Bluetooth: hidp: buffer overflow in hidp_process_report

CVE-2018-9363

The buffer length is unsigned at all layers, but gets cast to int and
checked in hidp_process_report and can lead to a buffer overflow.
Switch len parameter to unsigned int to resolve issue.

This affects 3.18 and newer kernels.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Fixes: a4b1b587 ("HID: Bluetooth: hidp: make sure input buffers are big enough")
Cc: Marcel Holtmann <marcel@holtmann.org>
Cc: Johan Hedberg <johan.hedberg@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: linux-bluetooth@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: security@kernel.org
Cc: kernel-team@android.com
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>