Re: [PATCH] media: mtk-jpeg: Fix use after free bug due to error path handling in mtk_jpeg_dec_device_run

[Alexandre Mergnat]

Reviewed-by: Alexandre Mergnat <amergnat@xxxxxxxxxxxx>

On 20/10/2023 06:07, Zheng Wang wrote:
> In mtk_jpeg_probe, &jpeg->job_timeout_work is bound with 
> mtk_jpeg_job_timeout_work. In mtk_jpeg_dec_device_run, if error happens 
> in mtk_jpeg_set_dec_dst, it will finally start the worker while mark the 
> job as finished by invoking v4l2_m2m_job_finish. There are two methods 
> to trigger the bug. If we remove the module, it which will call 
> mtk_jpeg_remove to make cleanup. The possible sequence is as follows, 
> which will cause a use-after-free bug. CPU0 CPU1 mtk_jpeg_dec_... | 
> start worker | |mtk_jpeg_job_timeout_work mtk_jpeg_remove | 
> v4l2_m2m_release | kfree(m2m_dev); | | | v4l2_m2m_get_curr_priv | 
> m2m_dev->curr_ctx //use If we close the file descriptor, which will call 
> mtk_jpeg_release, it will have a similar sequence. Fix this bug by start 
> timeout worker only if started jpegdec worker successfully so the 
> v4l2_m2m_job_finish will only be called on either 
> mtk_jpeg_job_timeout_work or mtk_jpeg_dec_device_run. This patch also 
> reverts commit c677d7ae8314 ("media: mtk-jpeg: Fix use after free bug 
> due to uncanceled work") for this patch also fixed the use-after-free 
> bug mentioned before. Before mtk_jpeg_remove is invoked, 
> mtk_jpeg_release must be invoked to close opened files. And it will call 
> v4l2_m2m_cancel_job to wait for the timeout worker finished so the 
> canceling in mtk_jpeg_remove is unnecessary.

--
Regards,
Alexandre