netfilter: nf_tables: reject constant set with timeout

This set combination is weird: it allows for elements to be
added/deleted, but once bound to the rule it cannot be updated anymore.
Eventually, all elements expire, leading to an empty set which cannot
be updated anymore. Reject this flags combination.

Cc: stable@vger.kernel.org
Fixes: 761da293 ("netfilter: nf_tables: add set timeout API support")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -5004,6 +5004,9 @@ static int nf_tables_newset(struct sk_buff *skb, const struct nfnl_info *info,
 		if ((flags & (NFT_SET_ANONYMOUS | NFT_SET_TIMEOUT | NFT_SET_EVAL)) ==
 			     (NFT_SET_ANONYMOUS | NFT_SET_TIMEOUT))
 			return -EOPNOTSUPP;
+		if ((flags & (NFT_SET_CONSTANT | NFT_SET_TIMEOUT)) ==
+			     (NFT_SET_CONSTANT | NFT_SET_TIMEOUT))
+			return -EOPNOTSUPP;
 	}
 
 	desc.dtype = 0;