linux-kernel - Re: [BUG] video: fbdev: broadsheetfb: Possible null function pointers

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Date:   Fri, 27 Jul 2018 09:49:41 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [BUG] video: fbdev: broadsheetfb: Possible null function pointers



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