ACPICA: Validate start object for acpi_walk_namespace.

Perform a sanity check on the start object to prevent problems
later. ACPICA BZ 1025.
This patch only adds additional input parameter validation, no actual
kernel suffering has been discovered.

Buglink: http://bugs.acpica.org/show_bug.cgi?id=1025
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpica/nsxfeval.c

@@ -605,11 +605,19 @@ acpi_walk_namespace(acpi_object_type type,
 		goto unlock_and_exit;
 	}
 
+	/* Now we can validate the starting node */
+
+	if (!acpi_ns_validate_handle(start_object)) {
+		status = AE_BAD_PARAMETER;
+		goto unlock_and_exit2;
+	}
+
 	status = acpi_ns_walk_namespace(type, start_object, max_depth,
 					ACPI_NS_WALK_UNLOCK,
 					descending_callback, ascending_callback,
 					context, return_value);
 
+      unlock_and_exit2:
 	(void)acpi_ut_release_mutex(ACPI_MTX_NAMESPACE);
 
       unlock_and_exit: