From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Zhang Boyang Date: Mon, 15 Aug 2022 02:04:58 +0800 Subject: [PATCH] font: Fix integer overflow in BMP index The BMP index (font->bmp_idx) is designed as a reverse lookup table of char entries (font->char_index), in order to speed up lookups for BMP chars (i.e. code < 0x10000). The values in BMP index are the subscripts of the corresponding char entries, stored in grub_uint16_t, while 0xffff means not found. This patch fixes the problem of large subscript truncated to grub_uint16_t, leading BMP index to return wrong char entry or report false miss. The code now checks for bounds and uses BMP index as a hint, and fallbacks to binary-search if necessary. On the occasion add a comment about BMP index is initialized to 0xffff. Signed-off-by: Zhang Boyang Reviewed-by: Daniel Kiper (cherry picked from commit afda8b60ba0712abe01ae1e64c5f7a067a0e6492) (cherry picked from commit 6d90568929e11739b56f09ebbce9185ca9c23519) --- grub-core/font/font.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/grub-core/font/font.c b/grub-core/font/font.c index d0e6340404..b208a28717 100644 --- a/grub-core/font/font.c +++ b/grub-core/font/font.c @@ -300,6 +300,8 @@ load_font_index (grub_file_t file, grub_uint32_t sect_length, struct font->bmp_idx = grub_malloc (0x10000 * sizeof (grub_uint16_t)); if (!font->bmp_idx) return 1; + + /* Init the BMP index array to 0xffff. */ grub_memset (font->bmp_idx, 0xff, 0x10000 * sizeof (grub_uint16_t)); @@ -328,7 +330,7 @@ load_font_index (grub_file_t file, grub_uint32_t sect_length, struct return 1; } - if (entry->code < 0x10000) + if (entry->code < 0x10000 && i < 0xffff) font->bmp_idx[entry->code] = i; last_code = entry->code; @@ -696,9 +698,12 @@ find_glyph (const grub_font_t font, grub_uint32_t code) /* Use BMP index if possible. */ if (code < 0x10000 && font->bmp_idx) { - if (font->bmp_idx[code] == 0xffff) - return 0; - return &table[font->bmp_idx[code]]; + if (font->bmp_idx[code] < 0xffff) + return &table[font->bmp_idx[code]]; + /* + * When we are here then lookup in BMP index result in miss, + * fallthough to binary-search. + */ } /* Do a binary search in `char_index', which is ordered by code point. */