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From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
To:     Jia-Ju Bai <baijiaju1990@gmail.com>
Cc:     dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [BUG] video: fbdev: broadsheetfb: Possible null function
 pointers
Date:   Fri, 27 Jul 2018 10:06:45 +0200
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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