From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Fri, 15 Jan 2021 20:03:20 +1100
Subject: [PATCH] term/gfxterm: Don't set up a font with glyphs that are too
big
Catch the case where we have a font so big that it causes the number of
rows or columns to be 0. Currently we continue and allocate a
virtual_screen.text_buffer of size 0. We then try to use that for glpyhs
and things go badly.
On the emu platform, malloc() may give us a valid pointer, in which case
we'll access heap memory which we shouldn't. Alternatively, it may give us
NULL, in which case we'll crash. For other platforms, if I understand
grub_memalign() correctly, we will receive a valid but small allocation
that we will very likely later overrun.
Prevent the creation of a virtual screen that isn't at least 40 cols
by 12 rows. This is arbitrary, but it seems that if your width or height
is half a standard 80x24 terminal, you're probably going to struggle to
read anything anyway.
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
grub-core/term/gfxterm.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/grub-core/term/gfxterm.c b/grub-core/term/gfxterm.c
index af7c090a3e7..b40fcce9151 100644
--- a/grub-core/term/gfxterm.c
+++ b/grub-core/term/gfxterm.c
@@ -232,6 +232,15 @@ grub_virtual_screen_setup (unsigned int x, unsigned int y,
virtual_screen.columns = virtual_screen.width / virtual_screen.normal_char_width;
virtual_screen.rows = virtual_screen.height / virtual_screen.normal_char_height;
+ /*
+ * There must be a minimum number of rows and columns for the screen to
+ * make sense. Arbitrarily pick half of 80x24. If either dimensions is 0
+ * we would allocate 0 bytes for the text_buffer.
+ */
+ if (virtual_screen.columns < 40 || virtual_screen.rows < 12)
+ return grub_error (GRUB_ERR_BAD_FONT,
+ "font: glyphs too large to fit on screen");
+
/* Allocate memory for text buffer. */
virtual_screen.text_buffer =
(struct grub_colored_char *) grub_malloc (virtual_screen.columns