Re: [PATCH] HID: wacom: Always increment hdev refcount within wacom_get_hdev_data
From: Ping Cheng <hidden>
Date: 2017-09-18 21:04:12
Also in:
linux-input
On Mon, Sep 18, 2017 at 9:27 AM, Jason Gerecke [off-list ref] 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: <redacted> # v4.9+
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>Reviewed-by: Ping Cheng <ping.cheng@wacom.com> Cheers, Ping
quoted hunk ↗ jump to hunk
--- drivers/hid/wacom_sys.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c index 735bfbbcaa82..906e654fb0ba 100644 --- a/drivers/hid/wacom_sys.c +++ b/drivers/hid/wacom_sys.c@@ -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" */ --2.14.1