Re: Re: [PATCH v3] media:exynos4-is: Fix a use after free in isp_video_release

[lyl2019@mail.ustc.edu.cn]

> -----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() ?

Lv Yunlong
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