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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_renegotiation_info.h"
#include "error/s2n_errno.h"
#include "stuffer/s2n_stuffer.h"
#include "tls/s2n_connection.h"
#include "tls/s2n_tls.h"
#include "tls/s2n_tls_parameters.h"
#include "utils/s2n_safety.h"
/**
* s2n-tls servers do NOT support renegotiation.
*
* We implement this extension to handle clients that require secure renegotiation support:
*= https://tools.ietf.org/rfc/rfc5746#4.3
*# In order to enable clients to probe, even servers that do not support
*# renegotiation MUST implement the minimal version of the extension
*# described in this document for initial handshakes, thus signaling
*# that they have been upgraded.
*/
static bool s2n_renegotiation_info_should_send(struct s2n_connection *conn);
static int s2n_renegotiation_info_send(struct s2n_connection *conn, struct s2n_stuffer *out);
static int s2n_renegotiation_info_recv(struct s2n_connection *conn, struct s2n_stuffer *extension);
static int s2n_renegotiation_info_if_missing(struct s2n_connection *conn);
const s2n_extension_type s2n_server_renegotiation_info_extension = {
.iana_value = TLS_EXTENSION_RENEGOTIATION_INFO,
.send = s2n_renegotiation_info_send,
.recv = s2n_renegotiation_info_recv,
.should_send = s2n_renegotiation_info_should_send,
.if_missing = s2n_renegotiation_info_if_missing,
/**
*= https://tools.ietf.org/rfc/rfc5746#3.6
*# Note that sending a "renegotiation_info" extension in response to a
*# ClientHello containing only the SCSV is an explicit exception to the
*# prohibition in RFC 5246, Section 7.4.1.4, on the server sending
*# unsolicited extensions and is only allowed because the client is
*# signaling its willingness to receive the extension via the
*# TLS_EMPTY_RENEGOTIATION_INFO_SCSV SCSV.
*
* This extension is technically a response extension, but doesn't
* follow any of the usual response extension rules.
* s2n-tls will therefore not treat it as a response extension.
*/
.is_response = false,
};
/**
*= https://tools.ietf.org/rfc/rfc5746#3.6
*# o If the secure_renegotiation flag is set to TRUE, the server MUST
*# include an empty "renegotiation_info" extension in the ServerHello
*# message.
*/
static bool s2n_renegotiation_info_should_send(struct s2n_connection *conn)
{
return conn && conn->secure_renegotiation && s2n_connection_get_protocol_version(conn) < S2N_TLS13;
}
/**
*= https://tools.ietf.org/rfc/rfc5746#3.6
*# o If the secure_renegotiation flag is set to TRUE, the server MUST
*# include an empty "renegotiation_info" extension in the ServerHello
*# message.
*/
static int s2n_renegotiation_info_send_initial(struct s2n_connection *conn, struct s2n_stuffer *out)
{
POSIX_GUARD(s2n_stuffer_write_uint8(out, 0));
return S2N_SUCCESS;
}
static int s2n_renegotiation_info_send_renegotiation(struct s2n_connection *conn, struct s2n_stuffer *out)
{
POSIX_ENSURE_REF(conn);
/* s2n-tls servers do not support renegotiation.
* We add the renegotiation version of this logic only for testing.
*/
POSIX_ENSURE(s2n_in_unit_test(), S2N_ERR_NOT_IN_UNIT_TEST);
/**
*= https://tools.ietf.org/rfc/rfc5746#3.7
*# This text applies if the connection's "secure_renegotiation" flag is
*# set to TRUE (if it is set to FALSE, see Section 4.4).
*/
POSIX_ENSURE(conn->secure_renegotiation, S2N_ERR_NO_RENEGOTIATION);
/**
*= https://tools.ietf.org/rfc/rfc5746#3.7
*# o The server MUST include a "renegotiation_info" extension
*# containing the saved client_verify_data and server_verify_data in
*# the ServerHello.
*/
const uint8_t verify_data_len = conn->handshake.finished_len;
POSIX_ENSURE_GT(verify_data_len, 0);
POSIX_GUARD(s2n_stuffer_write_uint8(out, verify_data_len * 2));
POSIX_GUARD(s2n_stuffer_write_bytes(out, conn->handshake.client_finished, verify_data_len));
POSIX_GUARD(s2n_stuffer_write_bytes(out, conn->handshake.server_finished, verify_data_len));
return S2N_SUCCESS;
}
static int s2n_renegotiation_info_send(struct s2n_connection *conn, struct s2n_stuffer *out)
{
if (s2n_handshake_is_renegotiation(conn)) {
POSIX_GUARD(s2n_renegotiation_info_send_renegotiation(conn, out));
} else {
POSIX_GUARD(s2n_renegotiation_info_send_initial(conn, out));
}
return S2N_SUCCESS;
}
/**
*= https://tools.ietf.org/rfc/rfc5746#3.4
*# o When a ServerHello is received, the client MUST check if it
*# includes the "renegotiation_info" extension:
*/
static int s2n_renegotiation_info_recv_initial(struct s2n_connection *conn, struct s2n_stuffer *extension)
{
POSIX_ENSURE_REF(conn);
/**
*= https://tools.ietf.org/rfc/rfc5746#3.4
*# * The client MUST then verify that the length of the
*# "renegotiated_connection" field is zero, and if it is not, MUST
*# abort the handshake (by sending a fatal handshake_failure alert).
*/
uint8_t renegotiated_connection_len = 0;
POSIX_GUARD(s2n_stuffer_read_uint8(extension, &renegotiated_connection_len));
POSIX_ENSURE(s2n_stuffer_data_available(extension) == 0, S2N_ERR_NON_EMPTY_RENEGOTIATION_INFO);
POSIX_ENSURE(renegotiated_connection_len == 0, S2N_ERR_NON_EMPTY_RENEGOTIATION_INFO);
/**
*= https://tools.ietf.org/rfc/rfc5746#3.4
*# * If the extension is present, set the secure_renegotiation flag to TRUE.
*/
conn->secure_renegotiation = 1;
return S2N_SUCCESS;
}
static int s2n_renegotiation_info_recv_renegotiation(struct s2n_connection *conn, struct s2n_stuffer *extension)
{
POSIX_ENSURE_REF(conn);
uint8_t verify_data_len = conn->handshake.finished_len;
POSIX_ENSURE_GT(verify_data_len, 0);
/**
*= https://tools.ietf.org/rfc/rfc5746#3.5
*# This text applies if the connection's "secure_renegotiation" flag is
*# set to TRUE (if it is set to FALSE, see Section 4.2).
*/
POSIX_ENSURE(conn->secure_renegotiation, S2N_ERR_NO_RENEGOTIATION);
/**
*= https://tools.ietf.org/rfc/rfc5746#3.5
*# o The client MUST then verify that the first half of the
*# "renegotiated_connection" field is equal to the saved
*# client_verify_data value, and the second half is equal to the
*# saved server_verify_data value. If they are not, the client MUST
*# abort the handshake.
*/
uint8_t renegotiated_connection_len = 0;
POSIX_GUARD(s2n_stuffer_read_uint8(extension, &renegotiated_connection_len));
POSIX_ENSURE(verify_data_len * 2 == renegotiated_connection_len, S2N_ERR_BAD_MESSAGE);
uint8_t *first_half = s2n_stuffer_raw_read(extension, verify_data_len);
POSIX_ENSURE_REF(first_half);
POSIX_ENSURE(s2n_constant_time_equals(first_half, conn->handshake.client_finished, verify_data_len),
S2N_ERR_BAD_MESSAGE);
uint8_t *second_half = s2n_stuffer_raw_read(extension, verify_data_len);
POSIX_ENSURE_REF(second_half);
POSIX_ENSURE(s2n_constant_time_equals(second_half, conn->handshake.server_finished, verify_data_len),
S2N_ERR_BAD_MESSAGE);
return S2N_SUCCESS;
}
/**
* Note that this extension must also work for SSLv3:
*= https://tools.ietf.org/rfc/rfc5746#4.5
*# Clients that support SSLv3 and offer secure renegotiation (either via SCSV or
*# "renegotiation_info") MUST accept the "renegotiation_info" extension
*# from the server, even if the server version is {0x03, 0x00}, and
*# behave as described in this specification.
*/
static int s2n_renegotiation_info_recv(struct s2n_connection *conn, struct s2n_stuffer *extension)
{
if (s2n_handshake_is_renegotiation(conn)) {
POSIX_GUARD(s2n_renegotiation_info_recv_renegotiation(conn, extension));
} else {
POSIX_GUARD(s2n_renegotiation_info_recv_initial(conn, extension));
}
return S2N_SUCCESS;
}
static int s2n_renegotiation_info_if_missing(struct s2n_connection *conn)
{
POSIX_ENSURE_REF(conn);
if (s2n_handshake_is_renegotiation(conn)) {
/**
*= https://tools.ietf.org/rfc/rfc5746#3.5
*# o When a ServerHello is received, the client MUST verify that the
*# "renegotiation_info" extension is present; if it is not, the
*# client MUST abort the handshake.
*/
POSIX_BAIL(S2N_ERR_NO_RENEGOTIATION);
} else {
/**
*= https://tools.ietf.org/rfc/rfc5746#3.4
*# * If the extension is not present, the server does not support
*# secure renegotiation; set secure_renegotiation flag to FALSE.
*# In this case, some clients may want to terminate the handshake
*# instead of continuing; see Section 4.1 for discussion.
*/
conn->secure_renegotiation = false;
/**
*= https://tools.ietf.org/rfc/rfc5746#4.1
*= type=exception
*= reason=Avoid interoperability problems
*# If clients wish to ensure that such attacks are impossible, they need
*# to terminate the connection immediately upon failure to receive the
*# extension without completing the handshake. Such clients MUST
*# generate a fatal "handshake_failure" alert prior to terminating the
*# connection. However, it is expected that many TLS servers that do
*# not support renegotiation (and thus are not vulnerable) will not
*# support this extension either, so in general, clients that implement
*# this behavior will encounter interoperability problems.
*
* TODO: https://github.com/aws/s2n-tls/issues/3528
*/
return S2N_SUCCESS;
}
}
/* Old-style extension functions -- remove after extensions refactor is complete */
int s2n_recv_server_renegotiation_info_ext(struct s2n_connection *conn, struct s2n_stuffer *extension)
{
return s2n_extension_recv(&s2n_server_renegotiation_info_extension, conn, extension);
}
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