linux-kernel - Re: [PATCH 2/5] drm/mediatek: Add cnt checking for coverity issue

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Date:   Mon, 12 Jun 2023 08:21:25 +0000
From:   CK Hu (胡俊光) <ck.hu@...iatek.com>
To:     Jason-JH Lin (林睿祥) 
        <Jason-JH.Lin@...iatek.com>,
        "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Singo Chang (張興國) 
        <Singo.Chang@...iatek.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Jason-ch Chen (陳建豪) 
        <Jason-ch.Chen@...iatek.com>,
        Shawn Sung (宋孝謙) 
        <Shawn.Sung@...iatek.com>,
        Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        Rex-BC Chen (陳柏辰) 
        <Rex-BC.Chen@...iatek.com>
Subject: Re: [PATCH 2/5] drm/mediatek: Add cnt checking for coverity issue

Hi, Jason:

On Fri, 2023-04-07 at 14:46 +0800, Jason-JH.Lin wrote:
> CERT-C Characters and Strings (CERT STR31-C)
> all_drm_priv[cnt] evaluates to an address that could be at negative
> offset of an array.
> 
> In mtk_drm_get_all_drm_priv():
> Guarantee that storage for strings has sufficient space for character
> data and the null terminator.
> 
> So change cnt to unsigned int and check its max value.
> 
> Signed-off-by: Jason-JH.Lin <jason-jh.lin@...iatek.com>
> Fixes: 1ef7ed48356c ("drm/mediatek: Modify mediatek-drm for mt8195
> multi mmsys support")
> ---
>  drivers/gpu/drm/mediatek/mtk_drm_drv.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> index 86255a066faf..fcfa10332166 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> @@ -378,7 +378,7 @@ static bool mtk_drm_get_all_drm_priv(struct
> device *dev)
>  	const struct of_device_id *of_id;
>  	struct device_node *node;
>  	struct device *drm_dev;
> -	int cnt = 0;
> +	unsigned int cnt = 0;
>  	int i, j;
>  
>  	for_each_child_of_node(phandle->parent, node) {
> @@ -397,7 +397,7 @@ static bool mtk_drm_get_all_drm_priv(struct
> device *dev)
>  			continue;
>  
>  		all_drm_priv[cnt] = dev_get_drvdata(drm_dev);
> -		if (all_drm_priv[cnt] && all_drm_priv[cnt]-
> >mtk_drm_bound)
> +		if (cnt < MAX_CRTC && all_drm_priv[cnt] &&
> all_drm_priv[cnt]->mtk_drm_bound)
>  			cnt++;


I would like to add below statement here:

		if (cnt == MAX_CRTC)
			break;

Regards,
CK

>  	}
>