From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Zhang Boyang <zhangboyang.id@gmail.com>

Date: Fri, 5 Aug 2022 00:51:20 +0800

Subject: [PATCH] font: Fix size overflow in grub_font_get_glyph_internal()

The length of memory allocation and file read may overflow. This patch

fixes the problem by using safemath macros.

There is a lot of code repetition like "(x * y + 7) / 8". It is unsafe

if overflow happens. This patch introduces grub_video_bitmap_calc_1bpp_bufsz().

It is safe replacement for such code. It has safemath-like prototype.

This patch also introduces grub_cast(value, pointer), it casts value to

typeof(*pointer) then store the value to *pointer. It returns true when

overflow occurs or false if there is no overflow. The semantics of arguments

and return value are designed to be consistent with other safemath macros.

Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

(cherry picked from commit 941d10ad6f1dcbd12fb613002249e29ba035f985)

---

 grub-core/font/font.c   | 17 +++++++++++++----

 include/grub/bitmap.h   | 18 ++++++++++++++++++

 include/grub/safemath.h |  2 ++

 3 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/grub-core/font/font.c b/grub-core/font/font.c

index 2f09a4a55b..6a3fbebbd8 100644

--- a/grub-core/font/font.c

+++ b/grub-core/font/font.c

@@ -739,7 +739,8 @@ grub_font_get_glyph_internal (grub_font_t font, grub_uint32_t code)

       grub_int16_t xoff;

       grub_int16_t yoff;

       grub_int16_t dwidth;

-      int len;

+      grub_ssize_t len;

+      grub_size_t sz;

       if (index_entry->glyph)

 	/* Return cached glyph.  */

@@ -768,9 +769,17 @@ grub_font_get_glyph_internal (grub_font_t font, grub_uint32_t code)

 	  return 0;

 	}

-      len = (width * height + 7) / 8;

-      glyph = grub_malloc (sizeof (struct grub_font_glyph) + len);

-      if (!glyph)

+      /* Calculate real struct size of current glyph. */

+      if (grub_video_bitmap_calc_1bpp_bufsz (width, height, &len) ||

+	  grub_add (sizeof (struct grub_font_glyph), len, &sz))

+	{

+	  remove_font (font);

+	  return 0;

+	}

+

+      /* Allocate and initialize the glyph struct. */

+      glyph = grub_malloc (sz);

+      if (glyph == NULL)

 	{

 	  remove_font (font);

 	  return 0;

diff --git a/include/grub/bitmap.h b/include/grub/bitmap.h

index 5728f8ca3a..0d9603f619 100644

--- a/include/grub/bitmap.h

+++ b/include/grub/bitmap.h

@@ -23,6 +23,7 @@

 #include <grub/symbol.h>

 #include <grub/types.h>

 #include <grub/video.h>

+#include <grub/safemath.h>

 struct grub_video_bitmap

 {

@@ -79,6 +80,23 @@ grub_video_bitmap_get_height (struct grub_video_bitmap *bitmap)

   return bitmap->mode_info.height;

 }

+/*

+ * Calculate and store the size of data buffer of 1bit bitmap in result.

+ * Equivalent to "*result = (width * height + 7) / 8" if no overflow occurs.

+ * Return true when overflow occurs or false if there is no overflow.

+ * This function is intentionally implemented as a macro instead of

+ * an inline function. Although a bit awkward, it preserves data types for

+ * safemath macros and reduces macro side effects as much as possible.

+ *

+ * XXX: Will report false overflow if width * height > UINT64_MAX.

+ */

+#define grub_video_bitmap_calc_1bpp_bufsz(width, height, result) \

+({ \

+  grub_uint64_t _bitmap_pixels; \

+  grub_mul ((width), (height), &_bitmap_pixels) ? 1 : \

+    grub_cast (_bitmap_pixels / GRUB_CHAR_BIT + !!(_bitmap_pixels % GRUB_CHAR_BIT), (result)); \

+})

+

 void EXPORT_FUNC (grub_video_bitmap_get_mode_info) (struct grub_video_bitmap *bitmap,

 						    struct grub_video_mode_info *mode_info);

diff --git a/include/grub/safemath.h b/include/grub/safemath.h

index c17b89bba1..bb0f826de1 100644

--- a/include/grub/safemath.h

+++ b/include/grub/safemath.h

@@ -30,6 +30,8 @@

 #define grub_sub(a, b, res)	__builtin_sub_overflow(a, b, res)

 #define grub_mul(a, b, res)	__builtin_mul_overflow(a, b, res)

+#define grub_cast(a, res)	grub_add ((a), 0, (res))

+

 #else

 #error gcc 5.1 or newer or clang 3.8 or newer is required

 #endif