netfilter: nftables: relax check for stateful expressions in set definition

Restore the original behaviour where users are allowed to add an element
with any stateful expression if the set definition specifies no stateful
expressions. Make sure upper maximum number of stateful expressions of
NFT_SET_EXPR_MAX is not reached.

Fixes: 8cfd9b0f ("netfilter: nftables: generalize set expressions support")
Fixes: 48b0ae04 ("netfilter: nftables: netlink support for several set element expressions")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -5281,6 +5281,7 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 	struct nft_expr *expr_array[NFT_SET_EXPR_MAX] = {};
 	struct nlattr *nla[NFTA_SET_ELEM_MAX + 1];
 	u8 genmask = nft_genmask_next(ctx->net);
+	u32 flags = 0, size = 0, num_exprs = 0;
 	struct nft_set_ext_tmpl tmpl;
 	struct nft_set_ext *ext, *ext2;
 	struct nft_set_elem elem;
@@ -5290,7 +5291,6 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 	struct nft_data_desc desc;
 	enum nft_registers dreg;
 	struct nft_trans *trans;
-	u32 flags = 0, size = 0;
 	u64 timeout;
 	u64 expiration;
 	int err, i;
@@ -5356,7 +5356,7 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 	if (nla[NFTA_SET_ELEM_EXPR]) {
 		struct nft_expr *expr;
 
-		if (set->num_exprs != 1)
+		if (set->num_exprs && set->num_exprs != 1)
 			return -EOPNOTSUPP;
 
 		expr = nft_set_elem_expr_alloc(ctx, set,
@@ -5365,8 +5365,9 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 			return PTR_ERR(expr);
 
 		expr_array[0] = expr;
+		num_exprs = 1;
 
-		if (set->exprs[0] && set->exprs[0]->ops != expr->ops) {
+		if (set->num_exprs && set->exprs[0]->ops != expr->ops) {
 			err = -EOPNOTSUPP;
 			goto err_set_elem_expr;
 		}
@@ -5375,12 +5376,10 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 		struct nlattr *tmp;
 		int left;
 
-		if (set->num_exprs == 0)
-			return -EOPNOTSUPP;
-
 		i = 0;
 		nla_for_each_nested(tmp, nla[NFTA_SET_ELEM_EXPRESSIONS], left) {
-			if (i == set->num_exprs) {
+			if (i == NFT_SET_EXPR_MAX ||
+			    (set->num_exprs && set->num_exprs == i)) {
 				err = -E2BIG;
 				goto err_set_elem_expr;
 			}
@@ -5394,14 +5393,15 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 				goto err_set_elem_expr;
 			}
 			expr_array[i] = expr;
+			num_exprs++;
 
-			if (expr->ops != set->exprs[i]->ops) {
+			if (set->num_exprs && expr->ops != set->exprs[i]->ops) {
 				err = -EOPNOTSUPP;
 				goto err_set_elem_expr;
 			}
 			i++;
 		}
-		if (set->num_exprs != i) {
+		if (set->num_exprs && set->num_exprs != i) {
 			err = -EOPNOTSUPP;
 			goto err_set_elem_expr;
 		}
@@ -5409,6 +5409,8 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 		err = nft_set_elem_expr_clone(ctx, set, expr_array);
 		if (err < 0)
 			goto err_set_elem_expr_clone;
+
+		num_exprs = set->num_exprs;
 	}
 
 	err = nft_setelem_parse_key(ctx, set, &elem.key.val,
@@ -5433,8 +5435,8 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 			nft_set_ext_add(&tmpl, NFT_SET_EXT_TIMEOUT);
 	}
 
-	if (set->num_exprs) {
-		for (i = 0; i < set->num_exprs; i++)
+	if (num_exprs) {
+		for (i = 0; i < num_exprs; i++)
 			size += expr_array[i]->ops->size;
 
 		nft_set_ext_add_length(&tmpl, NFT_SET_EXT_EXPRESSIONS,
@@ -5522,7 +5524,7 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 		*nft_set_ext_obj(ext) = obj;
 		obj->use++;
 	}
-	for (i = 0; i < set->num_exprs; i++)
+	for (i = 0; i < num_exprs; i++)
 		nft_set_elem_expr_setup(ext, i, expr_array);
 
 	trans = nft_trans_elem_alloc(ctx, NFT_MSG_NEWSETELEM, set);
@@ -5584,7 +5586,7 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 err_parse_key:
 	nft_data_release(&elem.key.val, NFT_DATA_VALUE);
 err_set_elem_expr:
-	for (i = 0; i < set->num_exprs && expr_array[i]; i++)
+	for (i = 0; i < num_exprs && expr_array[i]; i++)
 		nft_expr_destroy(ctx, expr_array[i]);
 err_set_elem_expr_clone:
 	return err;