1 files changed, 88 insertions, 0 deletions
diff --git a/src/liblzma/common/stream_flags_decoder.c b/src/liblzma/common/stream_flags_decoder.c
new file mode 100644
index 0000000..b8d263b
--- /dev/null
+++ b/src/liblzma/common/stream_flags_decoder.c
@@ -0,0 +1,88 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \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;
+}