUNC set. It does
       * not seem to work here :(, but it is supported by this code
       * anyway.
       * To be honest the code RELIES on that feature so this is really
       * broken with 2.2.x kernels.
       * I spend a day to figure out what's going on and I found out
       * that the following is happening:
       *
       * The packet comes from a random interface and the packet_rcv
       * hook is called with a clone of the packet. That code inserts
       * the packet into the receive queue of the packet socket.
       * If a filter is attached to that socket that filter is run
       * first - and there lies the problem. The default filter always
       * cuts the packet at the snaplen:
       *
       * # tcpdump -d
       * (000) ret      #68
       *
       * So the packet filter cuts down the packet. The recvfrom call
       * says "hey, it's only 68 bytes, it fits into the buffer" with
       * the result that we don't get the real packet length. This
       * is valid at least until kernel 2.2.17pre6.
       *
       * We currently handle this by making a copy of the filter
       * program, fixing all "ret" instructions with non-zero
       * operands to have an operand of 65535 so that the filter
       * doesn't truncate the packet, and supplying that modified
       * filter to the kernel.
       */

      caplen = packet_len;
      if (caplen > handle->snapshot)
            caplen = handle->snapshot;

      /* Run the packet filter if not using kernel filter */
      if (!handle->md.use_bpf && handle->fcode.bf_insns) {
            if (bpf_filter(handle->fcode.bf_insns, bp,
                            packet_len, caplen) == 0)
            {
                  /* rejected by filter */
                  return 0;
            }
      }

      /* Fill in our own header data */

      if (ioctl(handle->fd, SIOCGSTAMP, &pcap_header.ts) == -1) {
            snprintf(handle->errbuf, sizeof(handle->errbuf),
                   "ioctl: %s", pcap_strerror(errno));
            return -1;
      }
      pcap_header.caplen      = caplen;
      pcap_header.len         = packet_len;

      /*
       * Count the packet.
       *
       * Arguably, we should count them before we check the filter,
       * as on many other platforms "ps_recv" counts packets
       * handed to the filter rather than packets that passed
       * the filter, but if filtering is done in the kernel, we
       * can't get a count of packets that passed the filter,
       * and that would mean the meaning of "ps_recv" wouldn't
       * be the same on all Linux systems.
       *
       * XXX - it's not the same on all systems in any case;
       * ideally, we should have a "get the statistics" call
       * that supplies more counts and indicates which of them
       * it supplies, so that we supply a count of packets
       * handed to the filter only on platforms where that
       * information is available.
       *
       * We count them here even if we can get the packet count
       * from the kernel, as we can only determine at run time
       * whether we'll be able to get it from the kernel (if
       * HAVE_TPACKET_STATS isn't defined, we can't get it from
       * the kernel, but if it is defined, the library might
       * have been built with a 2.4 or later kernel, but we
       * might be running on a 2.2[.x] kernel without Alexey
       * Kuznetzov's turbopacket patches, and thus the kernel
       * might not be able to supply those statistics).  We
       * could, I guess, try, when opening the socket, to get
       * the statistics, and if we can not increment the count
       * here, but it's not clear that always incrementing
       * the count is more expensive than always testing a flag
       * in memory.
       */
      handle->md.stat.ps_recv++;

      /* Call the user supplied callback function */
      callback(userdata, &pcap_header, bp);

      return 1;
}

/*
 *  Get the statistics for the given packet capture handle.
 *  Reports the number of dropped packets iff the kernel supports
 *  the PACKET_STATISTICS "getsockopt()" argument (2.4 and later
 *  kernels, and 2.2[.x] kernels with Alexey Kuznetzov's turbopacket
 *  patches); otherwise, that information isn't available, and we lie
 *  and report 0 as the count of dropped packets.
 */
static int
pcap_stats_linux(pcap_t *handle, struct pcap_stat *stats)
{
#ifdef HAVE_TPACKET_STATS
      struct tpacket_stats kstats;
      socklen_t len = sizeof (struct tpacket_stats);
#endif

#ifdef HAVE_TPACKET_STATS
      /*
       * Try to get the packet counts from the kernel.
       */
      if (getsockopt(handle->fd, SOL_PACKET, PACKET_STATISTICS,
                  &kstats, &len) > -1) {
            /*
             * In "linux/net/packet/af_packet.c", at least in the
             * 2.4.9 kernel, "tp_packets" is incremented for every
             * packet that passes the packet filter *and* is
             * successfully queued on the socket; "tp_drops" is
             * incremented for every packet dropped because there's
             * not enough free space in the socket buffer.
             *
             * When the statistics are returned for a PACKET_STATISTICS
             * "getsockopt()" call, "tp_drops" is added to "tp_packets",
             * so that "tp_packets" counts all packets handed to
             * the PF_PACKET socket, including packets dropped because
             * there wasn't room on the socket buffer - but not
             * including packets that didn't pass the filter.
             *
             * In the BSD BPF, the count of received packets is
             * incremented for every packet handed to BPF, regardless
             * of whether it passed the filter.
             *
             * We can't make "pcap_stats()" work the same on both
             * platforms, but the best approximation is to return
             * "tp_packets" as the count of packets and "tp_drops"
             * as the count of drops.
             */
            handle->md.stat.ps_recv = kstats.tp_packets;
            handle->md.stat.ps_drop = kstats.tp_drops;
      }
      else
      {
            /*
             * If the error was EOPNOTSUPP, fall through, so that
             * if you build the library on a system with
             * "struct tpacket_stats" and run it on a system
             * that doesn't, it works as it does if the library
             * is built on a system without "struct tpacket_stats".
             */
            if (errno != EOPNOTSUPP) {
                  snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                      "pcap_stats: %s", pcap_strerror(errno));
                  return -1;
            }
      }
#endif
      /*
       * On systems where the PACKET_STATISTICS "getsockopt()" argument
       * is supported on PF_PACKET sockets:
       *
       *    "ps_recv" counts only packets that *passed* the filter,
       *    not packets that didn't pass the filter.  This includes
       *    packets later dropped because we ran out of buffer space.
       *
       *    "ps_drop" counts packets dropped because we ran out of
       *    buffer space.  It doesn't count packets dropped by the
       *    interface driver.  It counts only packets that passed
       *    the filter.
       *
       *    Both statistics include packets not yet read from the
       *    kernel by libpcap, and thus not yet seen by the application.
       *
       * On systems where the PACKET_STATISTICS "getsockopt()" argument
       * is not supported on PF_PACKET sockets:
       *
       *    "ps_recv" counts only packets that *passed* the filter,
       *    not packets that didn't pass the filter.  It does not
       *    count packets dropped because we ran out of buffer
       *    space.
       *
       *    "ps_drop" is not supported.
       *
       *    "ps_recv" doesn't include packets not yet read from
       *    the kernel by libpcap.
       */
      *stats = handle->md.stat;
      return 0;
}

/*
 * Description string for the "any" device.
 */
static const char any_descr[] = "Pseudo-device that captures on all interfaces";

int
pcap_platform_finddevs(pcap_if_t **alldevsp, char *errbuf)
{
      if (pcap_add_if(alldevsp, "any", 0, any_descr, errbuf) < 0)
            return (-1);

#ifdef HAVE_DAG_API
      if (dag_platform_finddevs(alldevsp, errbuf) < 0)
            return (-1);
#endif /* HAVE_DAG_API */

      return (0);
}

/*
 *  Attach the given BPF code to the packet capture device.
 */
static int
pcap_setfilter_linux(pcap_t *handle, struct bpf_program *filter)
{
#ifdef SO_ATTACH_FILTER
      struct sock_fprog fcode;
      int               can_filter_in_kernel;
      int               err = 0;
#endif

      if (!handle)
            return -1;
      if (!filter) {
              strncpy(handle->errbuf, "setfilter: No filter specified",
                  sizeof(handle->errbuf));
            return -1;
      }

      /* Make our private copy of the filter */

      if (install_bpf_program(handle, filter) < 0)
            /* install_bpf_program() filled in errbuf */
            return -1;

      /*
       * Run user level packet filter by default. Will be overriden if
       * installing a kernel filter succeeds.
       */
      handle->md.use_bpf = 0;

      /* Install kernel level filter if possible */

#ifdef SO_ATTACH_FILTER
#ifdef USHRT_MAX
      if (handle->fcode.bf_len > USHRT_MAX) {
            /*
             * fcode.len is an unsigned short for current kernel.
             * I have yet to see BPF-Code with that much
             * instructions but still it is possible. So for the
             * sake of correctness I added this check.
             */
            fprintf(stderr, "Warning: Filter too complex for kernel\n");
            fcode.filter = NULL;
            can_filter_in_kernel = 0;
      } else
#endif /* USHRT_MAX */
      {
            /*
             * Oh joy, the Linux kernel uses struct sock_fprog instead
             * of struct bpf_program and of course the length field is
             * of different size. Pointed out by Sebastian
             *
             * Oh, and we also need to fix it up so that all "ret"
             * instructions with non-zero operands have 65535 as the
             * operand, and so that, if we're in cooked mode, all
             * memory-reference instructions use special magic offsets
             * in references to the link-layer header and assume that
             * the link-layer payload begins at 0; "fix_program()"
             * will do that.
             */
            switch (fix_program(handle, &fcode)) {

            case -1:
            default:
                  /*
                   * Fatal error; just quit.
                   * (The "default" case shouldn't happen; we
                   * return -1 for that reason.)
                   */
                  return -1;

            case 0:
                  /*
                   * The program performed checks that we can't make
                   * work in the kernel.
                   */
                  can_filter_in_kernel = 0;
                  break;

            case 1:
                  /*
                   * We have a filter that'll work in the kernel.
                   */
                  can_filter_in_kernel = 1;
                  break;
            }
      }

      if (can_filter_in_kernel) {
            if ((err = set_kernel_filter(handle, &fcode)) == 0)
            {
                  /* Installation succeded - using kernel filter. */
                  handle->md.use_bpf = 1;
            }
            else if (err == -1)     /* Non-fatal error */
            {
                  /*
                   * Print a warning if we weren't able to install
                   * the filter for a reason other than "this kernel
                   * isn't configured to support socket filters.
                   */
                  if (errno != ENOPROTOOPT && errno != EOPNOTSUPP) {
                        fprintf(stderr,
                            "Warning: Kernel filter failed: %s\n",
                              pcap_strerror(errno));
                  }
            }
      }

      /*
       * If we're not using the kernel filter, get rid of any kernel
       * filter that might've been there before, e.g. because the
       * previous filter could work in the kernel, or because some other
       * code attached a filter to the socket by some means other than
       * calling "pcap_setfilter()".  Otherwise, the kernel filter may
       * filter out packets that would pass the new userland filter.
       */
      if (!handle->md.use_bpf)
            reset_kernel_filter(handle);

      /*
       * Free up the copy of the filter that was made by "fix_program()".
       */
      if (fcode.filter != NULL)
            free(fcode.filter);

      if (err == -2)
            /* Fatal error */
            return -1;
#endif /* SO_ATTACH_FILTER */

      return 0;
}

/*
 *  Linux uses the ARP hardware type to identify the type of an
 *  interface. pcap uses the DLT_xxx constants for this. This
 *  function takes a pointer to a "pcap_t", and an ARPHRD_xxx
 *  constant, as arguments, and sets "handle->linktype" to the
 *  appropriate DLT_XXX constant and sets "handle->offset" to
 *  the appropriate value (to make "handle->offset" plus link-layer
 *  header length be a multiple of 4, so that the link-layer payload
 *  will be aligned on a 4-byte boundary when capturing packets).
 *  (If the offset isn't set here, it'll be 0; add code as appropriate
 *  for cases where it shouldn't be 0.)
 *
 *  If "cooked_ok" is non-zero, we can use DLT_LINUX_SLL and capture
 *  in cooked mode; otherwise, we can't use cooked mode, so we have
 *  to pick some type that works in raw mode, or fail.
 *
 *  Sets the link type to -1 if unable to map the type.
 */
static void map_arphrd_to_dlt(pcap_t *handle, int arptype, int cooked_ok)
{
      switch (arptype) {

      case ARPHRD_ETHER:
      case ARPHRD_METRICOM:
      case ARPHRD_LOOPBACK:
            handle->linktype = DLT_EN10MB;
            handle->offset = 2;
            break;

      case ARPHRD_EETHER:
            handle->linktype = DLT_EN3MB;
            break;

      case ARPHRD_AX25:
            handle->linktype = DLT_AX25;
            break;

      case ARPHRD_PRONET:
            handle->linktype = DLT_PRONET;
            break;

      case ARPHRD_CHAOS:
            handle->linktype = DLT_CHAOS;
            break;

#ifndef ARPHRD_IEEE802_TR
#define ARPHRD_IEEE802_TR 800 /* From Linux 2.4 */
#endif
      case ARPHRD_IEEE802_TR:
      case ARPHRD_IEEE802:
            handle->linktype = DLT_IEEE802;
            handle->offset = 2;
            break;

      case ARPHRD_ARCNET:
            handle->linktype = DLT_ARCNET_LINUX;
            break;

#ifndef ARPHRD_FDDI     /* From Linux 2.2.13 */
#define ARPHRD_FDDI     774
#endif
      case ARPHRD_FDDI:
            handle->linktype = DLT_FDDI;
            handle->offset = 3;
            break;

#ifndef ARPHRD_ATM  /* FIXME: How to #include this? */
#define ARPHRD_ATM 19
#endif
      case ARPHRD_ATM:
            /*
             * The Classical IP implementation in ATM for Linux
             * supports both what RFC 1483 calls "LLC Encapsulation",
             * in which each packet has an LLC header, possibly
             * with a SNAP header as well, prepended to it, and
             * what RFC 1483 calls "VC Based Multiplexing", in which
             * different virtual circuits carry different network
             * layer protocols, and no header is prepended to packets.
             *
             * They both have an ARPHRD_ type of ARPHRD_ATM, so
             * you can't use the ARPHRD_ type to find out whether
             * captured packets will have an LLC header, and,
             * while there's a socket ioctl to *set* the encapsulation
             * type, there's no ioctl to *get* the encapsulation type.
             *
             * This means that
             *
             *    programs that dissect Linux Classical IP frames
             *    would have to check for an LLC header and,
             *    depending on whether they see one or not, dissect
             *    the frame as LLC-encapsulated or as raw IP (I
             *    don't know whether there's any traffic other than
             *    IP that would show up on the socket, or whether
             *    there's any support for IPv6 in the Linux
             *    Classical IP code);
             *
             *    filter expressions would have to compile into
             *    code that checks for an LLC header and does
             *    the right thing.
             *
             * Both of those are a nuisance - and, at least on systems
             * that support PF_PACKET sockets, we don't have to put
             * up with those nuisances; instead, we can just capture
             * in cooked mode.  That's what we'll do, if we can.
             * Otherwise, we'll just fail.
             */
            if (cooked_ok)
                  handle->linktype = DLT_LINUX_SLL;
            else
                  handle->linktype = -1;
            break;

#ifndef ARPHRD_IEEE80211  /* From Linux 2.4.6 */
#define ARPHRD_IEEE80211 801
#endif
      case ARPHRD_IEEE80211:
            handle->linktype = DLT_IEEE802_11;
            break;

#ifndef ARPHRD_IEEE80211_PRISM  /* From Linux 2.4.18 */
#define ARPHRD_IEEE80211_PRISM 802
#endif
      case ARPHRD_IEEE80211_PRISM:
            handle->linktype = DLT_PRISM_HEADER;
            break;

      case ARPHRD_PPP:
            /*
             * Some PPP code in the kernel supplies no link-layer
             * header whatsoever to PF_PACKET sockets; other PPP
             * code supplies PPP link-layer headers ("syncppp.c");
             * some PPP code might supply random link-layer
             * headers (PPP over ISDN - there's code in Ethereal,
             * for example, to cope with PPP-over-ISDN captures
             * with which the Ethereal developers have had to cope,
             * heuristically trying to determine which of the
             * oddball link-layer headers particular packets have).
             *
             * As such, we just punt, and run all PPP interfaces
             * in cooked mode, if we can; otherwise, we just treat
             * it as DLT_RAW, for now - if somebody needs to capture,
             * on a 2.0[.x] kernel, on PPP devices that supply a
             * link-layer header, they'll have to add code here to
             * map to the appropriate DLT_ type (possibly adding a
             * new DLT_ type, if necessary).
             */
            if (cooked_ok)
                  handle->linktype = DLT_LINUX_SLL;
            else {
                  /*
                   * XXX - handle ISDN types here?  We can't fall
                   * back on cooked sockets, so we'd have to
                   * figure out from the device name what type of
                   * link-layer encapsulation it's using, and map
                   * that to an appropriate DLT_ value, meaning
                   * we'd map "isdnN" devices to DLT_RAW (they
                   * supply raw IP packets with no link-layer
                   * header) and "isdY" devices to a new DLT_I4L_IP
                   * type that has only an Ethernet packet type as
                   * a link-layer header.
                   *
                   * But sometimes we seem to get random crap
                   * in the link-layer header when capturing on
                   * ISDN devices....
                   */
                  handle->linktype = DLT_RAW;
            }
            break;

#ifndef ARPHRD_CISCO
#define ARPHRD_CISCO 513 /* previously ARPHRD_HDLC */
#endif
      case ARPHRD_CISCO:
            handle->linktype = DLT_C_HDLC;
            break;

      /* Not sure if this is correct for all tunnels, but it
       * works for CIPE */
      case ARPHRD_TUNNEL:
#ifndef ARPHRD_SIT
#define ARPHRD_SIT 776  /* From Linux 2.2.13 */
#endif
      case ARPHRD_SIT:
      case ARPHRD_CSLIP:
      case ARPHRD_SLIP6:
      case ARPHRD_CSLIP6:
      case ARPHRD_ADAPT:
      case ARPHRD_SLIP:
#ifndef ARPHRD_RAWHDLC
#define ARPHRD_RAWHDLC 518
#endif
      case ARPHRD_RAWHDLC:
#ifndef ARPHRD_DLCI
#define ARPHRD_DLCI 15
#endif
      case ARPHRD_DLCI:
            /*
             * XXX - should some of those be mapped to DLT_LINUX_SLL
             * instead?  Should we just map all of them to DLT_LINUX_SLL?
             */
            handle->linktype = DLT_RAW;
            break;

#ifndef ARPHRD_FRAD
#define ARPHRD_FRAD 770
#endif
      case ARPHRD_FRAD:
            handle->linktype = DLT_FRELAY;
            break;

      case ARPHRD_LOCALTLK:
            handle->linktype = DLT_LTALK;
            break;

#ifndef ARPHRD_FCPP
#define ARPHRD_FCPP     784
#endif
      case ARPHRD_FCPP:
#ifndef ARPHRD_FCAL
#define ARPHRD_FCAL     785
#endif
      case ARPHRD_FCAL:
#ifndef ARPHRD_FCPL
#define ARPHRD_FCPL     786
#endif
      case ARPHRD_FCPL:
#ifndef ARPHRD_FCFABRIC
#define ARPHRD_FCFABRIC 787
#endif
      case ARPHRD_FCFABRIC:
            /*
             * We assume that those all mean RFC 2625 IP-over-
             * Fibre Channel, with the RFC 2625 header at
             * the beginning of the packet.
             */
            handle->linktype = DLT_IP_OVER_FC;
            break;

      case ARPHRD_IRDA:
            /* Don't expect IP packet out of this interfaces... */
            handle->linktype = DLT_LINUX_IRDA;
            /* We need to save packet direction for IrDA decoding,
             * so let's use "Linux-cooked" mode. Jean II */
            //handle->md.cooked = 1;
            break;

      default:
            handle->linktype = -1;
            break;
      }
}

/* ===== Functions to interface to the newer kernels ================== */

/*
 *  Try to open a packet socket using the new kernel interface.
 *  Returns 0 on failure.
 *  FIXME: 0 uses to mean success (Sebastian)
 */
static int
live_open_new(pcap_t *handle, const char *device, int promisc,
            int to_ms, char *ebuf)
{
#ifdef HAVE_PF_PACKET_SOCKETS
      int               sock_fd = -1, device_id, arptype;
      int               err;
      int               fatal_err = 0;
      struct packet_mreq      mr;

      /* One shot loop used for error handling - bail out with break */

      do {
            /*
             * Open a socket with protocol family packet. If a device is
             * given we try to open it in raw mode otherwise we use
             * the cooked interface.
             */
            sock_fd = device ?
                  socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))
                  : socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL));

            if (sock_fd == -1) {
                  snprintf(ebuf, PCAP_ERRBUF_SIZE, "socket: %s",
                         pcap_strerror(errno) );
                  break;
            }

            /* It seems the kernel supports the new interface. */
            handle->md.sock_packet = 0;

            /*
             * Get the interface index of the loopback device.
             * If the attempt fails, don't fail, just set the
             * "md.lo_ifindex" to -1.
             *
             * XXX - can there be more than one device that loops
             * packets back, i.e. devices other than "lo"?  If so,
             * we'd need to find them all, and have an array of
             * indices for them, and check all of them in
             * "pcap_read_packet()".
             */
            handle->md.lo_ifindex = iface_get_id(sock_fd, "lo", ebuf);

            /*
             * Default value for offset to align link-layer payload
             * on a 4-byte boundary.
             */
            handle->offset     = 0;

            /*
             * What kind of frames do we have to deal with? Fall back
             * to cooked mode if we have an unknown interface type.
             */

            if (device) {
                  /* Assume for now we don't need cooked mode. */
                  handle->md.cooked = 0;

                  arptype     = iface_get_arptype(sock_fd, device, ebuf);
                  if (arptype == -1) {
                        fatal_err = 1;
                        break;
                  }
                  map_arphrd_to_dlt(handle, arptype, 1);
                  if (handle->linktype == -1 ||
                      handle->linktype == DLT_LINUX_SLL ||
                      handle->linktype == DLT_LINUX_IRDA ||
                      (handle->linktype == DLT_EN10MB &&
                       (strncmp("isdn", device, 4) == 0 ||
                        strncmp("isdY", device, 4) == 0))) {
                        /*
                         * Unknown interface type (-1), or a
                         * device we explicitly chose to run
                         * in cooked mode (e.g., PPP devices),
                         * or an ISDN device (whose link-layer
                         * type we can only determine by using
                         * APIs that may be different on different
                         * kernels) - reopen in cooked mode.
                         */
                        if (close(sock_fd) == -1) {
                              snprintf(ebuf, PCAP_ERRBUF_SIZE,
                                     "close: %s", pcap_strerror(errno));
                              break;
                        }
                        sock_fd = socket(PF_PACKET, SOCK_DGRAM,
                                     htons(ETH_P_ALL));
                        if (sock_fd == -1) {
                              snprintf(ebuf, PCAP_ERRBUF_SIZE,
                                     "socket: %s", pcap_strerror(errno));
                              break;
                        }
                        handle->md.cooked = 1;

                        if (handle->linktype == -1) {
                              /*
                               * Warn that we're falling back on
                               * cooked mode; we may want to
                               * update "map_arphrd_to_dlt()"
                               * to handle the new type.
                               */
                              snprintf(ebuf, PCAP_ERRBUF_SIZE,
                                    "arptype %d not "
                                    "supported by libpcap - "
                                    "falling back to cooked "
                                    "socket",
                                    arptype);
                        }
                        /* IrDA capture is not a real "cooked" capture,
                         * it's IrLAP frames, not IP packets. */
                        if(handle->linktype != DLT_LINUX_IRDA)
                              handle->linktype = DLT_LINUX_SLL;
                  }

                  device_id = iface_get_id(sock_fd, device, ebuf);
                  if (device_id == -1)
                        break;

                  if ((err = iface_bind(sock_fd, device_id, ebuf)) < 0) {
                        if (err == -2)
                              fatal_err = 1;
                        break;
                  }
            } else {
                  /*
                   * This is cooked mode.
                   */
                  handle->md.cooked = 1;
                  handle->linktype = DLT_LINUX_SLL;

                  /*
                   * XXX - squelch GCC complaints about
                   * uninitialized variables; if we can't
                   * select promiscuous mode on all interfaces,
                   * we should move the code below into the
                   * "if (device)" branch of the "if" and
                   * get rid of the next statement.
                   */
                  device_id = -1;
            }

            /*
             * Select promiscuous mode on if "promisc" is set.
             *
             * Do not turn allmulti mode on if we don't select
             * promiscuous mode - on some devices (e.g., Orinoco
             * wireless interfaces), allmulti mode isn't supported
             * and the driver implements it by turning promiscuous
             * mode on, and that screws up the operation of the
             * card as a normal networking interface, and on no
             * other platform I know of does starting a non-
             * promiscuous capture affect which multicast packets
             * are received by the interface.
             */

            /*
             * Hmm, how can we set promiscuous mode on all interfaces?
             * I am not sure if that is possible at all.
             */

            if (device && promisc) {
                  memset(&mr, 0, sizeof(mr));
                  mr.mr_ifindex = device_id;
                  mr.mr_type    = PACKET_MR_PROMISC;
                  if (setsockopt(sock_fd, SOL_PACKET,
                        PACKET_ADD_MEMBERSHIP, &mr, sizeof(mr)) == -1)
                  {
                        snprintf(ebuf, PCAP_ERRBUF_SIZE,
                              "setsockopt: %s", pcap_strerror(errno));
                        break;
                  }
            }

            /* Save the socket FD in the pcap structure */

            handle->fd   = sock_fd;

            return 1;

      } while(0);

      if (sock_fd != -1)
            close(sock_fd);

      if (fatal_err)
            return -2;
      else
            return 0;
#else
      strncpy(ebuf,
            "New packet capturing interface not supported by build "
            "environment", PCAP_ERRBUF_SIZE);
      return 0;
#endif
}

#ifdef HAVE_PF_PACKET_SOCKETS
/*
 *  Return the index of the given device name. Fill ebuf and return
 *  -1 on failure.
 */
static int
iface_get_id(int fd, const char *device, char *ebuf)
{
      struct ifreq      ifr;

      memset(&ifr, 0, sizeof(ifr));
      strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

      if (ioctl(fd, SIOCGIFINDEX, &ifr) == -1) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE,
                   "ioctl: %s", pcap_strerror(errno));
            return -1;
      }

      return ifr.ifr_ifindex;
}

/*
 *  Bind the socket associated with FD to the given device.
 */
static int
iface_bind(int fd, int ifindex, char *ebuf)
{
      struct sockaddr_ll      sll;
      int               err;
      socklen_t         errlen = sizeof(err);

      memset(&sll, 0, sizeof(sll));
      sll.sll_family          = AF_PACKET;
      sll.sll_ifindex         = ifindex;
      sll.sll_protocol  = htons(ETH_P_ALL);

      if (bind(fd, (struct sockaddr *) &sll, sizeof(sll)) == -1) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE,
                   "bind: %s", pcap_strerror(errno));
            return -1;
      }

      /* Any pending errors, e.g., network is down? */

      if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &errlen) == -1) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE,
                  "getsockopt: %s", pcap_strerror(errno));
            return -2;
      }

      if (err > 0) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE,
                  "bind: %s", pcap_strerror(err));
            return -2;
      }

      return 0;
}

#endif


/* ===== Functions to interface to the older kernels ================== */

/*
 * With older kernels promiscuous mode is kind of interesting because we
 * have to reset the interface before exiting. The problem can't really
 * be solved without some daemon taking care of managing usage counts.
 * If we put the interface into promiscuous mode, we set a flag indicating
 * that we must take it out of that mode when the interface is closed,
 * and, when closing the interface, if that flag is set we take it out
 * of promiscuous mode.
 */

/*
 * List of pcaps for which we turned promiscuous mode on by hand.
 * If there are any such pcaps, we arrange to call "pcap_close_all()"
 * when we exit, and have it close all of them to turn promiscuous mode
 * off.
 */
static struct pcap *pcaps_to_close;

/*
 * TRUE if we've already called "atexit()" to cause "pcap_close_all()" to
 * be called on exit.
 */
static int did_atexit;

static void pcap_close_all(void)
{
      struct pcap *handle;

      while ((handle = pcaps_to_close) != NULL)
            pcap_close(handle);
}

static void pcap_close_linux( pcap_t *handle )
{
      struct pcap *p, *prevp;
      struct ifreq      ifr;

      if (handle->md.clear_promisc) {
            /*
             * We put the interface into promiscuous mode; take
             * it out of promiscuous mode.
             *
             * XXX - if somebody else wants it in promiscuous mode,
             * this code cannot know that, so it'll take it out
             * of promiscuous mode.  That's not fixable in 2.0[.x]
             * kernels.
             */
            memset(&ifr, 0, sizeof(ifr));
            strncpy(ifr.ifr_name, handle->md.device, sizeof(ifr.ifr_name));
            if (ioctl(handle->fd, SIOCGIFFLAGS, &ifr) == -1) {
                  fprintf(stderr,
                      "Can't restore interface flags (SIOCGIFFLAGS failed: %s).\n"
                      "Please adjust manually.\n"
                      "Hint: This can't happen with Linux >= 2.2.0.\n",
                      strerror(errno));
            } else {
                  if (ifr.ifr_flags & IFF_PROMISC) {
                        /*
                         * Promiscuous mode is currently on; turn it
                         * off.
                         */
                        ifr.ifr_flags &= ~IFF_PROMISC;
                        if (ioctl(handle->fd, SIOCSIFFLAGS, &ifr) == -1) {
                              fprintf(stderr,
                                  "Can't restore interface flags (SIOCSIFFLAGS failed: %s).\n"
                                  "Please adjust manually.\n"
                                  "Hint: This can't happen with Linux >= 2.2.0.\n",
                                  strerror(errno));
                        }
                  }
            }

            /*
             * Take this pcap out of the list of pcaps for which we
             * have to take the interface out of promiscuous mode.
             */
            for (p = pcaps_to_close, prevp = NULL; p != NULL;
                prevp = p, p = p->md.next) {
                  if (p == handle) {
                        /*
                         * Found it.  Remove it from the list.
                         */
                        if (prevp == NULL) {
                              /*
                               * It was at the head of the list.
                               */
                              pcaps_to_close = p->md.next;
                        } else {
                              /*
                               * It was in the middle of the list.
                               */
                              prevp->md.next = p->md.next;
                        }
                        break;
                  }
            }
      }

      if (handle->md.device != NULL)
            free(handle->md.device);
      handle->md.device = NULL;
      if (handle->buffer != NULL)
            free(handle->buffer);
      if (handle->fd >= 0)
            close(handle->fd);
}

/*
 *  Try to open a packet socket using the old kernel interface.
 *  Returns 0 on failure.
 *  FIXME: 0 uses to mean success (Sebastian)
 */
static int
live_open_old(pcap_t *handle, const char *device, int promisc,
            int to_ms, char *ebuf)
{
      int         arptype;
      struct ifreq      ifr;

      do {
            /* Open the socket */

            handle->fd = socket(PF_INET, SOCK_PACKET, htons(ETH_P_ALL));
            if (handle->fd == -1) {
                  snprintf(ebuf, PCAP_ERRBUF_SIZE,
                         "socket: %s", pcap_strerror(errno));
                  break;
            }

            /* It worked - we are using the old interface */
            handle->md.sock_packet = 1;

            /* ...which means we get the link-layer header. */
            handle->md.cooked = 0;

            /* Bind to the given device */

            if (!device) {
                    strncpy(ebuf, "pcap_open_live: The \"any\" device isn't supported on 2.0[.x]-kernel systems",
                        PCAP_ERRBUF_SIZE);
                  break;
            }
            if (iface_bind_old(handle->fd, device, ebuf) == -1)
                  break;

            /*
             * Try to get the link-layer type.
             */
            arptype = iface_get_arptype(handle->fd, device, ebuf);
            if (arptype == -1)
                  break;

            /*
             * Try to find the DLT_ type corresponding to that
             * link-layer type.
             */
            map_arphrd_to_dlt(handle, arptype, 0);
            if (handle->linktype == -1) {
                  snprintf(ebuf, PCAP_ERRBUF_SIZE,
                         "unknown arptype %d", arptype);
                  break;
            }

            /* Go to promisc mode if requested */

            if (promisc) {
                  memset(&ifr, 0, sizeof(ifr));
                  strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));
                  if (ioctl(handle->fd, SIOCGIFFLAGS, &ifr) == -1) {
                        snprintf(ebuf, PCAP_ERRBUF_SIZE,
                               "ioctl: %s", pcap_strerror(errno));
                        break;
                  }
                  if ((ifr.ifr_flags & IFF_PROMISC) == 0) {
                        /*
                         * Promiscuous mode isn't currently on,
                         * so turn it on, and remember that
                         * we should turn it off when the
                         * pcap_t is closed.
                         */

                        /*
                         * If we haven't already done so, arrange
                         * to have "pcap_close_all()" called when
                         * we exit.
                         */
                        if (!did_atexit) {
                              if (atexit(pcap_close_all) == -1) {
                                    /*
                                     * "atexit()" failed; don't
                                     * put the interface in
                                     * promiscuous mode, just
                                     * give up.
                                     */
                                    strncpy(ebuf, "atexit failed",
                                          PCAP_ERRBUF_SIZE);
                                    break;
                              }
                              did_atexit = 1;
                        }

                        ifr.ifr_flags |= IFF_PROMISC;
                        if (ioctl(handle->fd, SIOCSIFFLAGS, &ifr) == -1) {
                                snprintf(ebuf, PCAP_ERRBUF_SIZE,
                                     "ioctl: %s",
                                     pcap_strerror(errno));
                              break;
                        }
                        handle->md.clear_promisc = 1;

                        /*
                         * Add this to the list of pcaps
                         * to close when we exit.
                         */
                        handle->md.next = pcaps_to_close;
                        pcaps_to_close = handle;
                  }
            }

            /*
             * Default value for offset to align link-layer payload
             * on a 4-byte boundary.
             */
            handle->offset     = 0;

            return 1;

      } while (0);

      pcap_close_linux(handle);
      return 0;
}

/*
 *  Bind the socket associated with FD to the given device using the
 *  interface of the old kernels.
 */
static int
iface_bind_old(int fd, const char *device, char *ebuf)
{
      struct sockaddr   saddr;
      int         err;
      socklen_t   errlen = sizeof(err);

      memset(&saddr, 0, sizeof(saddr));
      strncpy(saddr.sa_data, device, sizeof(saddr.sa_data));
      if (bind(fd, &saddr, sizeof(saddr)) == -1) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE,
                   "bind: %s", pcap_strerror(errno));
            return -1;
      }

      /* Any pending errors, e.g., network is down? */

      if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &errlen) == -1) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE,
                  "getsockopt: %s", pcap_strerror(errno));
            return -1;
      }

      if (err > 0) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE,
                  "bind: %s", pcap_strerror(err));
            return -1;
      }

      return 0;
}


/* ===== System calls available on all supported kernels ============== */

/*
 *  Query the kernel for the MTU of the given interface.
 */
static int
iface_get_mtu(int fd, const char *device, char *ebuf)
{
      struct ifreq      ifr;

      if (!device)
            return BIGGER_THAN_ALL_MTUS;

      memset(&ifr, 0, sizeof(ifr));
      strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

      if (ioctl(fd, SIOCGIFMTU, &ifr) == -1) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE,
                   "ioctl: %s", pcap_strerror(errno));
            return -1;
      }

      return ifr.ifr_mtu;
}

/*
 *  Get the hardware type of the given interface as ARPHRD_xxx constant.
 */
static int
iface_get_arptype(int fd, const char *device, char *ebuf)
{
      struct ifreq      ifr;

      memset(&ifr, 0, sizeof(ifr));
      strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

      if (ioctl(fd, SIOCGIFHWADDR, &ifr) == -1) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE,
                   "ioctl: %s", pcap_strerror(errno));
            return -1;
      }

      return ifr.ifr_hwaddr.sa_family;
}

#ifdef SO_ATTACH_FILTER
static int
fix_program(pcap_t *handle, struct sock_fprog *fcode)
{
      size_t prog_size;
      register int i;
      register struct bpf_insn *p;
      struct bpf_insn *f;
      int len;

      /*
       * Make a copy of the filter, and modify that copy if
       * necessary.
       */
      prog_size = sizeof(*handle->fcode.bf_insns) * handle->fcode.bf_len;
      len = handle->fcode.bf_len;
      f = (struct bpf_insn *)malloc(prog_size);
      if (f == NULL) {
            snprintf(handle->errbuf, sizeof(handle->errbuf),
                   "malloc: %s", pcap_strerror(errno));
            return -1;
      }
      memcpy(f, handle->fcode.bf_insns, prog_size);
      fcode->len = len;
      fcode->filter = (struct sock_filter *) f;

      for (i = 0; i < len; ++i) {
            p = &f[i];
            /*
             * What type of instruction is this?
             */
            switch (BPF_CLASS(p->code)) {

            case BPF_RET:
                  /*
                   * It's a return instruction; is the snapshot
                   * length a constant, rather than the contents
                   * of the accumulator?
                   */
                  if (BPF_MODE(p->code) == BPF_K) {
                        /*
                         * Yes - if the value to be returned,
                         * i.e. the snapshot length, is anything
                         * other than 0, make it 65535, so that
                         * the packet is truncated by "recvfrom()",
                         * not by the filter.
                         *
                         * XXX - there's nothing we can easily do
                         * if it's getting the value from the
                         * accumulator; we'd have to insert
                         * code to force non-zero values to be
                         * 65535.
                         */
                        if (p->k != 0)
                              p->k = 65535;
                  }
                  break;

            case BPF_LD:
            case BPF_LDX:
                  /*
                   * It's a load instruction; is it loading
                   * from the packet?
                   */
                  switch (BPF_MODE(p->code)) {

                  case BPF_ABS:
                  case BPF_IND:
                  case BPF_MSH:
                        /*
                         * Yes; are we in cooked mode?
                         */
                        if (handle->md.cooked) {
                              /*
                               * Yes, so we need to fix this
                               * instruction.
                               */
                              if (fix_offset(p) < 0) {
                                    /*
                                     * We failed to do so.
                                     * Return 0, so our caller
                                     * knows to punt to userland.
                                     */
                                    return 0;
                              }
                        }
                        break;
                  }
                  break;
            }
      }
      return 1;   /* we succeeded */
}

static int
fix_offset(struct bpf_insn *p)
{
      /*
       * What's the offset?
       */
      if (p->k >= SLL_HDR_LEN) {
            /*
             * It's within the link-layer payload; that starts at an
             * offset of 0, as far as the kernel packet filter is
             * concerned, so subtract the length of the link-layer
             * header.
             */
            p->k -= SLL_HDR_LEN;
      } else if (p->k == 14) {
            /*
             * It's the protocol field; map it to the special magic
             * kernel offset for that field.
             */
            p->k = SKF_AD_OFF + SKF_AD_PROTOCOL;
      } else {
            /*
             * It's within the header, but it's not one of those
             * fields; we can't do that in the kernel, so punt
             * to userland.
             */
            return -1;
      }
      return 0;
}

static int
set_kernel_filter(pcap_t *handle, struct sock_fprog *fcode)
{
      int total_filter_on = 0;
      int save_mode;
      int ret;
      int save_errno;

      /*
       * The socket filter code doesn't discard all packets queued
       * up on the socket when the filter is changed; this means
       * that packets that don't match the new filter may show up
       * after the new filter is put onto the socket, if those
       * packets haven't yet been read.
       *
       * This means, for example, that if you do a tcpdump capture
       * with a filter, the first few packets in the capture might
       * be packets that wouldn't have passed the filter.
       *
       * We therefore discard all packets queued up on the socket
       * when setting a kernel filter.  (This isn't an issue for
       * userland filters, as the userland filtering is done after
       * packets are queued up.)
       *
       * To flush those packets, we put the socket in read-only mode,
       * and read packets from the socket until there are no more to
       * read.
       *
       * In order to keep that from being an infinite loop - i.e.,
       * to keep more packets from arriving while we're draining
       * the queue - we put the "total filter", which is a filter
       * that rejects all packets, onto the socket before draining
       * the queue.
       *
       * This code deliberately ignores any errors, so that you may
       * get bogus packets if an error occurs, rather than having
       * the filtering done in userland even if it could have been
       * done in the kernel.
       */
      if (setsockopt(handle->fd, SOL_SOCKET, SO_ATTACH_FILTER,
                   &total_fcode, sizeof(total_fcode)) == 0) {
            char drain[1];

            /*
             * Note that we've put the total filter onto the socket.
             */
            total_filter_on = 1;

            /*
             * Save the socket's current mode, and put it in
             * non-blocking mode; we drain it by reading packets
             * until we get an error (which is normally a
             * "nothing more to be read" error).
             */
            save_mode = fcntl(handle->fd, F_GETFL, 0);
            if (save_mode != -1 &&
                fcntl(handle->fd, F_SETFL, save_mode | O_NONBLOCK) >= 0) {
                  while (recv(handle->fd, &drain, sizeof drain,
                         MSG_TRUNC) >= 0)
                        ;
                  save_errno = errno;
                  fcntl(handle->fd, F_SETFL, save_mode);
                  if (save_errno != EAGAIN) {
                        /* Fatal error */
                        reset_kernel_filter(handle);
                        snprintf(handle->errbuf, sizeof(handle->errbuf),
                         "recv: %s", pcap_strerror(save_errno));
                        return -2;
                  }
            }
      }

      /*
       * Now attach the new filter.
       */
      ret = setsockopt(handle->fd, SOL_SOCKET, SO_ATTACH_FILTER,
                   fcode, sizeof(*fcode));
      if (ret == -1 && total_filter_on) {
            /*
             * Well, we couldn't set that filter on the socket,
             * but we could set the total filter on the socket.
             *
             * This could, for example, mean that the filter was
             * too big to put into the kernel, so we'll have to
             * filter in userland; in any case, we'll be doing
             * filtering in userland, so we need to remove the
             * total filter so we see packets.
             */
            save_errno = errno;

            /*
             * XXX - if this fails, we're really screwed;
             * we have the total filter on the socket,
             * and it won't come off.  What do we do then?
             */
            reset_kernel_filter(handle);

            errno = save_errno;
      }
      return ret;
}

static int
reset_kernel_filter(pcap_t *handle)
{
      /* setsockopt() barfs unless it get a dummy parameter */
      int dummy;

      return setsockopt(handle->fd, SOL_SOCKET, SO_DETACH_FILTER,
                           &dummy, sizeof(dummy));
}
#endif

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