TLS 1.3: Add pre_share_key last ext check
From RFC, pre_share_key must be the last one.
Add check for it. And with/without psk, it should
be check
@@ -1037,6 +1037,23 @@ static int ssl_tls13_parse_client_hello( mbedtls_ssl_context *ssl,
size_t extension_data_len;
const unsigned char *extension_data_end;
+ /* RFC 8446, page 57
+ *
+ * The "pre_shared_key" extension MUST be the last extension in the
+ * ClientHello (this facilitates implementation as described below).
+ * Servers MUST check that it is the last extension and otherwise fail
+ * the handshake with an "illegal_parameter" alert.
+ */
+ if( ssl->handshake->extensions_present & MBEDTLS_SSL_EXT_PRE_SHARED_KEY )
+ {
+ MBEDTLS_SSL_DEBUG_MSG(
+ 3, ( "pre_shared_key is not last extension." ) );
+ MBEDTLS_SSL_PEND_FATAL_ALERT(
+ MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER,
+ MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE );
+ return( MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE );
+ }
+
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 );
@@ -1146,19 +1163,18 @@ static int ssl_tls13_parse_client_hello( mbedtls_ssl_context *ssl,
break;
#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
-#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
case MBEDTLS_TLS_EXT_PRE_SHARED_KEY:
MBEDTLS_SSL_DEBUG_MSG( 3, ( "found pre_shared_key extension" ) );
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
/* Delay processing of the PSK identity once we have
* found out which algorithms to use. We keep a pointer
* to the buffer and the size for later processing.
*/
pre_shared_key_ext_start = p;
pre_shared_key_ext_end = extension_data_end;
-
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
ssl->handshake->extensions_present |= MBEDTLS_SSL_EXT_PRE_SHARED_KEY;
break;
-#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
#if defined(MBEDTLS_SSL_ALPN)
case MBEDTLS_TLS_EXT_ALPN:
@@ -1231,13 +1247,6 @@ static int ssl_tls13_parse_client_hello( mbedtls_ssl_context *ssl,
ret );
return( ret );
}
- /* If pre_shared_key is not last extension */
- if( p - pre_shared_key_ext_end )
- {
- ssl->handshake->update_checksum( ssl,
- pre_shared_key_ext_end,
- p - pre_shared_key_ext_end );
- }
}
else
#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
