Use the rsv2 field in the handshake header as an optional length field to facilitate future extensions

2 files changed, 44 insertions, 40 deletions

diff --git a/src/handshake.c b/src/handshake.c
index 47da0e4..82d47b8 100644
--- a/src/handshake.c
+++ b/src/handshake.c
@@ -98,10 +98,10 @@ fastd_buffer_t fastd_handshake_new_init(fastd_context_t *ctx, size_t tail_space)
 						   4+method_list_len + /* supported method name list */
 						   tail_space
 						   );
-	fastd_handshake_packet_t *request = buffer.data;
+	fastd_handshake_packet_t *packet = buffer.data;
 
-	request->rsv1 = 0;
-	request->rsv2 = 0;
+	packet->rsv = 0;
+	packet->tlv_len = 0;
 
 	fastd_handshake_add_uint8(ctx, &buffer, RECORD_HANDSHAKE_TYPE, 1);
 	fastd_handshake_add_uint8(ctx, &buffer, RECORD_MODE, ctx->conf->mode);
@@ -146,10 +146,10 @@ fastd_buffer_t fastd_handshake_new_reply(fastd_context_t *ctx, const fastd_hands
 						   extra_size +
 						   tail_space
 						   );
-	fastd_handshake_packet_t *request = buffer.data;
+	fastd_handshake_packet_t *packet = buffer.data;
 
-	request->rsv1 = 0;
-	request->rsv2 = 0;
+	packet->rsv = 0;
+	packet->tlv_len = 0;
 
 	fastd_handshake_add_uint8(ctx, &buffer, RECORD_HANDSHAKE_TYPE, AS_UINT8(handshake->records[RECORD_HANDSHAKE_TYPE])+1);
 	fastd_handshake_add_uint8(ctx, &buffer, RECORD_REPLY_CODE, 0);
@@ -186,15 +186,27 @@ void fastd_handshake_handle(fastd_context_t *ctx, fastd_socket_t *sock, const fa
 	fastd_handshake_t handshake = { .buffer = buffer };
 	fastd_handshake_packet_t *packet = buffer.data;
 
-	uint8_t *ptr = packet->tlv_data;
+	size_t len = buffer.len - sizeof(fastd_handshake_packet_t);
+	if (packet->tlv_len) {
+		size_t tlv_len = ntohs(packet->tlv_len);
+		if (tlv_len > len) {
+			pr_warn(ctx, "received a short handshake from %I", remote_addr);
+			goto end_free;
+		}
+
+		len = tlv_len;
+	}
+
+	uint8_t *ptr = packet->tlv_data, *end = packet->tlv_data + len;
+
 	while (true) {
-		if (ptr+4 > (uint8_t*)buffer.data + buffer.len)
+		if (ptr+4 > end)
 			break;
 
 		uint16_t type = ptr[0] + (ptr[1] << 8);
 		uint16_t len = ptr[2] + (ptr[3] << 8);
 
-		if (ptr+4+len > (uint8_t*)buffer.data + buffer.len)
+		if (ptr+4+len > end)
 			break;
 
 		if (type < RECORD_MAX) {
@@ -292,8 +304,8 @@ void fastd_handshake_handle(fastd_context_t *ctx, fastd_socket_t *sock, const fa
 			fastd_buffer_t reply_buffer = fastd_buffer_alloc(ctx, sizeof(fastd_handshake_packet_t), 0, 3*5 /* enough space for handshake type, reply code and error detail */);
 			fastd_handshake_packet_t *reply = reply_buffer.data;
 
-			reply->rsv1 = 0;
-			reply->rsv2 = 0;
+			reply->rsv = 0;
+			reply->tlv_len = 0;
 
 			fastd_handshake_add_uint8(ctx, &reply_buffer, RECORD_HANDSHAKE_TYPE, 2);
 			fastd_handshake_add_uint8(ctx, &reply_buffer, RECORD_REPLY_CODE, reply_code);
diff --git a/src/handshake.h b/src/handshake.h
index 2fae1ad..e548be3 100644
--- a/src/handshake.h
+++ b/src/handshake.h
@@ -59,8 +59,8 @@ typedef enum fastd_reply_code {
 
 
 typedef struct __attribute__((__packed__)) fastd_handshake_packet {
-	uint8_t rsv1;
-	uint16_t rsv2;
+	uint8_t rsv;
+	uint16_t tlv_len;
 	uint8_t tlv_data[];
 } fastd_handshake_packet_t;
 
@@ -82,50 +82,42 @@ fastd_buffer_t fastd_handshake_new_reply(fastd_context_t *ctx, const fastd_hands
 void fastd_handshake_handle(fastd_context_t *ctx, fastd_socket_t *sock, const fastd_peer_address_t *local_addr, const fastd_peer_address_t *remote_addr, fastd_peer_t *peer, fastd_buffer_t buffer);
 
 
-static inline void fastd_handshake_add(fastd_context_t *ctx, fastd_buffer_t *buffer, fastd_handshake_record_type_t type, size_t len, const void *data) {
-	if ((uint8_t*)buffer->data + buffer->len + 4 + len > (uint8_t*)buffer->base + buffer->base_len)
+static inline uint8_t* fastd_handshake_extend(fastd_context_t *ctx, fastd_buffer_t *buffer, fastd_handshake_record_type_t type, size_t len) {
+	uint8_t *dst = buffer->data + buffer->len;
+
+	if (buffer->data + buffer->len + 4 + len > buffer->base + buffer->base_len)
 		exit_bug(ctx, "not enough buffer allocated for handshake");
 
-	uint8_t *dst = (uint8_t*)buffer->data + buffer->len;
+	buffer->len += 4 + len;
+
+	fastd_handshake_packet_t *packet = buffer->data;
+	packet->tlv_len = htons(ntohs(packet->tlv_len) + 4 + len);
 
 	dst[0] = type;
 	dst[1] = type >> 8;
 	dst[2] = len;
 	dst[3] = len >> 8;
-	memcpy(dst+4, data, len);
 
-	buffer->len += 4 + len;
+	return dst+4;
 }
 
-static inline void fastd_handshake_add_uint8(fastd_context_t *ctx, fastd_buffer_t *buffer, fastd_handshake_record_type_t type, uint8_t value) {
-	if ((uint8_t*)buffer->data + buffer->len + 5 > (uint8_t*)buffer->base + buffer->base_len)
-		exit_bug(ctx, "not enough buffer allocated for handshake");
+static inline void fastd_handshake_add(fastd_context_t *ctx, fastd_buffer_t *buffer, fastd_handshake_record_type_t type, size_t len, const void *data) {
+	uint8_t *dst = fastd_handshake_extend(ctx, buffer, type, len);
 
-	uint8_t *dst = (uint8_t*)buffer->data + buffer->len;
+	memcpy(dst, data, len);
+}
 
-	dst[0] = type;
-	dst[1] = type >> 8;
-	dst[2] = 1;
-	dst[3] = 0;
-	dst[4] = value;
+static inline void fastd_handshake_add_uint8(fastd_context_t *ctx, fastd_buffer_t *buffer, fastd_handshake_record_type_t type, uint8_t value) {
+	uint8_t *dst = fastd_handshake_extend(ctx, buffer, type, 1);
 
-	buffer->len += 5;
+	dst[0] = value;
 }
 
 static inline void fastd_handshake_add_uint16(fastd_context_t *ctx, fastd_buffer_t *buffer, fastd_handshake_record_type_t type, uint16_t value) {
-	if ((uint8_t*)buffer->data + buffer->len + 6 > (uint8_t*)buffer->base + buffer->base_len)
-		exit_bug(ctx, "not enough buffer allocated for handshake");
-
-	uint8_t *dst = (uint8_t*)buffer->data + buffer->len;
-
-	dst[0] = type;
-	dst[1] = type >> 8;
-	dst[2] = 2;
-	dst[3] = 0;
-	dst[4] = value;
-	dst[5] = value >> 8;
+	uint8_t *dst = fastd_handshake_extend(ctx, buffer, type, 2);
 
-	buffer->len += 6;
+	dst[0] = value;
+	dst[1] = value >> 8;
 }