commit 64d3d2c83b30c751570faf0c5d527ff3da9f2036
Author: Beniamino Galvani <bgalvani@redhat.com>
Date:   Sun Aug 28 20:44:05 2016 +0100

    Handle binding upstream servers to an interface
    (--server=1.2.3.4@eth0) when the named interface
    is destroyed and recreated in the kernel.

diff --git a/src/dbus.c b/src/dbus.c
index 7379341..e56d8c7 100644
--- a/src/dbus.c
+++ b/src/dbus.c
@@ -161,6 +161,10 @@ static void add_update_server(union mysockaddr *addr,
   
   if (serv)
     {
+      serv->sfd = NULL;
+      serv->queries = 0;
+      serv->failed_queries = 0;
+
       if (interface)
 	strcpy(serv->interface, interface);
       else
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 69ae7a7..7b8020e 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -412,6 +412,7 @@ struct serverfd {
   int fd;
   union mysockaddr source_addr;
   char interface[IF_NAMESIZE+1];
+  unsigned int ifindex, used;
   struct serverfd *next;
 };
 
diff --git a/src/network.c b/src/network.c
index 792914b..d2bebcc 100644
--- a/src/network.c
+++ b/src/network.c
@@ -839,6 +839,7 @@ int local_bind(int fd, union mysockaddr *addr, char *intname, int is_tcp)
 static struct serverfd *allocate_sfd(union mysockaddr *addr, char *intname)
 {
   struct serverfd *sfd;
+  unsigned int ifindex = 0;
   int errsave;
 
   /* when using random ports, servers which would otherwise use
@@ -859,11 +860,15 @@ static struct serverfd *allocate_sfd(union mysockaddr *addr, char *intname)
 	return NULL;
 #endif
     }
+
+  if (intname && strlen(intname) != 0)
+    ifindex = if_nametoindex(intname); /* index == 0 when not binding to an interface */
       
   /* may have a suitable one already */
   for (sfd = daemon->sfds; sfd; sfd = sfd->next )
     if (sockaddr_isequal(&sfd->source_addr, addr) &&
-	strcmp(intname, sfd->interface) == 0)
+	strcmp(intname, sfd->interface) == 0 &&
+	ifindex == sfd->ifindex) 
       return sfd;
   
   /* need to make a new one. */
@@ -885,11 +890,13 @@ static struct serverfd *allocate_sfd(union mysockaddr *addr, char *intname)
       errno = errsave;
       return NULL;
     }
-    
+
   strcpy(sfd->interface, intname); 
   sfd->source_addr = *addr;
   sfd->next = daemon->sfds;
+  sfd->ifindex = ifindex;
   daemon->sfds = sfd;
+
   return sfd; 
 }
 
@@ -944,12 +951,16 @@ void check_servers(void)
 {
   struct irec *iface;
   struct server *new, *tmp, *ret = NULL;
+  struct serverfd *sfd, *tmpfd, **up;
   int port = 0;
 
   /* interface may be new since startup */
   if (!option_bool(OPT_NOWILD))
     enumerate_interfaces();
   
+  for (sfd = daemon->sfds; sfd; sfd = sfd->next)
+    sfd->used = 0;
+
   for (new = daemon->servers; new; new = tmp)
     {
       tmp = new->next;
@@ -987,6 +998,9 @@ void check_servers(void)
 	      free(new);
 	      continue;
 	    }
+
+	  if (new->sfd)
+	    new->sfd->used = 1;
 	}
       
       /* reverse order - gets it right. */
@@ -1019,6 +1033,20 @@ void check_servers(void)
 	}
     }
   
+  /* Remove unused sfds */
+  for (sfd = daemon->sfds, up = &daemon->sfds; sfd; sfd = tmpfd)
+    {
+       tmpfd = sfd->next;
+       if (!sfd->used) 
+	{
+	  *up = sfd->next;
+	  close(sfd->fd);
+	  free(sfd);
+	} 
+      else
+	up = &sfd->next;
+    }
+  
   daemon->servers = ret;
 }