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

[Linus Torvalds]

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

Proper patch in case syzbot can test this..

                  Linus
From b33ca195cecea478768de353b3ae976c07a65615 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxx>
Reported-by: syzbot <syzbot+1f29e126cf461c4de3b3@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
 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