linux-kernel - Re: [PATCH] media: mediatek: vcodec: Move a variable assignment behind condition checks in vdec_vp9_slice_single

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Message-ID: <0341924c-7f0a-28aa-eeae-f7de69ab36d8@xs4all.nl>
Date:   Mon, 17 Apr 2023 10:01:29 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Markus Elfring <Markus.Elfring@....de>,
        kernel-janitors@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
        Guo Zhengkui <guozhengkui@...o.com>,
        Haowen Bai <baihaowen@...zu.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Mingjia Zhang <mingjia.zhang@...iatek.com>,
        Tiffany Lin <tiffany.lin@...iatek.com>,
        Xiaoyong Lu <xiaoyong.lu@...iatek.com>,
        Yunfei Dong <yunfei.dong@...iatek.com>
Cc:     cocci@...ia.fr, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: mediatek: vcodec: Move a variable assignment
 behind condition checks in vdec_vp9_slice_single_decode()

On 14/04/2023 20:30, Markus Elfring wrote:
> Date: Fri, 14 Apr 2023 20:07:01 +0200
> 
> The address of a data structure member was determined before
> a corresponding null pointer check in the implementation of
> the function “vdec_vp9_slice_single_decode”.
> 
> Thus avoid the risk for undefined behaviour by moving the assignment
> for the variable “pfc” behind some condition checks.
> 
> This issue was detected by using the Coccinelle software.
> 
> Fixes: b0f407c19648ae9110c932c91d6e1b9381ec0aeb ("media: mediatek: vcodec: add vp9 decoder driver for mt8186")

Not a fix, it was never broken.

> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  .../media/platform/mediatek/vcodec/vdec/vdec_vp9_req_lat_if.c  | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_req_lat_if.c b/drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_req_lat_if.c
> index cf16cf2807f0..22b27f7b57bf 100644
> --- a/drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_req_lat_if.c
> +++ b/drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_req_lat_if.c
> @@ -1990,7 +1990,7 @@ static int vdec_vp9_slice_single_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
>  					struct vdec_fb *fb, bool *res_chg)
>  {
>  	struct vdec_vp9_slice_instance *instance = h_vdec;

Just drop these lines instead:

        if (!instance || !instance->ctx)
                return -EINVAL;

That can never happen.

Regards,

	Hans

> -	struct vdec_vp9_slice_pfc *pfc = &instance->sc_pfc;
> +	struct vdec_vp9_slice_pfc *pfc;
>  	struct vdec_vp9_slice_vsi *vsi;
>  	struct mtk_vcodec_ctx *ctx;
>  	int ret;
> @@ -2007,6 +2007,7 @@ static int vdec_vp9_slice_single_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
>  	if (!fb)
>  		return -EBUSY;
> 
> +	pfc = &instance->sc_pfc;
>  	vsi = &pfc->vsi;
> 
>  	ret = vdec_vp9_slice_setup_single(instance, bs, fb, pfc);
> --
> 2.40.0
>