netfilter: nf_tables: reject unsupported chain flags

Bail out if userspace sends unsupported chain flags.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -189,6 +189,9 @@ enum nft_chain_flags {
 	NFT_CHAIN_HW_OFFLOAD	= (1 << 1),
 	NFT_CHAIN_BINDING	= (1 << 2),
 };
+#define NFT_CHAIN_FLAGS		(NFT_CHAIN_BASE		| \
+				 NFT_CHAIN_HW_OFFLOAD	| \
+				 NFT_CHAIN_BINDING)
 
 /**
  * enum nft_chain_attributes - nf_tables chain netlink attributes

net/netfilter/nf_tables_api.c

@@ -2285,6 +2285,9 @@ static int nf_tables_newchain(struct net *net, struct sock *nlsk,
 	else if (chain)
 		flags = chain->flags;
 
+	if (flags & ~NFT_CHAIN_FLAGS)
+		return -EOPNOTSUPP;
+
 	nft_ctx_init(&ctx, net, skb, nlh, family, table, chain, nla);
 
 	if (chain != NULL) {