source: vbox/trunk/src/libs/liblzma-5.4.1/common/stream_flags_decoder.c

///////////////////////////////////////////////////////////////////////////////
//
/// \file       stream_flags_decoder.c
/// \brief      Decodes Stream Header and Stream Footer from .xz files
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "stream_flags_common.h"


static bool
stream_flags_decode(lzma_stream_flags *options, const uint8_t *in)
{
        // Reserved bits must be unset.
        if (in[0] != 0x00 || (in[1] & 0xF0))
                return true;

        options->version = 0;
        options->check = in[1] & 0x0F;

        return false;
}


extern LZMA_API(lzma_ret)
lzma_stream_header_decode(lzma_stream_flags *options, const uint8_t *in)
{
        // Magic
        if (memcmp(in, lzma_header_magic, sizeof(lzma_header_magic)) != 0)
                return LZMA_FORMAT_ERROR;

        // Verify the CRC32 so we can distinguish between corrupt
        // and unsupported files.
        const uint32_t crc = lzma_crc32(in + sizeof(lzma_header_magic),
                        LZMA_STREAM_FLAGS_SIZE, 0);
        if (crc != read32le(in + sizeof(lzma_header_magic)
                        + LZMA_STREAM_FLAGS_SIZE)) {
#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
                return LZMA_DATA_ERROR;
#endif
        }

        // Stream Flags
        if (stream_flags_decode(options, in + sizeof(lzma_header_magic)))
                return LZMA_OPTIONS_ERROR;

        // Set Backward Size to indicate unknown value. That way
        // lzma_stream_flags_compare() can be used to compare Stream Header
        // and Stream Footer while keeping it useful also for comparing
        // two Stream Footers.
        options->backward_size = LZMA_VLI_UNKNOWN;

        return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_stream_footer_decode(lzma_stream_flags *options, const uint8_t *in)
{
        // Magic
        if (memcmp(in + sizeof(uint32_t) * 2 + LZMA_STREAM_FLAGS_SIZE,
                        lzma_footer_magic, sizeof(lzma_footer_magic)) != 0)
                return LZMA_FORMAT_ERROR;

        // CRC32
        const uint32_t crc = lzma_crc32(in + sizeof(uint32_t),
                        sizeof(uint32_t) + LZMA_STREAM_FLAGS_SIZE, 0);
        if (crc != read32le(in)) {
#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
                return LZMA_DATA_ERROR;
#endif
        }

        // Stream Flags
        if (stream_flags_decode(options, in + sizeof(uint32_t) * 2))
                return LZMA_OPTIONS_ERROR;

        // Backward Size
        options->backward_size = read32le(in + sizeof(uint32_t));
        options->backward_size = (options->backward_size + 1) * 4;

        return LZMA_OK;
}