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LibCompress: Make the Zlib decompressor fail gracefuly

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This commit adds a verify-less try_create method to the Zlib
decompressor to allow for graceful failures of parsing the
Zlib headers.
This commit is contained in:
Idan Horowitz 2021-03-15 17:03:42 +02:00 • committed by Andreas Kling
parent a7b5a58509
commit f532421c9c
2 changed files with 33 additions and 19 deletions
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45
Userland/Libraries/LibCompress/Zlib.cpp
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@ -24,7 +24,6 @@
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <AK/Assertions.h>
#include <AK/Span.h>
#include <AK/Types.h>
#include <AK/Vector.h>
@ -33,26 +32,38 @@
namespace Compress {
Zlib::Zlib(ReadonlyBytes data)
Optional<Zlib> Zlib::try_create(ReadonlyBytes data)
{
m_input_data = data;
if (data.size() < 6)
return {}; // header + footer size is 6
Zlib zlib { data };
u8 compression_info = data.at(0);
u8 flags = data.at(1);
m_compression_method = compression_info & 0xF;
m_compression_info = (compression_info >> 4) & 0xF;
m_check_bits = flags & 0xF;
m_has_dictionary = (flags >> 5) & 0x1;
m_compression_level = (flags >> 6) & 0x3;
m_checksum = 0;
zlib.m_compression_method = compression_info & 0xF;
zlib.m_compression_info = (compression_info >> 4) & 0xF;
zlib.m_check_bits = flags & 0xF;
zlib.m_has_dictionary = (flags >> 5) & 0x1;
zlib.m_compression_level = (flags >> 6) & 0x3;
VERIFY(m_compression_method == 8);
VERIFY(m_compression_info == 7);
VERIFY(!m_has_dictionary);
VERIFY((compression_info * 256 + flags) % 31 == 0);
if (zlib.m_compression_method != 8 || zlib.m_compression_info > 7)
return {}; // non-deflate compression
m_data_bytes = data.slice(2, data.size() - 2 - 4);
if (zlib.m_has_dictionary)
return {}; // we dont support pre-defined dictionaries
if ((compression_info * 256 + flags) % 31 != 0)
return {}; // error correction code doesnt match
zlib.m_data_bytes = data.slice(2, data.size() - 2 - 4);
return zlib;
}
Zlib::Zlib(const ReadonlyBytes& data)
: m_input_data(data)
{
}
Optional<ByteBuffer> Zlib::decompress()
@ -62,8 +73,10 @@ Optional<ByteBuffer> Zlib::decompress()
Optional<ByteBuffer> Zlib::decompress_all(ReadonlyBytes bytes)
{
Zlib zlib { bytes };
return zlib.decompress();
auto zlib = try_create(bytes);
if (!zlib.has_value())
return {};
return zlib->decompress();
}
u32 Zlib::checksum()