This is a note to let you know that I've just added the patch titled HID: wacom: Always increment hdev refcount within wacom_get_hdev_data to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: hid-wacom-always-increment-hdev-refcount-within-wacom_get_hdev_data.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 2a5e597c6bb1b873e473e5f57147e9e5d2755430 Mon Sep 17 00:00:00 2001 From: Jason Gerecke <killertofu@xxxxxxxxx> Date: Mon, 18 Sep 2017 09:27:42 -0700 Subject: HID: wacom: Always increment hdev refcount within wacom_get_hdev_data From: Jason Gerecke <killertofu@xxxxxxxxx> commit 2a5e597c6bb1b873e473e5f57147e9e5d2755430 upstream. 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") Signed-off-by: Jason Gerecke <jason.gerecke@xxxxxxxxx> Reviewed-by: Ping Cheng <ping.cheng@xxxxxxxxx> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/hid/wacom_sys.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/drivers/hid/wacom_sys.c +++ b/drivers/hid/wacom_sys.c @@ -611,8 +611,10 @@ static struct wacom_hdev_data *wacom_get /* 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" */ Patches currently in stable-queue which might be from killertofu@xxxxxxxxx are queue-4.9/hid-wacom-always-increment-hdev-refcount-within-wacom_get_hdev_data.patch queue-4.9/hid-wacom-bits-shifted-too-much-for-9th-and-10th-buttons.patch