Add support for a new big-endian handshake format

Because of strange dicisions in the past, fastd currently uses little endian
type and length values in its handshake. As the common network byte order is
big endian, changing the handshake format would be preferable.

This commit adds support for a new big-endian handshake. For now, fastd will
continue to send little-endian handshakes so ensure backwarts compatiblity, but
if it receives a big-endian handshake, it will respond with a big-endian one.

1 files changed, 44 insertions, 24 deletions

diff --git a/src/handshake.c b/src/handshake.c
index a55844f..7dd5b44 100644
--- a/src/handshake.c
+++ b/src/handshake.c
@@ -78,8 +78,11 @@ static inline uint32_t as_uint32(const fastd_handshake_record_t *record) {
 }
 
 /** Reads a TLV record as a 16bit integer (little endian) */
-static inline uint16_t as_uint16_le(const fastd_handshake_record_t *record) {
-	return as_uint8(record) | (uint16_t)record->data[1] << 8;
+static inline uint16_t as_uint16_endian(const fastd_handshake_record_t *record, bool little_endian) {
+	if (little_endian)
+		return as_uint8(record) | (uint16_t)record->data[1] << 8;
+	else
+		return as_uint16(record);
 }
 
 /** Reads a TLV record as a variable-length integer (little endian) */
@@ -157,7 +160,7 @@ static fastd_string_stack_t * parse_string_list(const uint8_t *data, size_t len)
 }
 
 /** Allocates and initializes a new handshake packet */
-static fastd_buffer_t new_handshake(uint8_t type, const fastd_method_info_t *method, bool with_method_list, size_t tail_space) {
+static fastd_handshake_buffer_t new_handshake(uint8_t type, bool little_endian, const fastd_method_info_t *method, bool with_method_list, size_t tail_space) {
 	size_t version_len = strlen(FASTD_VERSION);
 	size_t protocol_len = strlen(conf.protocol->name);
 	size_t method_len = method ? strlen(method->name) : 0;
@@ -168,22 +171,24 @@ static fastd_buffer_t new_handshake(uint8_t type, const fastd_method_info_t *met
 	if (with_method_list)
 		method_list = create_method_list(&method_list_len);
 
-	fastd_buffer_t buffer = fastd_buffer_alloc(sizeof(fastd_handshake_packet_t), 1,
-						   3*5 +               /* handshake type, mode, reply code */
-						   6 +                 /* MTU */
-						   4+version_len +     /* version name */
-						   4+protocol_len +    /* protocol name */
-						   4+method_len +      /* method name */
-						   4+method_list_len + /* supported method name list */
-						   tail_space);
-	fastd_handshake_packet_t *packet = buffer.data;
+	fastd_handshake_buffer_t buffer = {
+		.buffer = fastd_buffer_alloc(sizeof(fastd_handshake_packet_t), 1,
+					     3*5 +               /* handshake type, mode, reply code */
+					     6 +                 /* MTU */
+					     4+version_len +     /* version name */
+					     4+protocol_len +    /* protocol name */
+					     4+method_len +      /* method name */
+					     4+method_list_len + /* supported method name list */
+					     tail_space),
+		.little_endian = little_endian};
+	fastd_handshake_packet_t *packet = buffer.buffer.data;
 
 	packet->rsv = 0;
 	packet->tlv_len = 0;
 
 	fastd_handshake_add_uint8(&buffer, RECORD_HANDSHAKE_TYPE, type);
 	fastd_handshake_add_uint8(&buffer, RECORD_MODE, conf.mode);
-	fastd_handshake_add_uint16_le(&buffer, RECORD_MTU, conf.mtu);
+	fastd_handshake_add_uint16_endian(&buffer, RECORD_MTU, conf.mtu);
 
 	fastd_handshake_add(&buffer, RECORD_VERSION_NAME, version_len, FASTD_VERSION);
 	fastd_handshake_add(&buffer, RECORD_PROTOCOL_NAME, protocol_len, conf.protocol->name);
@@ -200,13 +205,13 @@ static fastd_buffer_t new_handshake(uint8_t type, const fastd_method_info_t *met
 }
 
 /** Allocates and initializes a new initial handshake packet */
-fastd_buffer_t fastd_handshake_new_init(size_t tail_space) {
-	return new_handshake(1, NULL, !conf.secure_handshakes, tail_space);
+fastd_handshake_buffer_t fastd_handshake_new_init(size_t tail_space) {
+	return new_handshake(1, true, NULL, !conf.secure_handshakes, tail_space);
 }
 
 /** Allocates and initializes a new reply handshake packet */
-fastd_buffer_t fastd_handshake_new_reply(uint8_t type, const fastd_method_info_t *method, bool with_method_list, size_t tail_space) {
-	fastd_buffer_t buffer = new_handshake(type, method, with_method_list, tail_space);
+fastd_handshake_buffer_t fastd_handshake_new_reply(uint8_t type, bool little_endian, const fastd_method_info_t *method, bool with_method_list, size_t tail_space) {
+	fastd_handshake_buffer_t buffer = new_handshake(type, little_endian, method, with_method_list, tail_space);
 	fastd_handshake_add_uint8(&buffer, RECORD_REPLY_CODE, 0);
 	return buffer;
 }
@@ -258,8 +263,11 @@ static void print_error(const char *prefix, const fastd_peer_address_t *remote_a
 static void send_error(fastd_socket_t *sock, const fastd_peer_address_t *local_addr, const fastd_peer_address_t *remote_addr, fastd_peer_t *peer, const fastd_handshake_t *handshake, uint8_t reply_code, uint16_t error_detail) {
 	print_error("sending", remote_addr, reply_code, error_detail);
 
-	fastd_buffer_t buffer = fastd_buffer_alloc(sizeof(fastd_handshake_packet_t), 0, 3*5 /* enough space for handshake type, reply code and error detail */);
-	fastd_handshake_packet_t *reply = buffer.data;
+	fastd_handshake_buffer_t buffer = {
+		.buffer = fastd_buffer_alloc(sizeof(fastd_handshake_packet_t), 0, 3*5 /* enough space for handshake type, reply code and error detail */),
+		.little_endian = handshake->little_endian
+	};
+	fastd_handshake_packet_t *reply = buffer.buffer.data;
 
 	reply->rsv = 0;
 	reply->tlv_len = 0;
@@ -268,7 +276,7 @@ static void send_error(fastd_socket_t *sock, const fastd_peer_address_t *local_a
 	fastd_handshake_add_uint8(&buffer, RECORD_REPLY_CODE, reply_code);
 	fastd_handshake_add_uint(&buffer, RECORD_ERROR_DETAIL, error_detail);
 
-	fastd_send_handshake(sock, local_addr, remote_addr, peer, buffer);
+	fastd_send_handshake(sock, local_addr, remote_addr, peer, buffer.buffer);
 }
 
 /** Parses the TLV records of a handshake */
@@ -297,8 +305,20 @@ static inline fastd_handshake_t parse_tlvs(const fastd_buffer_t *buffer) {
 		if (ptr+4 > end)
 			break;
 
-		uint16_t type = ptr[0] + (ptr[1] << 8);
-		uint16_t len = ptr[2] + (ptr[3] << 8);
+		uint16_t type, len;
+
+		if (!handshake.little_endian) {
+			type = ptr[1] + (ptr[0] << 8);
+			len = ptr[3] + (ptr[2] << 8);
+
+			if (type > 0xff || (type == 0 && len > 0xff))
+				handshake.little_endian = true;
+		}
+
+		if (handshake.little_endian) {
+			type = ptr[0] + (ptr[1] << 8);
+			len = ptr[2] + (ptr[3] << 8);
+		}
 
 		if (ptr+4+len > end)
 			break;
@@ -343,9 +363,9 @@ static inline bool check_records(fastd_socket_t *sock, const fastd_peer_address_
 
 	if (!conf.secure_handshakes || handshake->type > 1) {
 		if (handshake->records[RECORD_MTU].length == 2) {
-			if (as_uint16_le(&handshake->records[RECORD_MTU]) != conf.mtu) {
+			if (as_uint16_endian(&handshake->records[RECORD_MTU], handshake->little_endian) != conf.mtu) {
 				pr_warn("MTU configuration differs with peer %I: local MTU is %u, remote MTU is %u",
-					remote_addr, conf.mtu, as_uint16_le(&handshake->records[RECORD_MTU]));
+					remote_addr, conf.mtu, as_uint16_endian(&handshake->records[RECORD_MTU], handshake->little_endian));
 			}
 		}
 	}