[PATCH 1/2] HID: winwing: fix use-after-free of the rumble work

["René Onier" <f3nr1l@me.com>]

winwing_remove() cancels the rumble work before it tears the device
down:

	if (data)
		cancel_work_sync(&data->rumble_work);

	hid_hw_close(hdev);
	hid_hw_stop(hdev);

Nothing keeps the work from being queued again after that cancel.
hid_hw_stop() unregisters the input device, and evdev_cleanup() flushes
it while it is still open: input_flush_device() -> input_ff_flush() ->
erase_effect() -> ff->playback(dev, id, 0). On a memoryless device that
is ml_ff_playback(), which marks a playing effect as aborting and calls
ml_play_effects(), handing the driver the combined - now zeroed -
effect. That is winwing_play_effect(), and it ends with

	return schedule_work(&data->rumble_work);

Unbinding, rmmod'ing or unplugging the device while an effect is playing
therefore queues the work again, after cancel_work_sync() has run.

The driver data is devm-allocated, and hid_device_remove() releases the
driver's devres group as soon as winwing_remove() returns. The pending
work then runs on freed memory: both the work_struct itself and the
report buffer winwing_haptic_rumble() writes into live in that
allocation.

Cancel the work once the device has been stopped instead. After
hid_hw_stop() has returned the input device is gone and no further
effect can be played, so a single cancel_work_sync() is enough. The
driver data is still valid at that point, since devres only runs after
winwing_remove() has returned, so a work item that is still running
while the transport goes down touches valid memory only; its
hid_hw_output_report() call simply fails once the low-level driver has
torn its endpoints down.

Fixes: 42d020b54edc ("HID: winwing: Enable rumble effects")
Signed-off-by: René Onier <f3nr1l@me.com>
---
 drivers/hid/hid-winwing.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/hid/hid-winwing.c b/drivers/hid/hid-winwing.c
index 19b92c2c65..e8030fdc14 100644
--- a/drivers/hid/hid-winwing.c
+++ b/drivers/hid/hid-winwing.c
@@ -391,11 +391,16 @@ static void winwing_remove(struct hid_device *hdev)
 
 	data = (struct winwing_drv_data *) hid_get_drvdata(hdev);
 
-	if (data)
-		cancel_work_sync(&data->rumble_work);
-
 	hid_hw_close(hdev);
 	hid_hw_stop(hdev);
+
+	/*
+	 * Only cancel the work once the input device is gone: stopping the
+	 * device flushes the force feedback effects, which plays them one
+	 * last time and queues the work again.
+	 */
+	if (data)
+		cancel_work_sync(&data->rumble_work);
 }
 
 static int winwing_input_configured(struct hid_device *hdev,
-- 
2.55.0