[SRU Bionic PATCH 1/3] fbcon: Disallow setting font bigger than screen size

Cengiz Can cengiz.can at canonical.com
Fri Aug 5 15:54:33 UTC 2022


From: Helge Deller <deller at gmx.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 at gmx.de>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Reviewed-by: Geert Uytterhoeven <geert at linux-m68k.org>
Cc: stable at vger.kernel.org # v4.14+
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
CVE-2021-33655
(cherry picked from commit f7e7c2ad446f359f54f4ea6a0a30b218e5edf134 linux-4.14.y)
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 drivers/video/fbdev/core/fbcon.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index bf0f17f3d62ad..a95a892c2a69a 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2446,6 +2446,11 @@ static int fbcon_set_font(struct vc_data *vc, struct console_font *font, unsigne
 	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))))
-- 
2.34.1




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