Fix logic error in Linux netlink code.

This could cause dnsmasq to enter a tight loop on systems
with a very large number of network interfaces.

CHANGELOG

@@ -11,6 +11,12 @@ version 2.77
 	    Thanks to Mozilla for funding the security audit 
 	    which spotted this bug.
 
+	    Fix logic error in Linux netlink code. This could
+	    cause dnsmasq to enter a tight loop on systems
+	    with a very large number of network interfaces.
+	    Thanks to Ivan Kokshaysky for the diagnosis and
+	    patch.
+
 
 version 2.76
             Include 0.0.0.0/8 in DNS rebind checks. This range 

src/netlink.c

@@ -188,11 +188,17 @@ int iface_enumerate(int family, void *parm, int (*callback)())
 	}
 
       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)
+	if (h->nlmsg_pid != netlink_pid || h->nlmsg_type == NLMSG_ERROR)
 	  {
 	    /* May be multicast arriving async */
 	    nl_async(h);
 	  }
+	else if (h->nlmsg_seq != seq)
+	  {
+	    /* May be part of incomplete response to previous request after
+	       ENOBUFS. Drop it. */
+	    continue;
+	  }
 	else if (h->nlmsg_type == NLMSG_DONE)
 	  return callback_ok;
 	else if (h->nlmsg_type == RTM_NEWADDR && family != AF_UNSPEC && family != AF_LOCAL)