linux-kernel - Re: [PATCH v2 1/1] drm/mediatek: Fix potential KP on 0 bytes nvmem cell read

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Message-ID: <5445a85890e411c02a69a2a8608779abb84a5ce4.camel@mediatek.com>
Date: Wed, 23 Oct 2024 05:15:22 +0000
From: CK Hu (胡俊光) <ck.hu@...iatek.com>
To: Peng Liu (刘鹏) <Peng.Liu@...iatek.com>,
	Mac Shen (沈俊) <Mac.Shen@...iatek.com>,
	"chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>, "simona@...ll.ch"
	<simona@...ll.ch>, Jitao Shi (石记涛)
	<jitao.shi@...iatek.com>, LIANKUN YANG (杨连坤)
	<Liankun.Yang@...iatek.com>, "p.zabel@...gutronix.de"
	<p.zabel@...gutronix.de>, "granquet@...libre.com" <granquet@...libre.com>,
	"airlied@...il.com" <airlied@...il.com>, "msp@...libre.com"
	<msp@...libre.com>, "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
	Rex-BC Chen (陳柏辰) <Rex-BC.Chen@...iatek.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
CC: "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, Project_Global_Chrome_Upstream_Group
	<Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: Re: [PATCH v2 1/1] drm/mediatek: Fix potential KP on 0 bytes nvmem
 cell read

Hi, Liankun:

On Fri, 2024-09-27 at 17:03 +0800, Liankun Yang wrote:
> If the len is 0, kernel crash will occur when performing operations.
> Add the len check conditions to prevent kernel crash.
> 
> Fixes: f70ac097a2cf ("drm/mediatek: Add MT8195 Embedded DisplayPort driver")
> Signed-off-by: Liankun Yang <liankun.yang@...iatek.com>
> ---
> Changes in V2:
> - Fix the commit title.
> - Remove blank line between the Fixes and Signe-off-by.
> - Modify the judgment writing method.
> Per suggestion from the previous thread:
> https://patchwork.kernel.org/project/linux-mediatek/patch/20240925084116.28848-1-liankun.yang@mediatek.com/
> ---
>  drivers/gpu/drm/mediatek/mtk_dp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
> index d8796a904eca..9ecdf62398ee 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dp.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dp.c
> @@ -1082,7 +1082,7 @@ static void mtk_dp_get_calibration_data(struct mtk_dp *mtk_dp)
>  	buf = (u32 *)nvmem_cell_read(cell, &len);
>  	nvmem_cell_put(cell);
>  
> -	if (IS_ERR(buf) || ((len / sizeof(u32)) != 4)) {

In original code, when len = 0, no kernel panic occur.
Nacked by me.

Regards,
CK


> +	if (IS_ERR(buf) || !len || ((len / sizeof(u32)) != 4)) {
>  		dev_warn(dev, "Failed to read nvmem_cell_read\n");
>  
>  		if (!IS_ERR(buf))