From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Zhang Boyang <zhangboyang.id@gmail.com>
Date: Fri, 28 Oct 2022 21:31:39 +0800
Subject: [PATCH] normal/charset: Fix an integer overflow in
 grub_unicode_aglomerate_comb()

The out->ncomb is a bit-field of 8 bits. So, the max possible value is 255.
However, code in grub_unicode_aglomerate_comb() doesn't check for an
overflow when incrementing out->ncomb. If out->ncomb is already 255,
after incrementing it will get 0 instead of 256, and cause illegal
memory access in subsequent processing.

This patch introduces GRUB_UNICODE_NCOMB_MAX to represent the max
acceptable value of ncomb. The code now checks for this limit and
ignores additional combining characters when limit is reached.

Reported-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
(cherry picked from commit da90d62316a3b105d2fbd7334d6521936bd6dcf6)
(cherry picked from commit 26fafec86000b5322837722a115279ef03922ca6)
(cherry picked from commit 872fba1c44dee2ab5cb36b2c7a883847f91ed907)
---
 grub-core/normal/charset.c | 3 +++
 include/grub/unicode.h     | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/grub-core/normal/charset.c b/grub-core/normal/charset.c
index 7b2de12001..4849cf06f7 100644
--- a/grub-core/normal/charset.c
+++ b/grub-core/normal/charset.c
@@ -472,6 +472,9 @@ grub_unicode_aglomerate_comb (const grub_uint32_t *in, grub_size_t inlen,
 	  if (!haveout)
 	    continue;
 
+	  if (out->ncomb == GRUB_UNICODE_NCOMB_MAX)
+	    continue;
+
 	  if (comb_type == GRUB_UNICODE_COMB_MC
 	      || comb_type == GRUB_UNICODE_COMB_ME
 	      || comb_type == GRUB_UNICODE_COMB_MN)
diff --git a/include/grub/unicode.h b/include/grub/unicode.h
index 4de986a857..c4f6fca043 100644
--- a/include/grub/unicode.h
+++ b/include/grub/unicode.h
@@ -147,7 +147,9 @@ struct grub_unicode_glyph
   grub_uint8_t bidi_level:6; /* minimum: 6 */
   enum grub_bidi_type bidi_type:5; /* minimum: :5 */
 
+#define GRUB_UNICODE_NCOMB_MAX ((1 << 8) - 1)
   unsigned ncomb:8;
+
   /* Hint by unicode subsystem how wide this character usually is.
      Real width is determined by font. Set only in UTF-8 stream.  */
   int estimated_width:8;
