src/netlink.c - thekelleys/dnsmasq - Gitiles

 /* dnsmasq is Copyright (c) 2000-2016 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"

 #ifdef HAVE_LINUX_NETWORK

 #include <linux/types.h>
 #include <linux/netlink.h>
 #include <linux/rtnetlink.h>

 /* linux 2.6.19 buggers up the headers, patch it up here. */
 #ifndef IFA_RTA
 #  define IFA_RTA(r)  \
        ((struct rtattr*)(((char*)(r)) + NLMSG_ALIGN(sizeof(struct ifaddrmsg))))

 #  include <linux/if_addr.h>
 #endif

 #ifndef NDA_RTA
 #  define NDA_RTA(r) ((struct rtattr*)(((char*)(r)) + NLMSG_ALIGN(sizeof(struct ndmsg))))
 #endif


 static struct iovec iov;
 static u32 netlink_pid;

 static void nl_async(struct nlmsghdr *h);

 void netlink_init(void)
 {
   struct sockaddr_nl addr;
   socklen_t slen = sizeof(addr);

   addr.nl_family = AF_NETLINK;
   addr.nl_pad = 0;
   addr.nl_pid = 0; /* autobind */
   addr.nl_groups = RTMGRP_IPV4_ROUTE;
   if (option_bool(OPT_CLEVERBIND))
     addr.nl_groups |= RTMGRP_IPV4_IFADDR;
 #ifdef HAVE_IPV6
   addr.nl_groups |= RTMGRP_IPV6_ROUTE;
   if (option_bool(OPT_CLEVERBIND))
     addr.nl_groups |= RTMGRP_IPV6_IFADDR;
 #endif
 #ifdef HAVE_DHCP6
   if (daemon->doing_ra || daemon->doing_dhcp6)
     addr.nl_groups |= RTMGRP_IPV6_IFADDR;
 #endif

   /* May not be able to have permission to set multicast groups don't die in that case */
   if ((daemon->netlinkfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE)) != -1)
     {
       if (bind(daemon->netlinkfd, (struct sockaddr *)&addr, sizeof(addr)) == -1)
 	{
 	  addr.nl_groups = 0;
 	  if (errno != EPERM || bind(daemon->netlinkfd, (struct sockaddr *)&addr, sizeof(addr)) == -1)
 	    daemon->netlinkfd = -1;
 	}
     }

   if (daemon->netlinkfd == -1 ||
       getsockname(daemon->netlinkfd, (struct sockaddr *)&addr, &slen) == 1)
     die(_("cannot create netlink socket: %s"), NULL, EC_MISC);

   /* save pid assigned by bind() and retrieved by getsockname() */
   netlink_pid = addr.nl_pid;

   iov.iov_len = 100;
   iov.iov_base = safe_malloc(iov.iov_len);
 }

 static ssize_t netlink_recv(void)
 {
   struct msghdr msg;
   struct sockaddr_nl nladdr;
   ssize_t rc;

   while (1)
     {
       msg.msg_control = NULL;
       msg.msg_controllen = 0;
       msg.msg_name = &nladdr;
       msg.msg_namelen = sizeof(nladdr);
       msg.msg_iov = &iov;
       msg.msg_iovlen = 1;
       msg.msg_flags = 0;

       while ((rc = recvmsg(daemon->netlinkfd, &msg, MSG_PEEK | MSG_TRUNC)) == -1 && errno == EINTR);

       /* make buffer big enough */
       if (rc != -1 && (msg.msg_flags & MSG_TRUNC))
 	{
 	  /* Very new Linux kernels return the actual size needed, older ones always return truncated size */
 	  if ((size_t)rc == iov.iov_len)
 	    {
 	      if (expand_buf(&iov, rc + 100))
 		continue;
 	    }
 	  else
 	    expand_buf(&iov, rc);
 	}

       /* read it for real */
       msg.msg_flags = 0;
       while ((rc = recvmsg(daemon->netlinkfd, &msg, 0)) == -1 && errno == EINTR);

       /* Make sure this is from the kernel */
       if (rc == -1 || nladdr.nl_pid == 0)
 	break;
     }

   /* discard stuff which is truncated at this point (expand_buf() may fail) */
   if (msg.msg_flags & MSG_TRUNC)
     {
       rc = -1;
       errno = ENOMEM;
     }

   return rc;
 }


 /* family = AF_UNSPEC finds ARP table entries.
    family = AF_LOCAL finds MAC addresses. */
 int iface_enumerate(int family, void *parm, int (*callback)())
 {
   struct sockaddr_nl addr;
   struct nlmsghdr *h;
   ssize_t len;
   static unsigned int seq = 0;
   int callback_ok = 1;

   struct {
     struct nlmsghdr nlh;
     struct rtgenmsg g;
   } req;

   addr.nl_family = AF_NETLINK;
   addr.nl_pad = 0;
   addr.nl_groups = 0;
   addr.nl_pid = 0; /* address to kernel */

  again:
   if (family == AF_UNSPEC)
     req.nlh.nlmsg_type = RTM_GETNEIGH;
   else if (family == AF_LOCAL)
     req.nlh.nlmsg_type = RTM_GETLINK;
   else
     req.nlh.nlmsg_type = RTM_GETADDR;

   req.nlh.nlmsg_len = sizeof(req);
   req.nlh.nlmsg_flags = NLM_F_ROOT | NLM_F_MATCH | NLM_F_REQUEST | NLM_F_ACK;
   req.nlh.nlmsg_pid = 0;
   req.nlh.nlmsg_seq = ++seq;
   req.g.rtgen_family = family;

   /* Don't block in recvfrom if send fails */
   while(retry_send(sendto(daemon->netlinkfd, (void *)&req, sizeof(req), 0,
 			  (struct sockaddr *)&addr, sizeof(addr))));

   if (errno != 0)
     return 0;

   while (1)
     {
       if ((len = netlink_recv()) == -1)
 	{
 	  if (errno == ENOBUFS)
 	    {
 	      sleep(1);
 	      goto again;
 	    }
 	  return 0;
 	}

       for (h = (struct nlmsghdr *)iov.iov_base; NLMSG_OK(h, (size_t)len); h = NLMSG_NEXT(h, len))
 	if (h->nlmsg_seq != seq || h->nlmsg_pid != netlink_pid || h->nlmsg_type == NLMSG_ERROR)
 	  {
 	    /* May be multicast arriving async */
 	    nl_async(h);
 	  }
 	else if (h->nlmsg_type == NLMSG_DONE)
 	  return callback_ok;
 	else if (h->nlmsg_type == RTM_NEWADDR && family != AF_UNSPEC && family != AF_LOCAL)
 	  {
 	    struct ifaddrmsg *ifa = NLMSG_DATA(h);
 	    struct rtattr *rta = IFA_RTA(ifa);
 	    unsigned int len1 = h->nlmsg_len - NLMSG_LENGTH(sizeof(*ifa));

 	    if (ifa->ifa_family == family)
 	      {
 		if (ifa->ifa_family == AF_INET)
 		  {
 		    struct in_addr netmask, addr, broadcast;
 		    char *label = NULL;

 		    netmask.s_addr = htonl(~(in_addr_t)0 << (32 - ifa->ifa_prefixlen));

 		    addr.s_addr = 0;
 		    broadcast.s_addr = 0;

 		    while (RTA_OK(rta, len1))
 		      {
 			if (rta->rta_type == IFA_LOCAL)
 			  addr = *((struct in_addr *)(rta+1));
 			else if (rta->rta_type == IFA_BROADCAST)
 			  broadcast = *((struct in_addr *)(rta+1));
 			else if (rta->rta_type == IFA_LABEL)
 			  label = RTA_DATA(rta);

 			rta = RTA_NEXT(rta, len1);
 		      }

 		    if (addr.s_addr && callback_ok)
 		      if (!((*callback)(addr, ifa->ifa_index, label,  netmask, broadcast, parm)))
 			callback_ok = 0;
 		  }
 #ifdef HAVE_IPV6
 		else if (ifa->ifa_family == AF_INET6)
 		  {
 		    struct in6_addr *addrp = NULL;
 		    u32 valid = 0, preferred = 0;
 		    int flags = 0;

 		    while (RTA_OK(rta, len1))
 		      {
 			if (rta->rta_type == IFA_ADDRESS)
 			  addrp = ((struct in6_addr *)(rta+1));
 			else if (rta->rta_type == IFA_CACHEINFO)
 			  {
 			    struct ifa_cacheinfo *ifc = (struct ifa_cacheinfo *)(rta+1);
 			    preferred = ifc->ifa_prefered;
 			    valid = ifc->ifa_valid;
 			  }
 			rta = RTA_NEXT(rta, len1);
 		      }

 		    if (ifa->ifa_flags & IFA_F_TENTATIVE)
 		      flags |= IFACE_TENTATIVE;

 		    if (ifa->ifa_flags & IFA_F_DEPRECATED)
 		      flags |= IFACE_DEPRECATED;

 		    if (!(ifa->ifa_flags & IFA_F_TEMPORARY))
 		      flags |= IFACE_PERMANENT;

 		    if (addrp && callback_ok)
 		      if (!((*callback)(addrp, (int)(ifa->ifa_prefixlen), (int)(ifa->ifa_scope),
 					(int)(ifa->ifa_index), flags,
 					(int) preferred, (int)valid, parm)))
 			callback_ok = 0;
 		  }
 #endif
 	      }
 	  }
 	else if (h->nlmsg_type == RTM_NEWNEIGH && family == AF_UNSPEC)
 	  {
 	    struct ndmsg *neigh = NLMSG_DATA(h);
 	    struct rtattr *rta = NDA_RTA(neigh);
 	    unsigned int len1 = h->nlmsg_len - NLMSG_LENGTH(sizeof(*neigh));
 	    size_t maclen = 0;
 	    char *inaddr = NULL, *mac = NULL;

 	    while (RTA_OK(rta, len1))
 	      {
 		if (rta->rta_type == NDA_DST)
 		  inaddr = (char *)(rta+1);
 		else if (rta->rta_type == NDA_LLADDR)
 		  {
 		    maclen = rta->rta_len - sizeof(struct rtattr);
 		    mac = (char *)(rta+1);
 		  }

 		rta = RTA_NEXT(rta, len1);
 	      }

 	    if (!(neigh->ndm_state & (NUD_NOARP | NUD_INCOMPLETE | NUD_FAILED)) &&
 		inaddr && mac && callback_ok)
 	      if (!((*callback)(neigh->ndm_family, inaddr, mac, maclen, parm)))
 		callback_ok = 0;
 	  }
 #ifdef HAVE_DHCP6
 	else if (h->nlmsg_type == RTM_NEWLINK && family == AF_LOCAL)
 	  {
 	    struct ifinfomsg *link =  NLMSG_DATA(h);
 	    struct rtattr *rta = IFLA_RTA(link);
 	    unsigned int len1 = h->nlmsg_len - NLMSG_LENGTH(sizeof(*link));
 	    char *mac = NULL;
 	    size_t maclen = 0;

 	    while (RTA_OK(rta, len1))
 	      {
 		if (rta->rta_type == IFLA_ADDRESS)
 		  {
 		    maclen = rta->rta_len - sizeof(struct rtattr);
 		    mac = (char *)(rta+1);
 		  }

 		rta = RTA_NEXT(rta, len1);
 	      }

 	    if (mac && callback_ok && !((link->ifi_flags & (IFF_LOOPBACK | IFF_POINTOPOINT))) &&
 		!((*callback)((int)link->ifi_index, (unsigned int)link->ifi_type, mac, maclen, parm)))
 	      callback_ok = 0;
 	  }
 #endif
     }
 }

 void netlink_multicast(void)
 {
   ssize_t len;
   struct nlmsghdr *h;
   int flags;

   /* don't risk blocking reading netlink messages here. */
   if ((flags = fcntl(daemon->netlinkfd, F_GETFL)) == -1 ||
       fcntl(daemon->netlinkfd, F_SETFL, flags | O_NONBLOCK) == -1)
     return;

   if ((len = netlink_recv()) != -1)
     for (h = (struct nlmsghdr *)iov.iov_base; NLMSG_OK(h, (size_t)len); h = NLMSG_NEXT(h, len))
       nl_async(h);

   /* restore non-blocking status */
   fcntl(daemon->netlinkfd, F_SETFL, flags);
 }

 static void nl_async(struct nlmsghdr *h)
 {
   if (h->nlmsg_type == NLMSG_ERROR)
     {
       struct nlmsgerr *err = NLMSG_DATA(h);
       if (err->error != 0)
 	my_syslog(LOG_ERR, _("netlink returns error: %s"), strerror(-(err->error)));
     }
   else if (h->nlmsg_pid == 0 && h->nlmsg_type == RTM_NEWROUTE)
     {
       /* We arrange to receive netlink multicast messages whenever the network route is added.
 	 If this happens and we still have a DNS packet in the buffer, we re-send it.
 	 This helps on DoD links, where frequently the packet which triggers dialling is
 	 a DNS query, which then gets lost. By re-sending, we can avoid the lookup
 	 failing. */
       struct rtmsg *rtm = NLMSG_DATA(h);

       if (rtm->rtm_type == RTN_UNICAST && rtm->rtm_scope == RT_SCOPE_LINK)
 	queue_event(EVENT_NEWROUTE);
     }
   else if (h->nlmsg_type == RTM_NEWADDR || h->nlmsg_type == RTM_DELADDR)
     queue_event(EVENT_NEWADDR);
 }
 #endif
	/* dnsmasq is Copyright (c) 2000-2016 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"

	#ifdef HAVE_LINUX_NETWORK

	#include <linux/types.h>
	#include <linux/netlink.h>
	#include <linux/rtnetlink.h>

	/* linux 2.6.19 buggers up the headers, patch it up here. */
	#ifndef IFA_RTA
	# define IFA_RTA(r) \
	((struct rtattr)(((char)(r)) + NLMSG_ALIGN(sizeof(struct ifaddrmsg))))

	# include <linux/if_addr.h>
	#endif

	#ifndef NDA_RTA
	# define NDA_RTA(r) ((struct rtattr)(((char)(r)) + NLMSG_ALIGN(sizeof(struct ndmsg))))
	#endif


	static struct iovec iov;
	static u32 netlink_pid;

	static void nl_async(struct nlmsghdr *h);

	void netlink_init(void)
	{
	struct sockaddr_nl addr;
	socklen_t slen = sizeof(addr);

	addr.nl_family = AF_NETLINK;
	addr.nl_pad = 0;
	addr.nl_pid = 0; /* autobind */
	addr.nl_groups = RTMGRP_IPV4_ROUTE;
	if (option_bool(OPT_CLEVERBIND))
	addr.nl_groups \|= RTMGRP_IPV4_IFADDR;
	#ifdef HAVE_IPV6
	addr.nl_groups \|= RTMGRP_IPV6_ROUTE;
	if (option_bool(OPT_CLEVERBIND))
	addr.nl_groups \|= RTMGRP_IPV6_IFADDR;
	#endif
	#ifdef HAVE_DHCP6
	if (daemon->doing_ra \|\| daemon->doing_dhcp6)
	addr.nl_groups \|= RTMGRP_IPV6_IFADDR;
	#endif

	/* May not be able to have permission to set multicast groups don't die in that case */
	if ((daemon->netlinkfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE)) != -1)
	{
	if (bind(daemon->netlinkfd, (struct sockaddr *)&addr, sizeof(addr)) == -1)
	{
	addr.nl_groups = 0;
	if (errno != EPERM \|\| bind(daemon->netlinkfd, (struct sockaddr *)&addr, sizeof(addr)) == -1)
	daemon->netlinkfd = -1;
	}
	}

	if (daemon->netlinkfd == -1 \|\|
	getsockname(daemon->netlinkfd, (struct sockaddr *)&addr, &slen) == 1)
	die(_("cannot create netlink socket: %s"), NULL, EC_MISC);

	/* save pid assigned by bind() and retrieved by getsockname() */
	netlink_pid = addr.nl_pid;

	iov.iov_len = 100;
	iov.iov_base = safe_malloc(iov.iov_len);
	}

	static ssize_t netlink_recv(void)
	{
	struct msghdr msg;
	struct sockaddr_nl nladdr;
	ssize_t rc;

	while (1)
	{
	msg.msg_control = NULL;
	msg.msg_controllen = 0;
	msg.msg_name = &nladdr;
	msg.msg_namelen = sizeof(nladdr);
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	msg.msg_flags = 0;

	while ((rc = recvmsg(daemon->netlinkfd, &msg, MSG_PEEK \| MSG_TRUNC)) == -1 && errno == EINTR);

	/* make buffer big enough */
	if (rc != -1 && (msg.msg_flags & MSG_TRUNC))
	{
	/* Very new Linux kernels return the actual size needed, older ones always return truncated size */
	if ((size_t)rc == iov.iov_len)
	{
	if (expand_buf(&iov, rc + 100))
	continue;
	}
	else
	expand_buf(&iov, rc);
	}

	/* read it for real */
	msg.msg_flags = 0;
	while ((rc = recvmsg(daemon->netlinkfd, &msg, 0)) == -1 && errno == EINTR);

	/* Make sure this is from the kernel */
	if (rc == -1 \|\| nladdr.nl_pid == 0)
	break;
	}

	/* discard stuff which is truncated at this point (expand_buf() may fail) */
	if (msg.msg_flags & MSG_TRUNC)
	{
	rc = -1;
	errno = ENOMEM;
	}

	return rc;
	}


	/* family = AF_UNSPEC finds ARP table entries.
	family = AF_LOCAL finds MAC addresses. */
	int iface_enumerate(int family, void parm, int (callback)())
	{
	struct sockaddr_nl addr;
	struct nlmsghdr *h;
	ssize_t len;
	static unsigned int seq = 0;
	int callback_ok = 1;

	struct {
	struct nlmsghdr nlh;
	struct rtgenmsg g;
	} req;

	addr.nl_family = AF_NETLINK;
	addr.nl_pad = 0;
	addr.nl_groups = 0;
	addr.nl_pid = 0; /* address to kernel */

	again:
	if (family == AF_UNSPEC)
	req.nlh.nlmsg_type = RTM_GETNEIGH;
	else if (family == AF_LOCAL)
	req.nlh.nlmsg_type = RTM_GETLINK;
	else
	req.nlh.nlmsg_type = RTM_GETADDR;

	req.nlh.nlmsg_len = sizeof(req);
	req.nlh.nlmsg_flags = NLM_F_ROOT \| NLM_F_MATCH \| NLM_F_REQUEST \| NLM_F_ACK;
	req.nlh.nlmsg_pid = 0;
	req.nlh.nlmsg_seq = ++seq;
	req.g.rtgen_family = family;

	/* Don't block in recvfrom if send fails */
	while(retry_send(sendto(daemon->netlinkfd, (void *)&req, sizeof(req), 0,
	(struct sockaddr *)&addr, sizeof(addr))));

	if (errno != 0)
	return 0;

	while (1)
	{
	if ((len = netlink_recv()) == -1)
	{
	if (errno == ENOBUFS)
	{
	sleep(1);
	goto again;
	}
	return 0;
	}

	for (h = (struct nlmsghdr *)iov.iov_base; NLMSG_OK(h, (size_t)len); h = NLMSG_NEXT(h, len))
	if (h->nlmsg_seq != seq \|\| h->nlmsg_pid != netlink_pid \|\| h->nlmsg_type == NLMSG_ERROR)
	{
	/* May be multicast arriving async */
	nl_async(h);
	}
	else if (h->nlmsg_type == NLMSG_DONE)
	return callback_ok;
	else if (h->nlmsg_type == RTM_NEWADDR && family != AF_UNSPEC && family != AF_LOCAL)
	{
	struct ifaddrmsg *ifa = NLMSG_DATA(h);
	struct rtattr *rta = IFA_RTA(ifa);
	unsigned int len1 = h->nlmsg_len - NLMSG_LENGTH(sizeof(*ifa));

	if (ifa->ifa_family == family)
	{
	if (ifa->ifa_family == AF_INET)
	{
	struct in_addr netmask, addr, broadcast;
	char *label = NULL;

	netmask.s_addr = htonl(~(in_addr_t)0 << (32 - ifa->ifa_prefixlen));

	addr.s_addr = 0;
	broadcast.s_addr = 0;

	while (RTA_OK(rta, len1))
	{
	if (rta->rta_type == IFA_LOCAL)
	addr = ((struct in_addr )(rta+1));
	else if (rta->rta_type == IFA_BROADCAST)
	broadcast = ((struct in_addr )(rta+1));
	else if (rta->rta_type == IFA_LABEL)
	label = RTA_DATA(rta);

	rta = RTA_NEXT(rta, len1);
	}

	if (addr.s_addr && callback_ok)
	if (!((*callback)(addr, ifa->ifa_index, label, netmask, broadcast, parm)))
	callback_ok = 0;
	}
	#ifdef HAVE_IPV6
	else if (ifa->ifa_family == AF_INET6)
	{
	struct in6_addr *addrp = NULL;
	u32 valid = 0, preferred = 0;
	int flags = 0;

	while (RTA_OK(rta, len1))
	{
	if (rta->rta_type == IFA_ADDRESS)
	addrp = ((struct in6_addr *)(rta+1));
	else if (rta->rta_type == IFA_CACHEINFO)
	{
	struct ifa_cacheinfo ifc = (struct ifa_cacheinfo )(rta+1);
	preferred = ifc->ifa_prefered;
	valid = ifc->ifa_valid;
	}
	rta = RTA_NEXT(rta, len1);
	}

	if (ifa->ifa_flags & IFA_F_TENTATIVE)
	flags \|= IFACE_TENTATIVE;

	if (ifa->ifa_flags & IFA_F_DEPRECATED)
	flags \|= IFACE_DEPRECATED;

	if (!(ifa->ifa_flags & IFA_F_TEMPORARY))
	flags \|= IFACE_PERMANENT;

	if (addrp && callback_ok)
	if (!((*callback)(addrp, (int)(ifa->ifa_prefixlen), (int)(ifa->ifa_scope),
	(int)(ifa->ifa_index), flags,
	(int) preferred, (int)valid, parm)))
	callback_ok = 0;
	}
	#endif
	}
	}
	else if (h->nlmsg_type == RTM_NEWNEIGH && family == AF_UNSPEC)
	{
	struct ndmsg *neigh = NLMSG_DATA(h);
	struct rtattr *rta = NDA_RTA(neigh);
	unsigned int len1 = h->nlmsg_len - NLMSG_LENGTH(sizeof(*neigh));
	size_t maclen = 0;
	char inaddr = NULL, mac = NULL;

	while (RTA_OK(rta, len1))
	{
	if (rta->rta_type == NDA_DST)
	inaddr = (char *)(rta+1);
	else if (rta->rta_type == NDA_LLADDR)
	{
	maclen = rta->rta_len - sizeof(struct rtattr);
	mac = (char *)(rta+1);
	}

	rta = RTA_NEXT(rta, len1);
	}

	if (!(neigh->ndm_state & (NUD_NOARP \| NUD_INCOMPLETE \| NUD_FAILED)) &&
	inaddr && mac && callback_ok)
	if (!((*callback)(neigh->ndm_family, inaddr, mac, maclen, parm)))
	callback_ok = 0;
	}
	#ifdef HAVE_DHCP6
	else if (h->nlmsg_type == RTM_NEWLINK && family == AF_LOCAL)
	{
	struct ifinfomsg *link = NLMSG_DATA(h);
	struct rtattr *rta = IFLA_RTA(link);
	unsigned int len1 = h->nlmsg_len - NLMSG_LENGTH(sizeof(*link));
	char *mac = NULL;
	size_t maclen = 0;

	while (RTA_OK(rta, len1))
	{
	if (rta->rta_type == IFLA_ADDRESS)
	{
	maclen = rta->rta_len - sizeof(struct rtattr);
	mac = (char *)(rta+1);
	}

	rta = RTA_NEXT(rta, len1);
	}

	if (mac && callback_ok && !((link->ifi_flags & (IFF_LOOPBACK \| IFF_POINTOPOINT))) &&
	!((*callback)((int)link->ifi_index, (unsigned int)link->ifi_type, mac, maclen, parm)))
	callback_ok = 0;
	}
	#endif
	}
	}

	void netlink_multicast(void)
	{
	ssize_t len;
	struct nlmsghdr *h;
	int flags;

	/* don't risk blocking reading netlink messages here. */
	if ((flags = fcntl(daemon->netlinkfd, F_GETFL)) == -1 \|\|
	fcntl(daemon->netlinkfd, F_SETFL, flags \| O_NONBLOCK) == -1)
	return;

	if ((len = netlink_recv()) != -1)
	for (h = (struct nlmsghdr *)iov.iov_base; NLMSG_OK(h, (size_t)len); h = NLMSG_NEXT(h, len))
	nl_async(h);

	/* restore non-blocking status */
	fcntl(daemon->netlinkfd, F_SETFL, flags);
	}

	static void nl_async(struct nlmsghdr *h)
	{
	if (h->nlmsg_type == NLMSG_ERROR)
	{
	struct nlmsgerr *err = NLMSG_DATA(h);
	if (err->error != 0)
	my_syslog(LOG_ERR, _("netlink returns error: %s"), strerror(-(err->error)));
	}
	else if (h->nlmsg_pid == 0 && h->nlmsg_type == RTM_NEWROUTE)
	{
	/* We arrange to receive netlink multicast messages whenever the network route is added.
	If this happens and we still have a DNS packet in the buffer, we re-send it.
	This helps on DoD links, where frequently the packet which triggers dialling is
	a DNS query, which then gets lost. By re-sending, we can avoid the lookup
	failing. */
	struct rtmsg *rtm = NLMSG_DATA(h);

	if (rtm->rtm_type == RTN_UNICAST && rtm->rtm_scope == RT_SCOPE_LINK)
	queue_event(EVENT_NEWROUTE);
	}
	else if (h->nlmsg_type == RTM_NEWADDR \|\| h->nlmsg_type == RTM_DELADDR)
	queue_event(EVENT_NEWADDR);
	}
	#endif