netfilter: nf_tables: fix underflow in object reference counter

JIRA: https://issues.redhat.com/browse/RHEL-1720
JIRA: https://issues.redhat.com/browse/RHEL-1721
Upstream Status: commit d6b4786

commit d6b4786
Author: Pablo Neira Ayuso <pablo@netfilter.org>
Date:   Fri Jun 16 15:20:08 2023 +0200

    netfilter: nf_tables: fix underflow in object reference counter

    Since ("netfilter: nf_tables: drop map element references from
    preparation phase"), integration with commit protocol is better,
    therefore drop the workaround that b91d903 ("netfilter: nf_tables:
    fix leaking object reference count") provides.

    Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Signed-off-by: Florian Westphal <fwestpha@redhat.com>

Author: fw-strlen

net/netfilter/nf_tables_api.c

@@ -6442,19 +6442,19 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 	if (flags)
 		*nft_set_ext_flags(ext) = flags;
 
+	if (obj) {
+		*nft_set_ext_obj(ext) = obj;
+		obj->use++;
+	}
 	if (ulen > 0) {
 		if (nft_set_ext_check(&tmpl, NFT_SET_EXT_USERDATA, ulen) < 0) {
 			err = -EINVAL;
-			goto err_elem_userdata;
+			goto err_elem_free;
 		}
 		udata = nft_set_ext_userdata(ext);
 		udata->len = ulen - 1;
 		nla_memcpy(&udata->data, nla[NFTA_SET_ELEM_USERDATA], ulen);
 	}
-	if (obj) {
-		*nft_set_ext_obj(ext) = obj;
-		obj->use++;
-	}
 	err = nft_set_elem_expr_setup(ctx, &tmpl, ext, expr_array, num_exprs);
 	if (err < 0)
 		goto err_elem_free;
@@ -6509,9 +6509,6 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 err_element_clash:
 	kfree(trans);
 err_elem_free:
-	if (obj)
-		obj->use--;
-err_elem_userdata:
 	nft_set_elem_destroy(set, elem.priv, true);
 err_parse_data:
 	if (nla[NFTA_SET_ELEM_DATA] != NULL)