platform/x86: dell-wmi-sysman: Make init_bios_attributes() ACPI object parsing more robust

Make init_bios_attributes() ACPI object parsing more robust:
1. Always check that the type of the return ACPI object is package, rather
   then only checking this for instance_id == 0
2. Check that the package has the minimum amount of elements which will
   be consumed by the populate_foo_data() for the attr_type

Note/TODO: The populate_foo_data() functions should also be made more
robust. The should check the type of each of the elements matches the
type which they expect and in case of populate_enum_data()
obj->package.count should be passed to it as an argument and it should
re-check this itself since it consume a variable number of elements.

Fixes: e8a60aa7 ("platform/x86: Introduce support for Systems Management Driver over WMI for Dell Systems")
Cc: Divya Bharathi <Divya_Bharathi@dell.com>
Cc: Mario Limonciello <mario.limonciello@dell.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20210321121607.35717-1-hdegoede@redhat.com

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

@@ -399,6 +399,7 @@ static int init_bios_attributes(int attr_type, const char *guid)
 	union acpi_object *obj = NULL;
 	union acpi_object *elements;
 	struct kset *tmp_set;
+	int min_elements;
 
 	/* instance_id needs to be reset for each type GUID
 	 * also, instance IDs are unique within GUID but not across
@@ -409,14 +410,38 @@ static int init_bios_attributes(int attr_type, const char *guid)
 	retval = alloc_attributes_data(attr_type);
 	if (retval)
 		return retval;
+
+	switch (attr_type) {
+	case ENUM:	min_elements = 8;	break;
+	case INT:	min_elements = 9;	break;
+	case STR:	min_elements = 8;	break;
+	case PO:	min_elements = 4;	break;
+	default:
+		pr_err("Error: Unknown attr_type: %d\n", attr_type);
+		return -EINVAL;
+	}
+
 	/* need to use specific instance_id and guid combination to get right data */
 	obj = get_wmiobj_pointer(instance_id, guid);
-	if (!obj || obj->type != ACPI_TYPE_PACKAGE)
+	if (!obj)
 		return -ENODEV;
-	elements = obj->package.elements;
 
 	mutex_lock(&wmi_priv.mutex);
-	while (elements) {
+	while (obj) {
+		if (obj->type != ACPI_TYPE_PACKAGE) {
+			pr_err("Error: Expected ACPI-package type, got: %d\n", obj->type);
+			retval = -EIO;
+			goto err_attr_init;
+		}
+
+		if (obj->package.count < min_elements) {
+			pr_err("Error: ACPI-package does not have enough elements: %d < %d\n",
+			       obj->package.count, min_elements);
+			goto nextobj;
+		}
+
+		elements = obj->package.elements;
+
 		/* sanity checking */
 		if (elements[ATTR_NAME].type != ACPI_TYPE_STRING) {
 			pr_debug("incorrect element type\n");
@@ -481,7 +506,6 @@ static int init_bios_attributes(int attr_type, const char *guid)
 		kfree(obj);
 		instance_id++;
 		obj = get_wmiobj_pointer(instance_id, guid);
-		elements = obj ? obj->package.elements : NULL;
 	}
 
 	mutex_unlock(&wmi_priv.mutex);