HID: wiimote: discard invalid EXT data reports

If an extension device isn't initialized properly, or during hardware
initialization, a device might send extension data which is all 0xff.
This is ambigious because this is also a valid normal data report. But
it is impossible, under normal conditions, to trigger valid reports with
all 0xff. Hence, we can safely ignore them.

Signed-off-by: David Herrmann <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

drivers/hid/hid-wiimote-core.c

···
 static void handler_ext(struct wiimote_data *wdata, const __u8 *payload,
 			size_t len)
 {
+	static const __u8 invalid[21] = { 0xff, 0xff, 0xff, 0xff,
+					  0xff, 0xff, 0xff, 0xff,
+					  0xff, 0xff, 0xff, 0xff,
+					  0xff, 0xff, 0xff, 0xff,
+					  0xff, 0xff, 0xff, 0xff,
+					  0xff };
 	const __u8 *iter, *mods;
 	const struct wiimod_ops *ops;
 	bool is_mp;
 
-	if (len < 6)
+	if (len > 21)
+		len = 21;
+	if (len < 6 || !memcmp(payload, invalid, len))
 		return;
 
 	/* if MP is active, track MP slot hotplugging */