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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: Mon, 15 Aug 2022 02:04:58 +0800
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Subject: [PATCH] font: Fix integer overflow in BMP index
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The BMP index (font->bmp_idx) is designed as a reverse lookup table of
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char entries (font->char_index), in order to speed up lookups for BMP
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chars (i.e. code < 0x10000). The values in BMP index are the subscripts
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of the corresponding char entries, stored in grub_uint16_t, while 0xffff
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means not found.
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This patch fixes the problem of large subscript truncated to grub_uint16_t,
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leading BMP index to return wrong char entry or report false miss. The
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code now checks for bounds and uses BMP index as a hint, and fallbacks
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to binary-search if necessary.
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On the occasion add a comment about BMP index is initialized to 0xffff.
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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 afda8b60ba0712abe01ae1e64c5f7a067a0e6492)
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---
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grub-core/font/font.c | 13 +++++++++----
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1 file changed, 9 insertions(+), 4 deletions(-)
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diff --git a/grub-core/font/font.c b/grub-core/font/font.c
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index d0e6340404..b208a28717 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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@@ -300,6 +300,8 @@ load_font_index (grub_file_t file, grub_uint32_t sect_length, struct
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font->bmp_idx = grub_malloc (0x10000 * sizeof (grub_uint16_t));
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if (!font->bmp_idx)
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return 1;
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+
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+ /* Init the BMP index array to 0xffff. */
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grub_memset (font->bmp_idx, 0xff, 0x10000 * sizeof (grub_uint16_t));
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@@ -328,7 +330,7 @@ load_font_index (grub_file_t file, grub_uint32_t sect_length, struct
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return 1;
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}
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- if (entry->code < 0x10000)
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+ if (entry->code < 0x10000 && i < 0xffff)
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font->bmp_idx[entry->code] = i;
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last_code = entry->code;
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@@ -696,9 +698,12 @@ find_glyph (const grub_font_t font, grub_uint32_t code)
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/* Use BMP index if possible. */
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if (code < 0x10000 && font->bmp_idx)
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{
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- if (font->bmp_idx[code] == 0xffff)
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- return 0;
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- return &table[font->bmp_idx[code]];
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+ if (font->bmp_idx[code] < 0xffff)
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+ return &table[font->bmp_idx[code]];
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+ /*
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+ * When we are here then lookup in BMP index result in miss,
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+ * fallthough to binary-search.
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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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