bpf.c

   1 /*
   2  * dhcpcd - DHCP client daemon
   3  * Copyright (c) 2006-2008 Roy Marples <roy@marples.name>
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  */
  26
  27 #include <sys/types.h>
  28 #include <sys/ioctl.h>
  29 #include <sys/socket.h>
  30 #include <sys/uio.h>
  31
  32 #include <net/bpf.h>
  33 #include <net/if.h>
  34 #include <arpa/inet.h>
  35
  36 #include <errno.h>
  37 #include <fcntl.h>
  38 #include <paths.h>
  39 #include <stdio.h>
  40 #include <stdlib.h>
  41 #include <string.h>
  42 #include <syslog.h>
  43 #include <unistd.h>
  44
  45 #include "config.h"
  46 #include "common.h"
  47 #include "dhcp.h"
  48 #include "net.h"
  49 #include "bpf-filter.h"
  50
  51 int
  52 open_socket(struct interface *iface, int protocol)
  53 {
  54         int fd = -1;
  55         int *fdp = NULL;
  56         struct ifreq ifr;
  57         int buf_len = 0;
  58         struct bpf_version pv;
  59         struct bpf_program pf;
  60 #ifdef BIOCIMMEDIATE
  61         int flags;
  62 #endif
  63 #ifdef _PATH_BPF
  64         fd = open(_PATH_BPF, O_RDWR | O_NONBLOCK);
  65 #else
  66         char *device;
  67         int n = 0;
  68
  69         device = xmalloc(sizeof(char) * PATH_MAX);
  70         do {
  71                 snprintf(device, PATH_MAX, "/dev/bpf%d", n++);
  72                 fd = open(device, O_RDWR | O_NONBLOCK);
  73         } while (fd == -1 && errno == EBUSY);
  74         free(device);
  75 #endif
  76
  77         if (fd == -1)
  78                 return -1;
  79
  80         if (ioctl(fd, BIOCVERSION, &pv) == -1)
  81                 goto eexit;
  82         if (pv.bv_major != BPF_MAJOR_VERSION ||
  83             pv.bv_minor < BPF_MINOR_VERSION) {
  84                 syslog(LOG_ERR, "BPF version mismatch - recompile");
  85                 goto eexit;
  86         }
  87
  88         memset(&ifr, 0, sizeof(ifr));
  89         strlcpy(ifr.ifr_name, iface->name, sizeof(ifr.ifr_name));
  90         if (ioctl(fd, BIOCSETIF, &ifr) == -1)
  91                 goto eexit;
  92
  93         /* Get the required BPF buffer length from the kernel. */
  94         if (ioctl(fd, BIOCGBLEN, &buf_len) == -1)
  95                 goto eexit;
  96         if (iface->buffer_size != (size_t)buf_len) {
  97                 free(iface->buffer);
  98                 iface->buffer_size = buf_len;
  99                 iface->buffer = xmalloc(buf_len);
 100                 iface->buffer_len = iface->buffer_pos = 0;
 101         }
 102
 103 #ifdef BIOCIMMEDIATE
 104         flags = 1;
 105         if (ioctl(fd, BIOCIMMEDIATE, &flags) == -1)
 106                 goto eexit;
 107 #endif
 108
 109         /* Install the DHCP filter */
 110         if (protocol == ETHERTYPE_ARP) {
 111                 pf.bf_insns = UNCONST(arp_bpf_filter);
 112                 pf.bf_len = arp_bpf_filter_len;
 113                 fdp = &iface->arp_fd;
 114         } else {
 115                 pf.bf_insns = UNCONST(dhcp_bpf_filter);
 116                 pf.bf_len = dhcp_bpf_filter_len;
 117                 fdp = &iface->raw_fd;
 118         }
 119         if (ioctl(fd, BIOCSETF, &pf) == -1)
 120                 goto eexit;
 121         if (set_cloexec(fd) == -1)
 122                 goto eexit;
 123         if (fdp) {
 124                 if (*fdp != -1)
 125                         close(*fdp);
 126                 *fdp = fd;
 127         }
 128         return fd;
 129
 130 eexit:
 131         free(iface->buffer);
 132         iface->buffer = NULL;
 133         close(fd);
 134         return -1;
 135 }
 136
 137 ssize_t
 138 send_raw_packet(const struct interface *iface, int protocol,
 139     const void *data, ssize_t len)
 140 {
 141         struct iovec iov[2];
 142         struct ether_header hw;
 143         int fd;
 144
 145         memset(&hw, 0, ETHER_HDR_LEN);
 146         memset(&hw.ether_dhost, 0xff, ETHER_ADDR_LEN);
 147         hw.ether_type = htons(protocol);
 148         iov[0].iov_base = &hw;
 149         iov[0].iov_len = ETHER_HDR_LEN;
 150         iov[1].iov_base = UNCONST(data);
 151         iov[1].iov_len = len;
 152         if (protocol == ETHERTYPE_ARP)
 153                 fd = iface->arp_fd;
 154         else
 155                 fd = iface->raw_fd;
 156         return writev(fd, iov, 2);
 157 }
 158
 159 /* BPF requires that we read the entire buffer.
 160  * So we pass the buffer in the API so we can loop on >1 packet. */
 161 ssize_t
 162 get_raw_packet(struct interface *iface, int protocol,
 163     void *data, ssize_t len)
 164 {
 165         int fd = -1;
 166         struct bpf_hdr packet;
 167         ssize_t bytes;
 168         const unsigned char *payload;
 169
 170         if (protocol == ETHERTYPE_ARP)
 171                 fd = iface->arp_fd;
 172         else
 173                 fd = iface->raw_fd;
 174
 175         for (;;) {
 176                 if (iface->buffer_len == 0) {
 177                         bytes = read(fd, iface->buffer, iface->buffer_size);
 178                         if (bytes == -1)
 179                                 return errno == EAGAIN ? 0 : -1;
 180                         else if ((size_t)bytes < sizeof(packet))
 181                                 return -1;
 182                         iface->buffer_len = bytes;
 183                         iface->buffer_pos = 0;
 184                 }
 185                 bytes = -1;
 186                 memcpy(&packet, iface->buffer + iface->buffer_pos,
 187                     sizeof(packet));
 188                 if (packet.bh_caplen != packet.bh_datalen)
 189                         goto next; /* Incomplete packet, drop. */
 190                 if (iface->buffer_pos + packet.bh_caplen + packet.bh_hdrlen >
 191                     iface->buffer_len)
 192                         goto next; /* Packet beyond buffer, drop. */
 193                 payload = iface->buffer + packet.bh_hdrlen + ETHER_HDR_LEN;
 194                 bytes = packet.bh_caplen - ETHER_HDR_LEN;
 195                 if (bytes > len)
 196                         bytes = len;
 197                 memcpy(data, payload, bytes);
 198 next:
 199                 iface->buffer_pos += BPF_WORDALIGN(packet.bh_hdrlen +
 200                     packet.bh_caplen);
 201                 if (iface->buffer_pos >= iface->buffer_len)
 202                         iface->buffer_len = iface->buffer_pos = 0;
 203                 if (bytes != -1)
 204                         return bytes;
 205         }
 206 }