src/bpf.c

/* dnsmasq is Copyright (c) 2000-2012 Simon Kelley

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 dated June, 1991, or
   (at your option) version 3 dated 29 June, 2007.
 
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
     
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "dnsmasq.h"

#if defined(HAVE_BSD_NETWORK) || defined(HAVE_SOLARIS_NETWORK)
#include <ifaddrs.h>

#if defined(HAVE_BSD_NETWORK) && !defined(__APPLE__)
#include <sys/param.h>
#include <sys/sysctl.h>
#include <net/route.h>
#include <net/if_dl.h>
#include <netinet/if_ether.h>

#ifndef SA_SIZE
#define SA_SIZE(sa)                                             \
    (  (!(sa) || ((struct sockaddr *)(sa))->sa_len == 0) ?      \
        sizeof(long)            :                               \
        1 + ( (((struct sockaddr *)(sa))->sa_len - 1) | (sizeof(long) - 1) ) )
#endif

int arp_enumerate(void *parm, int (*callback)())
{
  int mib[6];
  size_t needed;
  char *next;
  struct rt_msghdr *rtm;
  struct sockaddr_inarp *sin2;
  struct sockaddr_dl *sdl;
  struct iovec buff;
  int rc;

  buff.iov_base = NULL;
  buff.iov_len = 0;

  mib[0] = CTL_NET;
  mib[1] = PF_ROUTE;
  mib[2] = 0;
  mib[3] = AF_INET;
  mib[4] = NET_RT_FLAGS;
#ifdef RTF_LLINFO
  mib[5] = RTF_LLINFO;
#else
  mib[5] = 0;
#endif	
  if (sysctl(mib, 6, NULL, &needed, NULL, 0) == -1 || needed == 0)
    return 0;

  while (1) 
    {
      if (!expand_buf(&buff, needed))
	return 0;
      if ((rc = sysctl(mib, 6, buff.iov_base, &needed, NULL, 0)) == 0 ||
	  errno != ENOMEM)
	break;
      needed += needed / 8;
    }
  if (rc == -1)
    return 0;
  
  for (next = buff.iov_base ; next < (char *)buff.iov_base + needed; next += rtm->rtm_msglen)
    {
      rtm = (struct rt_msghdr *)next;
      sin2 = (struct sockaddr_inarp *)(rtm + 1);
      sdl = (struct sockaddr_dl *)((char *)sin2 + SA_SIZE(sin2));
      if (!(*callback)(AF_INET, &sin2->sin_addr, LLADDR(sdl), sdl->sdl_alen, parm))
	return 0;
    }

  return 1;
}
#endif


int iface_enumerate(int family, void *parm, int (*callback)())
{
  struct ifaddrs *head, *addrs;
  int errsav, ret = 0;

  if (family == AF_UNSPEC)
#if defined(HAVE_BSD_NETWORK) && !defined(__APPLE__)
    return  arp_enumerate(parm, callback);
#else
  return 0; /* need code for Solaris and MacOS*/
#endif

  /* AF_LINK doesn't exist in Linux, so we can't use it in our API */
  if (family == AF_LOCAL)
    family = AF_LINK;

  if (getifaddrs(&head) == -1)
    return 0;

  for (addrs = head; addrs; addrs = addrs->ifa_next)
    {
      if (addrs->ifa_addr->sa_family == family)
	{
	  int iface_index = if_nametoindex(addrs->ifa_name);

	  if (iface_index == 0)
	    continue;

	  if (family == AF_INET)
	    {
	      struct in_addr addr, netmask, broadcast;
	      addr = ((struct sockaddr_in *) addrs->ifa_addr)->sin_addr;
	      netmask = ((struct sockaddr_in *) addrs->ifa_netmask)->sin_addr;
	      broadcast = ((struct sockaddr_in *) addrs->ifa_broadaddr)->sin_addr; 
	      if (!((*callback)(addr, iface_index, netmask, broadcast, parm)))
		goto err;
	    }
#ifdef HAVE_IPV6
	  else if (family == AF_INET6)
	    {
	      struct in6_addr *addr = &((struct sockaddr_in6 *) addrs->ifa_addr)->sin6_addr;
	      unsigned char *netmask = (unsigned char *) &((struct sockaddr_in6 *) addrs->ifa_netmask)->sin6_addr;
	      int scope_id = ((struct sockaddr_in6 *) addrs->ifa_addr)->sin6_scope_id;
	      int i, j, prefix = 0;
	      
	      for (i = 0; i < IN6ADDRSZ; i++, prefix += 8) 
                if (netmask[i] != 0xff)
		  break;
       
	      if (i != IN6ADDRSZ && netmask[i]) 
                for (j = 7; j > 0; j--, prefix++) 
		  if ((netmask[i] & (1 << j)) == 0)
		    break;
	      
	      /* voodoo to clear interface field in address */
	      if (!option_bool(OPT_NOWILD) && IN6_IS_ADDR_LINKLOCAL(addr))
		{
		  addr->s6_addr[2] = 0;
		  addr->s6_addr[3] = 0;
		}
	      
	      if (!((*callback)(addr, prefix, scope_id, iface_index, 0, parm)))
		goto err;
	}
#endif
#ifdef HAVE_DHCP6      
	  else if (family == AF_LINK)
	    { 
	      /* Assume ethernet again here */
	      struct sockaddr_dl *sdl = (struct sockaddr_dl *) addrs->ifa_addr;
	      if (sdl->sdl_alen != 0 && 
		  !((*callback)(iface_index, ARPHRD_ETHER, LLADDR(sdl), sdl->sdl_alen, parm)))
		goto err;
	    }
#endif 
	}
    }
  
  ret = 1;

 err:
  errsav = errno;
  freeifaddrs(head);  
  errno = errsav;

  return ret;
}
#endif


#if defined(HAVE_BSD_NETWORK) && defined(HAVE_DHCP)
#include <net/bpf.h>

void init_bpf(void)
{
  int i = 0;

  while (1) 
    {
      sprintf(daemon->dhcp_buff, "/dev/bpf%d", i++);
      if ((daemon->dhcp_raw_fd = open(daemon->dhcp_buff, O_RDWR, 0)) != -1)
	return;

      if (errno != EBUSY)
	die(_("cannot create DHCP BPF socket: %s"), NULL, EC_BADNET);
    }	     
}

void send_via_bpf(struct dhcp_packet *mess, size_t len,
		  struct in_addr iface_addr, struct ifreq *ifr)
{
   /* Hairy stuff, packet either has to go to the
      net broadcast or the destination can't reply to ARP yet,
      but we do know the physical address. 
      Build the packet by steam, and send directly, bypassing
      the kernel IP stack */
  
  struct ether_header ether; 
  struct ip ip;
  struct udphdr {
    u16 uh_sport;               /* source port */
    u16 uh_dport;               /* destination port */
    u16 uh_ulen;                /* udp length */
    u16 uh_sum;                 /* udp checksum */
  } udp;
  
  u32 i, sum;
  struct iovec iov[4];

  /* Only know how to do ethernet on *BSD */
  if (mess->htype != ARPHRD_ETHER || mess->hlen != ETHER_ADDR_LEN)
    {
      my_syslog(MS_DHCP | LOG_WARNING, _("DHCP request for unsupported hardware type (%d) received on %s"), 
		mess->htype, ifr->ifr_name);
      return;
    }
   
  ifr->ifr_addr.sa_family = AF_LINK;
  if (ioctl(daemon->dhcpfd, SIOCGIFADDR, ifr) < 0)
    return;
  
  memcpy(ether.ether_shost, LLADDR((struct sockaddr_dl *)&ifr->ifr_addr), ETHER_ADDR_LEN);
  ether.ether_type = htons(ETHERTYPE_IP);
  
  if (ntohs(mess->flags) & 0x8000)
    {
      memset(ether.ether_dhost, 255,  ETHER_ADDR_LEN);
      ip.ip_dst.s_addr = INADDR_BROADCAST;
    }
  else
    {
      memcpy(ether.ether_dhost, mess->chaddr, ETHER_ADDR_LEN); 
      ip.ip_dst.s_addr = mess->yiaddr.s_addr;
    }
  
  ip.ip_p = IPPROTO_UDP;
  ip.ip_src.s_addr = iface_addr.s_addr;
  ip.ip_len = htons(sizeof(struct ip) + 
		    sizeof(struct udphdr) +
		    len) ;
  ip.ip_hl = sizeof(struct ip) / 4;
  ip.ip_v = IPVERSION;
  ip.ip_tos = 0;
  ip.ip_id = htons(0);
  ip.ip_off = htons(0x4000); /* don't fragment */
  ip.ip_ttl = IPDEFTTL;
  ip.ip_sum = 0;
  for (sum = 0, i = 0; i < sizeof(struct ip) / 2; i++)
    sum += ((u16 *)&ip)[i];
  while (sum>>16)
    sum = (sum & 0xffff) + (sum >> 16);  
  ip.ip_sum = (sum == 0xffff) ? sum : ~sum;
  
  udp.uh_sport = htons(daemon->dhcp_server_port);
  udp.uh_dport = htons(daemon->dhcp_client_port);
  if (len & 1)
    ((char *)mess)[len] = 0; /* for checksum, in case length is odd. */
  udp.uh_sum = 0;
  udp.uh_ulen = sum = htons(sizeof(struct udphdr) + len);
  sum += htons(IPPROTO_UDP);
  sum += ip.ip_src.s_addr & 0xffff;
  sum += (ip.ip_src.s_addr >> 16) & 0xffff;
  sum += ip.ip_dst.s_addr & 0xffff;
  sum += (ip.ip_dst.s_addr >> 16) & 0xffff;
  for (i = 0; i < sizeof(struct udphdr)/2; i++)
    sum += ((u16 *)&udp)[i];
  for (i = 0; i < (len + 1) / 2; i++)
    sum += ((u16 *)mess)[i];
  while (sum>>16)
    sum = (sum & 0xffff) + (sum >> 16);
  udp.uh_sum = (sum == 0xffff) ? sum : ~sum;
  
  ioctl(daemon->dhcp_raw_fd, BIOCSETIF, ifr);
  
  iov[0].iov_base = &ether;
  iov[0].iov_len = sizeof(ether);
  iov[1].iov_base = &ip;
  iov[1].iov_len = sizeof(ip);
  iov[2].iov_base = &udp;
  iov[2].iov_len = sizeof(udp);
  iov[3].iov_base = mess;
  iov[3].iov_len = len;

  while (writev(daemon->dhcp_raw_fd, iov, 4) == -1 && retry_send());
}

#endif