linux-kernel - [PATCH 4.19 09/31] fbcon: Disallow setting font bigger than screen size

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Message-Id: <20220711090538.122095708@linuxfoundation.org>
Date:   Mon, 11 Jul 2022 11:06:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Helge Deller <deller@....de>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH 4.19 09/31] fbcon: Disallow setting font bigger than screen size

From: Helge Deller <deller@....de>

commit 65a01e601dbba8b7a51a2677811f70f783766682 upstream.

Prevent that users set a font size which is bigger than the physical screen.
It's unlikely this may happen (because screens are usually much larger than the
fonts and each font char is limited to 32x32 pixels), but it may happen on
smaller screens/LCD displays.

Signed-off-by: Helge Deller <deller@....de>
Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: stable@...r.kernel.org # v4.14+
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/video/fbdev/core/fbcon.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2468,6 +2468,11 @@ static int fbcon_set_font(struct vc_data
 	if (charcount != 256 && charcount != 512)
 		return -EINVAL;
 
+	/* font bigger than screen resolution ? */
+	if (w > FBCON_SWAP(info->var.rotate, info->var.xres, info->var.yres) ||
+	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
+		return -EINVAL;
+
 	/* Make sure drawing engine can handle the font */
 	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
 	    !(info->pixmap.blit_y & (1 << (font->height - 1))))