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From c140a086838e7c9af87842036f891b8393a8c4bc Mon Sep 17 00:00:00 2001
From: Zhang Boyang <zhangboyang.id@gmail.com>
Date: Sun, 14 Aug 2022 18:09:38 +0800
Subject: [PATCH 08/14] font: Fix integer underflow in binary search of char
index
If search target is less than all entries in font->index then "hi"
variable is set to -1, which translates to SIZE_MAX and leads to errors.
This patch fixes the problem by replacing the entire binary search code
with the libstdc++'s std::lower_bound() implementation.
Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
grub-core/font/font.c | 40 ++++++++++++++++++++++------------------
1 file changed, 22 insertions(+), 18 deletions(-)
diff --git a/grub-core/font/font.c b/grub-core/font/font.c
index e4cb0d867..abd412a5e 100644
--- a/grub-core/font/font.c
+++ b/grub-core/font/font.c
@@ -688,12 +688,12 @@ read_be_int16 (grub_file_t file, grub_int16_t * value)
static inline struct char_index_entry *
find_glyph (const grub_font_t font, grub_uint32_t code)
{
- struct char_index_entry *table;
- grub_size_t lo;
- grub_size_t hi;
- grub_size_t mid;
+ struct char_index_entry *table, *first, *end;
+ grub_size_t len;
table = font->char_index;
+ if (table == NULL)
+ return NULL;
/* Use BMP index if possible. */
if (code < 0x10000 && font->bmp_idx)
@@ -706,25 +706,29 @@ find_glyph (const grub_font_t font, grub_uint32_t code)
*/
}
- /* Do a binary search in `char_index', which is ordered by code point. */
- lo = 0;
- hi = font->num_chars - 1;
-
- if (!table)
- return 0;
+ /*
+ * Do a binary search in char_index which is ordered by code point.
+ * The code below is the same as libstdc++'s std::lower_bound().
+ */
+ first = table;
+ len = font->num_chars;
+ end = first + len;
- while (lo <= hi)
+ while (len > 0)
{
- mid = lo + (hi - lo) / 2;
- if (code < table[mid].code)
- hi = mid - 1;
- else if (code > table[mid].code)
- lo = mid + 1;
+ grub_size_t half = len >> 1;
+ struct char_index_entry *middle = first + half;
+
+ if (middle->code < code)
+ {
+ first = middle + 1;
+ len = len - half - 1;
+ }
else
- return &table[mid];
+ len = half;
}
- return 0;
+ return (first < end && first->code == code) ? first : NULL;
}
/* Get a glyph for the Unicode character CODE in FONT. The glyph is loaded
--
2.30.2
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