netfilter: nf_tables: hide clash bit from userspace

Its a kernel implementation detail, at least at this time:

We can later decide to revert this patch if there is a compelling
reason, but then we should also remove the ifdef that prevents exposure
of ip_conntrack_status enum IPS_NAT_CLASH value in the uapi header.

Clash entries are not included in dumps (true for both old /proc
and ctnetlink) either.  So for now exclude the clash bit when dumping.

Fixes: 7e5c6aa ("netfilter: nf_tables: add packets conntrack state to debug trace info")
Link: https://lore.kernel.org/netfilter-devel/[email protected]/
Signed-off-by: Florian Westphal <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>

Author: Florian Westphal

net/netfilter/nf_tables_trace.c

@@ -127,6 +127,9 @@ static int nf_trace_fill_ct_info(struct sk_buff *nlskb,
 		if (nla_put_be32(nlskb, NFTA_TRACE_CT_ID, (__force __be32)id))
 			return -1;
 
+		/* Kernel implementation detail, withhold this from userspace for now */
+		status &= ~IPS_NAT_CLASH;
+
 		if (status && nla_put_be32(nlskb, NFTA_TRACE_CT_STATUS, htonl(status)))
 			return -1;
 	}