linux-kernel - Re: [PATCH v2] video: fbdev: cirrusfb: check pixclock to avoid divide by zero

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Message-ID: <CAMuHMdXcO1K7da=4Ck2X0Rc_pfaM32dDKf0EfdDXNG0HL18h5Q@mail.gmail.com>
Date:   Thu, 28 Oct 2021 10:05:00 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     George Kennedy <george.kennedy@...cle.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Sam Ravnborg <sam@...nborg.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] video: fbdev: cirrusfb: check pixclock to avoid divide
 by zero

On Wed, Oct 27, 2021 at 10:32 PM George Kennedy
<george.kennedy@...cle.com> wrote:
> Do a sanity check on pixclock value to avoid divide by zero.
>
> If the pixclock value is zero, the cirrusfb driver will round up
> pixclock to get the derived frequency as close to maxclock as
> possible.
>
> Syzkaller reported a divide error in cirrusfb_check_pixclock.
>
> divide error: 0000 [#1] SMP KASAN PTI
> CPU: 0 PID: 14938 Comm: cirrusfb_test Not tainted 5.15.0-rc6 #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2
> RIP: 0010:cirrusfb_check_var+0x6f1/0x1260
>
> Call Trace:
>  fb_set_var+0x398/0xf90
>  do_fb_ioctl+0x4b8/0x6f0
>  fb_ioctl+0xeb/0x130
>  __x64_sys_ioctl+0x19d/0x220
>  do_syscall_64+0x3a/0x80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Signed-off-by: George Kennedy <george.kennedy@...cle.com>

Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds