linux-kernel - Re: [PATCH] media: saa7134: Fix a NULL pointer dereference in saa7134

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Date:   Fri, 28 Jan 2022 11:17:24 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zhou Qingyang <zhou1615@....edu>
Cc:     kjlu@....edu, Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Tasos Sahanidis <tasos@...ossah.com>,
        Yang Yingliang <yangyingliang@...wei.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: saa7134: Fix a NULL pointer dereference in
 saa7134_initdev()

On Tue, Jan 25, 2022 at 01:19:30AM +0800, Zhou Qingyang wrote:
> In saa7134_initdev(), the return value of vdev_init() is assigned to
> dev->video_dev and there is a dereference of it after that. The return
> value of vdev_init() will be NULL on the failure allocation, which could
> lead to 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: a9622391acb ("V4L/DVB (6792): Fix VBI support")
> 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/saa7134/saa7134-core.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/media/pci/saa7134/saa7134-core.c b/drivers/media/pci/saa7134/saa7134-core.c
> index 96328b0af164..0de0b00540b6 100644
> --- a/drivers/media/pci/saa7134/saa7134-core.c
> +++ b/drivers/media/pci/saa7134/saa7134-core.c
> @@ -1202,6 +1202,11 @@ static int saa7134_initdev(struct pci_dev *pci_dev,
>  		pr_info("%s: Overlay support disabled.\n", dev->name);
>  
>  	dev->video_dev = vdev_init(dev,&saa7134_video_template,"video");
> +	if (!dev->video_dev) {
> +		err = -ENOMEM;
> +		goto err_unregister_video;
> +	}
> +
>  	dev->video_dev->ctrl_handler = &dev->ctrl_handler;
>  	dev->video_dev->lock = &dev->lock;
>  	dev->video_dev->queue = &dev->video_vbq;
> @@ -1224,6 +1229,11 @@ static int saa7134_initdev(struct pci_dev *pci_dev,
>  	       dev->name, video_device_node_name(dev->video_dev));
>  
>  	dev->vbi_dev = vdev_init(dev, &saa7134_video_template, "vbi");
> +	if (!dev->vbi_dev) {
> +		err = -ENOMEM;
> +		goto err_unregister_video;
> +	}
> +
>  	dev->vbi_dev->ctrl_handler = &dev->ctrl_handler;
>  	dev->vbi_dev->lock = &dev->lock;
>  	dev->vbi_dev->queue = &dev->vbi_vbq;
> -- 
> 2.25.1
> 

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