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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/extensions/s2n_server_supported_versions.h"
#include <stdint.h>
#include <sys/param.h>
#include "tls/extensions/s2n_supported_versions.h"
#include "tls/s2n_alerts.h"
#include "tls/s2n_cipher_preferences.h"
#include "tls/s2n_tls.h"
#include "tls/s2n_tls_parameters.h"
#include "utils/s2n_safety.h"
/**
* Specified in https://tools.ietf.org/html/rfc8446#section-4.2.1
*
* "A server which negotiates TLS 1.3 MUST respond by sending a
* "supported_versions" extension containing the selected version value
* (0x0304)."
*
* Structure:
* Extension type (2 bytes)
* Extension size (2 bytes)
* Selected Version (2 byte)
**/
static int s2n_server_supported_versions_send(struct s2n_connection *conn, struct s2n_stuffer *out);
static int s2n_server_supported_versions_recv(struct s2n_connection *conn, struct s2n_stuffer *in);
const s2n_extension_type s2n_server_supported_versions_extension = {
.iana_value = TLS_EXTENSION_SUPPORTED_VERSIONS,
.is_response = true,
.send = s2n_server_supported_versions_send,
.recv = s2n_server_supported_versions_recv,
.should_send = s2n_extension_send_if_tls13_connection,
.if_missing = s2n_extension_noop_if_missing,
};
static int s2n_server_supported_versions_send(struct s2n_connection *conn, struct s2n_stuffer *out)
{
POSIX_GUARD(s2n_stuffer_write_uint8(out, conn->server_protocol_version / 10));
POSIX_GUARD(s2n_stuffer_write_uint8(out, conn->server_protocol_version % 10));
return S2N_SUCCESS;
}
static int s2n_extensions_server_supported_versions_process(struct s2n_connection *conn, struct s2n_stuffer *extension)
{
uint8_t highest_supported_version = conn->client_protocol_version;
uint8_t minimum_supported_version = s2n_unknown_protocol_version;
POSIX_GUARD_RESULT(s2n_connection_get_minimum_supported_version(conn, &minimum_supported_version));
POSIX_ENSURE(highest_supported_version >= minimum_supported_version, S2N_ERR_PROTOCOL_VERSION_UNSUPPORTED);
uint8_t server_version_parts[S2N_TLS_PROTOCOL_VERSION_LEN];
POSIX_GUARD(s2n_stuffer_read_bytes(extension, server_version_parts, S2N_TLS_PROTOCOL_VERSION_LEN));
uint16_t server_version = (server_version_parts[0] * 10) + server_version_parts[1];
/**
*= https://tools.ietf.org/rfc/rfc8446#4.1.4
*# The value of selected_version in the HelloRetryRequest
*# "supported_versions" extension MUST be retained in the ServerHello,
*# and a client MUST abort the handshake with an "illegal_parameter"
*# alert if the value changes.
**/
if (s2n_is_hello_retry_handshake(conn) && !s2n_is_hello_retry_message(conn)) {
POSIX_ENSURE(conn->server_protocol_version == server_version,
S2N_ERR_BAD_MESSAGE);
}
POSIX_ENSURE_GTE(server_version, S2N_TLS13);
POSIX_ENSURE_LTE(server_version, highest_supported_version);
POSIX_ENSURE_GTE(server_version, minimum_supported_version);
conn->server_protocol_version = server_version;
return S2N_SUCCESS;
}
static int s2n_server_supported_versions_recv(struct s2n_connection *conn, struct s2n_stuffer *in)
{
if (s2n_connection_get_protocol_version(conn) < S2N_TLS13) {
return S2N_SUCCESS;
}
S2N_ERROR_IF(s2n_extensions_server_supported_versions_process(conn, in) < 0, S2N_ERR_BAD_MESSAGE);
return S2N_SUCCESS;
}
/* Old-style extension functions -- remove after extensions refactor is complete */
int s2n_extensions_server_supported_versions_size(struct s2n_connection *conn)
{
return 6;
}
int s2n_extensions_server_supported_versions_recv(struct s2n_connection *conn, struct s2n_stuffer *extension)
{
return s2n_extension_recv(&s2n_server_supported_versions_extension, conn, extension);
}
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