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Subject: Re: [PATCH v3] media:exynos4-is: Fix a use after free in
 isp_video_release
To:     lyl2019@mail.ustc.edu.cn
Cc:     s.nawrocki@samsung.com, mchehab@kernel.org, krzk@kernel.org,
        linux-media@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210427132734.5212-1-lyl2019@mail.ustc.edu.cn>
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 <3f2f155c.72fa7.179408b6b2e.Coremail.lyl2019@mail.ustc.edu.cn>
From:   Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <c3f03430-e595-38a8-b60d-4a338c751c04@xs4all.nl>
Date:   Thu, 6 May 2021 09:23:19 +0200
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On 06/05/2021 09:19, lyl2019@mail.ustc.edu.cn wrote:
> 
> 
> 
>> -----原始邮件-----
>> 发件人: "Hans Verkuil" <hverkuil@xs4all.nl>
>> 发送时间: 2021-05-05 17:31:04 (星期三)
>> 收件人: "Lv Yunlong" <lyl2019@mail.ustc.edu.cn>, s.nawrocki@samsung.com, mchehab@kernel.org, krzk@kernel.org
>> 抄送: linux-media@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org
>> 主题: Re: [PATCH v3] media:exynos4-is: Fix a use after free in isp_video_release
>>
>> Hi Lv Yunlong,
>>
>> On 27/04/2021 15:27, Lv Yunlong wrote:
>>> In isp_video_release, file->private_data is freed via
>>> _vb2_fop_release()->v4l2_fh_release(). But the freed
>>> file->private_data is still used in v4l2_fh_is_singular_file()
>>> ->v4l2_fh_is_singular(file->private_data), which is a use
>>> after free bug.
>>>
>>> My patch sets file->private_data to NULL after _vb2_fop_release()
>>> to avoid the use after free, and uses a variable 'is_singular_file'
>>> to keep the original function unchanged.
>>
>> Actually, it is the use of 'is_singular_file' that fixes the bug,
>> the 'file->private_data = NULL;' is unnecessary here.
>>
>> That said, it would be a really good idea if in a separate patch you
>> make v4l2_fh_release() more robust by setting filp->private_data to
>> NULL after the kfree(fh).
>>
>> Regards,
>>
>> 	Hans
>>
>>>
>>> Fixes: 34947b8aebe3f ("[media] exynos4-is: Add the FIMC-IS ISP capture DMA driver")
>>> Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
>>> ---
>>>  drivers/media/platform/exynos4-is/fimc-isp-video.c | 8 ++++++--
>>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/media/platform/exynos4-is/fimc-isp-video.c b/drivers/media/platform/exynos4-is/fimc-isp-video.c
>>> index 612b9872afc8..c07dcb0bccc2 100644
>>> --- a/drivers/media/platform/exynos4-is/fimc-isp-video.c
>>> +++ b/drivers/media/platform/exynos4-is/fimc-isp-video.c
>>> @@ -306,17 +306,21 @@ static int isp_video_release(struct file *file)
>>>  	struct fimc_is_video *ivc = &isp->video_capture;
>>>  	struct media_entity *entity = &ivc->ve.vdev.entity;
>>>  	struct media_device *mdev = entity->graph_obj.mdev;
>>> +	bool is_singular_file;
>>>  
>>>  	mutex_lock(&isp->video_lock);
>>>  
>>> -	if (v4l2_fh_is_singular_file(file) && ivc->streaming) {
>>> +	is_singular_file = v4l2_fh_is_singular_file(file);
>>> +
>>> +	if (is_singular_file && ivc->streaming) {
>>>  		media_pipeline_stop(entity);
>>>  		ivc->streaming = 0;
>>>  	}
>>>  
>>>  	_vb2_fop_release(file, NULL);
>>> +	file->private_data = NULL;
>>>  
>>> -	if (v4l2_fh_is_singular_file(file)) {
>>> +	if (is_singular_file) {
>>>  		fimc_pipeline_call(&ivc->ve, close);
>>>  
>>>  		mutex_lock(&mdev->graph_mutex);
>>>
>>
> 
> 
> Ok, thanks for your suggestion.
> 
> Do you means i need submit a new path to set filp->private_data = NULL
> after kfree(fh) in v4l2_fh_release() ?

Yes, so one updated patch for fimc-isp-video.c and a second patch for v4l2-fh.c.

Regards,

	Hans

> 
> Lv Yunlong
>