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GCZ: Don't trust GetBlockCompressedSize

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It comes unverified from the file, and a maliciously crafted file could
trigger not one, but two buffer overflows in the heap.
This commit is contained in:
Scott Mansell
2026-07-26 18:13:13 +12:00
committed by OatmealDome
parent 87d5e731af
commit 7bcf78b7ea
1 changed files with 23 additions and 13 deletions
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36
Source/Core/DiscIO/CompressedBlob.cpp
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@@ -31,6 +31,8 @@
namespace DiscIO
{
static constexpr u64 uncompressed_flag = 1ULL << 63;
bool IsGCZBlob(File::DirectIOFile& file);
CompressedBlobReader::CompressedBlobReader(File::DirectIOFile file, std::string filename)
@@ -80,9 +82,9 @@ std::unique_ptr<BlobReader> CompressedBlobReader::CopyReader() const
// IMPORTANT: Calling this function invalidates all earlier pointers gotten from this function.
u64 CompressedBlobReader::GetBlockCompressedSize(u64 block_num) const
{
u64 start = m_block_pointers[block_num];
u64 start = m_block_pointers[block_num] & ~uncompressed_flag;
if (block_num < m_header.num_blocks - 1)
return m_block_pointers[block_num + 1] - start;
return (m_block_pointers[block_num + 1] & ~uncompressed_flag) - start;
else if (block_num == m_header.num_blocks - 1)
return m_header.compressed_data_size - start;
else
@@ -93,21 +95,29 @@ u64 CompressedBlobReader::GetBlockCompressedSize(u64 block_num) const
bool CompressedBlobReader::GetBlock(u64 block_num, u8* out_ptr)
{
bool uncompressed = false;
u32 comp_block_size = (u32)GetBlockCompressedSize(block_num);
u64 read_size = GetBlockCompressedSize(block_num);
u64 offset = m_block_pointers[block_num] + m_data_offset;
if (offset & (1ULL << 63))
if (offset & uncompressed_flag)
{
if (comp_block_size != m_header.block_size)
if (read_size != m_header.block_size)
{
ERROR_LOG_FMT(DISCIO, "Uncompressed block with wrong size");
return false;
}
uncompressed = true;
offset &= ~(1ULL << 63);
offset &= ~uncompressed_flag;
}
else
{
if (read_size > m_zlib_buffer.size())
{
ERROR_LOG_FMT(DISCIO, "Compressed block is too large");
return false;
}
}
// clear unused part of zlib buffer. maybe this can be deleted when it works fully.
memset(&m_zlib_buffer[comp_block_size], 0, m_zlib_buffer.size() - comp_block_size);
if (!m_file.OffsetRead(offset, m_zlib_buffer.data(), comp_block_size))
if (!m_file.OffsetRead(offset, m_zlib_buffer.data(), read_size))
{
ERROR_LOG_FMT(DISCIO, "The disc image \"{}\" is truncated, some of the data is missing.",
m_file_name);
@@ -115,7 +125,7 @@ bool CompressedBlobReader::GetBlock(u64 block_num, u8* out_ptr)
}
// First, check hash.
const u32 block_hash = Common::HashAdler32(m_zlib_buffer.data(), comp_block_size);
const u32 block_hash = Common::HashAdler32(m_zlib_buffer.data(), read_size);
if (block_hash != m_hashes[block_num])
{
ERROR_LOG_FMT(DISCIO,
@@ -126,13 +136,13 @@ bool CompressedBlobReader::GetBlock(u64 block_num, u8* out_ptr)
if (uncompressed)
{
std::copy_n(m_zlib_buffer.begin(), comp_block_size, out_ptr);
std::copy_n(m_zlib_buffer.begin(), m_header.block_size, out_ptr);
}
else
{
z_stream z = {};
z.next_in = m_zlib_buffer.data();
z.avail_in = comp_block_size;
z.avail_in = read_size;
if (z.avail_in > m_header.block_size)
{
ERROR_LOG_FMT(DISCIO, "Compressed block size is larger than uncompressed block size");