linux-kernel - Re: [syzbot] BUG: unable to handle kernel paging request in vga16fb

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Message-ID: <CAMuHMdUtjd7Uf9VPEEztL+raasLdRqfMN55S8B8Nqoh0vxuk1g@mail.gmail.com>
Date:   Mon, 30 Aug 2021 17:00:49 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        syzbot <syzbot+04168c8063cfdde1db5e@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Colin King <colin.king@...onical.com>,
        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>,
        Masahiro Yamada <masahiroy@...nel.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] BUG: unable to handle kernel paging request in vga16fb_fillrect

Hi Tetsuo,

On Mon, Aug 30, 2021 at 4:53 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Mon, Aug 30, 2021 at 4:38 PM Tetsuo Handa
> <penguin-kernel@...ove.sakura.ne.jp> wrote:
> > On 2021/08/30 23:30, Geert Uytterhoeven wrote:
> > > The highest possible value of maxmem inside vga16fb_check_var()
> > > is 65536.
> >
> > Yes.
> >
> > >
> > > So I believe
> > >
> > >     if (array_size(vxres, vyres) > maxmem)
> > >
> > > should work fine.
> >
> > My intent is to check at common path than individual module so that we don't
> > need to add same check to every module. Same approach is proposed at
> > https://lkml.kernel.org/r/1630294223-7225-1-git-send-email-tcs_kernel@tencent.com .
>
> Which I believe is wrong.
> Thanks for the pointer, I will reply to the actual patch...

Upon second look, that patch is not really wrong, as the check happens
after calling into info->fbops->fb_check_var().

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