[PATCH nft] cache: provide a empty list for flowtables and objects when request fails

[Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>]

Old kernels do not support for dumping the flowtable and object lists,
provide an empty list instead to unbreak the cache initialization.

Fixes: 560963c4d41e ("cache: add hashtable cache for flowtable")
Fixes: 45a84088ecbd ("cache: add hashtable cache for object")
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
---
 src/cache.c | 38 ++++++++++++++++++++++----------------
 1 file changed, 22 insertions(+), 16 deletions(-)

diff --git a/src/cache.c b/src/cache.c
index 8300ce8e707a..15eb4522eb75 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -415,8 +415,7 @@ static int obj_cache_init(struct netlink_ctx *ctx, struct table *table,
 }
 
 static struct nftnl_obj_list *obj_cache_dump(struct netlink_ctx *ctx,
-					     const struct table *table,
-					     int *err)
+					     const struct table *table)
 {
 	struct nftnl_obj_list *obj_list;
 
@@ -424,12 +423,15 @@ static struct nftnl_obj_list *obj_cache_dump(struct netlink_ctx *ctx,
 				    table->handle.table.name, NULL,
 				    0, true, false);
 	if (!obj_list) {
-                if (errno == EINTR) {
-			*err = -1;
+                if (errno == EINTR)
 			return NULL;
-		}
-		*err = 0;
-		return NULL;
+
+		/* old kernels do not support this, provide an empty list. */
+		obj_list = nftnl_obj_list_alloc();
+		if (!obj_list)
+	                memory_allocation_error();
+
+		return obj_list;
 	}
 
 	return obj_list;
@@ -500,20 +502,22 @@ static int ft_cache_init(struct netlink_ctx *ctx, struct table *table,
 }
 
 static struct nftnl_flowtable_list *ft_cache_dump(struct netlink_ctx *ctx,
-						  const struct table *table,
-						  int *err)
+						  const struct table *table)
 {
 	struct nftnl_flowtable_list *ft_list;
 
 	ft_list = mnl_nft_flowtable_dump(ctx, table->handle.family,
 					 table->handle.table.name);
 	if (!ft_list) {
-                if (errno == EINTR) {
-			*err = -1;
+                if (errno == EINTR)
 			return NULL;
-		}
-		*err = 0;
-		return NULL;
+
+		/* old kernels do not support this, provide an empty list. */
+		ft_list = nftnl_flowtable_list_alloc();
+		if (!ft_list)
+	                memory_allocation_error();
+
+		return ft_list;
 	}
 
 	return ft_list;
@@ -628,11 +632,12 @@ static int cache_init_objects(struct netlink_ctx *ctx, unsigned int flags)
 			}
 		}
 		if (flags & NFT_CACHE_FLOWTABLE_BIT) {
-			ft_list = ft_cache_dump(ctx, table, &ret);
+			ft_list = ft_cache_dump(ctx, table);
 			if (!ft_list) {
 				ret = -1;
 				goto cache_fails;
 			}
+
 			ret = ft_cache_init(ctx, table, ft_list);
 
 			nftnl_flowtable_list_free(ft_list);
@@ -643,11 +648,12 @@ static int cache_init_objects(struct netlink_ctx *ctx, unsigned int flags)
 			}
 		}
 		if (flags & NFT_CACHE_OBJECT_BIT) {
-			obj_list = obj_cache_dump(ctx, table, &ret);
+			obj_list = obj_cache_dump(ctx, table);
 			if (!obj_list) {
 				ret = -1;
 				goto cache_fails;
 			}
+
 			ret = obj_cache_init(ctx, table, obj_list);
 
 			nftnl_obj_list_free(obj_list);
-- 
2.20.1