fbcon: Disallow setting font bigger than screen size

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@gmx.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: stable@vger.kernel.org # v4.14+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index e9b6f053f5bd35f6d9fcdaf92850dcccb18fcfc8..a97e94b1c84f0b156c314289953f6f5d88ba276b 100644 (file)
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2445,6 +2445,11 @@ 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))))