platform/x86: dell-wmi-sysman: fix a NULL pointer dereference

An upcoming Dell platform is causing a NULL pointer dereference
in dell-wmi-sysman initialization.  Validate that the input from
BIOS matches correct ACPI types and abort module initialization
if it fails.
Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Tested-by: Perry Yuan <perry_yuan@dell.com>
Link: https://lore.kernel.org/r/20210129172654.2326751-1-mario.limonciello@dell.com
[hdegoede@redhat.com: Drop redundant release_attributes_data() call]
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/dell-wmi-sysman/sysman.c

@@ -419,13 +419,17 @@ static int init_bios_attributes(int attr_type, const char *guid)
 		return retval;
 	/* need to use specific instance_id and guid combination to get right data */
 	obj = get_wmiobj_pointer(instance_id, guid);
-	if (!obj)
+	if (!obj || obj->type != ACPI_TYPE_PACKAGE)
 		return -ENODEV;
 	elements = obj->package.elements;
 
 	mutex_lock(&wmi_priv.mutex);
 	while (elements) {
 		/* sanity checking */
+		if (elements[ATTR_NAME].type != ACPI_TYPE_STRING) {
+			pr_debug("incorrect element type\n");
+			goto nextobj;
+		}
 		if (strlen(elements[ATTR_NAME].string.pointer) == 0) {
 			pr_debug("empty attribute found\n");
 			goto nextobj;