netfilter: nf_tables: fix underflow in chain reference counter

Set element addition error path decrements reference counter on chains
twice: once on element release and again via nft_data_release().

Then, d6b4786 ("netfilter: nf_tables: fix underflow in object
reference counter") incorrectly fixed this by removing the stateful
object reference count decrement.

Restore the stateful object decrement as in b91d903 ("netfilter:
nf_tables: fix leaking object reference count") and let
nft_data_release() decrement the chain reference counter, so this is
done only once.

Fixes: d6b4786 ("netfilter: nf_tables: fix underflow in object reference counter")
Fixes: 628bd3e ("netfilter: nf_tables: drop map element references from preparation phase")
Signed-off-by: Pablo Neira Ayuso <[email protected]>

Author: ummakynes

net/netfilter/nf_tables_api.c

@@ -6771,7 +6771,9 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 err_element_clash:
 	kfree(trans);
 err_elem_free:
-	nft_set_elem_destroy(set, elem.priv, true);
+	nf_tables_set_elem_destroy(ctx, set, elem.priv);
+	if (obj)
+		obj->use--;
 err_parse_data:
 	if (nla[NFTA_SET_ELEM_DATA] != NULL)
 		nft_data_release(&elem.data.val, desc.type);