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

BugLink: http://bugs.launchpad.net/bugs/1584953

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>
(cherry picked from commit f13f2aee)
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

net/netfilter/nf_conntrack_expect.c

@@ -596,11 +596,18 @@ static int exp_proc_init(struct net *net)
 {
 #ifdef CONFIG_NF_CONNTRACK_PROCFS
 	struct proc_dir_entry *proc;
+	kuid_t root_uid;
+	kgid_t root_gid;
 
 	proc = proc_create("nf_conntrack_expect", 0440, net->proc_net,
 			   &exp_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 /* CONFIG_NF_CONNTRACK_PROCFS */
 	return 0;
 }

net/netfilter/nf_conntrack_standalone.c

@@ -392,11 +392,18 @@ static const struct file_operations ct_cpu_seq_fops = {
 static int nf_conntrack_standalone_init_proc(struct net *net)
 {
 	struct proc_dir_entry *pde;
+	kuid_t root_uid;
+	kgid_t root_gid;
 
 	pde = proc_create("nf_conntrack", 0440, net->proc_net, &ct_file_ops);
 	if (!pde)
 		goto out_nf_conntrack;
 
+	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(pde, root_uid, root_gid);
+
 	pde = proc_create("nf_conntrack", S_IRUGO, net->proc_net_stat,
 			  &ct_cpu_seq_fops);
 	if (!pde)

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;
 }

net/netfilter/x_tables.c

@@ -26,6 +26,7 @@
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/audit.h>
+#include <linux/user_namespace.h>
 #include <net/net_namespace.h>
 
 #include <linux/netfilter/x_tables.h>
@@ -1229,6 +1230,8 @@ int xt_proto_init(struct net *net, u_int8_t af)
 #ifdef CONFIG_PROC_FS
 	char buf[XT_FUNCTION_MAXNAMELEN];
 	struct proc_dir_entry *proc;
+	kuid_t root_uid;
+	kgid_t root_gid;
 #endif
 
 	if (af >= ARRAY_SIZE(xt_prefix))
@@ -1236,12 +1239,17 @@ int xt_proto_init(struct net *net, u_int8_t af)
 
 
 #ifdef CONFIG_PROC_FS
+	root_uid = make_kuid(net->user_ns, 0);
+	root_gid = make_kgid(net->user_ns, 0);
+
 	strlcpy(buf, xt_prefix[af], sizeof(buf));
 	strlcat(buf, FORMAT_TABLES, sizeof(buf));
 	proc = proc_create_data(buf, 0440, net->proc_net, &xt_table_ops,
 				(void *)(unsigned long)af);
 	if (!proc)
 		goto out;
+	if (uid_valid(root_uid) && gid_valid(root_gid))
+		proc_set_user(proc, root_uid, root_gid);
 
 	strlcpy(buf, xt_prefix[af], sizeof(buf));
 	strlcat(buf, FORMAT_MATCHES, sizeof(buf));
@@ -1249,6 +1257,8 @@ int xt_proto_init(struct net *net, u_int8_t af)
 				(void *)(unsigned long)af);
 	if (!proc)
 		goto out_remove_tables;
+	if (uid_valid(root_uid) && gid_valid(root_gid))
+		proc_set_user(proc, root_uid, root_gid);
 
 	strlcpy(buf, xt_prefix[af], sizeof(buf));
 	strlcat(buf, FORMAT_TARGETS, sizeof(buf));
@@ -1256,6 +1266,8 @@ int xt_proto_init(struct net *net, u_int8_t af)
 				(void *)(unsigned long)af);
 	if (!proc)
 		goto out_remove_matches;
+	if (uid_valid(root_uid) && gid_valid(root_gid))
+		proc_set_user(proc, root_uid, root_gid);
 #endif
 
 	return 0;