Re: [PATCH] media: mtk-jpeg: Fix use after free bug due to uncanceled work

[Guenter Roeck]

On Thu, Mar 02, 2023 at 05:37:15PM +0800, Zheng Wang wrote:
> In mtk_jpeg_probe, &jpeg->job_timeout_work is bound with
> mtk_jpeg_job_timeout_work. Then mtk_jpeg_dec_device_run
> and mtk_jpeg_enc_device_run may be called to start the
> work.
> If we remove the module which will call mtk_jpeg_remove
> to make cleanup, there may be a unfinished work. The
> possible sequence is as follows, which will cause a
> typical UAF bug.
> 
> Fix it by canceling the work before cleanup in the mtk_jpeg_remove
> 
> CPU0                  CPU1
> 
>                     |mtk_jpeg_job_timeout_work
> mtk_jpeg_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/mediatek/jpeg/mtk_jpeg_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c b/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
> index 969516a940ba..364513e7897e 100644
> --- a/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
> +++ b/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
> @@ -1793,7 +1793,7 @@ static int mtk_jpeg_probe(struct platform_device *pdev)
>  static int mtk_jpeg_remove(struct platform_device *pdev)
>  {
>  	struct mtk_jpeg_dev *jpeg = platform_get_drvdata(pdev);
> -
> +	cancel_delayed_work(&jpeg->job_timeout_work);

The empty line is needed (coding style). Also, this doesn't cancel
the worker if it is already running. This should probably be
cancel_delayed_work_sync(). Even then the question is if it is
possible that new work is queued before the device is unregistered.

Guenter

>  	pm_runtime_disable(&pdev->dev);
>  	video_unregister_device(jpeg->vdev);
>  	v4l2_m2m_release(jpeg->m2m_dev);
> -- 
> 2.25.1
>