Input: xpad - prevent spurious input from wired Xbox 360 controllers

commit 1ff5fa3c upstream.

After initially connecting a wired Xbox 360 controller or sending it
a command to change LEDs, a status/response packet is interpreted as
controller input. This causes the state of buttons represented in
byte 2 of the controller data packet to be incorrect until the next
valid input packet. Wireless Xbox 360 controllers are not affected.

Writing a new value to the LED device while holding the Start button
and running jstest is sufficient to reproduce this bug. An event will
come through with the Start button released.

Xboxdrv also won't attempt to read controller input from a packet
where byte 0 is non-zero. It also checks that byte 1 is 0x14, but
that value differs between wired and wireless controllers and this
code is shared by both. I think just checking byte 0 is enough to
eliminate unwanted packets.

The following are some examples of 3-byte status packets I saw:
01 03 02
02 03 00
03 03 03
08 03 00
Signed-off-by: Cameron Gutman <aicommander@gmail.com>
Signed-off-by: Pavel Rojtberg <rojtberg@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/input/joystick/xpad.c

@@ -415,6 +415,10 @@ static void xpad360_process_packet(struct usb_xpad *xpad,
 {
 	struct input_dev *dev = xpad->dev;
 
+	/* valid pad data */
+	if (data[0] != 0x00)
+		return;
+
 	/* digital pad */
 	if (xpad->mapping & MAP_DPAD_TO_BUTTONS) {
 		/* dpad as buttons (left, right, up, down) */