netfilter: nftables: add set expression flags

The set flag NFT_SET_EXPR provides a hint to the kernel that userspace
supports for multiple expressions per set element. In the same
direction, NFT_DYNSET_F_EXPR specifies that dynset expression defines
multiple expressions per set element.

This allows new userspace software with old kernels to bail out with
EOPNOTSUPP. This update is similar to ef516e86 ("netfilter:
nf_tables: reintroduce the NFT_SET_CONCAT flag"). The NFT_SET_EXPR flag
needs to be set on when the NFTA_SET_EXPRESSIONS attribute is specified.
The NFT_SET_EXPR flag is not set on with NFTA_SET_EXPR to retain
backward compatibility in old userspace binaries.

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

include/uapi/linux/netfilter/nf_tables.h

@@ -293,6 +293,7 @@ enum nft_rule_compat_attributes {
  * @NFT_SET_EVAL: set can be updated from the evaluation path
  * @NFT_SET_OBJECT: set contains stateful objects
  * @NFT_SET_CONCAT: set contains a concatenation
+ * @NFT_SET_EXPR: set contains expressions
  */
 enum nft_set_flags {
 	NFT_SET_ANONYMOUS		= 0x1,
@@ -303,6 +304,7 @@ enum nft_set_flags {
 	NFT_SET_EVAL			= 0x20,
 	NFT_SET_OBJECT			= 0x40,
 	NFT_SET_CONCAT			= 0x80,
+	NFT_SET_EXPR			= 0x100,
 };
 
 /**
@@ -706,6 +708,7 @@ enum nft_dynset_ops {
 
 enum nft_dynset_flags {
 	NFT_DYNSET_F_INV	= (1 << 0),
+	NFT_DYNSET_F_EXPR	= (1 << 1),
 };
 
 /**

net/netfilter/nf_tables_api.c

@@ -4162,7 +4162,7 @@ static int nf_tables_newset(struct net *net, struct sock *nlsk,
 		if (flags & ~(NFT_SET_ANONYMOUS | NFT_SET_CONSTANT |
 			      NFT_SET_INTERVAL | NFT_SET_TIMEOUT |
 			      NFT_SET_MAP | NFT_SET_EVAL |
-			      NFT_SET_OBJECT | NFT_SET_CONCAT))
+			      NFT_SET_OBJECT | NFT_SET_CONCAT | NFT_SET_EXPR))
 			return -EOPNOTSUPP;
 		/* Only one of these operations is supported */
 		if ((flags & (NFT_SET_MAP | NFT_SET_OBJECT)) ==
@@ -4304,6 +4304,10 @@ static int nf_tables_newset(struct net *net, struct sock *nlsk,
 		struct nlattr *tmp;
 		int left;
 
+		if (!(flags & NFT_SET_EXPR)) {
+			err = -EINVAL;
+			goto err_set_alloc_name;
+		}
 		i = 0;
 		nla_for_each_nested(tmp, nla[NFTA_SET_EXPRESSIONS], left) {
 			if (i == NFT_SET_EXPR_MAX) {

net/netfilter/nft_dynset.c

@@ -19,6 +19,7 @@ struct nft_dynset {
 	enum nft_registers		sreg_key:8;
 	enum nft_registers		sreg_data:8;
 	bool				invert;
+	bool				expr;
 	u8				num_exprs;
 	u64				timeout;
 	struct nft_expr			*expr_array[NFT_SET_EXPR_MAX];
@@ -175,11 +176,12 @@ static int nft_dynset_init(const struct nft_ctx *ctx,
 
 	if (tb[NFTA_DYNSET_FLAGS]) {
 		u32 flags = ntohl(nla_get_be32(tb[NFTA_DYNSET_FLAGS]));
-
-		if (flags & ~NFT_DYNSET_F_INV)
+		if (flags & ~(NFT_DYNSET_F_INV | NFT_DYNSET_F_EXPR))
 			return -EOPNOTSUPP;
 		if (flags & NFT_DYNSET_F_INV)
 			priv->invert = true;
+		if (flags & NFT_DYNSET_F_EXPR)
+			priv->expr = true;
 	}
 
 	set = nft_set_lookup_global(ctx->net, ctx->table,
@@ -261,6 +263,9 @@ static int nft_dynset_init(const struct nft_ctx *ctx,
 		struct nlattr *tmp;
 		int left;
 
+		if (!priv->expr)
+			return -EINVAL;
+
 		i = 0;
 		nla_for_each_nested(tmp, tb[NFTA_DYNSET_EXPRESSIONS], left) {
 			if (i == NFT_SET_EXPR_MAX) {