Re: [PATCH] media: pci: cx23855-video.c: Fix a NULL pointer dereference in cx23885_video_register()

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jan 25, 2022 at 01:16:18AM +0800, Zhou Qingyang wrote:
> In cx23885_video_register(), the return value of cx23885_vdev_init() is
> assigned to dev->video_dev and there is a dereference of it after that.
> the return value of cx23885_vdev_init() could be NULL on failure of
> allocation, which could lead to a NULL pointer dereference.
> 
> the same as dev->vbi_dev.
> 
> Fix this bug by adding a NULL check of dev->video_dev and dev->vbi_dev.
> 
> 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@umn.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-video.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/media/pci/cx23885/cx23885-video.c b/drivers/media/pci/cx23885/cx23885-video.c
> index a380e0920a21..1b95109eff8c 100644
> --- a/drivers/media/pci/cx23885/cx23885-video.c
> +++ b/drivers/media/pci/cx23885/cx23885-video.c
> @@ -1353,6 +1353,11 @@ int cx23885_video_register(struct cx23885_dev *dev)
>  	/* register Video device */
>  	dev->video_dev = cx23885_vdev_init(dev, dev->pci,
>  		&cx23885_video_template, "video");
> +	if (!dev->video_dev) {
> +		err = -ENOMEM;
> +		goto fail_unreg;
> +	}
> +
>  	dev->video_dev->queue = &dev->vb2_vidq;
>  	dev->video_dev->device_caps = V4L2_CAP_READWRITE | V4L2_CAP_STREAMING |
>  				      V4L2_CAP_AUDIO | V4L2_CAP_VIDEO_CAPTURE;
> @@ -1381,6 +1386,11 @@ int cx23885_video_register(struct cx23885_dev *dev)
>  	/* register VBI device */
>  	dev->vbi_dev = cx23885_vdev_init(dev, dev->pci,
>  		&cx23885_vbi_template, "vbi");
> +	if (!dev->vbi_dev) {
> +		err = -ENOMEM;
> +		goto fail_unreg;
> +	}
> +
>  	dev->vbi_dev->queue = &dev->vb2_vbiq;
>  	dev->vbi_dev->device_caps = V4L2_CAP_READWRITE | V4L2_CAP_STREAMING |
>  				    V4L2_CAP_AUDIO | V4L2_CAP_VBI_CAPTURE;
> -- 
> 2.25.1
> 

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