linux-kernel - Re: [PATCH] media: rockchip/rga: fix potential use after free

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Date:   Sat, 9 Nov 2019 12:08:01 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Pan Bian <bianpan2016@....com>, Jacob Chen <jacob-chen@...wrt.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>
Cc:     linux-media@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: rockchip/rga: fix potential use after free

On 11/5/19 4:55 PM, Pan Bian wrote:
> The variable vga->vfd is an alias for vfd. Therefore, releasing vfd and
> then unregister vga->vfd will lead to a use after free bug. In fact, the
> free operation and the unregister operation are reversed.
> 
> Signed-off-by: Pan Bian <bianpan2016@....com>
> ---
>  drivers/media/platform/rockchip/rga/rga.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/platform/rockchip/rga/rga.c b/drivers/media/platform/rockchip/rga/rga.c
> index e9ff12b6b5bb..613b868fce33 100644
> --- a/drivers/media/platform/rockchip/rga/rga.c
> +++ b/drivers/media/platform/rockchip/rga/rga.c
> @@ -901,9 +901,9 @@ static int rga_probe(struct platform_device *pdev)
>  	return 0;
>  
>  rel_vdev:
> -	video_device_release(vfd);
> -unreg_video_dev:
>  	video_unregister_device(rga->vfd);
> +unreg_video_dev:
> +	video_device_release(vfd);
>  unreg_v4l2_dev:
>  	v4l2_device_unregister(&rga->v4l2_dev);
>  err_put_clk:
> 

This isn't right, you need to update the goto labels as well.

With this change unreg_video_dev releases the vdev, while rel_vdev
unregisters it. Very confusing.

I'd also rename unreg_video_dev to unreg_vdev to be consistent with
rel_vdev.

Regards,

	Hans