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

["CK Hu (胡俊光)" <ck.hu@mediatek.com>]

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@mediatek.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))