[PATCH v2] media: cedrus: fix use after free bug in cedrus_remove due to race condition

[Zheng Wang]

In cedrus_probe, dev->watchdog_work is bound with cedrus_watchdog function.
In cedrus_device_run, it will started by schedule_delayed_work. If there is
an unfinished work in cedrus_remove, there may be a race condition and 
trigger UAF bug.

CPU0                  CPU1

                    |cedrus_watchdog
cedrus_remove       |
  v4l2_m2m_release  |
  kfree(m2m_dev)    |
                    |
                    | v4l2_m2m_get_curr_priv
                    |   m2m_dev //use

Fix it by canceling the worker in cedrus_remove.

Fixes: 7c38a551bda1 ("media: cedrus: Add watchdog for job completion")
Signed-off-by: Zheng Wang <zyytlz.wz at 163.com>
---
v2:
- use cancel_delayed_work_sync instead and add Fixes
label suggested by Hans Verkuil
---
 drivers/staging/media/sunxi/cedrus/cedrus.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.c b/drivers/staging/media/sunxi/cedrus/cedrus.c
index a43d5ff66716..a50a4d0a8f71 100644
--- a/drivers/staging/media/sunxi/cedrus/cedrus.c
+++ b/drivers/staging/media/sunxi/cedrus/cedrus.c
@@ -547,6 +547,7 @@ static int cedrus_remove(struct platform_device *pdev)
 {
 	struct cedrus_dev *dev = platform_get_drvdata(pdev);
 
+	cancel_delayed_work_sync(&dev->watchdog_work);
 	if (media_devnode_is_registered(dev->mdev.devnode)) {
 		media_device_unregister(&dev->mdev);
 		v4l2_m2m_unregister_media_controller(dev->m2m_dev);
-- 
2.25.1