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

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 region
devices only readable by root. Otherwise we disclose physical address
information.

Fixes: 802f4be6feee ("libnvdimm: Add 'resource' sysfs attribute to regions")
Cc: <stable@vger.kernel.org>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Reported-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/region_devs.c

@@ -562,8 +562,12 @@ static umode_t region_visible(struct kobject *kobj, struct attribute *a, int n)
 	if (!is_nd_pmem(dev) && a == &dev_attr_badblocks.attr)
 		return 0;
 
-	if (!is_nd_pmem(dev) && a == &dev_attr_resource.attr)
-		return 0;
+	if (a == &dev_attr_resource.attr) {
+		if (is_nd_pmem(dev))
+			return 0400;
+		else
+			return 0;
+	}
 
 	if (a == &dev_attr_deep_flush.attr) {
 		int has_flush = nvdimm_has_flush(nd_region);