BugLink: https://bugs.launchpad.net/bugs/1848780

commit 93ddb1f5 upstream.

The driver was accessing its struct usb_interface in its release()
callback without holding a reference. This would lead to a
use-after-free whenever the device was disconnected while the character
device was still open.

Fixes: 66e3e591 ("usb: Add driver for Altus Metrum ChaosKey device (v2)")
Cc: stable <stable@vger.kernel.org>     # 4.1
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191009153848.8664-3-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>