record: make CCS handling stricter in TLS 1.3

In TLS 1.3, the change_cipher_spec messages received under the
following conditions should be treated as unexpected record type:
containing value other than 0x01, or received after the handshake.

Signed-off-by: Daiki Ueno <dueno@redhat.com>

2 files changed, 24 insertions, 2 deletions

diff --git a/lib/record.c b/lib/record.c
index 19f5b52282..73c484ed56 100644
--- a/lib/record.c
+++ b/lib/record.c
@@ -1331,8 +1331,15 @@ _gnutls_recv_in_buffers(gnutls_session_t session, content_type_t type,
 	if (bufel == NULL)
 		return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 
-	if (vers && vers->tls13_sem && record.type == GNUTLS_CHANGE_CIPHER_SPEC &&
-	    record.length == 1 && session->internals.handshake_in_progress) {
+	if (vers && vers->tls13_sem && record.type == GNUTLS_CHANGE_CIPHER_SPEC) {
+		/* if the CCS has value other than 0x01, or arrives
+		 * after Finished, abort the connection */
+		if (record.length != 1 ||
+		    *((uint8_t *) _mbuffer_get_udata_ptr(bufel) +
+		      record.header_size) != 0x01 ||
+		    !session->internals.handshake_in_progress)
+			return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET);
+
 		_gnutls_read_log("discarding change cipher spec in TLS1.3\n");
 		/* we use the same mechanism to retry as when
 		 * receiving multiple empty TLS packets */
diff --git a/tests/tls13/change_cipher_spec.c b/tests/tls13/change_cipher_spec.c
index 1a9b80c817..09ef786789 100644
--- a/tests/tls13/change_cipher_spec.c
+++ b/tests/tls13/change_cipher_spec.c
@@ -134,6 +134,11 @@ static void client(int fd, unsigned ccs_check)
 	if (ret < 0)
 		fail("client: recv did not succeed as expected: %s\n", gnutls_strerror(ret));
 
+	/* send change cipher spec, this should fail in the server */
+	do {
+		ret = send(fd, "\x14\x03\x03\x00\x01\x01", 6, 0);
+	} while(ret == -1 && (errno == EINTR || errno == EAGAIN));
+
 	close(fd);
 
 	gnutls_deinit(session);
@@ -217,6 +222,7 @@ static void server(int fd, unsigned ccs_check)
 	int ret;
 	gnutls_session_t session;
 	gnutls_certificate_credentials_t x509_cred;
+	char buf[64];
 
 	/* this must be called once in the program
 	 */
@@ -276,6 +282,15 @@ static void server(int fd, unsigned ccs_check)
 	if (ret < 0)
 		fail("server: gnutls_record_send did not succeed as expected: %s\n", gnutls_strerror(ret));
 
+	/* receive CCS and fail */
+	do {
+		ret = gnutls_record_recv(session, buf, sizeof(buf));
+	} while (ret == GNUTLS_E_AGAIN || ret == GNUTLS_E_INTERRUPTED);
+
+	if (ret != GNUTLS_E_UNEXPECTED_PACKET)
+		fail("server: incorrect alert sent: %d != %d\n",
+		     ret, GNUTLS_E_UNEXPECTED_PACKET);
+
 	close(fd);
 	gnutls_deinit(session);