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LibGfx/OpenType: Ensure Cmap subtable offset is within expected range

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Tim Ledbetter 2023-11-11 17:06:17 +00:00 committed by Andreas Kling
parent 6d1a1daff9
commit cdfe893717
Notes: sideshowbarker 2024-07-16 17:05:37 +09:00 
Author: https://github.com/tcl3
Commit: https://github.com/SerenityOS/serenity/commit/cdfe893717
Pull-request: https://github.com/SerenityOS/serenity/pull/21894
2 changed files with 11 additions and 2 deletions
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11
Tests/LibTTF/TestCmap.cpp
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@ -11,7 +11,7 @@ TEST_CASE(test_cmap_format_4)
{
// clang-format off
// Big endian.
u8 cmap_table[] =
Array<u8, 52> const cmap_table =
{
// https://docs.microsoft.com/en-us/typography/opentype/spec/cmap#cmap-header
0, 0, // uint16 version
@ -54,7 +54,7 @@ TEST_CASE(test_cmap_format_4)
0, 0,
};
// clang-format on
auto cmap = OpenType::Cmap::from_slice({ cmap_table, sizeof cmap_table }).value();
auto cmap = OpenType::Cmap::from_slice(cmap_table.span()).value();
cmap.set_active_index(0);
// Format 4 can't handle code points > 0xffff.
@ -78,4 +78,11 @@ TEST_CASE(test_cmap_format_4)
EXPECT_EQ(cmap.glyph_id_for_code_point(0xfeff), 0u);
EXPECT_EQ(cmap.glyph_id_for_code_point(0xffff), 0xffffu);
EXPECT_EQ(cmap.glyph_id_for_code_point(0x1'0000), 0u);
// Set the number of subtables to a value, where the record offset for the last subtable is greater than the
// total table size. We should not crash if a Cmap table is truncated in this way.
auto malformed_cmap_table = cmap_table;
malformed_cmap_table[3] = 13;
auto cmap_with_invalid_subtable_offset = OpenType::Cmap::from_slice(malformed_cmap_table.span()).value();
EXPECT(!cmap_with_invalid_subtable_offset.subtable(12).has_value());
}

2
Userland/Libraries/LibGfx/Font/OpenType/Cmap.cpp
View file

@ -68,6 +68,8 @@ Optional<Cmap::Subtable> Cmap::subtable(u32 index) const
return {};
}
u32 record_offset = (u32)Sizes::TableHeader + index * (u32)Sizes::EncodingRecord;
if (record_offset + (u32)Offsets::EncodingRecord_Offset >= m_slice.size())
return {};
u16 platform_id = be_u16(m_slice.offset(record_offset));
u16 encoding_id = be_u16(m_slice.offset(record_offset + (u32)Offsets::EncodingRecord_EncodingID));
u32 subtable_offset = be_u32(m_slice.offset(record_offset + (u32)Offsets::EncodingRecord_Offset));