# \[BUG\] video: fbdev: broadsheetfb: Possible null function pointers

- List: linux-fbdev
- 4 messages, 2 authors
- Page: https://ratatoskr.run/linux-fbdev/2018/07/5343174/t

## \[BUG\] video: fbdev: broadsheetfb: Possible null function pointers

- From: bai \<hidden\>
- Date: 2018-07-26 14:17:50 
- Message: https://ratatoskr.run/linux-fbdev/2018/07/5343174.md

```text
In Linux-4.16, drivers/video/fbdev/broadsheetfb.c,

158. static void broadsheet_mmio_send_cmdargs(...) {
             ......
163.     par->board->mmio_write(...);
             ......
166.     par->board->mmio_write(...);
167. }

For x86 kernel configuration, I find that there is no assignment of the 
function pointer ".mmio_write" in the kernel code.
So calling the function pointer in lines 163 and 166 may cause a null 
pointer dereference.

In this file, there are many calls to this function pointer...


Best wishes,
Jia-Ju Bai
```

## Re: \[BUG\] video: fbdev: broadsheetfb: Possible null function pointers

- From: Bartlomiej Zolnierkiewicz \<hidden\>
- Date: 2018-07-26 14:34:59 
- Message: https://ratatoskr.run/linux-fbdev/2018/07/5343188.md

```text
On Thursday, July 26, 2018 10:17:44 PM bai wrote:
> In Linux-4.16, drivers/video/fbdev/broadsheetfb.c,
> 
> 158. static void broadsheet_mmio_send_cmdargs(...) {
>              ......
> 163.     par->board->mmio_write(...);
>              ......
> 166.     par->board->mmio_write(...);
> 167. }
> 
> For x86 kernel configuration, I find that there is no assignment of the 
> function pointer ".mmio_write" in the kernel code.
> So calling the function pointer in lines 163 and 166 may cause a null 
> pointer dereference.
> 
> In this file, there are many calls to this function pointer...

This is a platform driver and it won't be used on x86 (actually it is
used only by single ARM PXA board). The dependency for FB_BROADSHEET
in Kconfig file could be improved to i.e.

	depends on FB && (ARCH_PXA || COMPILE_TEST)

but there is no bug there.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

```

## Re: \[BUG\] video: fbdev: broadsheetfb: Possible null function pointers

- From: Jia-Ju Bai \<hidden\>
- Date: 2018-07-27 01:49:50 
- Message: https://ratatoskr.run/linux-fbdev/2018/07/5343574.md

```text


On 2018/7/26 22:34, Bartlomiej Zolnierkiewicz wrote:
> On Thursday, July 26, 2018 10:17:44 PM bai wrote:
>> In Linux-4.16, drivers/video/fbdev/broadsheetfb.c,
>>
>> 158. static void broadsheet_mmio_send_cmdargs(...) {
>>               ......
>> 163.     par->board->mmio_write(...);
>>               ......
>> 166.     par->board->mmio_write(...);
>> 167. }
>>
>> For x86 kernel configuration, I find that there is no assignment of the
>> function pointer ".mmio_write" in the kernel code.
>> So calling the function pointer in lines 163 and 166 may cause a null
>> pointer dereference.
>>
>> In this file, there are many calls to this function pointer...
> This is a platform driver and it won't be used on x86 (actually it is
> used only by single ARM PXA board). The dependency for FB_BROADSHEET
> in Kconfig file could be improved to i.e.
>
> 	depends on FB && (ARCH_PXA || COMPILE_TEST)
>
> but there is no bug there.

Thanks for the reply :)
So I want to submit a patch of updating Kconfig in 
drivers/video/fbdev/Kconfig:

config FB_BROADSHEET
     tristate "E-Ink Broadsheet/Epson S1D13521 controller support"
-    depends on FB
+   depends on FB && (ARCH_PXA || COMPILE_TEST)
     select FB_SYS_FILLRECT
     select FB_SYS_COPYAREA
     select FB_SYS_IMAGEBLIT
     select FB_SYS_FOPS
     select FB_DEFERRED_IO


Do you think it is okay?


Best wishes,
Jia-Ju Bai
```

## Re: \[BUG\] video: fbdev: broadsheetfb: Possible null function pointers

- From: Bartlomiej Zolnierkiewicz \<hidden\>
- Date: 2018-07-27 08:06:51 
- Message: https://ratatoskr.run/linux-fbdev/2018/07/5343726.md

```text
On Friday, July 27, 2018 09:49:41 AM Jia-Ju Bai wrote:
> 
> On 2018/7/26 22:34, Bartlomiej Zolnierkiewicz wrote:
> > On Thursday, July 26, 2018 10:17:44 PM bai wrote:
> >> In Linux-4.16, drivers/video/fbdev/broadsheetfb.c,
> >>
> >> 158. static void broadsheet_mmio_send_cmdargs(...) {
> >>               ......
> >> 163.     par->board->mmio_write(...);
> >>               ......
> >> 166.     par->board->mmio_write(...);
> >> 167. }
> >>
> >> For x86 kernel configuration, I find that there is no assignment of the
> >> function pointer ".mmio_write" in the kernel code.
> >> So calling the function pointer in lines 163 and 166 may cause a null
> >> pointer dereference.
> >>
> >> In this file, there are many calls to this function pointer...
> > This is a platform driver and it won't be used on x86 (actually it is
> > used only by single ARM PXA board). The dependency for FB_BROADSHEET
> > in Kconfig file could be improved to i.e.
> >
> > 	depends on FB && (ARCH_PXA || COMPILE_TEST)
> >
> > but there is no bug there.
> 
> Thanks for the reply :)
> So I want to submit a patch of updating Kconfig in 
> drivers/video/fbdev/Kconfig:
> 
> config FB_BROADSHEET
>      tristate "E-Ink Broadsheet/Epson S1D13521 controller support"
> -    depends on FB
> +   depends on FB && (ARCH_PXA || COMPILE_TEST)
>      select FB_SYS_FILLRECT
>      select FB_SYS_COPYAREA
>      select FB_SYS_IMAGEBLIT
>      select FB_SYS_FOPS
>      select FB_DEFERRED_IO
> 
> 
> Do you think it is okay?

Please read Documentation/process/submitting-patches.rst.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

```