Add logic to switch to TLS 1.2
Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index fc8ffa7..0f7448f 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -710,6 +710,75 @@
/*
* Functions for parsing and processing Server Hello
*/
+static int ssl_tls13_is_supported_versions_ext_present(
+ mbedtls_ssl_context *ssl,
+ const unsigned char *buf,
+ const unsigned char *end )
+{
+ const unsigned char *p = buf;
+ size_t legacy_session_id_echo_len;
+ size_t extensions_len;
+ const unsigned char *extensions_end;
+
+ /*
+ * Check there is enough data to access the legacy_session_id_echo vector
+ * length.
+ * - legacy_version, 2 bytes
+ * - random MBEDTLS_SERVER_HELLO_RANDOM_LEN bytes
+ * - legacy_session_id_echo 1 byte
+ */
+ MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, MBEDTLS_SERVER_HELLO_RANDOM_LEN + 3 );
+ p += MBEDTLS_SERVER_HELLO_RANDOM_LEN + 2;
+ legacy_session_id_echo_len = *p;
+
+ /*
+ * Jump to the extensions, jumping over:
+ * - legacy_session_id_echo (legacy_session_id_echo_len + 1) bytes
+ * - cipher_suite 2 bytes
+ * - legacy_compression_method 1 byte
+ */
+ p += legacy_session_id_echo_len + 4;
+
+ /* Case of no extension */
+ if( p == end )
+ return( 0 );
+
+ /* ...
+ * Extension extensions<6..2^16-1>;
+ * ...
+ * struct {
+ * ExtensionType extension_type; (2 bytes)
+ * opaque extension_data<0..2^16-1>;
+ * } Extension;
+ */
+ MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, 2 );
+ extensions_len = MBEDTLS_GET_UINT16_BE( p, 0 );
+ p += 2;
+
+ /* Check extensions do not go beyond the buffer of data. */
+ MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, extensions_len );
+ extensions_end = p + extensions_len;
+
+ while( p < extensions_end )
+ {
+ unsigned int extension_type;
+ size_t extension_data_len;
+
+ MBEDTLS_SSL_CHK_BUF_READ_PTR( p, extensions_end, 4 );
+ extension_type = MBEDTLS_GET_UINT16_BE( p, 0 );
+ extension_data_len = MBEDTLS_GET_UINT16_BE( p, 2 );
+ p += 4;
+
+ if( extension_type == MBEDTLS_TLS_EXT_SUPPORTED_VERSIONS )
+ return( 1 );
+
+ MBEDTLS_SSL_CHK_BUF_READ_PTR( p, extensions_end, extension_data_len );
+ p += extension_data_len;
+ }
+
+ return( 0 );
+}
+
/* Returns a negative value on failure, and otherwise
* - SSL_SERVER_HELLO_COORDINATE_HELLO or
* - SSL_SERVER_HELLO_COORDINATE_HRR
@@ -755,8 +824,10 @@
/* Fetch and preprocess
* Returns a negative value on failure, and otherwise
* - SSL_SERVER_HELLO_COORDINATE_HELLO or
- * - SSL_SERVER_HELLO_COORDINATE_HRR
+ * - SSL_SERVER_HELLO_COORDINATE_HRR or
+ * - SSL_SERVER_HELLO_COORDINATE_TLS1_2
*/
+#define SSL_SERVER_HELLO_COORDINATE_TLS1_2 2
static int ssl_tls13_server_hello_coordinate( mbedtls_ssl_context *ssl,
unsigned char **buf,
size_t *buf_len )
@@ -767,6 +838,36 @@
MBEDTLS_SSL_HS_SERVER_HELLO,
buf, buf_len ) );
+ MBEDTLS_SSL_PROC_CHK_NEG( ssl_tls13_is_supported_versions_ext_present(
+ ssl, *buf, *buf + *buf_len ) );
+ if( ret == 0 )
+ {
+ /* If the supported versions extension is not present but we were
+ * expecting it, abort the handshake. Otherwise, switch to TLS 1.2
+ * handshake.
+ */
+ if( ssl->handshake->min_minor_ver > MBEDTLS_SSL_MINOR_VERSION_3 )
+ {
+ MBEDTLS_SSL_PEND_FATAL_ALERT( MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER,
+ MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER );
+ return( MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER );
+ }
+
+ ssl->keep_current_message = 1;
+ ssl->minor_ver = MBEDTLS_SSL_MINOR_VERSION_3;
+ mbedtls_ssl_add_hs_msg_to_checksum( ssl, MBEDTLS_SSL_HS_SERVER_HELLO,
+ *buf, *buf_len );
+
+ if( mbedtls_ssl_conf_tls13_some_ephemeral_enabled( ssl ) )
+ {
+ ret = ssl_tls13_reset_key_share( ssl );
+ if( ret != 0 )
+ return( ret );
+ }
+
+ return( SSL_SERVER_HELLO_COORDINATE_TLS1_2 );
+ }
+
ret = ssl_server_hello_is_hrr( ssl, *buf, *buf + *buf_len );
switch( ret )
{
@@ -888,7 +989,6 @@
const unsigned char *extensions_end;
uint16_t cipher_suite;
const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
- int supported_versions_ext_found = 0;
int fatal_alert = 0;
/*
@@ -1068,10 +1168,6 @@
break;
case MBEDTLS_TLS_EXT_SUPPORTED_VERSIONS:
- supported_versions_ext_found = 1;
- MBEDTLS_SSL_DEBUG_MSG( 3,
- ( "found supported_versions extension" ) );
-
ret = ssl_tls13_parse_supported_versions_ext( ssl,
p,
extension_data_end );
@@ -1122,13 +1218,6 @@
p += extension_data_len;
}
- if( !supported_versions_ext_found )
- {
- MBEDTLS_SSL_DEBUG_MSG( 1, ( "supported_versions not found" ) );
- fatal_alert = MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER;
- goto cleanup;
- }
-
cleanup:
if( fatal_alert == MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT )
@@ -1317,6 +1406,12 @@
else
is_hrr = ( ret == SSL_SERVER_HELLO_COORDINATE_HRR );
+ if( ret == SSL_SERVER_HELLO_COORDINATE_TLS1_2 )
+ {
+ ret = 0;
+ goto cleanup;
+ }
+
MBEDTLS_SSL_PROC_CHK( ssl_tls13_parse_server_hello( ssl, buf,
buf + buf_len,
is_hrr ) );