On Mon, 18 Sep 2017, Jason Gerecke wrote:
> The wacom_get_hdev_data function is used to find and return a reference to
> the "other half" of a Wacom device (i.e., the touch device associated with
> a pen, or vice-versa). To ensure these references are properly accounted
> for, the function is supposed to automatically increment the refcount before
> returning. This was not done, however, for devices which have pen & touch
> on different interfaces of the same USB device. This can lead to a WARNING
> ("refcount_t: underflow; use-after-free") when removing the module or device
> as we call kref_put() more times than kref_get(). Triggering an "actual" use-
> after-free would be difficult since both devices will disappear nearly-
> simultaneously. To silence this warning and prevent the potential error, we
> need to increment the refcount for all cases within wacom_get_hdev_data.
>
> Fixes: 41372d5d40 ("HID: wacom: Augment 'oVid' and 'oPid' with heuristics for HID_GENERIC")
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.9+
> Signed-off-by: Jason Gerecke <jason.gerecke@xxxxxxxxx>
Applied to for-4.14/upstream-fixes.
--
Jiri Kosina
SUSE Labs