[PATCH v2 1/4] fbcon: Disallow setting font bigger than screen size

From: Helge Deller <deller@gmx.de>
To: linux-fbdev@vger.kernel.org, daniel.vetter@ffwll.ch,
	dri-devel@lists.freedesktop.org, deller@gmx.de
Subject: [PATCH v2 1/4] fbcon: Disallow setting font bigger than screen size
Date: Sat, 25 Jun 2022 14:24:59 +0200	[thread overview]
Message-ID: <20220625122502.68095-2-deller@gmx.de> (raw)
In-Reply-To: <20220625122502.68095-1-deller@gmx.de>

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@gmx.de>
Cc: stable@vger.kernel.org # v4.14+
---
 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 c4e91715ef00..e162d5e753e5 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2469,6 +2469,11 @@ static int fbcon_set_font(struct vc_data *vc, struct console_font *font,
 	if (charcount != 256 && charcount != 512)
 		return -EINVAL;

+	/* font bigger than screen resolution ? */
+	if (font->width  > FBCON_SWAP(info->var.rotate, info->var.xres, info->var.yres) ||
+	    font->height > 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))))
--
2.35.3

