Handle changing interface indexes when binding DHCP sockets.

CHANGELOG

@@ -39,6 +39,14 @@ version 2.87
 	a local NODATA answer. The pre-2.86 behaviour is still available,
 	by configuring --address=/example.com/1.2.3.4 --local=/example.com/
 
+        Fix problem with binding DHCP sockets to an individual interface.
+	Despite the fact that the system call tales the interface _name_ as
+	a parameter, it actually, binds the socket to interface _index_.
+	Deleting the interface and creating a new one with the same name
+	leaves the socket bound to the old index. (Creating new sockets
+	always allocates a fresh index, they are not reused). We now
+	take this behaviour into account and keep up with changing indexes.
+
 	
 version 2.86
 	Handle DHCPREBIND requests in the DHCPv6 server code.

src/dhcp-common.c

@@ -566,12 +566,16 @@ char *whichdevice(void)
       }
 
   if (found)
-    return found->name;
+    {
+      char *ret = safe_malloc(strlen(found->name)+1);
+      strcpy(ret, found->name);
+      return ret;
+    }
   
   return NULL;
 }
  
-void  bindtodevice(char *device, int fd)
+static int bindtodevice(char *device, int fd)
 {
   size_t len = strlen(device)+1;
   if (len > IFNAMSIZ)
@@ -579,7 +583,33 @@ void  bindtodevice(char *device, int fd)
   /* only allowed by root. */
   if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, device, len) == -1 &&
       errno != EPERM)
-    die(_("failed to set SO_BINDTODEVICE on DHCP socket: %s"), NULL, EC_BADNET);
+    return 2;
+  
+  return 1;
+}
+
+int bind_dhcp_devices(char *bound_device)
+{
+  int ret = 0;
+
+  if (bound_device)
+    {
+      if (daemon->dhcp)
+	{
+	  if (!daemon->relay4)
+	    ret |= bindtodevice(bound_device, daemon->dhcpfd);
+	  
+	  if (daemon->enable_pxe && daemon->pxefd != -1)
+	    ret |= bindtodevice(bound_device, daemon->pxefd);
+	}
+      
+#if defined(HAVE_DHCP6)
+      if (daemon->doing_dhcp6 && !daemon->relay6)
+	ret |= bindtodevice(bound_device, daemon->dhcp6fd);
+#endif
+    }
+  
+  return ret;
 }
 #endif
 

src/dnsmasq.c

@@ -388,27 +388,8 @@ int main (int argc, char **argv)
       /* after enumerate_interfaces()  */
       bound_device = whichdevice();
 
-      if (daemon->dhcp)
+      if ((did_bind = bind_dhcp_devices(bound_device)) & 2)
-	{
+	die(_("failed to set SO_BINDTODEVICE on DHCP socket: %s"), NULL, EC_BADNET);	
-	  if (!daemon->relay4 && bound_device)
-	    {
-	      bindtodevice(bound_device, daemon->dhcpfd);
-	      did_bind = 1;
-	    }
-	  if (daemon->enable_pxe && bound_device && daemon->pxefd != -1)
-	    {
-	      bindtodevice(bound_device, daemon->pxefd);
-	      did_bind = 1;
-	    }
-	}
-#endif
-
-#if defined(HAVE_LINUX_NETWORK) && defined(HAVE_DHCP6)
-      if (daemon->doing_dhcp6 && !daemon->relay6 && bound_device)
-	{
-	  bindtodevice(bound_device, daemon->dhcp6fd);
-	  did_bind = 1;
-	}
 #endif
     }
   else 
@@ -1100,6 +1081,17 @@ int main (int argc, char **argv)
 #endif
       
 #ifdef HAVE_DHCP
+#  if defined(HAVE_LINUX_NETWORK)
+      if (bind_dhcp_devices(bound_device) & 2)
+	{
+	  static int warned = 0;
+	  if (!warned)
+	    {
+	      my_syslog(LOG_ERR, _("error binding DHCP socket to device %s"), bound_device);
+	      warned = 1;
+	    }
+	}
+# endif
       if (daemon->dhcp || daemon->relay4)
 	{
 	  poll_listen(daemon->dhcpfd, POLLIN);

src/dnsmasq.h

@@ -1715,7 +1715,7 @@ struct dhcp_config *find_config(struct dhcp_config *configs,
 int config_has_mac(struct dhcp_config *config, unsigned char *hwaddr, int len, int type);
 #ifdef HAVE_LINUX_NETWORK
 char *whichdevice(void);
-void bindtodevice(char *device, int fd);
+int bind_dhcp_devices(char *bound_device);
 #endif
 #  ifdef HAVE_DHCP6
 void display_opts6(void);