linux-kernel - Re: [PATCH] media: hantro: fix use after free bug in hantro

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Date:   Mon, 13 Mar 2023 16:09:40 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Zheng Wang <zyytlz.wz@....com>, ezequiel@...guardiasur.com.ar
Cc:     p.zabel@...gutronix.de, mchehab@...nel.org,
        linux-media@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        linux-kernel@...r.kernel.org, hackerzheng666@...il.com,
        1395428693sheep@...il.com, alex000young@...il.com
Subject: Re: [PATCH] media: hantro: fix use after free bug in hantro_remove
 due to race condition

On 13/03/2023 16:08, Hans Verkuil wrote:
> On 07/03/2023 16:41, Zheng Wang wrote:
>> 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@....com>
>> ---
>>  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);
> 
> Use cancel_delayed_work_sync(): that ensures the code waits for a running
> watchdog function to finish.
> 
> Ditto for the other patch.

And also the cedrus and rkvdec patches.

Regards,

	Hans

> 
> Regards,
> 
> 	Hans
> 
>>  	media_device_unregister(&vpu->mdev);
>>  	hantro_remove_dec_func(vpu);
>>  	hantro_remove_enc_func(vpu);
>