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

[Jernej Škrabec]

Dne ponedeljek, 13. marec 2023 ob 17:31:20 CET je Zheng Wang napisal(a):
> 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@xxxxxxx>
> ---
> 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(+)
> 

Acked-by: Jernej Skrabec <jernej.skrabec@xxxxxxxxx>

Best regards,
Jernej

> 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);