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LibCompress: Implement block size validation for XZ streams

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Tim Schumacher 2023-04-01 11:08:46 +02:00 committed by Andreas Kling
parent 20f1a29202
commit ad31265e60
Notes: sideshowbarker 2024-07-17 06:38:11 +09:00 
Author: https://github.com/timschumi
Commit: https://github.com/SerenityOS/serenity/commit/ad31265e60
Pull-request: https://github.com/SerenityOS/serenity/pull/18126
3 changed files with 51 additions and 17 deletions
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16
Tests/LibCompress/TestXz.cpp
View file

@ -303,8 +303,8 @@ TEST_CASE(xz_utils_bad_0_nonempty_index)
auto stream = MUST(try_make<FixedMemoryStream>(compressed));
auto decompressor = MUST(Compress::XzDecompressor::create(move(stream)));
// TODO: The index is currently not checked against the actual blocks.
(void)decompressor->read_until_eof(PAGE_SIZE);
auto buffer_or_error = decompressor->read_until_eof(PAGE_SIZE);
EXPECT(buffer_or_error.is_error());
}
TEST_CASE(xz_utils_bad_0pad_empty)
@ -963,8 +963,8 @@ TEST_CASE(xz_utils_bad_2_index_1)
auto stream = MUST(try_make<FixedMemoryStream>(compressed));
auto decompressor = MUST(Compress::XzDecompressor::create(move(stream)));
// TODO: The index is currently not checked against the actual blocks.
(void)decompressor->read_until_eof(PAGE_SIZE);
auto buffer_or_error = decompressor->read_until_eof(PAGE_SIZE);
EXPECT(buffer_or_error.is_error());
}
TEST_CASE(xz_utils_bad_2_index_2)
@ -981,8 +981,8 @@ TEST_CASE(xz_utils_bad_2_index_2)
auto stream = MUST(try_make<FixedMemoryStream>(compressed));
auto decompressor = MUST(Compress::XzDecompressor::create(move(stream)));
// TODO: The index is currently not checked against the actual blocks.
(void)decompressor->read_until_eof(PAGE_SIZE);
auto buffer_or_error = decompressor->read_until_eof(PAGE_SIZE);
EXPECT(buffer_or_error.is_error());
}
TEST_CASE(xz_utils_bad_2_index_3)
@ -1060,8 +1060,8 @@ TEST_CASE(xz_utils_bad_3_index_uncomp_overflow)
auto stream = MUST(try_make<FixedMemoryStream>(compressed));
auto decompressor = MUST(Compress::XzDecompressor::create(move(stream)));
// TODO: The index is currently not checked against the actual blocks, so the overflow never occurs in the first place.
(void)decompressor->read_until_eof(PAGE_SIZE);
auto buffer_or_error = decompressor->read_until_eof(PAGE_SIZE);
EXPECT(buffer_or_error.is_error());
}
auto const xz_utils_hello_world = "Hello\nWorld!\n"sv;

41
Userland/Libraries/LibCompress/Xz.cpp
View file

@ -254,11 +254,13 @@ ErrorOr<Bytes> XzDecompressor::read_some(Bytes bytes)
if (m_current_block_stream.has_value()) {
// We have already processed a block, so we weed to clean up trailing data before the next block starts.
auto unpadded_size = m_stream->read_bytes() - m_current_block_start_offset;
// 3.3. Block Padding:
// "Block Padding MUST contain 0-3 null bytes to make the size of
// the Block a multiple of four bytes. This can be needed when
// the size of Compressed Data is not a multiple of four."
while (m_stream->read_bytes() % 4 != 0) {
for (size_t i = 0; (unpadded_size + i) % 4 != 0; i++) {
auto padding_byte = TRY(m_stream->read_value<u8>());
// "If any of the bytes in Block Padding are not null bytes, the decoder
@ -284,12 +286,22 @@ ErrorOr<Bytes> XzDecompressor::read_some(Bytes bytes)
// TODO: Block content checks are currently unimplemented as a whole, independent of the check type.
// For now, we only make sure to remove the correct amount of bytes from the stream.
TRY(m_stream->discard(*maybe_check_size));
unpadded_size += *maybe_check_size;
if (m_current_block_expected_uncompressed_size.has_value()) {
if (*m_current_block_expected_uncompressed_size != m_current_block_uncompressed_size)
return Error::from_string_literal("Uncompressed size of XZ block does not match the expected value");
}
TRY(m_processed_blocks.try_append({
.uncompressed_size = m_current_block_uncompressed_size,
.unpadded_size = unpadded_size,
}));
}
auto start_of_current_block = m_stream->read_bytes();
// Ensure that the start of the block is aligned to a multiple of four (in theory, everything in XZ is).
// This allows us to make sure that the block padding is correct without having to store the block start offset explicitly.
VERIFY(start_of_current_block % 4 == 0);
// The first byte between Block Header (3.1.1. Block Header Size) and Index (4.1. Index Indicator) overlap.
@ -306,6 +318,9 @@ ErrorOr<Bytes> XzDecompressor::read_some(Bytes bytes)
// Section 1.2."
u64 number_of_records = TRY(m_stream->read_value<XzMultibyteInteger>());
if (m_processed_blocks.size() != number_of_records)
return Error::from_string_literal("Number of Records in XZ Index does not match the number of processed Blocks");
// 4.3. List of Records:
// "List of Records consists of as many Records as indicated by the
// Number of Records field:"
@ -338,9 +353,11 @@ ErrorOr<Bytes> XzDecompressor::read_some(Bytes bytes)
// "If the decoder has decoded all the Blocks of the Stream, it
// MUST verify that the contents of the Records match the real
// Unpadded Size and Uncompressed Size of the respective Blocks."
// TODO: Validation of unpadded and uncompressed size against the actual blocks is currently unimplemented.
(void)unpadded_size;
(void)uncompressed_size;
if (m_processed_blocks[i].uncompressed_size != uncompressed_size)
return Error::from_string_literal("Uncompressed size of XZ Block does not match the Index");
if (m_processed_blocks[i].unpadded_size != unpadded_size)
return Error::from_string_literal("Unpadded size of XZ Block does not match the Index");
}
// 4.4. Index Padding:
@ -391,9 +408,12 @@ ErrorOr<Bytes> XzDecompressor::read_some(Bytes bytes)
// Another XZ Stream might follow, so we just unset the current information and continue on the next read.
m_stream_flags.clear();
m_processed_blocks.clear();
return bytes.trim(0);
}
m_current_block_start_offset = start_of_current_block;
// 3.1.1. Block Header Size:
// "This field contains the size of the Block Header field,
// including the Block Header Size field itself. Valid values are
@ -445,9 +465,9 @@ ErrorOr<Bytes> XzDecompressor::read_some(Bytes bytes)
// "Uncompressed Size is stored using the encoding described in Section 1.2."
u64 uncompressed_size = TRY(header_stream.read_value<XzMultibyteInteger>());
m_current_block_uncompressed_size = uncompressed_size;
m_current_block_expected_uncompressed_size = uncompressed_size;
} else {
m_current_block_uncompressed_size.clear();
m_current_block_expected_uncompressed_size.clear();
}
// 3.1.5. List of Filter Flags:
@ -505,9 +525,14 @@ ErrorOr<Bytes> XzDecompressor::read_some(Bytes bytes)
return Error::from_string_literal("Stored XZ block header CRC32 does not match the stored CRC32");
m_current_block_stream = move(new_block_stream);
m_current_block_uncompressed_size = 0;
}
return TRY((*m_current_block_stream)->read_some(bytes));
auto result = TRY((*m_current_block_stream)->read_some(bytes));
m_current_block_uncompressed_size += result.size();
return result;
}
ErrorOr<size_t> XzDecompressor::write_some(ReadonlyBytes)

11
Userland/Libraries/LibCompress/Xz.h
View file

@ -14,6 +14,7 @@
#include <AK/NonnullOwnPtr.h>
#include <AK/OwnPtr.h>
#include <AK/Stream.h>
#include <AK/Vector.h>
namespace Compress {
@ -116,7 +117,15 @@ private:
bool m_found_last_stream_footer { false };
Optional<MaybeOwned<Stream>> m_current_block_stream {};
Optional<u64> m_current_block_uncompressed_size {};
Optional<u64> m_current_block_expected_uncompressed_size {};
u64 m_current_block_uncompressed_size {};
u64 m_current_block_start_offset {};
struct BlockMetadata {
u64 uncompressed_size {};
u64 unpadded_size {};
};
Vector<BlockMetadata> m_processed_blocks;
};
}