netfilter: conntrack: do not dump other netns's conntrack entries via proc

We should skip the conntracks that belong to a different namespace,
otherwise other unrelated netns's conntrack entries will be dumped via
/proc/net/nf_conntrack.

Fixes: 56d52d48 ("netfilter: conntrack: use a single hashtable for all namespaces")
Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_standalone.c

@@ -205,6 +205,7 @@ static int ct_seq_show(struct seq_file *s, void *v)
 	struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(hash);
 	const struct nf_conntrack_l3proto *l3proto;
 	const struct nf_conntrack_l4proto *l4proto;
+	struct net *net = seq_file_net(s);
 	int ret = 0;
 
 	NF_CT_ASSERT(ct);
@@ -215,6 +216,9 @@ static int ct_seq_show(struct seq_file *s, void *v)
 	if (NF_CT_DIRECTION(hash))
 		goto release;
 
+	if (!net_eq(nf_ct_net(ct), net))
+		goto release;
+
 	l3proto = __nf_ct_l3proto_find(nf_ct_l3num(ct));
 	NF_CT_ASSERT(l3proto);
 	l4proto = __nf_ct_l4proto_find(nf_ct_l3num(ct), nf_ct_protonum(ct));