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

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

commit c1fb3542074fd0c4d901d778bd52455111e4eb6f 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: bf9bccc14c05 ("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>