fbcon: Disallow setting font bigger than screen size

mainline inclusion
from mainline-v5.19-rc6
commit 65a01e60
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I5IQ4M
CVE: CVE-2021-33655

--------------------------------

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: NHelge Deller <deller@gmx.de>
Reviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Cc: stable@vger.kernel.org # v4.14+
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

drivers/video/fbdev/core/fbcon.c

@@ -2441,6 +2441,11 @@ 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 (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))))