linux-kernel - Re: [PATCH] video: fbdev: vga16fb: fix OOB write in vga16fb

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Message-ID: <CAHk-=wguwhFpjhyMtDaH2hhjoV62gDgByC=aPyTrW9CkM5hqvA@mail.gmail.com>
Date:   Fri, 14 May 2021 10:29:47 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Daniel Vetter <daniel@...ll.ch>,
        syzbot <syzbot+1f29e126cf461c4de3b3@...kaller.appspotmail.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Colin King <colin.king@...onical.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jani Nikula <jani.nikula@...el.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        "Antonino A. Daplas" <adaplas@...il.com>
Subject: Re: [PATCH] video: fbdev: vga16fb: fix OOB write in vga16fb_imageblit()

On Fri, May 14, 2021 at 9:20 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> Currently it is impossible to control upper limit of rows/columns values
> based on amount of memory reserved for the graphical screen, for
> resize_screen() calls vc->vc_sw->con_resize() only if vc->vc_mode is not
> already KD_GRAPHICS

Honestly, the saner approach would seem to be to simply error out if
vc_mode is KD_GRAPHICS.

Doing VT_RESIZE while in KD_GRAPHICS mode seems _very_ questionable,
and is clearly currently very buggy.

So why not just say "that clearly already doesn't work, so make it
explicitly not permitted"?

              Linus