libnvdimm, namespace: make 'resource' attribute only readable by root

BugLink: http://bugs.launchpad.net/bugs/1744873

commit c1fb3542 upstream.

For the same reason that /proc/iomem returns 0's for non-root readers
and acpi tables are root-only, make the 'resource' attribute for
namespace devices only readable by root. Otherwise we disclose physical
address information.

Fixes: bf9bccc1 ("libnvdimm: pmem label sets and namespace instantiation")
Reported-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/nvdimm/namespace_devs.c

@@ -1305,7 +1305,7 @@ static umode_t namespace_visible(struct kobject *kobj,
 	if (a == &dev_attr_resource.attr) {
 		if (is_namespace_blk(dev))
 			return 0;
-		return a->mode;
+		return 0400;
 	}
 
 	if (is_namespace_pmem(dev) || is_namespace_blk(dev)) {