platform: improve workaround for deleting IPv4 route with libnl guessing route scope

Previously, we always lookup the cache for libnl objects and used those for
delete_object(). This was necessary, because libnl guesses and overwrites
the IPv4 route scope.

Newer libnl no longer overwrites the scope if set explicitly to RT_SCOPE_NOWHERE.
So, this workaround is no longer needed. Indeed there might be cases, where it is
harmful, because we might guess the wrong scope.

This was fixed in libnl3 in commits
  https://github.com/thom311/libnl/commit/85ec9c7ad80c60f4f619472f2bb9d9595da93b26
  https://github.com/thom311/libnl/commit/015c4ee59b786fec35118c2a963532b3e05ba5a2

https://bugzilla.gnome.org/show_bug.cgi?id=726273

Signed-off-by: Thomas Haller <thaller@redhat.com>

1 files changed, 32 insertions, 21 deletions

diff --git a/src/platform/nm-linux-platform.c b/src/platform/nm-linux-platform.c
index 68ed1966a5..2ecd92bcb7 100644
--- a/src/platform/nm-linux-platform.c
+++ b/src/platform/nm-linux-platform.c
@@ -1494,17 +1494,13 @@ delete_object (NMPlatform *platform, struct nl_object *obj)
 {
 	NMLinuxPlatformPrivate *priv = NM_LINUX_PLATFORM_GET_PRIVATE (platform);
 	auto_nl_object struct nl_object *obj_cleanup = obj;
-	auto_nl_object struct nl_object *cached_object = NULL;
-	struct nl_object *object;
+	struct nl_object *object = obj;
 	int object_type;
 	int nle;
 
 	object_type = object_type_from_nl_object (obj);
 	g_return_val_if_fail (object_type != OBJECT_TYPE_UNKNOWN, FALSE);
 
-	cached_object = nm_nl_cache_search (choose_cache_by_type (platform, object_type), obj);
-	object = cached_object ? cached_object : obj;
-
 	switch (object_type) {
 	case OBJECT_TYPE_LINK:
 		nle = rtnl_link_delete (priv->nlh, (struct rtnl_link *) object);
@@ -3327,25 +3323,40 @@ ip4_route_delete (NMPlatform *platform, int ifindex, in_addr_t network, int plen
 {
 	in_addr_t gateway = 0;
 	struct nl_object *route = build_rtnl_route (AF_INET, ifindex, &network, plen, &gateway, metric, 0);
+	uint8_t scope = RT_SCOPE_NOWHERE;
 
 	g_return_val_if_fail (route, FALSE);
 
-	/* When searching for a matching IPv4 route to delete, the kernel
-	 * searches for a matching scope, unless the RTM_DELROUTE message
-	 * specifies RT_SCOPE_NOWHERE (see fib_table_delete()).
-	 *
-	 * However, if we set the scope of @rtnlroute to RT_SCOPE_NOWHERE (or
-	 * leave it unset), rtnl_route_build_msg() will reset the scope to
-	 * rtnl_route_guess_scope() -- which might be the wrong scope.
-	 *
-	 * As a workaround, we set the scope to RT_SCOPE_UNIVERSE, so libnl
-	 * will not overwrite it. But this only works if we guess correctly.
-	 *
-	 * As a better workaround, we don't use @rtnlroute as argument for
-	 * rtnl_route_delete(), but we look into our cache, if we already have
-	 * this route ready.
-	 **/
-	rtnl_route_set_scope ((struct rtnl_route *) route, RT_SCOPE_UNIVERSE);
+	if (!_nl_has_capability (1 /* NL_CAPABILITY_ROUTE_BUILD_MSG_SET_SCOPE */)) {
+		/* When searching for a matching IPv4 route to delete, the kernel
+		 * searches for a matching scope, unless the RTM_DELROUTE message
+		 * specifies RT_SCOPE_NOWHERE (see fib_table_delete()).
+		 *
+		 * However, if we set the scope of @rtnlroute to RT_SCOPE_NOWHERE (or
+		 * leave it unset), rtnl_route_build_msg() will reset the scope to
+		 * rtnl_route_guess_scope() -- which probably guesses wrong.
+		 *
+		 * As a workaround, we look at the cached route and use that scope.
+		 *
+		 * Newer versions of libnl, no longer reset the scope if explicitly set to RT_SCOPE_NOWHERE.
+		 * So, this workaround is only needed unless we have NL_CAPABILITY_ROUTE_BUILD_MSG_SET_SCOPE.
+		 **/
+		struct nl_object *cached_object;
+
+		cached_object = nm_nl_cache_search (choose_cache_by_type (platform, OBJECT_TYPE_IP4_ROUTE), route);
+		if (cached_object) {
+			scope = rtnl_route_get_scope ((struct rtnl_route *) cached_object);
+			nl_object_put (cached_object);
+		}
+
+		if (scope == RT_SCOPE_NOWHERE) {
+			/* If we would set the scope to RT_SCOPE_NOWHERE, libnl would guess the scope.
+			 * But probably it will guess 'link' because we don't set the next hop
+			 * of the route we are about to delete. A better guess is 'global'. */
+			scope = RT_SCOPE_UNIVERSE;
+		}
+	}
+	rtnl_route_set_scope ((struct rtnl_route *) route, scope);
 
 	return delete_object (platform, route);
 }