[PATCH] Input: xpad - reject short Xbox One packets before len-relative share-button index

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

xpadone_process_packet() receives len directly from urb->actual_length
and uses it to index the share-button byte at data[len - 18] or
data[len - 26].  Since both len and data[0] are under the device's
control, a broken controller can send a GIP_CMD_INPUT packet with
actual_length < 18 (e.g. 5 bytes) and reach this code path, causing
accesses beyond the actual array.

Since len is u32, 5 - 26 wraps to 0xFFFFFFEB, and data[0xFFFFFFEB] can
dereference about 4 GiB past the 64-byte usb_alloc_coherent() idata
buffer.  On a KASAN system this is an immediate splat otherwise the read
will either fault on an unmapped page (DoS) or pull a bit from arbitrary
kernel memory and report it as KEY_RECORD.

Fix this all up by properly bounds checking the value provided by the
device.

Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Fixes: 4ef46367073b ("Input: xpad - fix Share button on Xbox One controllers")
Cc: stable <stable@kernel.org>
Assisted-by: gkh_clanker_t1000
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/input/joystick/xpad.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/input/joystick/xpad.c b/drivers/input/joystick/xpad.c
index d6fc3d6006bb..7d99fe0ecf91 100644
--- a/drivers/input/joystick/xpad.c
+++ b/drivers/input/joystick/xpad.c
@@ -1110,10 +1110,13 @@ static void xpadone_process_packet(struct usb_xpad *xpad, u16 cmd, unsigned char
 		input_report_key(dev, BTN_START,  data[4] & BIT(2));
 		input_report_key(dev, BTN_SELECT, data[4] & BIT(3));
 		if (xpad->mapping & MAP_SHARE_BUTTON) {
-			if (xpad->mapping & MAP_SHARE_OFFSET)
-				input_report_key(dev, KEY_RECORD, data[len - 26] & BIT(0));
-			else
-				input_report_key(dev, KEY_RECORD, data[len - 18] & BIT(0));
+			if (xpad->mapping & MAP_SHARE_OFFSET) {
+				if (len >= 26)
+					input_report_key(dev, KEY_RECORD, data[len - 26] & BIT(0));
+			} else {
+				if (len >= 18)
+					input_report_key(dev, KEY_RECORD, data[len - 18] & BIT(0));
+			}
 		}
 
 		/* buttons A,B,X,Y */
-- 
2.53.0