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HID: wacom: Always increment hdev refcount within wacom_get_hdev_data

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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@vger.kernel.org> # v4.9+
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Jason Gerecke 2017-09-18 09:27:42 -07:00 committed by Jiri Kosina
parent 92380b572d
commit 2a5e597c6b
1 changed files with 3 additions and 1 deletions
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4
drivers/hid/wacom_sys.c
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@ -668,8 +668,10 @@ static struct wacom_hdev_data *wacom_get_hdev_data(struct hid_device *hdev)
/* Try to find an already-probed interface from the same device */
list_for_each_entry(data, &wacom_udev_list, list) {
if (compare_device_paths(hdev, data->dev, '/'))
if (compare_device_paths(hdev, data->dev, '/')) {
kref_get(&data->kref);
return data;
}
}
/* Fallback to finding devices that appear to be "siblings" */