Handle binding upstream servers to an interface

(--server=1.2.3.4@eth0) when the named interface
is destroyed and recreated in the kernel.

CHANGELOG

@@ -30,6 +30,11 @@ version 2.77
 	    and are now converted to names like
 	    <prefix>--ffff-1-2-3-4.<domain>
 
+	    Handle binding upstream servers to an interface 
+	    (--server=1.2.3.4@eth0) when the named interface
+	    is destroyed and recreated in the kernel. Thanks to 
+	    Beniamino Galvani for the patch.
+
 
 version 2.76
             Include 0.0.0.0/8 in DNS rebind checks. This range 

src/dnsmasq.h

@@ -488,6 +488,7 @@ struct serverfd {
   int fd;
   union mysockaddr source_addr;
   char interface[IF_NAMESIZE+1];
+  unsigned int ifindex, used;
   struct serverfd *next;
 };
 

src/network.c

@@ -1204,6 +1204,7 @@ 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
@@ -1224,11 +1225,15 @@ 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. */
@@ -1250,11 +1255,13 @@ 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; 
 }
 
@@ -1429,12 +1436,16 @@ void check_servers(void)
 {
   struct irec *iface;
   struct server *serv;
+  struct serverfd *sfd, *tmp, **up;
   int port = 0, count;
 
   /* interface may be new since startup */
   if (!option_bool(OPT_NOWILD))
     enumerate_interfaces(0);
   
+  for (sfd = daemon->sfds; sfd; sfd = sfd->next)
+    sfd->used = 0;
+
 #ifdef HAVE_DNSSEC
  /* Disable DNSSEC validation when using server=/domain/.... servers
     unless there's a configured trust anchor. */
@@ -1505,6 +1516,8 @@ void check_servers(void)
 	      serv->flags |= SERV_MARK;
 	      continue;
 	    }
+
+	  serv->sfd->used = 1;
 	}
       
       if (!(serv->flags & SERV_NO_REBIND) && !(serv->flags & SERV_LITERAL_ADDRESS))
@@ -1547,6 +1560,20 @@ void check_servers(void)
   if (count - 1 > SERVERS_LOGGED)
     my_syslog(LOG_INFO, _("using %d more nameservers"), count - SERVERS_LOGGED - 1);
 
+  /* Remove unused sfds */
+  for (sfd = daemon->sfds, up = &daemon->sfds; sfd; sfd = tmp)
+    {
+       tmp = sfd->next;
+       if (!sfd->used) 
+	{
+	  *up = sfd->next;
+	  close(sfd->fd);
+	  free(sfd);
+	} 
+      else
+	up = &sfd->next;
+    }
+  
   cleanup_servers();
 }