6 files changed, 43 insertions, 14 deletions

diff --git a/src/liblzma/common/stream_decoder.c b/src/liblzma/common/stream_decoder.c
index 884c4e9d..5360d87c 100644
--- a/src/liblzma/common/stream_decoder.c
+++ b/src/liblzma/common/stream_decoder.c
@@ -294,9 +294,8 @@ stream_decode(lzma_coder *coder, lzma_allocator *allocator,
 
 		// Compare that the Stream Flags fields are identical in
 		// both Stream Header and Stream Footer.
-		if (!lzma_stream_flags_equal(&coder->stream_flags,
-				&footer_flags))
-			return LZMA_DATA_ERROR;
+		return_if_error(lzma_stream_flags_compare(
+				&coder->stream_flags, &footer_flags));
 
 		if (!coder->concatenated)
 			return LZMA_STREAM_END;
diff --git a/src/liblzma/common/stream_encoder.c b/src/liblzma/common/stream_encoder.c
index b21ee652..8748f52e 100644
--- a/src/liblzma/common/stream_encoder.c
+++ b/src/liblzma/common/stream_encoder.c
@@ -180,6 +180,7 @@ stream_encode(lzma_coder *coder, lzma_allocator *allocator,
 
 		// Encode the Stream Footer into coder->buffer.
 		const lzma_stream_flags stream_flags = {
+			.version = 0,
 			.backward_size = lzma_index_size(coder->index),
 			.check = coder->block_options.check,
 		};
@@ -247,6 +248,7 @@ lzma_stream_encoder_init(lzma_next_coder *next, lzma_allocator *allocator,
 
 	// Encode the Stream Header
 	lzma_stream_flags stream_flags = {
+		.version = 0,
 		.check = check,
 	};
 	return_if_error(lzma_stream_header_encode(
diff --git a/src/liblzma/common/stream_flags_common.c b/src/liblzma/common/stream_flags_common.c
index c44b3ff2..aaa9fe02 100644
--- a/src/liblzma/common/stream_flags_common.c
+++ b/src/liblzma/common/stream_flags_common.c
@@ -24,17 +24,31 @@ const uint8_t lzma_header_magic[6] = { 0xFF, 0x4C, 0x5A, 0x4D, 0x41, 0x00 };
 const uint8_t lzma_footer_magic[2] = { 0x59, 0x5A };
 
 
-extern LZMA_API lzma_bool
-lzma_stream_flags_equal(const lzma_stream_flags *a, const lzma_stream_flags *b)
+extern LZMA_API lzma_ret
+lzma_stream_flags_compare(
+		const lzma_stream_flags *a, const lzma_stream_flags *b)
 {
+	// We can compare only version 0 structures.
+	if (a->version != 0 || b->version != 0)
+		return LZMA_HEADER_ERROR;
+
+	// Check type
+	if ((unsigned int)(a->check) > LZMA_CHECK_ID_MAX
+			|| (unsigned int)(b->check) > LZMA_CHECK_ID_MAX)
+		return LZMA_PROG_ERROR;
+
 	if (a->check != b->check)
-		return false;
+		return LZMA_DATA_ERROR;
 
 	// Backward Sizes are compared only if they are known in both.
 	if (a->backward_size != LZMA_VLI_VALUE_UNKNOWN
-			&& b->backward_size != LZMA_VLI_VALUE_UNKNOWN
-			&& a->backward_size != b->backward_size)
-		return false;
+			&& b->backward_size != LZMA_VLI_VALUE_UNKNOWN) {
+		if (!is_backward_size_valid(a) || !is_backward_size_valid(b))
+			return LZMA_PROG_ERROR;
+
+		if (a->backward_size != b->backward_size)
+			return LZMA_DATA_ERROR;
+	}
 
-	return true;
+	return LZMA_OK;
 }
diff --git a/src/liblzma/common/stream_flags_common.h b/src/liblzma/common/stream_flags_common.h
index 6e57857b..f422b02a 100644
--- a/src/liblzma/common/stream_flags_common.h
+++ b/src/liblzma/common/stream_flags_common.h
@@ -28,4 +28,13 @@
 extern const uint8_t lzma_header_magic[6];
 extern const uint8_t lzma_footer_magic[2];
 
+
+static inline bool
+is_backward_size_valid(const lzma_stream_flags *options)
+{
+	return options->backward_size >= LZMA_BACKWARD_SIZE_MIN
+			&& options->backward_size <= LZMA_BACKWARD_SIZE_MAX
+			&& (options->backward_size & 3) == 0;
+}
+
 #endif
diff --git a/src/liblzma/common/stream_flags_decoder.c b/src/liblzma/common/stream_flags_decoder.c
index ccc1539d..a54ce813 100644
--- a/src/liblzma/common/stream_flags_decoder.c
+++ b/src/liblzma/common/stream_flags_decoder.c
@@ -27,6 +27,7 @@ stream_flags_decode(lzma_stream_flags *options, const uint8_t *in)
 	if (in[0] != 0x00 || (in[1] & 0xF0))
 		return true;
 
+	options->version = 0;
 	options->check = in[1] & 0x0F;
 
 	return false;
@@ -53,7 +54,7 @@ lzma_stream_header_decode(lzma_stream_flags *options, const uint8_t *in)
 		return LZMA_HEADER_ERROR;
 
 	// Set Backward Size to indicate unknown value. That way
-	// lzma_stream_flags_equal can be used to compare Stream Header
+	// 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_VALUE_UNKNOWN;
diff --git a/src/liblzma/common/stream_flags_encoder.c b/src/liblzma/common/stream_flags_encoder.c
index 1d736a8a..88ed81e0 100644
--- a/src/liblzma/common/stream_flags_encoder.c
+++ b/src/liblzma/common/stream_flags_encoder.c
@@ -39,6 +39,9 @@ lzma_stream_header_encode(const lzma_stream_flags *options, uint8_t *out)
 	assert(sizeof(lzma_header_magic) + LZMA_STREAM_FLAGS_SIZE
 			+ 4 == LZMA_STREAM_HEADER_SIZE);
 
+	if (options->version != 0)
+		return LZMA_HEADER_ERROR;
+
 	// Magic
 	memcpy(out, lzma_header_magic, sizeof(lzma_header_magic));
 
@@ -63,10 +66,11 @@ lzma_stream_footer_encode(const lzma_stream_flags *options, uint8_t *out)
 	assert(2 * 4 + LZMA_STREAM_FLAGS_SIZE + sizeof(lzma_footer_magic)
 			== LZMA_STREAM_HEADER_SIZE);
 
+	if (options->version != 0)
+		return LZMA_HEADER_ERROR;
+
 	// Backward Size
-	if (options->backward_size < LZMA_BACKWARD_SIZE_MIN
-			|| options->backward_size > LZMA_BACKWARD_SIZE_MAX
-			|| (options->backward_size & 3))
+	if (!is_backward_size_valid(options))
 		return LZMA_PROG_ERROR;
 
 	integer_write_32(out + 4, options->backward_size / 4 - 1);