linux-kernel - Re: [PATCH] media: mtk-vcodec: Fix a NULL pointer dereference in mtk_vcodec_fw_scp

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Date:   Fri, 28 Jan 2022 11:17:02 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zhou Qingyang <zhou1615@....edu>
Cc:     kjlu@....edu, Tiffany Lin <tiffany.lin@...iatek.com>,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: mtk-vcodec: Fix a NULL pointer dereference in
 mtk_vcodec_fw_scp_init()

On Tue, Jan 25, 2022 at 01:07:31AM +0800, Zhou Qingyang wrote:
> In mtk_vcodec_fw_scp_init(), devm_kzalloc() is assigned to fw and there is
> a dereference of it right after that, which could lead to NULL pointer
> dereference on failure of devm_kzalloc().
> 
> Fix this bug by adding a NULL check of fw.
> 
> 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: 46233e91fa24 ("media: mtk-vcodec: move firmware implementations into their own files")
> 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/platform/mtk-vcodec/mtk_vcodec_fw_scp.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/media/platform/mtk-vcodec/mtk_vcodec_fw_scp.c b/drivers/media/platform/mtk-vcodec/mtk_vcodec_fw_scp.c
> index d8e66b645bd8..aa36bee51d01 100644
> --- a/drivers/media/platform/mtk-vcodec/mtk_vcodec_fw_scp.c
> +++ b/drivers/media/platform/mtk-vcodec/mtk_vcodec_fw_scp.c
> @@ -65,6 +65,9 @@ struct mtk_vcodec_fw *mtk_vcodec_fw_scp_init(struct mtk_vcodec_dev *dev)
>  	}
>  
>  	fw = devm_kzalloc(&dev->plat_dev->dev, sizeof(*fw), GFP_KERNEL);
> +	if (!fw)
> +		return ERR_PTR(-ENOMEM);
> +
>  	fw->type = SCP;
>  	fw->ops = &mtk_vcodec_rproc_msg;
>  	fw->scp = scp;
> -- 
> 2.25.1
> 

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