platform/x86: wmi: Break possible infinite loop when parsing GUID

The while-loop may break on one of the two conditions, either ID string
is empty or GUID matches. The second one, may never be reached if the
parsed string is not correct GUID. In such a case the loop will never
advance to check the next ID.

Break possible infinite loop by factoring out guid_parse_and_compare()
helper which may be moved to the generic header for everyone later on
and preventing from similar mistake in the future.

Interestingly that firstly it appeared when WMI was turned into a bus
driver, but later when duplicated GUIDs were checked, the while-loop
has been replaced by for-loop and hence no mistake made again.

Fixes: a48e233 ("platform/x86: wmi: add context pointer field to struct wmi_device_id")
Fixes: 844af95 ("platform/x86: wmi: Turn WMI into a bus driver")
Signed-off-by: Andy Shevchenko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Tested-by: Armin Wolf <[email protected]>
Reviewed-by: Hans de Goede <[email protected]>
Signed-off-by: Hans de Goede <[email protected]>

Author: andy-shev

drivers/platform/x86/wmi.c

@@ -136,6 +136,16 @@ static acpi_status find_guid(const char *guid_string, struct wmi_block **out)
 	return AE_NOT_FOUND;
 }
 
+static bool guid_parse_and_compare(const char *string, const guid_t *guid)
+{
+	guid_t guid_input;
+
+	if (guid_parse(string, &guid_input))
+		return false;
+
+	return guid_equal(&guid_input, guid);
+}
+
 static const void *find_guid_context(struct wmi_block *wblock,
 				     struct wmi_driver *wdriver)
 {
@@ -146,11 +156,7 @@ static const void *find_guid_context(struct wmi_block *wblock,
 		return NULL;
 
 	while (*id->guid_string) {
-		guid_t guid_input;
-
-		if (guid_parse(id->guid_string, &guid_input))
-			continue;
-		if (guid_equal(&wblock->gblock.guid, &guid_input))
+		if (guid_parse_and_compare(id->guid_string, &wblock->gblock.guid))
 			return id->context;
 		id++;
 	}
@@ -895,11 +901,7 @@ static int wmi_dev_match(struct device *dev, struct device_driver *driver)
 		return 0;
 
 	while (*id->guid_string) {
-		guid_t driver_guid;
-
-		if (WARN_ON(guid_parse(id->guid_string, &driver_guid)))
-			continue;
-		if (guid_equal(&driver_guid, &wblock->gblock.guid))
+		if (guid_parse_and_compare(id->guid_string, &wblock->gblock.guid))
 			return 1;
 
 		id++;