4.9-stable review patch. If anyone has any objections, please let me know.
------------------
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" */