TLS 1.3: Do not send handshake data in handshake step handlers
Send data (call to mbedtls_ssl_flush_output()) only from
the loop over the handshake steps. That way, we do not
have to take care of the partial writings (MBEDTLS_ERR_SSL_WANT_WRITE
error code) on the network in handshake step handlers.
Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 9ed5dfa..6735000 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -1231,10 +1231,11 @@
int mbedtls_ssl_fetch_input( mbedtls_ssl_context *ssl, size_t nb_want );
int mbedtls_ssl_write_handshake_msg_ext( mbedtls_ssl_context *ssl,
- int update_checksum );
+ int update_checksum,
+ uint8_t force_flush );
static inline int mbedtls_ssl_write_handshake_msg( mbedtls_ssl_context *ssl )
{
- return( mbedtls_ssl_write_handshake_msg_ext( ssl, 1 /* update checksum */ ) );
+ return( mbedtls_ssl_write_handshake_msg_ext( ssl, 1 /* update checksum */, 1 /* force flush */ ) );
}
int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, uint8_t force_flush );
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 5f80ed5..5105625 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -2368,7 +2368,8 @@
* - ssl->out_msg: the record contents (handshake headers + content)
*/
int mbedtls_ssl_write_handshake_msg_ext( mbedtls_ssl_context *ssl,
- int update_checksum )
+ int update_checksum,
+ uint8_t force_flush )
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
const size_t hs_len = ssl->out_msglen - 4;
@@ -2495,7 +2496,7 @@
else
#endif
{
- if( ( ret = mbedtls_ssl_write_record( ssl, SSL_FORCE_FLUSH ) ) != 0 )
+ if( ( ret = mbedtls_ssl_write_record( ssl, force_flush ) ) != 0 )
{
MBEDTLS_SSL_DEBUG_RET( 1, "ssl_write_record", ret );
return( ret );
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index adb18ab..f3e5a0a 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -2693,6 +2693,21 @@
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+ /*
+ * We may have not been able to send to the peer all the handshake data
+ * that were written into the output buffer by the previous handshake step:
+ * the write to the network callback returned with the
+ * #MBEDTLS_ERR_SSL_WANT_WRITE error code.
+ * We proceed to the next handshake step only when all data from the
+ * previous one have been sent to the peer, thus we make sure that this is
+ * the case here by calling `mbedtls_ssl_flush_output()`. The function may
+ * return with the #MBEDTLS_ERR_SSL_WANT_WRITE error code in which case
+ * we have to wait before to go ahead.
+ * In the case of TLS 1.3, handshake step handlers do not send data to the
+ * peer. Data are only sent here and through
+ * `mbedtls_ssl_handle_pending_alert` in case an error that triggered an
+ * alert occured.
+ */
if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
return( ret );
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 4fee3b0..a54207c 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -103,7 +103,7 @@
/* Add reserved 4 bytes for handshake header */
msg_with_header_len = msg_len + 4;
ssl->out_msglen = msg_with_header_len;
- MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_write_handshake_msg_ext( ssl, 0 ) );
+ MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_write_handshake_msg_ext( ssl, 0, 0 ) );
cleanup:
return( ret );
@@ -1483,7 +1483,6 @@
MBEDTLS_SSL_PROC_CHK( ssl_tls13_finalize_finished_message( ssl ) );
MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_tls13_finish_handshake_msg( ssl,
buf_len, msg_len ) );
- MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_flush_output( ssl ) );
cleanup:
@@ -1564,8 +1563,6 @@
MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write change cipher spec" ) );
- MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_flush_output( ssl ) );
-
/* Write CCS message */
MBEDTLS_SSL_PROC_CHK( ssl_tls13_write_change_cipher_spec_body(
ssl, ssl->out_msg,
@@ -1578,7 +1575,7 @@
MBEDTLS_SSL_PROC_CHK( ssl_tls13_finalize_change_cipher_spec( ssl ) );
/* Dispatch message */
- MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_write_record( ssl, 1 ) );
+ MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_write_record( ssl, 0 ) );
cleanup: