Re: [PATCH] media: hantro: fix use after free bug in hantro_remove due to race condition

[Hans Verkuil]

On 07/03/2023 16:41, Zheng Wang wrote:
> In hantro_probe, vpu->watchdog_work is bound with
> hantro_watchdog. Then hantro_end_prepare_run may
> be called to start the work.
> 
> If we close the file or remove the module which will
> call hantro_release and hantro_remove to make cleanup,
> there may be a unfinished work. The possible sequence
> is as follows, which will cause a typical UAF bug.
> 
> The same thing will happen in hantro_release, and use
> ctx after freeing it.
> 
> Fix it by canceling the work before cleanup in hantro_release.
> 
> CPU0                  CPU1
> 
>                     |hantro_watchdog
> hantro_remove     |
>   v4l2_m2m_release  |
>     kfree(m2m_dev); |
>                     |
>                     | v4l2_m2m_get_curr_priv
>                     |   m2m_dev->curr_ctx //use
> 
> Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
> ---
>  drivers/media/platform/verisilicon/hantro_drv.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/media/platform/verisilicon/hantro_drv.c b/drivers/media/platform/verisilicon/hantro_drv.c
> index b0aeedae7b65..80bd856a4da9 100644
> --- a/drivers/media/platform/verisilicon/hantro_drv.c
> +++ b/drivers/media/platform/verisilicon/hantro_drv.c
> @@ -1099,6 +1099,7 @@ static int hantro_remove(struct platform_device *pdev)
>  
>  	v4l2_info(&vpu->v4l2_dev, "Removing %s\n", pdev->name);
>  
> +	cancel_delayed_work(&vpu->watchdog_work);

Use cancel_delayed_work_sync(): that ensures the code waits for a running
watchdog function to finish.

Ditto for the other patch.

Regards,

	Hans

>  	media_device_unregister(&vpu->mdev);
>  	hantro_remove_dec_func(vpu);
>  	hantro_remove_enc_func(vpu);