netfilter: Set /proc/net entries owner to root in namespace

Various files are owned by root with 0440 permission. Reading them is
impossible in an unprivileged user namespace, interfering with firewall
tools. For instance, iptables-save relies on /proc/net/ip_tables_names
contents to dump only loaded tables.

This patch assigned ownership of the following files to root in the
current namespace:

- /proc/net/*_tables_names
- /proc/net/*_tables_matches
- /proc/net/*_tables_targets
- /proc/net/nf_conntrack
- /proc/net/nf_conntrack_expect
- /proc/net/netfilter/nfnetlink_log

A mapping for root must be available, so this order should be followed:

unshare(CLONE_NEWUSER);
/* Setup the mapping */
unshare(CLONE_NEWNET);

Signed-off-by: Philip Whineray <phil@firehol.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 13 insertions, 2 deletions

diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
index 740cce4685ac..dea467647c90 100644
--- a/net/netfilter/nfnetlink_log.c
+++ b/net/netfilter/nfnetlink_log.c
@@ -1064,15 +1064,26 @@ static int __net_init nfnl_log_net_init(struct net *net)
 {
 	unsigned int i;
 	struct nfnl_log_net *log = nfnl_log_pernet(net);
+#ifdef CONFIG_PROC_FS
+	struct proc_dir_entry *proc;
+	kuid_t root_uid;
+	kgid_t root_gid;
+#endif
 
 	for (i = 0; i < INSTANCE_BUCKETS; i++)
 		INIT_HLIST_HEAD(&log->instance_table[i]);
 	spin_lock_init(&log->instances_lock);
 
 #ifdef CONFIG_PROC_FS
-	if (!proc_create("nfnetlink_log", 0440,
-			 net->nf.proc_netfilter, &nful_file_ops))
+	proc = proc_create("nfnetlink_log", 0440,
+			   net->nf.proc_netfilter, &nful_file_ops);
+	if (!proc)
 		return -ENOMEM;
+
+	root_uid = make_kuid(net->user_ns, 0);
+	root_gid = make_kgid(net->user_ns, 0);
+	if (uid_valid(root_uid) && gid_valid(root_gid))
+		proc_set_user(proc, root_uid, root_gid);
 #endif
 	return 0;
 }