sysfs: Restrict mounting sysfs

Don't allow mounting sysfs unless the caller has CAP_SYS_ADMIN rights
over the net namespace.  The principle here is if you create or have
capabilities over it you can mount it, otherwise you get to live with
what other people have mounted.

Instead of testing this with a straight forward ns_capable call,
perform this check the long and torturous way with kobject helpers,
this keeps direct knowledge of namespaces out of sysfs, and preserves
the existing sysfs abstractions.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/lib/kobject.c b/lib/kobject.c
index 4a1f33d43548..3bbde222c90f 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -915,6 +915,21 @@ const struct kobj_ns_type_operations *kobj_ns_ops(struct kobject *kobj)
 	return kobj_child_ns_ops(kobj->parent);
 }
 
+bool kobj_ns_current_may_mount(enum kobj_ns_type type)
+{
+	bool may_mount = false;
+
+	if (type == KOBJ_NS_TYPE_NONE)
+		return true;
+
+	spin_lock(&kobj_ns_type_lock);
+	if ((type > KOBJ_NS_TYPE_NONE) && (type < KOBJ_NS_TYPES) &&
+	    kobj_ns_ops_tbl[type])
+		may_mount = kobj_ns_ops_tbl[type]->current_may_mount();
+	spin_unlock(&kobj_ns_type_lock);
+
+	return may_mount;
+}
 
 void *kobj_ns_grab_current(enum kobj_ns_type type)
 {