src/liblzma/common/block_decoder.c

///////////////////////////////////////////////////////////////////////////////
//
/// \file       block_decoder.c
/// \brief      Decodes .xz Blocks
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "block_decoder.h"
#include "filter_decoder.h"
#include "check.h"


struct lzma_coder_s {
	enum {
		SEQ_CODE,
		SEQ_PADDING,
		SEQ_CHECK,
	} sequence;

	/// The filters in the chain; initialized with lzma_raw_decoder_init().
	lzma_next_coder next;

	/// Decoding options; we also write Compressed Size and Uncompressed
	/// Size back to this structure when the decoding has been finished.
	lzma_block *block;

	/// Compressed Size calculated while decoding
	lzma_vli compressed_size;

	/// Uncompressed Size calculated while decoding
	lzma_vli uncompressed_size;

	/// Maximum allowed Compressed Size; this takes into account the
	/// size of the Block Header and Check fields when Compressed Size
	/// is unknown.
	lzma_vli compressed_limit;

	/// Position when reading the Check field
	size_t check_pos;

	/// Check of the uncompressed data
	lzma_check_state check;
};


static inline bool
update_size(lzma_vli *size, lzma_vli add, lzma_vli limit)
{
	if (limit > LZMA_VLI_MAX)
		limit = LZMA_VLI_MAX;

	if (limit < *size || limit - *size < add)
		return true;

	*size += add;

	return false;
}


static inline bool
is_size_valid(lzma_vli size, lzma_vli reference)
{
	return reference == LZMA_VLI_UNKNOWN || reference == size;
}


static lzma_ret
block_decode(lzma_coder *coder, const lzma_allocator *allocator,
		const uint8_t *restrict in, size_t *restrict in_pos,
		size_t in_size, uint8_t *restrict out,
		size_t *restrict out_pos, size_t out_size, lzma_action action)
{
	switch (coder->sequence) {
	case SEQ_CODE: {
		const size_t in_start = *in_pos;
		const size_t out_start = *out_pos;

		const lzma_ret ret = coder->next.code(coder->next.coder,
				allocator, in, in_pos, in_size,
				out, out_pos, out_size, action);

		const size_t in_used = *in_pos - in_start;
		const size_t out_used = *out_pos - out_start;

		// NOTE: We compare to compressed_limit here, which prevents
		// the total size of the Block growing past LZMA_VLI_MAX.
		if (update_size(&coder->compressed_size, in_used,
					coder->compressed_limit)
				|| update_size(&coder->uncompressed_size,
					out_used,
					coder->block->uncompressed_size))
			return LZMA_DATA_ERROR;

		lzma_check_update(&coder->check, coder->block->check,
				out + out_start, out_used);

		if (ret != LZMA_STREAM_END)
			return ret;

		// Compressed and Uncompressed Sizes are now at their final
		// values. Verify that they match the values given to us.
		if (!is_size_valid(coder->compressed_size,
					coder->block->compressed_size)
				|| !is_size_valid(coder->uncompressed_size,
					coder->block->uncompressed_size))
			return LZMA_DATA_ERROR;

		// Copy the values into coder->block. The caller
		// may use this information to construct Index.
		coder->block->compressed_size = coder->compressed_size;
		coder->block->uncompressed_size = coder->uncompressed_size;

		coder->sequence = SEQ_PADDING;
	}

	// Fall through

	case SEQ_PADDING:
		// Compressed Data is padded to a multiple of four bytes.
		while (coder->compressed_size & 3) {
			if (*in_pos >= in_size)
				return LZMA_OK;

			// We use compressed_size here just get the Padding
			// right. The actual Compressed Size was stored to
			// coder->block already, and won't be modified by
			// us anymore.
			++coder->compressed_size;

			if (in[(*in_pos)++] != 0x00)
				return LZMA_DATA_ERROR;
		}

		if (coder->block->check == LZMA_CHECK_NONE)
			return LZMA_STREAM_END;

		lzma_check_finish(&coder->check, coder->block->check);
		coder->sequence = SEQ_CHECK;

	// Fall through

	case SEQ_CHECK: {
		const size_t check_size = lzma_check_size(coder->block->check);
		lzma_bufcpy(in, in_pos, in_size, coder->block->raw_check,
				&coder->check_pos, check_size);
		if (coder->check_pos < check_size)
			return LZMA_OK;

		// Validate the Check only if we support it.
		// coder->check.buffer may be uninitialized
		// when the Check ID is not supported.
		if (lzma_check_is_supported(coder->block->check)
				&& memcmp(coder->block->raw_check,
					coder->check.buffer.u8,
					check_size) != 0)
			return LZMA_DATA_ERROR;

		return LZMA_STREAM_END;
	}
	}

	return LZMA_PROG_ERROR;
}


static void
block_decoder_end(lzma_coder *coder, const lzma_allocator *allocator)
{
	lzma_next_end(&coder->next, allocator);
	lzma_free(coder, allocator);
	return;
}


extern lzma_ret
lzma_block_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
		lzma_block *block)
{
	lzma_next_coder_init(&lzma_block_decoder_init, next, allocator);

	// Validate the options. lzma_block_unpadded_size() does that for us
	// except for Uncompressed Size and filters. Filters are validated
	// by the raw decoder.
	if (lzma_block_unpadded_size(block) == 0
			|| !lzma_vli_is_valid(block->uncompressed_size))
		return LZMA_PROG_ERROR;

	// Allocate and initialize *next->coder if needed.
	if (next->coder == NULL) {
		next->coder = lzma_alloc(sizeof(lzma_coder), allocator);
		if (next->coder == NULL)
			return LZMA_MEM_ERROR;

		next->code = &block_decode;
		next->end = &block_decoder_end;
		next->coder->next = LZMA_NEXT_CODER_INIT;
	}

	// Basic initializations
	next->coder->sequence = SEQ_CODE;
	next->coder->block = block;
	next->coder->compressed_size = 0;
	next->coder->uncompressed_size = 0;

	// If Compressed Size is not known, we calculate the maximum allowed
	// value so that encoded size of the Block (including Block Padding)
	// is still a valid VLI and a multiple of four.
	next->coder->compressed_limit
			= block->compressed_size == LZMA_VLI_UNKNOWN
				? (LZMA_VLI_MAX & ~LZMA_VLI_C(3))
					- block->header_size
					- lzma_check_size(block->check)
				: block->compressed_size;

	// Initialize the check. It's caller's problem if the Check ID is not
	// supported, and the Block decoder cannot verify the Check field.
	// Caller can test lzma_check_is_supported(block->check).
	next->coder->check_pos = 0;
	lzma_check_init(&next->coder->check, block->check);

	// Initialize the filter chain.
	return lzma_raw_decoder_init(&next->coder->next, allocator,
			block->filters);
}


extern LZMA_API(lzma_ret)
lzma_block_decoder(lzma_stream *strm, lzma_block *block)
{
	lzma_next_strm_init(lzma_block_decoder_init, strm, block);

	strm->internal->supported_actions[LZMA_RUN] = true;
	strm->internal->supported_actions[LZMA_FINISH] = true;

	return LZMA_OK;
}