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

[Guenter Roeck <linux@roeck-us.net>]

On 3/8/23 19:58, Zheng Hacker wrote:
> Hi,
> 
> Thanks for your reply. I think you're right. I don't know if there is
> other method to stop new work from enqueing. Could you please give me
> some advice about the fix?
> 

Top-posting is discouraged.

Anyway -
I don't know the code well enough to suggest a solution.
It all depends on the driver architecture. The maintainers might
have a better idea.

A worse problem appears to be that the worker is also canceled
from mtk_jpeg_enc_irq() and mtk_jpeg_dec_irq(). Those are non-threaded
interrupt handlers which, as far as I know, must not sleep and thus
can not call cancel_delayed_work_sync(). I have no idea how to solve
that problem either.

Guenter

> Regards,
> Zheng
> 
> Guenter Roeck <linux@roeck-us.net> 于2023年3月9日周四 08:27写道：
>>
>> 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@163.com>
>>> ---
>>>   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
>>>