1 files changed, 115 insertions, 0 deletions
diff --git a/src/liblzma/common/block_header_decoder.c b/src/liblzma/common/block_header_decoder.c
new file mode 100644
index 0000000..c4935dc
--- /dev/null
+++ b/src/liblzma/common/block_header_decoder.c
@@ -0,0 +1,115 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \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;
+}