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///////////////////////////////////////////////////////////////////////////////
//
/// \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"
extern LZMA_API(lzma_ret)
lzma_block_header_decode(lzma_block *block,
const 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.
// Catch unexpected NULL pointers.
if (block == NULL || block->filters == NULL || in == NULL)
return LZMA_PROG_ERROR;
// 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;
}
// Versions 0 and 1 are supported. If a newer version was specified,
// we need to downgrade it.
if (block->version > 1)
block->version = 1;
// This isn't a Block Header option, but since the decompressor will
// read it if version >= 1, it's better to initialize it here than
// to expect the caller to do it since in almost all cases this
// should be false.
block->ignore_check = false;
// 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) != read32le(in + in_size)) {
#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
return LZMA_DATA_ERROR;
#endif
}
// 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] & 3U) + 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) {
lzma_filters_free(block->filters, allocator);
return ret;
}
}
// Padding
while (in_pos < in_size) {
if (in[in_pos++] != 0x00) {
lzma_filters_free(block->filters, allocator);
// Possibly some new field present so use
// LZMA_OPTIONS_ERROR instead of LZMA_DATA_ERROR.
return LZMA_OPTIONS_ERROR;
}
}
return LZMA_OK;
}
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