linux-kernel - Re: [PATCH v2] fbmem: don't allow too huge resolutions

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Message-ID: <CAMuHMdX_AM4Dg-5d9D5M=7V-PjGQZ6hYWWMmhTc4tvuq_PcdDg@mail.gmail.com>
Date:   Wed, 1 Sep 2021 09:12:45 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        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 <syzkaller-bugs@...glegroups.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2] fbmem: don't allow too huge resolutions

On Wed, Sep 1, 2021 at 3:15 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
> syzbot is reporting page fault at vga16fb_fillrect() [1], for
> vga16fb_check_var() is failing to detect multiplication overflow.
>
>   if (vxres * vyres > maxmem) {
>     vyres = maxmem / vxres;
>     if (vyres < yres)
>       return -ENOMEM;
>   }
>
> Since no module would accept too huge resolutions where multiplication
> overflow happens, let's reject in the common path.
>
> Link: https://syzkaller.appspot.com/bug?extid=04168c8063cfdde1db5e [1]
> Reported-by: syzbot <syzbot+04168c8063cfdde1db5e@...kaller.appspotmail.com>
> Debugged-by: Randy Dunlap <rdunlap@...radead.org>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

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