Fonts: Support FONT_EXTRA_WORDS macros for built-in fonts
syzbot has reported an issue in the framebuffer layer, where a malicious
user may overflow our built-in font data buffers.
In order to perform a reliable range check, subsystems need to know
`FONTDATAMAX` for each built-in font. Unfortunately, our font descriptor,
`struct console_font` does not contain `FONTDATAMAX`, and is part of the
UAPI, making it infeasible to modify it.
For user-provided fonts, the framebuffer layer resolves this issue by
reserving four extra words at the beginning of data buffers. Later,
whenever a function needs to access them, it simply uses the following
macros:
Recently we have gathered all the above macros to <linux/font.h>. Let us
do the same thing for built-in fonts, prepend four extra words (including
`FONTDATAMAX`) to their data buffers, so that subsystems can use these
macros for all fonts, no matter built-in or user-provided.
This patch depends on patch "fbdev, newport_con: Move FONT_EXTRA_WORDS
macros into linux/font.h".
Cc: stable@vger.kernel.org
Link: https://syzkaller.appspot.com/bug?id=08b8be45afea11888776f897895aef9ad1c3ecfd
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/ef18af00c35fb3cc826048a5f70924ed6ddce95b.1600953813.git.yepeilin.cs@gmail.com
diff --git a/lib/fonts/font_acorn_8x8.c b/lib/fonts/font_acorn_8x8.c
index 0ff0e85..069b3e8 100644
--- a/lib/fonts/font_acorn_8x8.c
+++ b/lib/fonts/font_acorn_8x8.c
@@ -3,7 +3,10 @@
#include <linux/font.h>
-static const unsigned char acorndata_8x8[] = {
+#define FONTDATAMAX 2048
+
+static struct font_data acorndata_8x8 = {
+{ 0, 0, FONTDATAMAX, 0 }, {
/* 00 */ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* ^@ */
/* 01 */ 0x7e, 0x81, 0xa5, 0x81, 0xbd, 0x99, 0x81, 0x7e, /* ^A */
/* 02 */ 0x7e, 0xff, 0xbd, 0xff, 0xc3, 0xe7, 0xff, 0x7e, /* ^B */
@@ -260,14 +263,14 @@ static const unsigned char acorndata_8x8[] = {
/* FD */ 0x38, 0x04, 0x18, 0x20, 0x3c, 0x00, 0x00, 0x00,
/* FE */ 0x00, 0x00, 0x3c, 0x3c, 0x3c, 0x3c, 0x00, 0x00,
/* FF */ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
-};
+} };
const struct font_desc font_acorn_8x8 = {
.idx = ACORN8x8_IDX,
.name = "Acorn8x8",
.width = 8,
.height = 8,
- .data = acorndata_8x8,
+ .data = acorndata_8x8.data,
#ifdef CONFIG_ARCH_ACORN
.pref = 20,
#else
