src/dnsmasq.c

/* dnsmasq is Copyright (c) 2000-2006 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.

   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.
*/

#include "dnsmasq.h"

static char *compile_opts = 
#ifndef HAVE_IPV6
"no-"
#endif
"IPv6 "
#ifndef HAVE_GETOPT_LONG
"no-"
#endif
"GNU-getopt "
#ifdef HAVE_BROKEN_RTC
"no-RTC "
#endif
#ifndef HAVE_ISC_READER
"no-"
#endif
"ISC-leasefile "
#ifndef HAVE_DBUS
"no-"
#endif
"DBus "
#ifdef NO_GETTEXT
"no-"
#endif
"I18N ";

static pid_t pid;
static int pipewrite;

static int set_dns_listeners(struct daemon *daemon, fd_set *set, int maxfd);
static void check_dns_listeners(struct daemon *daemon, fd_set *set, time_t now);
static void sig_handler(int sig);

int main (int argc, char **argv)
{
  struct daemon *daemon;
  int bind_fallback = 0;
  int bad_capabilities = 0;
  time_t now, last = 0;
  struct sigaction sigact;
  struct iname *if_tmp;
  int flags, piperead, pipefd[2];
  unsigned char sig;

#ifndef NO_GETTEXT
  setlocale(LC_ALL, "");
  bindtextdomain("dnsmasq", LOCALEDIR); 
  textdomain("dnsmasq");
#endif

  pid = 0;
 
  sigact.sa_handler = sig_handler;
  sigact.sa_flags = 0;
  sigemptyset(&sigact.sa_mask);
  sigaction(SIGUSR1, &sigact, NULL);
  sigaction(SIGHUP, &sigact, NULL);
  sigaction(SIGTERM, &sigact, NULL);
  sigaction(SIGALRM, &sigact, NULL);
  sigaction(SIGCHLD, &sigact, NULL);

  /* ignore SIGPIPE */
  sigact.sa_handler = SIG_IGN;
  sigaction(SIGPIPE, &sigact, NULL);

  daemon = read_opts(argc, argv, compile_opts);
  
  if (daemon->edns_pktsz < PACKETSZ)
    daemon->edns_pktsz = PACKETSZ;
  daemon->packet_buff_sz = daemon->edns_pktsz > DNSMASQ_PACKETSZ ? 
    daemon->edns_pktsz : DNSMASQ_PACKETSZ;
  daemon->packet = safe_malloc(daemon->packet_buff_sz);
  
  if (!daemon->lease_file)
    {
      if (daemon->dhcp)
	daemon->lease_file = LEASEFILE;
    }
#ifndef HAVE_ISC_READER
  else if (!daemon->dhcp)
    die(_("ISC dhcpd integration not available: set HAVE_ISC_READER in src/config.h"), NULL);
#endif
  
#ifdef HAVE_LINUX_NETWORK
  netlink_init(daemon);
#elif !(defined(IP_RECVDSTADDR) && \
	defined(IP_RECVIF) && \
	defined(IP_SENDSRCADDR))
  if (!(daemon->options & OPT_NOWILD))
    {
      bind_fallback = 1;
      daemon->options |= OPT_NOWILD;
    }
#endif

  daemon->interfaces = NULL;
  if (!enumerate_interfaces(daemon))
    die(_("failed to find list of interfaces: %s"), NULL);
    
  if (daemon->options & OPT_NOWILD) 
    {
      daemon->listeners = create_bound_listeners(daemon);

      for (if_tmp = daemon->if_names; if_tmp; if_tmp = if_tmp->next)
	if (if_tmp->name && !if_tmp->used)
	  die(_("unknown interface %s"), if_tmp->name);
  
      for (if_tmp = daemon->if_addrs; if_tmp; if_tmp = if_tmp->next)
	if (!if_tmp->used)
	  {
	    prettyprint_addr(&if_tmp->addr, daemon->namebuff);
	    die(_("no interface with address %s"), daemon->namebuff);
	  }
    }
  else if (!(daemon->listeners = create_wildcard_listeners(daemon->port)))
    die(_("failed to create listening socket: %s"), NULL);
  
  forward_init(1);
  cache_init(daemon->cachesize, daemon->options & OPT_LOG);

  now = dnsmasq_time();
  
  if (daemon->dhcp)
    {
#if !defined(HAVE_LINUX_NETWORK) && !defined(IP_RECVIF)
      int c;
      struct iname *tmp;
      for (c = 0, tmp = daemon->if_names; tmp; tmp = tmp->next)
	if (!tmp->isloop)
	  c++;
      if (c != 1)
	die(_("must set exactly one interface on broken systems without IP_RECVIF"), NULL);
#endif
      dhcp_init(daemon);
      lease_init(daemon, now);
    }

  if (daemon->options & OPT_DBUS)
#ifdef HAVE_DBUS
    {
      char *err;
      daemon->dbus = NULL;
      daemon->watches = NULL;
      if ((err = dbus_init(daemon)))
	die(_("DBus error: %s"), err);
    }
#else
  die(_("DBus not available: set HAVE_DBUS in src/config.h"), NULL);
#endif
  
  /* If query_port is set then create a socket now, before dumping root
     for use to access nameservers without more specific source addresses.
     This allows query_port to be a low port */
  if (daemon->query_port)
    {
      union  mysockaddr addr;
      addr.in.sin_family = AF_INET;
      addr.in.sin_addr.s_addr = INADDR_ANY;
      addr.in.sin_port = htons(daemon->query_port);
#ifdef HAVE_SOCKADDR_SA_LEN
      addr.in.sin_len = sizeof(struct sockaddr_in);
#endif
      allocate_sfd(&addr, &daemon->sfds);
#ifdef HAVE_IPV6
      addr.in6.sin6_family = AF_INET6;
      addr.in6.sin6_addr = in6addr_any;
      addr.in6.sin6_port = htons(daemon->query_port);
      addr.in6.sin6_flowinfo = 0;
      addr.in6.sin6_scope_id = 0;
#ifdef HAVE_SOCKADDR_SA_LEN
      addr.in6.sin6_len = sizeof(struct sockaddr_in6);
#endif
      allocate_sfd(&addr, &daemon->sfds);
#endif
    }
  
  /* Use a pipe to carry signals back to the event loop in a race-free manner */
  if (pipe(pipefd) == -1 ||
      (flags = fcntl(pipefd[0], F_GETFL)) == -1 ||
      fcntl(pipefd[0], F_SETFL, flags | O_NONBLOCK) == -1 ||
      (flags = fcntl(pipefd[1], F_GETFL)) == -1 ||
      fcntl(pipefd[1], F_SETFL, flags | O_NONBLOCK) == -1)
    die(_("cannot create pipe: %s"), NULL);
  
  piperead = pipefd[0];
  pipewrite = pipefd[1];
  /* prime the pipe to load stuff first time. */
  sig = SIGHUP; 
  write(pipewrite, &sig, 1);
 
  if (!(daemon->options & OPT_DEBUG)) 
    {
      FILE *pidfile;
      struct passwd *ent_pw = daemon->username ? getpwnam(daemon->username) : NULL;
      fd_set test_set;
      int maxfd, i; 

#ifdef HAVE_LINUX_NETWORK
      cap_user_header_t hdr = NULL;
      cap_user_data_t data = NULL; 
      
      /* On linux, we keep CAP_NETADMIN (for ARP-injection) and
	 CAP_NET_RAW (for icmp) if we're doing dhcp */
      if (ent_pw)
	{
	  hdr = safe_malloc(sizeof(*hdr));
	  data = safe_malloc(sizeof(*data));
	  hdr->version = _LINUX_CAPABILITY_VERSION;
	  hdr->pid = 0; /* this process */
	  data->effective = data->permitted = data->inheritable =
	    (1 << CAP_NET_ADMIN) | (1 << CAP_NET_RAW) |
	    (1 << CAP_SETGID) | (1 << CAP_SETUID);
	  	  
	  /* Tell kernel to not clear capabilities when dropping root */
	  if (capset(hdr, data) == -1 || prctl(PR_SET_KEEPCAPS, 1) == -1)
	    {
	      bad_capabilities = errno;
	      ent_pw = NULL;
	    }
	}
#endif

      FD_ZERO(&test_set);
      maxfd = set_dns_listeners(daemon, &test_set, -1);
#ifdef HAVE_DBUS
      maxfd = set_dbus_listeners(daemon, maxfd, &test_set, &test_set, &test_set);
#endif
      
      /* The following code "daemonizes" the process. 
	 See Stevens section 12.4 */
      
#ifndef NO_FORK
      if (!(daemon->options & OPT_NO_FORK))
	{
	  if (fork() != 0 )
	    exit(0);
	  
	  setsid();
	  
	  if (fork() != 0)
	    exit(0);
	}
#endif
      
      chdir("/");
      umask(022); /* make pidfile 0644 */
      
      /* write pidfile _after_ forking ! */
      if (daemon->runfile && (pidfile = fopen(daemon->runfile, "w")))
      	{
	  fprintf(pidfile, "%d\n", (int) getpid());
	  fclose(pidfile);
	}
      
      umask(0);

      for (i=0; i<64; i++)
	{
	  if (i == piperead || i == pipewrite)
	    continue;

#ifdef HAVE_LINUX_NETWORK
	  if (i == daemon->netlinkfd)
	    continue;
#endif
	  
	  if (daemon->dhcp && 
	      (i == fileno(daemon->lease_stream) || 
#ifndef HAVE_LINUX_NETWORK
	       i == daemon->dhcp_raw_fd ||
	       i == daemon->dhcp_icmp_fd ||
#endif
	       i == daemon->dhcpfd))
	    continue;

	  if (i <= maxfd && FD_ISSET(i, &test_set))
	    continue;

	  close(i);
	}

      /* Change uid and gid for security */
      if (ent_pw)
	{
	  gid_t dummy;
	  struct group *gp;

	  /* remove all supplimentary groups */
	  setgroups(0, &dummy);
	  /* change group for /etc/ppp/resolv.conf 
	     otherwise get the group for "nobody" */
	  if ((daemon->groupname && (gp = getgrnam(daemon->groupname))) || 
	      (gp = getgrgid(ent_pw->pw_gid)))
	    setgid(gp->gr_gid); 
	  /* finally drop root */
	  setuid(ent_pw->pw_uid);

#ifdef HAVE_LINUX_NETWORK
	  data->effective = data->permitted = 
	    (1 << CAP_NET_ADMIN) | (1 << CAP_NET_RAW);
	  data->inheritable = 0;
	  
	  /* lose the setuid and setgid capbilities */
	  capset(hdr, data);
#endif
	}
    }
#ifdef HAVE_LINUX_NETWORK
  else
     prctl(PR_SET_DUMPABLE, 1);
#endif

  openlog("dnsmasq", 
	  DNSMASQ_LOG_OPT(daemon->options & OPT_DEBUG), 
	  DNSMASQ_LOG_FAC(daemon->options & OPT_DEBUG));
  
  if (daemon->cachesize != 0)
    syslog(LOG_INFO, _("started, version %s cachesize %d"), VERSION, daemon->cachesize);
  else
    syslog(LOG_INFO, _("started, version %s cache disabled"), VERSION);

  syslog(LOG_INFO, _("compile time options: %s"), compile_opts);

#ifdef HAVE_DBUS
  if (daemon->options & OPT_DBUS)
    {
      if (daemon->dbus)
	syslog(LOG_INFO, _("DBus support enabled: connected to system bus"));
      else
	syslog(LOG_INFO, _("DBus support enabled: bus connection pending"));
    }
#endif

  if (bind_fallback)
    syslog(LOG_WARNING, _("setting --bind-interfaces option because of OS limitations"));
  
  if (!(daemon->options & OPT_NOWILD)) 
    for (if_tmp = daemon->if_names; if_tmp; if_tmp = if_tmp->next)
      if (if_tmp->name && !if_tmp->used)
	syslog(LOG_WARNING, _("warning: interface %s does not currently exist"), if_tmp->name);
   
  if (daemon->dhcp)
    {
      struct dhcp_context *dhcp_tmp;
      
      for (dhcp_tmp = daemon->dhcp; dhcp_tmp; dhcp_tmp = dhcp_tmp->next)
	{
	  prettyprint_time(daemon->dhcp_buff2, dhcp_tmp->lease_time);
	  strcpy(daemon->dhcp_buff, inet_ntoa(dhcp_tmp->start));
	  syslog(LOG_INFO, 
		 (dhcp_tmp->flags & CONTEXT_STATIC) ? 
		 _("DHCP, static leases only on %.0s%s, lease time %s") :
		 _("DHCP, IP range %s -- %s, lease time %s"),
		 daemon->dhcp_buff, inet_ntoa(dhcp_tmp->end), daemon->dhcp_buff2);
	}
    }

  if (!(daemon->options & OPT_DEBUG) && (getuid() == 0 || geteuid() == 0))
    {
      if (bad_capabilities)
	{
	  errno = bad_capabilities;
	  syslog(LOG_WARNING, _("warning: setting capabilities failed: %m"));
	}
      syslog(LOG_WARNING, _("running as root"));
    }
  
  check_servers(daemon);
  
  pid = getpid();

  while (1)
    {
      int maxfd;
      struct timeval t, *tp = NULL;
      fd_set rset, wset, eset;

      t.tv_sec = 0; /* no warning */
      
      FD_ZERO(&rset);
      FD_ZERO(&wset);
      FD_ZERO(&eset);
      
      maxfd = set_dns_listeners(daemon, &rset, -1);
	
#ifdef HAVE_DBUS
      /* Whilst polling for the dbus, wake every quarter second */
      if ((daemon->options & OPT_DBUS) && !daemon->dbus)
	{
	  tp = &t;
	  tp->tv_sec = 0;
	  tp->tv_usec = 250000;
	}

      maxfd = set_dbus_listeners(daemon, maxfd, &rset, &wset, &eset);
#endif	
  
      if (daemon->dhcp)
	{
	  FD_SET(daemon->dhcpfd, &rset);
	  if (daemon->dhcpfd > maxfd)
	    maxfd = daemon->dhcpfd;
	}

#ifdef HAVE_LINUX_NETWORK
      FD_SET(daemon->netlinkfd, &rset);
      if (daemon->netlinkfd > maxfd)
	maxfd = daemon->netlinkfd;
#endif
      
      FD_SET(piperead, &rset);
      if (piperead > maxfd)
	maxfd = piperead;
      
      if (select(maxfd+1, &rset, &wset, &eset, tp) < 0)
	{
	  /* otherwise undefined after error */
	  FD_ZERO(&rset); FD_ZERO(&wset); FD_ZERO(&eset);
	}

      now = dnsmasq_time();

      /* Check for changes to resolv files once per second max. */
      /* Don't go silent for long periods if the clock goes backwards. */
      if (last == 0 || difftime(now, last) > 1.0 || difftime(now, last) < 1.0)
	{
	  last = now;

#ifdef HAVE_ISC_READER
	  if (daemon->lease_file && !daemon->dhcp)
	    load_dhcp(daemon, now);
#endif

	  if (!(daemon->options & OPT_NO_POLL))
	    {
	      struct resolvc *res = daemon->resolv_files, *latest = NULL;
	      struct stat statbuf;
	      time_t last_change = 0;
	      /* There may be more than one possible file. 
		 Go through and find the one which changed _last_.
		 Warn of any which can't be read. */
	      while (res)
		{
		  if (stat(res->name, &statbuf) == -1)
		    {
		      if (!res->logged)
			syslog(LOG_WARNING, _("failed to access %s: %m"), res->name);
		      res->logged = 1;
		    }
		  else
		    {
		      res->logged = 0;
		      if (statbuf.st_mtime != res->mtime)
			{
			  res->mtime = statbuf.st_mtime;
			  if (difftime(res->mtime, last_change) > 0.0)
			    {
			      last_change = res->mtime;
			      latest = res;
			    }
			}
		    }
		  res = res->next;
		}
	  
	      if (latest)
		{
		  reload_servers(latest->name, daemon);
		  check_servers(daemon);
		}
	    }
	}

      if (FD_ISSET(piperead, &rset))
	{
	  if (read(piperead, &sig, 1) == 1)
	    switch (sig)
	      {
	      case SIGHUP:
		clear_cache_and_reload(daemon);
		if (daemon->resolv_files && (daemon->options & OPT_NO_POLL))
		  {
		    reload_servers(daemon->resolv_files->name, daemon);
		    check_servers(daemon);
		  }
		break;
		
	      case SIGUSR1:
		dump_cache(daemon, now);
		break;
		
	      case SIGALRM:
		if (daemon->dhcp)
		  lease_update_file(daemon);
		break;
		
	      case SIGTERM:
		syslog(LOG_INFO, _("exiting on receipt of SIGTERM"));
		if (daemon->dhcp)
		  fclose(daemon->lease_stream);
		exit(0);

	      case SIGCHLD:
		/* See Stevens 5.10 */
		while (waitpid(-1, NULL, WNOHANG) > 0)
		  daemon->num_kids--;
		break;

	      }
	}

#ifdef HAVE_LINUX_NETWORK
      if (FD_ISSET(daemon->netlinkfd, &rset))
	netlink_multicast(daemon);
#endif
      
#ifdef HAVE_DBUS
      /* if we didn't create a DBus connection, retry now. */ 
      if ((daemon->options & OPT_DBUS) && !daemon->dbus)
	{
	  char *err;
	  if ((err = dbus_init(daemon)))
	    syslog(LOG_WARNING, _("DBus error: %s"), err);
	  if (daemon->dbus)
	    syslog(LOG_INFO, _("connected to system DBus"));
	}
      check_dbus_listeners(daemon, &rset, &wset, &eset);
#endif

      check_dns_listeners(daemon, &rset, now);
      
      if (daemon->dhcp && FD_ISSET(daemon->dhcpfd, &rset))
	dhcp_packet(daemon, now);
    }
}

static void sig_handler(int sig)
{
  if (pid == 0)
    {
      /* ignore anything other than TERM during startup */
      if (sig == SIGTERM)
	exit(0);
    }
  else if (pid == getpid())
    {
      /* master process */
      unsigned char sigchr = sig;
      int errsave = errno;
      write(pipewrite, &sigchr, 1);
      errno = errsave;
    }
  else
    {
      /* alarm is used to kill children after a fixed time. */
      if (sig == SIGALRM)
	exit(0);
    }
}


void clear_cache_and_reload(struct daemon *daemon)
{
  cache_reload(daemon->options, daemon->namebuff, daemon->domain_suffix, daemon->addn_hosts);
  if (daemon->dhcp)
    {
      if (daemon->options & OPT_ETHERS)
	dhcp_read_ethers(daemon);
      dhcp_update_configs(daemon->dhcp_conf);
      lease_update_from_configs(daemon); 
      lease_update_file(daemon); 
      lease_update_dns(daemon);
    }
}

static int set_dns_listeners(struct daemon *daemon, fd_set *set, int maxfd)
{
  struct serverfd *serverfdp;
  struct listener *listener;

  for (serverfdp = daemon->sfds; serverfdp; serverfdp = serverfdp->next)
    {
      FD_SET(serverfdp->fd, set);
      if (serverfdp->fd > maxfd)
	maxfd = serverfdp->fd;
    }
	  
  for (listener = daemon->listeners; listener; listener = listener->next)
    {
      FD_SET(listener->fd, set);
      if (listener->fd > maxfd)
	maxfd = listener->fd;
      FD_SET(listener->tcpfd, set);
      if (listener->tcpfd > maxfd)
	maxfd = listener->tcpfd;
    }

  return maxfd;
}

static void check_dns_listeners(struct daemon *daemon, fd_set *set, time_t now)
{
  struct serverfd *serverfdp;
  struct listener *listener;	  

   for (serverfdp = daemon->sfds; serverfdp; serverfdp = serverfdp->next)
     if (FD_ISSET(serverfdp->fd, set))
       reply_query(serverfdp, daemon, now);

   for (listener = daemon->listeners; listener; listener = listener->next)
     {
       if (FD_ISSET(listener->fd, set))
	 receive_query(listener, daemon, now);
       
       if (FD_ISSET(listener->tcpfd, set))
	 {
	   int confd;
	  	   
	   while((confd = accept(listener->tcpfd, NULL, NULL)) == -1 && errno == EINTR);
	      
	   if (confd != -1)
	     {
	       struct irec *iface = NULL;
	       
	       if (daemon->options & OPT_NOWILD)
		 iface = listener->iface;
	       else
		 {
		   union mysockaddr tcp_addr;
		   socklen_t tcp_len = sizeof(union mysockaddr);
		   /* Check for allowed interfaces when binding the wildcard address:
		      we do this by looking for an interface with the same address as 
		      the local address of the TCP connection, then looking to see if that's
		      an allowed interface. As a side effect, we get the netmask of the
		      interface too, for localisation. */
		   
		   /* interface may be new since startup */
		   if (enumerate_interfaces(daemon) &&
		       getsockname(confd, (struct sockaddr *)&tcp_addr, &tcp_len) != -1)
		     for (iface = daemon->interfaces; iface; iface = iface->next)
		       if (sockaddr_isequal(&iface->addr, &tcp_addr))
			 break;
		 }
	       
	       if ((daemon->num_kids >= MAX_PROCS) || !iface)
		 close(confd);
#ifndef NO_FORK
	       else if (!(daemon->options & OPT_DEBUG) && fork())
		 {
		   daemon->num_kids++;
		   close(confd);
		 }
#endif
	       else
		 {
		   unsigned char *buff;
		   struct server *s; 
		   int flags;
		   struct in_addr dst_addr_4;

		   dst_addr_4.s_addr = 0;

		   /* Arrange for SIGALARM after CHILD_LIFETIME seconds to
		      terminate the process. */
		   if (!(daemon->options & OPT_DEBUG))
		     alarm(CHILD_LIFETIME);
		   
		   /* start with no upstream connections. */
		   for (s = daemon->servers; s; s = s->next)
		     s->tcpfd = -1; 
		   
		   /* The connected socket inherits non-blocking
		      attribute from the listening socket. 
		      Reset that here. */
		   if ((flags = fcntl(confd, F_GETFL, 0)) != -1)
		     fcntl(confd, F_SETFL, flags & ~O_NONBLOCK);
		   
		   if (listener->family == AF_INET)
		     dst_addr_4 = iface->addr.in.sin_addr;
		   
		   buff = tcp_request(daemon, confd, now, dst_addr_4, iface->netmask);
		   
		   if (!(daemon->options & OPT_DEBUG))
		     exit(0);
		      
		   close(confd);
		   if (buff)
		     free(buff);
		   for (s = daemon->servers; s; s = s->next)
		     if (s->tcpfd != -1)
		       close(s->tcpfd);
		 }
	     }
	 }
     }
}

int make_icmp_sock(void)
{
  int fd, flags;
  int zeroopt = 0;

  if ((fd = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP)) != -1)
    {
      if ((flags = fcntl(fd, F_GETFL, 0)) == -1 ||
	  fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1 ||
	  setsockopt(fd, SOL_SOCKET, SO_DONTROUTE, &zeroopt, sizeof(zeroopt)) == -1)
	{
	  close(fd);
	  fd = -1;
	}
    }

  return fd;
}

int icmp_ping(struct daemon *daemon, struct in_addr addr)
{
  /* Try and get an ICMP echo from a machine. */

  /* Note that whilst in the three second wait, we check for 
     (and service) events on the DNS sockets, (so doing that
     better not use any resources our caller has in use...)
     but we remain deaf to signals or further DHCP packets. */

  int fd;
  struct sockaddr_in saddr;
  struct { 
    struct ip ip;
    struct icmp icmp;
  } packet;
  unsigned short id = rand16();
  unsigned int i, j;
  int gotreply = 0;
  time_t start, now;

#ifdef HAVE_LINUX_NETWORK
  if ((fd = make_icmp_sock()) == -1)
    return 0;
#else
  int opt = 2000;
  fd = daemon->dhcp_icmp_fd;
  setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt));
#endif

  saddr.sin_family = AF_INET;
  saddr.sin_port = 0;
  saddr.sin_addr = addr;
#ifdef HAVE_SOCKADDR_SA_LEN
  saddr.sin_len = sizeof(struct sockaddr_in);
#endif
  
  memset(&packet.icmp, 0, sizeof(packet.icmp));
  packet.icmp.icmp_type = ICMP_ECHO;
  packet.icmp.icmp_id = id;
  for (j = 0, i = 0; i < sizeof(struct icmp) / 2; i++)
    j += ((u16 *)&packet.icmp)[i];
  while (j>>16)
    j = (j & 0xffff) + (j >> 16);  
  packet.icmp.icmp_cksum = (j == 0xffff) ? j : ~j;
  
  while (sendto(fd, (char *)&packet.icmp, sizeof(struct icmp), 0, 
		(struct sockaddr *)&saddr, sizeof(saddr)) == -1 &&
	 retry_send());
  
  for (now = start = dnsmasq_time(); 
       difftime(now, start) < (float)PING_WAIT;)
    {
      struct timeval tv;
      fd_set rset;
      struct sockaddr_in faddr;
      int maxfd; 
      socklen_t len = sizeof(faddr);
      
      tv.tv_usec = 250000;
      tv.tv_sec = 0; 
      
      FD_ZERO(&rset);
      FD_SET(fd, &rset);
      maxfd = set_dns_listeners(daemon, &rset, fd);
		
      if (select(maxfd+1, &rset, NULL, NULL, &tv) < 0)
	FD_ZERO(&rset);
      
      now = dnsmasq_time();
      check_dns_listeners(daemon, &rset, now);
      
      if (FD_ISSET(fd, &rset) &&
	  recvfrom(fd, &packet, sizeof(packet), 0,
		   (struct sockaddr *)&faddr, &len) == sizeof(packet) &&
	  saddr.sin_addr.s_addr == faddr.sin_addr.s_addr &&
	  packet.icmp.icmp_type == ICMP_ECHOREPLY &&
	  packet.icmp.icmp_seq == 0 &&
	  packet.icmp.icmp_id == id)
	{
	  gotreply = 1;
	  break;
	}
    }
  
#ifdef HAVE_LINUX_NETWORK
  close(fd);
#else
  opt = 1;
  setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt));
#endif

  return gotreply;
}