/* * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved. * * Licensed under the Apache License, Version 2.0 (the "License"). * You may not use this file except in compliance with the License. * A copy of the License is located at * * http://aws.amazon.com/apache2.0 * * or in the "license" file accompanying this file. This file is distributed * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either * express or implied. See the License for the specific language governing * permissions and limitations under the License. */ #include "tls/s2n_server_extensions.h" #include "stuffer/s2n_stuffer.h" #include "tls/extensions/s2n_extension_list.h" #include "tls/extensions/s2n_server_supported_versions.h" #include "tls/s2n_connection.h" #include "utils/s2n_safety.h" /* An empty list will just contain the uint16_t list size */ #define S2N_EMPTY_EXTENSION_LIST_SIZE sizeof(uint16_t) int s2n_server_extensions_send(struct s2n_connection *conn, struct s2n_stuffer *out) { uint32_t data_available_before_extensions = s2n_stuffer_data_available(out); if (s2n_is_hello_retry_message(conn)) { POSIX_GUARD(s2n_extension_list_send(S2N_EXTENSION_LIST_HELLO_RETRY_REQUEST, conn, out)); } else if (conn->actual_protocol_version >= S2N_TLS13) { POSIX_GUARD(s2n_extension_list_send(S2N_EXTENSION_LIST_SERVER_HELLO_TLS13, conn, out)); } else { POSIX_GUARD(s2n_extension_list_send(S2N_EXTENSION_LIST_SERVER_HELLO_DEFAULT, conn, out)); } /* The ServerHello extension list size (uint16_t) is NOT written if the list is empty. * This is to support older clients written before extensions existed that might fail * on any unexpected bytes at the end of the ServerHello. * * This behavior is outlined in the TLS1.2 RFC: https://tools.ietf.org/html/rfc5246#appendix-A.4.1 * * This behavior does not affect TLS1.3, which always requires at least the supported_version extension * so will never produce an empty list. */ if (s2n_stuffer_data_available(out) - data_available_before_extensions == S2N_EMPTY_EXTENSION_LIST_SIZE) { POSIX_GUARD(s2n_stuffer_wipe_n(out, S2N_EMPTY_EXTENSION_LIST_SIZE)); } return S2N_SUCCESS; } int s2n_server_extensions_recv(struct s2n_connection *conn, struct s2n_stuffer *in) { s2n_parsed_extensions_list parsed_extension_list = { 0 }; POSIX_GUARD(s2n_extension_list_parse(in, &parsed_extension_list)); /** * Process supported_versions first so that we know which extensions list to use. * - If the supported_versions extension exists, then it will set server_protocol_version. * - If the supported_versions extension does not exist, then the server_protocol_version will remain * unknown and we will use the default list of allowed extension types. **/ POSIX_GUARD(s2n_extension_process(&s2n_server_supported_versions_extension, conn, &parsed_extension_list)); if (s2n_is_hello_retry_message(conn)) { /** *= https://www.rfc-editor.org/rfc/rfc8446#4.1.4 *# Otherwise, the client MUST process all extensions in the *# HelloRetryRequest */ POSIX_GUARD(s2n_extension_list_process(S2N_EXTENSION_LIST_HELLO_RETRY_REQUEST, conn, &parsed_extension_list)); } else if (conn->server_protocol_version >= S2N_TLS13) { POSIX_GUARD(s2n_extension_list_process(S2N_EXTENSION_LIST_SERVER_HELLO_TLS13, conn, &parsed_extension_list)); } else { POSIX_GUARD(s2n_extension_list_process(S2N_EXTENSION_LIST_SERVER_HELLO_DEFAULT, conn, &parsed_extension_list)); } return S2N_SUCCESS; }