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normal/charset: Fix an integer overflow in grub_unicode_aglomerate_comb()

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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>
This commit is contained in:
Zhang Boyang 2022-10-28 21:31:39 +08:00 committed by Daniel Kiper
parent 22b77b87e1
commit 1514678888
2 changed files with 5 additions and 0 deletions
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3
grub-core/normal/charset.c
View File

@ -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)

2
include/grub/unicode.h
View File

@ -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;