Re: [PATCH] video: fbdev: vga16fb: fix OOB write in vga16fb_imageblit()

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: 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>,
	"Maciej W. Rozycki" <macro@orcam.me.uk>,
	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 11:23:29 -0700	[thread overview]
Message-ID: <CAHk-=winm7rEueQ2moqMZWWNNywu_9eVUrT7g0a30C8fhJojTQ@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=whN=zrJ8BOLaGsJDH8d3sXLEoXA2DVsCq40OAUc1npOOw@mail.gmail.com>

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On Fri, May 14, 2021 at 10:37 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> IOW, something like this would seem fairly simple and straightforward:

Proper patch in case syzbot can test this..

                  Linus

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From b33ca195cecea478768de353b3ae976c07a65615 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 14 May 2021 11:06:12 -0700
Subject: [PATCH] vt: don't allow text-mode resizing when in KD_GRAPHICS mode

The VT layer itself just keeps track of the underlying text contents
just fine, but if the underlying hardware driver has a con_resize()
function, we can't just ignore it when in KD_GRAPHICS mode.

So just refuse to do a text mode resize if we're not in text mode.

Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by: syzbot <syzbot+1f29e126cf461c4de3b3@syzkaller.appspotmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 drivers/tty/vt/vt.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 01645e87b3d5..f24e627b7402 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1171,8 +1171,13 @@ static inline int resize_screen(struct vc_data *vc, int width, int height,
 	/* Resizes the resolution of the display adapater */
 	int err = 0;
 
-	if (vc->vc_mode != KD_GRAPHICS && vc->vc_sw->con_resize)
+	if (vc->vc_sw->con_resize) {
+		// If we have a resize function but are in KD_GRAPHICS mode,
+		// we can't actually do a resize and need to error out.
+		if (vc->vc_mode == KD_GRAPHICS)
+			return -EINVAL;
 		err = vc->vc_sw->con_resize(vc, width, height, user);
+	}
 
 	return err;
 }
-- 
2.31.1.365.ga2a05a39c5

