netfilter: nf_conncount: don't skip eviction when age is negative

commit 4cd273bb upstream.

(not in Linus's tree now, but in nf.git + linux-next.git already.)

age is signed integer, so result can be negative when the timestamps
have a large delta.  In this case we want to discard the entry.

Instead of using age >= 2 || age < 0, just make it unsigned.

Fixes: b36e4523 ("netfilter: nf_conncount: fix garbage collection confirm race")
Reviewed-by: Shawn Bohrer <sbohrer@cloudflare.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

[mfo: backport: use older file name, nf_conncount.c -> xt_connlimit.c]
Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

net/netfilter/xt_connlimit.c

@@ -141,7 +141,7 @@ find_or_evict(struct net *net, struct xt_connlimit_conn *conn)
 	const struct nf_conntrack_tuple_hash *found;
 	unsigned long a, b;
 	int cpu = raw_smp_processor_id();
-	__s32 age;
+	u32 age;
 
 	found = nf_conntrack_find_get(net, &conn->zone, &conn->tuple);
 	if (found)