cope with errors during route traversal

Fixes #1909.

net/if.go

@@ -57,8 +57,7 @@ func EnsureInterfaceAndMcastRoute(ifaceName string) (*net.Interface, error) {
 		return iface, err
 	}
 	for update := range ch {
-		link, _ := netlink.LinkByIndex(update.Route.LinkIndex)
-		if link.Attrs().Name == ifaceName && update.Route.Dst.IP.Equal(dest) {
+		if update.Route.LinkIndex == iface.Index && update.Route.Dst.IP.Equal(dest) {
 			break
 		}
 	}

net/route.go

@@ -41,12 +41,14 @@ func forEachRoute(ignoreIfaceNames map[string]struct{}, check func(name string,
 	}
 	for _, route := range routes {
 		link, err := netlink.LinkByIndex(route.LinkIndex)
-		if err == nil {
-			if _, found := ignoreIfaceNames[link.Attrs().Name]; found {
-				continue
-			}
+		if err != nil {
+			continue
 		}
-		if err := check(link.Attrs().Name, route); err != nil {
+		ifaceName := link.Attrs().Name
+		if _, found := ignoreIfaceNames[ifaceName]; found {
+			continue
+		}
+		if err := check(ifaceName, route); err != nil {
 			return err
 		}
 	}