proc: make proc entries inherit ownership from parent

There are certain parameters that belong to net namespace and that are
exported in /proc. They should be controllable by the container's owner,
but are currently owned by global root and thus not available.

Let's change proc code to inherit ownership of parent entry, and when
create per-ns "net" proc entry set it up as owned by container's owner.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

fs/proc/generic.c

@@ -390,6 +390,8 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
 	atomic_set(&ent->count, 1);
 	spin_lock_init(&ent->pde_unload_lock);
 	INIT_LIST_HEAD(&ent->pde_openers);
+	proc_set_user(ent, (*parent)->uid, (*parent)->gid);
+
 out:
 	return ent;
 }

fs/proc/proc_net.c

@@ -21,6 +21,7 @@
 #include <linux/bitops.h>
 #include <linux/mount.h>
 #include <linux/nsproxy.h>
+#include <linux/uidgid.h>
 #include <net/net_namespace.h>
 #include <linux/seq_file.h>
 
@@ -185,6 +186,8 @@ const struct file_operations proc_net_operations = {
 static __net_init int proc_net_ns_init(struct net *net)
 {
 	struct proc_dir_entry *netd, *net_statd;
+	kuid_t uid;
+	kgid_t gid;
 	int err;
 
 	err = -ENOMEM;
@@ -199,6 +202,16 @@ static __net_init int proc_net_ns_init(struct net *net)
 	netd->parent = &proc_root;
 	memcpy(netd->name, "net", 4);
 
+	uid = make_kuid(net->user_ns, 0);
+	if (!uid_valid(uid))
+		uid = netd->uid;
+
+	gid = make_kgid(net->user_ns, 0);
+	if (!gid_valid(gid))
+		gid = netd->gid;
+
+	proc_set_user(netd, uid, gid);
+
 	err = -EEXIST;
 	net_statd = proc_net_mkdir(net, "stat", netd);
 	if (!net_statd)