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

[Zheng Hacker]

Hi,

This patch just fix the race condition in hantro_remove. All of the
analysis is made by static analysis.
So it may be false positives.
Please feel free to let me know if there is something I've missed.

Regards,
Zheng

Zheng Wang <zyytlz.wz@xxxxxxx> 于2023年3月7日周二 23:43写道：
>
> 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);
>         media_device_unregister(&vpu->mdev);
>         hantro_remove_dec_func(vpu);
>         hantro_remove_enc_func(vpu);
> --
> 2.25.1
>