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/*
* 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 "tls/extensions/s2n_extension_list.h"
#include "tls/extensions/s2n_server_supported_versions.h"
#include "tls/s2n_connection.h"
#include "stuffer/s2n_stuffer.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://tools.ietf.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;
}
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