linux-kernel - Re: [PATCH] media: media/pci: Fix a NULL pointer dereference in cx23885_417

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Date:   Fri, 28 Jan 2022 11:16:49 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zhou Qingyang <zhou1615@....edu>
Cc:     kjlu@....edu, Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: media/pci: Fix a NULL pointer dereference in
 cx23885_417_register()

On Tue, Jan 25, 2022 at 01:06:10AM +0800, Zhou Qingyang wrote:
> In cx23885_417_register(), the return value of cx23885_video_dev_alloc() 
> is assigned to dev->v4l_device() and there is a dereference of it after
> that. the return value of cx23885_video_dev_alloc() could be NULL on 
> failure of allocation, which could lead to a NULL pointer dereference.
> 
> Fix this bug by adding a NULL check of dev->v4l_device.
> 
> This bug was found by a static analyzer.
> 
> Builds with 'make allyesconfig' show no new warnings,
> and our static analyzer no longer warns about this code.
> 
> Fixes: 453afdd9ce33 ("[media] cx23885: convert to vb2")
> Signed-off-by: Zhou Qingyang <zhou1615@....edu>
> ---
> The analysis employs differential checking to identify inconsistent 
> security operations (e.g., checks or kfrees) between two code paths 
> and confirms that the inconsistent operations are not recovered in the
> current function or the callers, so they constitute bugs. 
> 
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
> 
>  drivers/media/pci/cx23885/cx23885-417.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/media/pci/cx23885/cx23885-417.c b/drivers/media/pci/cx23885/cx23885-417.c
> index 434677bd4ad1..fcc9c1117ed1 100644
> --- a/drivers/media/pci/cx23885/cx23885-417.c
> +++ b/drivers/media/pci/cx23885/cx23885-417.c
> @@ -1521,6 +1521,8 @@ int cx23885_417_register(struct cx23885_dev *dev)
>  	/* Allocate and initialize V4L video device */
>  	dev->v4l_device = cx23885_video_dev_alloc(tsport,
>  		dev->pci, &cx23885_mpeg_template, "mpeg");
> +	if (!dev->v4l_device)
> +		return -ENOMEM;
>  	q = &dev->vb2_mpegq;
>  	q->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
>  	q->io_modes = VB2_MMAP | VB2_USERPTR | VB2_DMABUF | VB2_READ;
> -- 
> 2.25.1
> 

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