HID: logitech-hidpp: check name retrieval return code

hidpp_devicenametype_get_device_name() may return a negative value on
protocol errors (for example, when the device is powered off).
Explicitly check this condition to avoid a long-running loop.

(0 cannot be returned as __name_length - index > 0, but check for it
anyway as it would otherwise result in an infinite loop.)
Signed-off-by: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-logitech-hidpp.c

@@ -484,10 +484,16 @@ static char *hidpp_get_device_name(struct hidpp_device *hidpp)
 	if (!name)
 		return NULL;
 
-	while (index < __name_length)
-		index += hidpp_devicenametype_get_device_name(hidpp,
+	while (index < __name_length) {
+		ret = hidpp_devicenametype_get_device_name(hidpp,
 			feature_index, index, name + index,
 			__name_length - index);
+		if (ret <= 0) {
+			kfree(name);
+			return NULL;
+		}
+		index += ret;
+	}
 
 	return name;
 }