platform: workaround deletion of IPv4 route with metric 0th/route-fixes-bgo741871

Deleting routes with metric 0 might end up deleting other
routes with a different metric.

Workaround this in platform to only delete a route with
metric 0 if such a route can be found prior to deletion.

Don't only look into the cache (which might be out of date).
Instead refetch the route we are about to delete to be sure.

There is still a race that we might end up deleting the wrong
route.

https://bugzilla.gnome.org/show_bug.cgi?id=741871
https://bugzilla.redhat.com/show_bug.cgi?id=1172780

1 files changed, 13 insertions, 0 deletions

diff --git a/src/platform/nm-linux-platform.c b/src/platform/nm-linux-platform.c
index d59b55bc1f..0c35376cdb 100644
--- a/src/platform/nm-linux-platform.c
+++ b/src/platform/nm-linux-platform.c
@@ -3912,6 +3912,19 @@ ip4_route_delete (NMPlatform *platform, int ifindex, in_addr_t network, int plen
 
 	cache = choose_cache_by_type (platform, OBJECT_TYPE_IP4_ROUTE);
 
+	if (metric == 0) {
+		/* Deleting an IPv4 route with metric 0 does not only delete an exectly matching route.
+		 * If no route with metric 0 exists, it might delete another route to the same destination.
+		 * For nm_platform_ip4_route_delete() we don't want this semantic.
+		 *
+		 * Instead, re-fetch the route from kernel, and if that fails, there is nothing to do.
+		 * On success, there is still a race that we might end up deleting the wrong route. */
+		if (!refresh_object (platform, (struct nl_object *) route, FALSE, NM_PLATFORM_REASON_INTERNAL)) {
+			rtnl_route_put ((struct rtnl_route *) route);
+			return TRUE;
+		}
+	}
+
 	/* when deleting an IPv4 route, several fields of the provided route must match.
 	 * Lookup in the cache so that we hopefully get the right values. */
 	cached_object = (struct rtnl_route *) nl_cache_search (cache, route);