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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Zhang Boyang <zhangboyang.id@gmail.com>
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Date: Sun, 14 Aug 2022 18:09:38 +0800
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Subject: [PATCH] font: Fix integer underflow in binary search of char index
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If search target is less than all entries in font->index then "hi"
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variable is set to -1, which translates to SIZE_MAX and leads to errors.
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This patch fixes the problem by replacing the entire binary search code
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with the libstdc++'s std::lower_bound() implementation.
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Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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(cherry picked from commit c140a086838e7c9af87842036f891b8393a8c4bc)
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---
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grub-core/font/font.c | 40 ++++++++++++++++++++++------------------
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1 file changed, 22 insertions(+), 18 deletions(-)
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diff --git a/grub-core/font/font.c b/grub-core/font/font.c
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index b208a28717..193dfec045 100644
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--- a/grub-core/font/font.c
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+++ b/grub-core/font/font.c
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@@ -688,12 +688,12 @@ read_be_int16 (grub_file_t file, grub_int16_t * value)
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static inline struct char_index_entry *
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find_glyph (const grub_font_t font, grub_uint32_t code)
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{
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- struct char_index_entry *table;
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- grub_size_t lo;
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- grub_size_t hi;
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- grub_size_t mid;
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+ struct char_index_entry *table, *first, *end;
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+ grub_size_t len;
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table = font->char_index;
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+ if (table == NULL)
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+ return NULL;
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/* Use BMP index if possible. */
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if (code < 0x10000 && font->bmp_idx)
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@@ -706,25 +706,29 @@ find_glyph (const grub_font_t font, grub_uint32_t code)
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*/
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}
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- /* Do a binary search in `char_index', which is ordered by code point. */
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- lo = 0;
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- hi = font->num_chars - 1;
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+ /*
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+ * Do a binary search in char_index which is ordered by code point.
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+ * The code below is the same as libstdc++'s std::lower_bound().
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+ */
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+ first = table;
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+ len = font->num_chars;
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+ end = first + len;
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- if (!table)
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- return 0;
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-
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- while (lo <= hi)
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+ while (len > 0)
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{
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- mid = lo + (hi - lo) / 2;
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- if (code < table[mid].code)
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- hi = mid - 1;
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- else if (code > table[mid].code)
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- lo = mid + 1;
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+ grub_size_t half = len >> 1;
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+ struct char_index_entry *middle = first + half;
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+
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+ if (middle->code < code)
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+ {
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+ first = middle + 1;
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+ len = len - half - 1;
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+ }
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else
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- return &table[mid];
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+ len = half;
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}
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- return 0;
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+ return (first < end && first->code == code) ? first : NULL;
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}
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/* Get a glyph for the Unicode character CODE in FONT. The glyph is loaded
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