netfilter: nf_tables: add nft_set_elem_expr_alloc()

Add helper function to create stateful expression.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_tables.h

@@ -666,6 +666,10 @@ static inline struct nft_object **nft_set_ext_obj(const struct nft_set_ext *ext)
 	return nft_set_ext(ext, NFT_SET_EXT_OBJREF);
 }
 
+struct nft_expr *nft_set_elem_expr_alloc(const struct nft_ctx *ctx,
+					 const struct nft_set *set,
+					 const struct nlattr *attr);
+
 void *nft_set_elem_init(const struct nft_set *set,
 			const struct nft_set_ext_tmpl *tmpl,
 			const u32 *key, const u32 *key_end, const u32 *data,

net/netfilter/nf_tables_api.c

@@ -4779,6 +4779,36 @@ static struct nft_trans *nft_trans_elem_alloc(struct nft_ctx *ctx,
 	return trans;
 }
 
+struct nft_expr *nft_set_elem_expr_alloc(const struct nft_ctx *ctx,
+					 const struct nft_set *set,
+					 const struct nlattr *attr)
+{
+	struct nft_expr *expr;
+	int err;
+
+	expr = nft_expr_init(ctx, attr);
+	if (IS_ERR(expr))
+		return expr;
+
+	err = -EOPNOTSUPP;
+	if (!(expr->ops->type->flags & NFT_EXPR_STATEFUL))
+		goto err_set_elem_expr;
+
+	if (expr->ops->type->flags & NFT_EXPR_GC) {
+		if (set->flags & NFT_SET_TIMEOUT)
+			goto err_set_elem_expr;
+		if (!set->ops->gc_init)
+			goto err_set_elem_expr;
+		set->ops->gc_init(set);
+	}
+
+	return expr;
+
+err_set_elem_expr:
+	nft_expr_destroy(ctx, expr);
+	return ERR_PTR(err);
+}
+
 void *nft_set_elem_init(const struct nft_set *set,
 			const struct nft_set_ext_tmpl *tmpl,
 			const u32 *key, const u32 *key_end,

net/netfilter/nft_dynset.c

@@ -206,21 +206,10 @@ static int nft_dynset_init(const struct nft_ctx *ctx,
 		if (!(set->flags & NFT_SET_EVAL))
 			return -EINVAL;
 
-		priv->expr = nft_expr_init(ctx, tb[NFTA_DYNSET_EXPR]);
+		priv->expr = nft_set_elem_expr_alloc(ctx, set,
+						     tb[NFTA_DYNSET_EXPR]);
 		if (IS_ERR(priv->expr))
 			return PTR_ERR(priv->expr);
-
-		err = -EOPNOTSUPP;
-		if (!(priv->expr->ops->type->flags & NFT_EXPR_STATEFUL))
-			goto err1;
-
-		if (priv->expr->ops->type->flags & NFT_EXPR_GC) {
-			if (set->flags & NFT_SET_TIMEOUT)
-				goto err1;
-			if (!set->ops->gc_init)
-				goto err1;
-			set->ops->gc_init(set);
-		}
 	}
 
 	nft_set_ext_prepare(&priv->tmpl);