Bridge driver to detect and remove stale network

Signed-off-by: Alessandro Boch <aboch@docker.com>

libnetwork/drivers/bridge/bridge.go

@@ -588,13 +588,26 @@ func (d *driver) createNetwork(config *networkConfiguration) error {
 	defer osl.InitOSContext()()
 
 	networkList := d.getNetworks()
-	for _, nw := range networkList {
+	for i, nw := range networkList {
 		nw.Lock()
 		nwConfig := nw.config
 		nw.Unlock()
 		if err := nwConfig.Conflicts(config); err != nil {
-			return types.ForbiddenErrorf("cannot create network %s (%s): conflicts with network %s (%s): %s",
-				config.ID, config.BridgeName, nwConfig.ID, nwConfig.BridgeName, err.Error())
+			if config.DefaultBridge {
+				// We encountered and identified a stale default network
+				// We must delete it as libnetwork is the source of thruth
+				// The default network being created must be the only one
+				// This can happen only from docker 1.12 on ward
+				logrus.Infof("Removing stale default bridge network %s (%s)", nwConfig.ID, nwConfig.BridgeName)
+				if err := d.DeleteNetwork(nwConfig.ID); err != nil {
+					logrus.Warnf("Failed to remove stale default network: %s (%s): %v. Will remove from store.", nwConfig.ID, nwConfig.BridgeName, err)
+					d.storeDelete(nwConfig)
+				}
+				networkList = append(networkList[:i], networkList[i+1:]...)
+			} else {
+				return types.ForbiddenErrorf("cannot create network %s (%s): conflicts with network %s (%s): %s",
+					config.ID, config.BridgeName, nwConfig.ID, nwConfig.BridgeName, err.Error())
+			}
 		}
 	}
 
@@ -762,12 +775,6 @@ func (d *driver) DeleteNetwork(nid string) error {
 		return err
 	}
 
-	// Cannot remove network if endpoints are still present
-	if len(n.endpoints) != 0 {
-		err = ActiveEndpointsError(n.id)
-		return err
-	}
-
 	// We only delete the bridge when it's not the default bridge. This is keep the backward compatible behavior.
 	if !config.DefaultBridge {
 		if err := d.nlh.LinkDel(n.bridge.Link); err != nil {