Re: [PATCH] backlight: pcf50633: pdata may be a null pointer, null pointer dereference cause crash

From: Daniel Thompson <daniel.thompson@linaro.org>
To: Wenjia Zhao <driverfuzzing@gmail.com>
Cc: Lee Jones <lee.jones@linaro.org>,
	Jingoo Han <jingoohan1@gmail.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] backlight: pcf50633: pdata may be a null pointer, null pointer dereference cause crash
Date: Tue, 2 Feb 2021 09:25:41 +0000	[thread overview]
Message-ID: <20210202092541.2wvzpe53mavrd47x@maple.lan> (raw)
In-Reply-To: <1612190499-73818-1-git-send-email-driverfuzzing@gmail.com>

On Mon, Feb 01, 2021 at 08:41:38AM -0600, Wenjia Zhao wrote:
> Signed-off-by: Wenjia Zhao <driverfuzzing@gmail.com>

There should be a patch description here explaining why the patch
is needed and how it works.

> ---
>  drivers/video/backlight/pcf50633-backlight.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/backlight/pcf50633-backlight.c b/drivers/video/backlight/pcf50633-backlight.c
> index 540dd338..43267af 100644
> --- a/drivers/video/backlight/pcf50633-backlight.c
> +++ b/drivers/video/backlight/pcf50633-backlight.c
> @@ -127,7 +127,8 @@ static int pcf50633_bl_probe(struct platform_device *pdev)
>  
>  	platform_set_drvdata(pdev, pcf_bl);
>  
> -	pcf50633_reg_write(pcf_bl->pcf, PCF50633_REG_LEDDIM, pdata->ramp_time);
> +  if (pdata)
> +    pcf50633_reg_write(pcf_bl->pcf, PCF50633_REG_LEDDIM, pdata->ramp_time);

Assuming you found this issue using a static analyzer then I think it
might be better to if an "if (!pdata) return -EINVAL" further up the
file instead.

In other words it is better to "document" (via the return code) that the
code does not support pdata == NULL than to add another untested code
path.

Daniel.