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

[Zheng Hacker]

Hi Kyrie,

After reviewing the code, I found anothe possible code path. As I am
not familiar with the module. It has high possibility it's wrong.
Could please help me check this? Very much appreciated for your
valuable time.

In summary, mtk_jpegdec_worker was set in mtk_jpeg_open and started in
mtk_jpeg_multicore_dec_device_run, which made it running on cpu1.
Inside the mtk_jpeg_multicore_dec_device_run, it will call
schedule_delayed_work  to start the timeout_work, which will make it
running on cpu2. Meanwhile, we can call
mtk_jpeg_release to cancel the job. But there might be a race between
mtk_jpegdec_worker and v4l2_m2m_cancel_job. It may call
v4l2_m2m_job_finish too early to wake up the event.
The remove will go on, the other race is as described earlier.

cpu0                         cpu1                  cpu2
(1)->device_run
mtk_jpeg_multicore
_dec_device_run
queue_work
(jpeg->workqueue,
&ctx->jpeg_work);
                      (2)mtk_jpegdec_worker
(3)mtk_jpeg_release
v4l2_m2m_cancel_job
wait event

                      schedule_delayed_work
                                            (4)mtk_jpeg_job_timeout_work
                      (5)v4l2_m2m_job_finish
                      wake up
(6)mtk_jpeg_remove
v4l2_m2m_release
kfree(m2m_dev)
                                            (7)v4l2_m2m_get_curr_priv

Kyrie Wu (吴晗) <Kyrie.Wu@xxxxxxxxxxxx> 于2023年3月8日周三 11:32写道：
>
> On Wed, 2023-03-08 at 10:20 +0800, Zheng Hacker wrote:
> > Hi Kyrie,
> >
> > Thank you for your careful analysis and response. I still have some
> > areas that I don't quite understand and would like to ask for
> > clarification. That is, how do the function pointers for stop
> > streaming, initialized as mtk_jpeg_enc_stop_streaming and
> > mtk_jpeg_dec_stop_streaming, ensure that the worker is canceled? I
> > would greatly appreciate your response.
> >
> > Best regards,
> > Zheng
>
> Dear zheng,
>
> For stop streaming, what I mean is that stoppping jpeg decoding or
> encoding.
> Ok, let me introduce the sw flow of stop streaming:
> Firstly, the app will call v4l2_m2m_ioctl_streamoff, which will call
> v4l2_m2m_cancel_job, if it finds a job running(as you note, cpu1 is
> running), it will wait event, the event is wake up by
> v4l2_m2m_job_finish function. And v4l2_m2m_job_finish is called by jpeg
> dec/enc irq handler, which means that the waitting would result mtk hw
> to finish dec/enc, irq will occur and irq handler would cancel timeout
> worker. The follow is shown as blow.
> v4l2_m2m_ioctl_streamoff
>    v4l2_m2m_cancel_job                mtk_jpeg_enc_irq/mtk_jpeg_dec_irq
>        wait evnet <------ wake up ------v4l2_m2m_job_finish
>                                         cancel timeout work
>
> As mentioned above, if it is normal stop streaming action, there will
> be no happen that the timeout worker does not canceled.
>
> But if mtk_jpeg_remove is called directly without above flow, it would
> cause lots of issues.
>
> Regards,
> Kyrie.
> >
> > Kyrie Wu (吴晗) <Kyrie.Wu@xxxxxxxxxxxx> 于2023年3月8日周三 10:02写道：
> > >
> > > On Tue, 2023-03-07 at 23:03 +0800, Zheng Hacker wrote:
> > > > The timer function was set in mtk_jpeg_probe with
> > > > mtk_jpeg_job_timeout_work function.
> > > > And the worker is started in mtk_jpeg_dec_device_run.
> > > > There are two functions (mtk_jpeg_enc_irq and mtk_jpeg_dec_irq)
> > > > which
> > > > may cancel the worker.
> > > > They are used as IRQ handler function which is saved as function
> > > > pointer in a variable.
> > > > In mtk_jpeg_probe, they are registered by devm_request_irq:
> > > >
> > > > ret = devm_request_irq(&pdev->dev,
> > > >                jpeg_irq,
> > > >                jpeg->variant->irq_handler,
> > > >                0,
> > > >                pdev->name, jpeg);
> > > >     if (ret) {
> > > >       dev_err(&pdev->dev, "Failed to request jpeg_irq %d (%d)\n",
> > > >         jpeg_irq, ret);
> > > >       return ret;
> > > >     }
> > > >
> > > > However, if we remove the module without triggering the irq, the
> > > > worker will never be removed.
> > > >
> > > > As for the schedule, mtk_jpeg_dec_device_run and
> > > > mtk_jpeg_enc_device_run will start the worker.
> > > > The schedule invoking is quite complicated. As far as I know, the
> > > > invoking chain is as follows:
> > > >
> > > > v4l2_m2m_init->v4l2_m2m_device_run_work->v4l2_m2m_try_run
> > > >
> > > > the v4l2_m2m_device_run_work function is also a worker which is
> > > > set
> > > > in
> > > > v4l2_m2m_init and started in
> > > > v4l2_m2m_schedule_next_job.
> > > >
> > > > Before calling remove function, the  mtk_jpeg_release was invoked
> > > > to
> > > > release the related resource.
> > > >
> > > > v4l2_m2m_cancel_job will cancel the job by calling
> > > > m2m_dev->m2m_ops->job_abort(m2m_ctx->priv).
> > > >
> > > > But this will only cancel the current queue by
> > > > list_del(&m2m_dev->curr_ctx->queue);
> > > >
> > > > I think this can not cancel the posted task mentioned before. So
> > > > I
> > > > think if mtk_jpeg_job_timeout_work
> > > >
> > > > is working on, and using jpeg->m2m_dev after freeing it in
> > > > mtk_jpeg_remove, it will cause a UAF bug.
> > > >
> > > > static int mtk_jpeg_release(struct file *file)
> > > > {
> > > >   struct mtk_jpeg_dev *jpeg = video_drvdata(file);
> > > >   struct mtk_jpeg_ctx *ctx = mtk_jpeg_fh_to_ctx(file-
> > > > >private_data);
> > > >
> > > >   mutex_lock(&jpeg->lock);
> > > >   v4l2_ctrl_handler_free(&ctx->ctrl_hdl);
> > > >   [1] v4l2_m2m_ctx_release(ctx->fh.m2m_ctx);
> > > >   v4l2_fh_del(&ctx->fh);
> > > >   v4l2_fh_exit(&ctx->fh);
> > > >   kfree(ctx);
> > > >   mutex_unlock(&jpeg->lock);
> > > >   return 0;
> > > > }
> > > >
> > > > void v4l2_m2m_ctx_release(struct v4l2_m2m_ctx *m2m_ctx)
> > > > {
> > > >   /* wait until the current context is dequeued from job_queue */
> > > >   [2] v4l2_m2m_cancel_job(m2m_ctx);
> > > >
> > > >   vb2_queue_release(&m2m_ctx->cap_q_ctx.q);
> > > >   vb2_queue_release(&m2m_ctx->out_q_ctx.q);
> > > >
> > > >   kfree(m2m_ctx);
> > > > }
> > > >
> > > > Note that all of this is static analysis, which may be false
> > > > positive.
> > > > Feel free to tell me if there is something I've missed.
> > > >
> > > > Regard,
> > > > Zheng
> > >
> > > Dear Zheng,
> > >
> > > You set up an application scenario:
> > > cpu1 is using the mtk-jpeg driver and timeout work has been
> > > scheduled.
> > > At the same time cpu0 wanted to remove the mtk-jpeg driver, which
> > > caused the UAF bug.
> > > I wonder if such an irrational application scenario could exist.
> > > This
> > > scenario, as you described, not only leads to the problems you
> > > mentioned, but also to output&capture memory leaks and unreleased
> > > resources, such as spinlock.
> > > Typically, if we want to remove the driver, we firstly do stop
> > > streaming, which ensures that the worker has been canceled.
> > > I agree with your changes from the perspective of strengthening the
> > > robustness of the driver code.
> > >
> > > Regards,
> > > Kyrie.
> > > >
> > > > Irui Wang (王瑞) <Irui.Wang@xxxxxxxxxxxx> 于2023年3月7日周二 18:23写道：
> > > > >
> > > > > Dear Angelo and Zheng,
> > > > >
> > > > > Thanks for your patch and comments.
> > > > >
> > > > > Dear Kyrie,
> > > > >
> > > > > Please help to check this, thanks.
> > > > >
> > > > > Best Regards
> > > > >
> > > > > On Tue, 2023-03-07 at 10:49 +0100, AngeloGioacchino Del Regno
> > > > > wrote:
> > > > > > Il 07/03/23 10:27, Zheng Hacker ha scritto:
> > > > > > > Hi,
> > > > > > >
> > > > > > > Is there anyone who can help with this? I can provide more
> > > > > > > details
> > > > > > > like invoking chain if needed.
> > > > > > >
> > > > > >
> > > > > > Providing more details is always good. Please do.
> > > > > >
> > > > > > Meanwhile, adding Irui Wang to the loop: he's doing mtk-jpeg.
> > > > > >
> > > > > > Regards,
> > > > > > Angelo
> > > > > >
> > > > > > > Thanks,
> > > > > > > Zheng
> > > > > > >
> > > > > > > Zheng Wang <zyytlz.wz@xxxxxxx> 于2023年3月6日周一 14:28写道：
> > > > > > > >
> > > > > > > > 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);
> > > > > > > >          pm_runtime_disable(&pdev->dev);
> > > > > > > >          video_unregister_device(jpeg->vdev);
> > > > > > > >          v4l2_m2m_release(jpeg->m2m_dev);
> > > > > > > > --
> > > > > > > > 2.25.1
> > > > > > > >
> > > > > >
> > > > > >
> > > > > >