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From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Maciej W. Rozycki" <macro@orcam.me.uk>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Daniel Vetter <daniel@ffwll.ch>,
	syzbot <syzbot+1f29e126cf461c4de3b3@syzkaller.appspotmail.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Colin King <colin.king@canonical.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jani Nikula <jani.nikula@intel.com>,
	Jiri Slaby <jirislaby@kernel.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	"Antonino A. Daplas" <adaplas@gmail.com>
Subject: Re: [PATCH] video: fbdev: vga16fb: fix OOB write in vga16fb_imageblit()
Date: Fri, 14 May 2021 14:10:44 -0700	[thread overview]
Message-ID: <CAHk-=wjkVAjfWrmmJnJe1_MriK9gezWCew_MU=MbQNzHbGopsQ@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wioOHwKNj8AmvXWV-oL60ae0jKswAHy9e6wCYYeA5EQXg@mail.gmail.com>

On Fri, May 14, 2021 at 1:32 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Another alternative would be to just delay the resize to when vcmode
> is put back to text mode again. That sounds somewhat reasonable to me,
> but it's a pretty big thing.

Actually thinking more about that option, it sounds horrible. It would
mean that we'd continue to use the old geometry for the actual VC
buffers for a random time, and then change it to the new geometry at
some arbitrary point.

So I think the only reasonable approach (apart from just my "don't do
that then") might be to just always call ->con_resize().

There are only actually three cases of "->con_resize()", so it might
not be too bad.

Looking at it, both sisusbcon_resize() and vgacon_resize() seem to be
trivially fine in KD_GRAPHICS mode.

vgacon already seems to have that "!vga_is_gfx" test, and does
vgacon_doresize() at vgacon_switch(). It might need to add a
vgacon_doresize() to the vgacon_blank() case 0 code so that it
actually does the right thing when going back to KD_TEXT mode.

And fbcon_resize() looks like it might be mostly ok with it too.
Again, there is a con_is_visible() test, and I suspect that might need
to be changed to

        if (con_is_visible(vc) && vc->vc_mode == KD_TEXT)

instead,  but it doesn't look _too_ bad.

So I think just removing the "vc->vc_mode != KD_GRAPHICS" test from
resize_screen() might be the way to go. That way, the low-level data
structures actually are in sync with the resize, and the "out of
bounds" bug should never happen.

Would you mind testing that?

               Linus

  reply	other threads:[~2021-05-14 21:11 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-02-19 17:33 BUG: unable to handle kernel paging request at ffffc90000669000, IP: [<ffffffff8139d84a>] bitfill_un Tommi Rantala
2019-12-10 16:38 ` BUG: unable to handle kernel paging request in sys_imageblit syzbot
2020-06-19  4:56   ` syzbot
2019-12-27  7:13 ` BUG: unable to handle kernel paging request in vga16fb_imageblit syzbot
2020-05-08  7:07 ` BUG: unable to handle kernel paging request in vga16fb_imageblit (2) syzbot
2021-05-01 20:31   ` [syzbot] " syzbot
2021-05-02  1:53   ` syzbot
2021-05-03 13:41     ` Tetsuo Handa
2021-05-07 11:09       ` Tetsuo Handa
2021-05-14 16:19         ` [PATCH] video: fbdev: vga16fb: fix OOB write in vga16fb_imageblit() Tetsuo Handa
2021-05-14 17:29           ` Linus Torvalds
2021-05-14 17:37             ` Linus Torvalds
2021-05-14 18:23               ` Linus Torvalds
2021-05-14 20:25             ` Maciej W. Rozycki
2021-05-14 20:32               ` Linus Torvalds
2021-05-14 21:10                 ` Linus Torvalds [this message]
2021-05-15  7:43                   ` [PATCH v2] tty: vt: always invoke vc->vc_sw->con_resize callback Tetsuo Handa
2021-05-15 16:21                     ` Maciej W. Rozycki
2021-05-15 16:32                       ` Maciej W. Rozycki
2021-05-15 16:41                         ` Linus Torvalds
2021-05-17 13:13                           ` Daniel Vetter
2021-05-15 16:11                 ` [PATCH] video: fbdev: vga16fb: fix OOB write in vga16fb_imageblit() Maciej W. Rozycki
2021-05-17 13:07                 ` Daniel Vetter
2021-05-17 13:10                   ` Daniel Vetter
2021-05-15  0:45               ` Tetsuo Handa
2020-05-12  6:55 ` BUG: unable to handle kernel paging request in bitfill_aligned syzbot
2020-10-06  8:18 ` BUG: unable to handle kernel paging request in cfb_imageblit syzbot
2020-12-18 15:26   ` syzbot
2020-12-18 15:27     ` Dmitry Vyukov

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