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

- Subsystems: FRAMEBUFFER LAYER, BACKLIGHT CLASS/SUBSYSTEM, THE REST
- Maintainers: Helge Deller, Lee Jones, Daniel Thompson, Jingoo Han, Linus Torvalds
- List: linux-fbdev
- 3 messages, 3 authors
- Page: https://ratatoskr.run/linux-fbdev/2021/02/6253806/t

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

- From: Wenjia Zhao \<hidden\>
- Date: 2021-02-01 14:46:12 
- Message: https://ratatoskr.run/linux-fbdev/2021/02/6253806.md

```text
Signed-off-by: Wenjia Zhao <redacted>
---
 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);
 
 	/*
 	 * Should be different from bl_props.brightness, so we do not exit
-- 
2.7.4

```

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

- From: Lee Jones \<hidden\>
- Date: 2021-02-02 08:29:44 
- Message: https://ratatoskr.run/linux-fbdev/2021/02/6254807.md

```text
On Mon, 01 Feb 2021, Wenjia Zhao wrote:

Please provide a suitable commit messages.

Describe the problem.
Describe the issue was found.
Describe the solution.  

> Signed-off-by: Wenjia Zhao <redacted>
> ---
>  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);

A tab should be 8 chars in Linux.

>  	/*
>  	 * Should be different from bl_props.brightness, so we do not exit

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog
```

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

- From: Daniel Thompson \<hidden\>
- Date: 2021-02-02 09:26:39 
- Message: https://ratatoskr.run/linux-fbdev/2021/02/6254897.md

```text
On Mon, Feb 01, 2021 at 08:41:38AM -0600, Wenjia Zhao wrote:
> Signed-off-by: Wenjia Zhao <redacted>

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.
```