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

[FUZZ DR]

Sorry about the missing description, I have a description at my local
commit. But the commit description disappeared when I used git send-email
to submit this patch.

backlight: pcf50633: pdata may be a null pointer, null pointer dereference
causes crash
pdata has been checked  at line 120 before dereference. However, it is used
without check at line 130. So just add the check,

 Signed-off-by: Wenjia Zhao <driverfuzzing at gmail.com>
---
 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
--

It is better to write a default value to the register if the ramp_time has
a default value. Then it does not need to return -EINVAL. It will keep
consistent with the behavior at line 120.

Daniel Thompson <daniel.thompson at linaro.org> 于2021年2月2日周二 上午3:25写道：

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