ACPICA: Return error if DerefOf resolves to a null package element.

Disallow the dereference of a reference (via index) to an uninitialized
package element. Provides compatibility with other ACPI
implementations. ACPICA BZ 1003.

References: https://bugs.acpica.org/show_bug.cgi?id=431
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpica/exoparg1.c

@@ -962,10 +962,17 @@ acpi_status acpi_ex_opcode_1A_0T_1R(struct acpi_walk_state *walk_state)
 					 */
 					return_desc =
 					    *(operand[0]->reference.where);
-					if (return_desc) {
-						acpi_ut_add_reference
-						    (return_desc);
+					if (!return_desc) {
+						/*
+						 * Element is NULL, do not allow the dereference.
+						 * This provides compatibility with other ACPI
+						 * implementations.
+						 */
+						return_ACPI_STATUS
+						    (AE_AML_UNINITIALIZED_ELEMENT);
 					}
+
+					acpi_ut_add_reference(return_desc);
 					break;
 
 				default: