root/src/liblzma/common/block_header_decoder.c

DEFINITIONS

1. free_properties
2. LZMA_API

///////////////////////////////////////////////////////////////////////////////
//
/// \file       block_header_decoder.c
/// \brief      Decodes Block Header 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 "common.h"
#include "check.h"


static void
free_properties(lzma_block *block, lzma_allocator *allocator)
{
        // Free allocated filter options. The last array member is not
        // touched after the initialization in the beginning of
        // lzma_block_header_decode(), so we don't need to touch that here.
        for (size_t i = 0; i < LZMA_FILTERS_MAX; ++i) {
                lzma_free(block->filters[i].options, allocator);
                block->filters[i].id = LZMA_VLI_UNKNOWN;
                block->filters[i].options = NULL;
        }

        return;
}


extern LZMA_API(lzma_ret)
lzma_block_header_decode(lzma_block *block,
                lzma_allocator *allocator, const uint8_t *in)
{
        // NOTE: We consider the header to be corrupt not only when the
        // CRC32 doesn't match, but also when variable-length integers
        // are invalid or over 63 bits, or if the header is too small
        // to contain the claimed information.

        // Initialize the filter options array. This way the caller can
        // safely free() the options even if an error occurs in this function.
        for (size_t i = 0; i <= LZMA_FILTERS_MAX; ++i) {
                block->filters[i].id = LZMA_VLI_UNKNOWN;
                block->filters[i].options = NULL;
        }

        // Always zero for now.
        block->version = 0;

        // Validate Block Header Size and Check type. The caller must have
        // already set these, so it is a programming error if this test fails.
        if (lzma_block_header_size_decode(in[0]) != block->header_size
                        || (unsigned int)(block->check) > LZMA_CHECK_ID_MAX)
                return LZMA_PROG_ERROR;

        // Exclude the CRC32 field.
        const size_t in_size = block->header_size - 4;

        // Verify CRC32
        if (lzma_crc32(in, in_size, 0) != unaligned_read32le(in + in_size))
                return LZMA_DATA_ERROR;

        // Check for unsupported flags.
        if (in[1] & 0x3C)
                return LZMA_OPTIONS_ERROR;

        // Start after the Block Header Size and Block Flags fields.
        size_t in_pos = 2;

        // Compressed Size
        if (in[1] & 0x40) {
                return_if_error(lzma_vli_decode(&block->compressed_size,
                                NULL, in, &in_pos, in_size));

                // Validate Compressed Size. This checks that it isn't zero
                // and that the total size of the Block is a valid VLI.
                if (lzma_block_unpadded_size(block) == 0)
                        return LZMA_DATA_ERROR;
        } else {
                block->compressed_size = LZMA_VLI_UNKNOWN;
        }

        // Uncompressed Size
        if (in[1] & 0x80)
                return_if_error(lzma_vli_decode(&block->uncompressed_size,
                                NULL, in, &in_pos, in_size));
        else
                block->uncompressed_size = LZMA_VLI_UNKNOWN;

        // Filter Flags
        const size_t filter_count = (in[1] & 3) + 1;
        for (size_t i = 0; i < filter_count; ++i) {
                const lzma_ret ret = lzma_filter_flags_decode(
                                &block->filters[i], allocator,
                                in, &in_pos, in_size);
                if (ret != LZMA_OK) {
                        free_properties(block, allocator);
                        return ret;
                }
        }

        // Padding
        while (in_pos < in_size) {
                if (in[in_pos++] != 0x00) {
                        free_properties(block, allocator);

                        // Possibly some new field present so use
                        // LZMA_OPTIONS_ERROR instead of LZMA_DATA_ERROR.
                        return LZMA_OPTIONS_ERROR;
                }
        }

        return LZMA_OK;
}