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s2n_client_hello.c
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s2n_client_hello.c
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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_client_hello.h"
#include <stdint.h>
#include <stdlib.h>
#include <sys/param.h>
#include <time.h>
#include "api/unstable/fingerprint.h"
#include "crypto/s2n_fips.h"
#include "crypto/s2n_hash.h"
#include "crypto/s2n_rsa_signing.h"
#include "error/s2n_errno.h"
#include "stuffer/s2n_stuffer.h"
#include "tls/extensions/s2n_client_server_name.h"
#include "tls/extensions/s2n_client_supported_groups.h"
#include "tls/extensions/s2n_extension_list.h"
#include "tls/extensions/s2n_server_key_share.h"
#include "tls/s2n_alerts.h"
#include "tls/s2n_auth_selection.h"
#include "tls/s2n_cipher_preferences.h"
#include "tls/s2n_cipher_suites.h"
#include "tls/s2n_connection.h"
#include "tls/s2n_handshake_type.h"
#include "tls/s2n_security_policies.h"
#include "tls/s2n_signature_algorithms.h"
#include "tls/s2n_tls.h"
#include "utils/s2n_bitmap.h"
#include "utils/s2n_random.h"
#include "utils/s2n_safety.h"
struct s2n_client_hello *s2n_connection_get_client_hello(struct s2n_connection *conn)
{
if (conn->client_hello.parsed != 1) {
return NULL;
}
return &conn->client_hello;
}
static uint32_t min_size(struct s2n_blob *blob, uint32_t max_length)
{
return blob->size < max_length ? blob->size : max_length;
}
static S2N_RESULT s2n_generate_client_session_id(struct s2n_connection *conn)
{
RESULT_ENSURE_REF(conn);
RESULT_ENSURE_REF(conn->config);
/* Session id already generated - no-op */
if (conn->session_id_len) {
return S2N_RESULT_OK;
}
/* Only generate the session id if using tickets */
bool generate = conn->config->use_tickets;
/* TLS1.3 doesn't require session ids. The field is actually renamed to legacy_session_id.
* However, we still set a session id if dealing with troublesome middleboxes
* (middlebox compatibility mode) or if trying to use a TLS1.2 ticket.
*/
if (conn->client_protocol_version >= S2N_TLS13) {
generate = s2n_is_middlebox_compat_enabled(conn) || conn->resume_protocol_version;
}
/* Session id not needed - no-op */
if (!generate) {
return S2N_RESULT_OK;
}
/* QUIC should not allow session ids for any reason.
*
*= https://www.rfc-editor.org/rfc/rfc9001#section-8.4
*# A server SHOULD treat the receipt of a TLS ClientHello with a non-empty
*# legacy_session_id field as a connection error of type PROTOCOL_VIOLATION.
*/
RESULT_ENSURE(!conn->quic_enabled, S2N_ERR_UNSUPPORTED_WITH_QUIC);
struct s2n_blob session_id = { 0 };
RESULT_GUARD_POSIX(s2n_blob_init(&session_id, conn->session_id, S2N_TLS_SESSION_ID_MAX_LEN));
RESULT_GUARD(s2n_get_public_random_data(&session_id));
conn->session_id_len = S2N_TLS_SESSION_ID_MAX_LEN;
return S2N_RESULT_OK;
}
ssize_t s2n_client_hello_get_raw_message_length(struct s2n_client_hello *ch)
{
POSIX_ENSURE_REF(ch);
return ch->raw_message.size;
}
ssize_t s2n_client_hello_get_raw_message(struct s2n_client_hello *ch, uint8_t *out, uint32_t max_length)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(out);
uint32_t len = min_size(&ch->raw_message, max_length);
POSIX_CHECKED_MEMCPY(out, ch->raw_message.data, len);
return len;
}
ssize_t s2n_client_hello_get_cipher_suites_length(struct s2n_client_hello *ch)
{
POSIX_ENSURE_REF(ch);
return ch->cipher_suites.size;
}
int s2n_client_hello_cb_done(struct s2n_connection *conn)
{
POSIX_ENSURE_REF(conn);
POSIX_ENSURE_REF(conn->config);
POSIX_ENSURE(conn->config->client_hello_cb_mode == S2N_CLIENT_HELLO_CB_NONBLOCKING, S2N_ERR_INVALID_STATE);
POSIX_ENSURE(conn->client_hello.callback_invoked == 1, S2N_ERR_ASYNC_NOT_PERFORMED);
POSIX_ENSURE(conn->client_hello.parsed == 1, S2N_ERR_INVALID_STATE);
conn->client_hello.callback_async_blocked = 0;
conn->client_hello.callback_async_done = 1;
return S2N_SUCCESS;
}
ssize_t s2n_client_hello_get_cipher_suites(struct s2n_client_hello *ch, uint8_t *out, uint32_t max_length)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(out);
POSIX_ENSURE_REF(ch->cipher_suites.data);
uint32_t len = min_size(&ch->cipher_suites, max_length);
POSIX_CHECKED_MEMCPY(out, ch->cipher_suites.data, len);
return len;
}
ssize_t s2n_client_hello_get_extensions_length(struct s2n_client_hello *ch)
{
POSIX_ENSURE_REF(ch);
return ch->extensions.raw.size;
}
ssize_t s2n_client_hello_get_extensions(struct s2n_client_hello *ch, uint8_t *out, uint32_t max_length)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(out);
POSIX_ENSURE_REF(ch->extensions.raw.data);
uint32_t len = min_size(&ch->extensions.raw, max_length);
POSIX_CHECKED_MEMCPY(out, ch->extensions.raw.data, len);
return len;
}
int s2n_client_hello_free_raw_message(struct s2n_client_hello *client_hello)
{
POSIX_ENSURE_REF(client_hello);
POSIX_GUARD(s2n_free(&client_hello->raw_message));
/* These point to data in the raw_message stuffer,
so we don't need to free them */
client_hello->cipher_suites.data = NULL;
client_hello->extensions.raw.data = NULL;
return 0;
}
int s2n_client_hello_free(struct s2n_client_hello **ch)
{
POSIX_ENSURE_REF(ch);
if (*ch == NULL) {
return S2N_SUCCESS;
}
POSIX_ENSURE((*ch)->alloced, S2N_ERR_INVALID_ARGUMENT);
POSIX_GUARD(s2n_client_hello_free_raw_message(*ch));
POSIX_GUARD(s2n_free_object((uint8_t **) ch, sizeof(struct s2n_client_hello)));
*ch = NULL;
return S2N_SUCCESS;
}
int s2n_collect_client_hello(struct s2n_client_hello *ch, struct s2n_stuffer *source)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(source);
uint32_t size = s2n_stuffer_data_available(source);
S2N_ERROR_IF(size == 0, S2N_ERR_BAD_MESSAGE);
POSIX_GUARD(s2n_realloc(&ch->raw_message, size));
POSIX_GUARD(s2n_stuffer_read(source, &ch->raw_message));
return 0;
}
static S2N_RESULT s2n_client_hello_verify_for_retry(struct s2n_connection *conn,
struct s2n_client_hello *old_ch, struct s2n_client_hello *new_ch,
uint8_t *previous_client_random)
{
RESULT_ENSURE_REF(conn);
RESULT_ENSURE_REF(old_ch);
RESULT_ENSURE_REF(new_ch);
RESULT_ENSURE_REF(previous_client_random);
if (!s2n_is_hello_retry_handshake(conn)) {
return S2N_RESULT_OK;
}
/*
*= https://www.rfc-editor.org/rfc/rfc8446#section-4.1.2
*# The client will also send a
*# ClientHello when the server has responded to its ClientHello with a
*# HelloRetryRequest. In that case, the client MUST send the same
*# ClientHello without modification, except as follows:
*
* All of the exceptions that follow are extensions.
*/
RESULT_ENSURE(old_ch->legacy_version == new_ch->legacy_version, S2N_ERR_BAD_MESSAGE);
RESULT_ENSURE(old_ch->compression_methods.size == new_ch->compression_methods.size, S2N_ERR_BAD_MESSAGE);
RESULT_ENSURE(s2n_constant_time_equals(old_ch->compression_methods.data, new_ch->compression_methods.data,
new_ch->compression_methods.size),
S2N_ERR_BAD_MESSAGE);
/* Some clients are not compliant with TLS 1.3 RFC, and send mismatching values in their second
* ClientHello. For increased compatibility, these checks are skipped outside of tests. The
* checks are still included in tests to ensure the s2n-tls client remains compliant.
*/
if (s2n_in_test()) {
/* In the past, the s2n-tls client updated the client random in the second ClientHello
* which is not allowed by RFC8446: https://github.com/aws/s2n-tls/pull/3311. Although the
* issue was addressed, its existence means that old versions of the s2n-tls client will
* fail this validation.
*/
RESULT_ENSURE(s2n_constant_time_equals(
previous_client_random,
conn->handshake_params.client_random,
S2N_TLS_RANDOM_DATA_LEN),
S2N_ERR_BAD_MESSAGE);
/* Some clients have been found to send a mismatching legacy session ID. */
RESULT_ENSURE(old_ch->session_id.size == new_ch->session_id.size, S2N_ERR_BAD_MESSAGE);
RESULT_ENSURE(s2n_constant_time_equals(old_ch->session_id.data, new_ch->session_id.data,
new_ch->session_id.size),
S2N_ERR_BAD_MESSAGE);
/* Some clients have been found to send a mismatching cipher suite list. */
RESULT_ENSURE(old_ch->cipher_suites.size == new_ch->cipher_suites.size, S2N_ERR_BAD_MESSAGE);
RESULT_ENSURE(s2n_constant_time_equals(old_ch->cipher_suites.data, new_ch->cipher_suites.data,
new_ch->cipher_suites.size),
S2N_ERR_BAD_MESSAGE);
}
/*
* Now enforce that the extensions also exactly match,
* except for the exceptions described in the RFC.
*/
for (size_t i = 0; i < s2n_array_len(s2n_supported_extensions); i++) {
s2n_parsed_extension *old_extension = &old_ch->extensions.parsed_extensions[i];
uint32_t old_size = old_extension->extension.size;
s2n_parsed_extension *new_extension = &new_ch->extensions.parsed_extensions[i];
uint32_t new_size = new_extension->extension.size;
/* The extension type is only set if the extension is present.
* Look for a non-zero-length extension.
*/
uint16_t extension_type = 0;
if (old_size != 0) {
extension_type = old_extension->extension_type;
} else if (new_size != 0) {
extension_type = new_extension->extension_type;
} else {
continue;
}
switch (extension_type) {
/*
*= https://www.rfc-editor.org/rfc/rfc8446#section-4.1.2
*# - If a "key_share" extension was supplied in the HelloRetryRequest,
*# replacing the list of shares with a list containing a single
*# KeyShareEntry from the indicated group.
*/
case TLS_EXTENSION_KEY_SHARE:
/* Handled when parsing the key share extension */
break;
/*
*= https://www.rfc-editor.org/rfc/rfc8446#section-4.1.2
*# - Removing the "early_data" extension (Section 4.2.10) if one was
*# present. Early data is not permitted after a HelloRetryRequest.
*/
case TLS_EXTENSION_EARLY_DATA:
RESULT_ENSURE(new_size == 0, S2N_ERR_BAD_MESSAGE);
break;
/*
*= https://www.rfc-editor.org/rfc/rfc8446#section-4.1.2
*# - Including a "cookie" extension if one was provided in the
*# HelloRetryRequest.
*/
case TLS_EXTENSION_COOKIE:
/* Handled when parsing the cookie extension */
break;
/*
*= https://www.rfc-editor.org/rfc/rfc8446#section-4.1.2
*# - Updating the "pre_shared_key" extension if present by recomputing
*# the "obfuscated_ticket_age" and binder values and (optionally)
*# removing any PSKs which are incompatible with the server's
*# indicated cipher suite.
*/
case TLS_EXTENSION_PRE_SHARED_KEY:
/* Handled when parsing the psk extension */
break;
/* Some clients have been found to send mismatching supported versions in their second
* ClientHello. The extension isn't compared byte-for-byte for increased compatibility
* with these clients.
*/
case TLS_EXTENSION_SUPPORTED_VERSIONS:
/* Additional HRR validation for the supported versions extension is performed when
* parsing the extension.
*/
break;
/*
* No more exceptions.
* All other extensions must match.
*/
default:
RESULT_ENSURE(old_size == new_size, S2N_ERR_BAD_MESSAGE);
RESULT_ENSURE(s2n_constant_time_equals(
new_extension->extension.data,
old_extension->extension.data,
old_size),
S2N_ERR_BAD_MESSAGE);
}
}
return S2N_RESULT_OK;
}
S2N_RESULT s2n_client_hello_parse_raw(struct s2n_client_hello *client_hello,
uint8_t client_protocol_version[S2N_TLS_PROTOCOL_VERSION_LEN],
uint8_t client_random[S2N_TLS_RANDOM_DATA_LEN])
{
RESULT_ENSURE_REF(client_hello);
struct s2n_stuffer in_stuffer = { 0 };
RESULT_GUARD_POSIX(s2n_stuffer_init_written(&in_stuffer, &client_hello->raw_message));
struct s2n_stuffer *in = &in_stuffer;
/**
* https://tools.ietf.org/rfc/rfc8446#4.1.2
* Structure of this message:
*
* uint16 ProtocolVersion;
* opaque Random[32];
*
* uint8 CipherSuite[2];
*
* struct {
* ProtocolVersion legacy_version = 0x0303;
* Random random;
* opaque legacy_session_id<0..32>;
* CipherSuite cipher_suites<2..2^16-2>;
* opaque legacy_compression_methods<1..2^8-1>;
* Extension extensions<8..2^16-1>;
* } ClientHello;
**/
/* legacy_version */
RESULT_GUARD_POSIX(s2n_stuffer_read_bytes(in, client_protocol_version, S2N_TLS_PROTOCOL_VERSION_LEN));
/* Encode the version as a 1 byte representation of the two protocol version bytes, with the
* major version in the tens place and the minor version in the ones place. For example, the
* TLS 1.2 protocol version is 0x0303, which is encoded as S2N_TLS12 (33).
*/
client_hello->legacy_version = (client_protocol_version[0] * 10) + client_protocol_version[1];
/* random */
RESULT_GUARD_POSIX(s2n_stuffer_erase_and_read_bytes(in, client_random, S2N_TLS_RANDOM_DATA_LEN));
/* legacy_session_id */
uint8_t session_id_len = 0;
RESULT_GUARD_POSIX(s2n_stuffer_read_uint8(in, &session_id_len));
RESULT_ENSURE(session_id_len <= S2N_TLS_SESSION_ID_MAX_LEN, S2N_ERR_BAD_MESSAGE);
uint8_t *session_id = s2n_stuffer_raw_read(in, session_id_len);
RESULT_ENSURE(session_id != NULL, S2N_ERR_BAD_MESSAGE);
RESULT_GUARD_POSIX(s2n_blob_init(&client_hello->session_id, session_id, session_id_len));
/* cipher suites */
uint16_t cipher_suites_length = 0;
RESULT_GUARD_POSIX(s2n_stuffer_read_uint16(in, &cipher_suites_length));
RESULT_ENSURE(cipher_suites_length > 0, S2N_ERR_BAD_MESSAGE);
RESULT_ENSURE(cipher_suites_length % S2N_TLS_CIPHER_SUITE_LEN == 0, S2N_ERR_BAD_MESSAGE);
uint8_t *cipher_suites = s2n_stuffer_raw_read(in, cipher_suites_length);
RESULT_ENSURE(cipher_suites != NULL, S2N_ERR_BAD_MESSAGE);
RESULT_GUARD_POSIX(s2n_blob_init(&client_hello->cipher_suites, cipher_suites, cipher_suites_length));
/* legacy_compression_methods */
uint8_t compression_methods_len = 0;
RESULT_GUARD_POSIX(s2n_stuffer_read_uint8(in, &compression_methods_len));
uint8_t *compression_methods = s2n_stuffer_raw_read(in, compression_methods_len);
RESULT_ENSURE(compression_methods != NULL, S2N_ERR_BAD_MESSAGE);
RESULT_GUARD_POSIX(s2n_blob_init(&client_hello->compression_methods, compression_methods, compression_methods_len));
/* extensions */
RESULT_GUARD_POSIX(s2n_extension_list_parse(in, &client_hello->extensions));
return S2N_RESULT_OK;
}
int s2n_parse_client_hello(struct s2n_connection *conn)
{
POSIX_ENSURE_REF(conn);
/* If a retry, move the old version of the client hello
* somewhere safe so we can compare it to the new client hello later.
*/
DEFER_CLEANUP(struct s2n_client_hello previous_hello_retry = conn->client_hello,
s2n_client_hello_free_raw_message);
if (s2n_is_hello_retry_handshake(conn)) {
POSIX_CHECKED_MEMSET(&conn->client_hello, 0, sizeof(struct s2n_client_hello));
}
POSIX_GUARD(s2n_collect_client_hello(&conn->client_hello, &conn->handshake.io));
/* The ClientHello version must be TLS12 after a HelloRetryRequest */
if (s2n_is_hello_retry_handshake(conn)) {
POSIX_ENSURE_EQ(conn->client_hello_version, S2N_TLS12);
}
if (conn->client_hello_version == S2N_SSLv2) {
POSIX_GUARD(s2n_sslv2_client_hello_recv(conn));
return S2N_SUCCESS;
}
/* Save the current client_random for comparison in the case of a retry */
uint8_t previous_client_random[S2N_TLS_RANDOM_DATA_LEN] = { 0 };
POSIX_CHECKED_MEMCPY(previous_client_random, conn->handshake_params.client_random,
S2N_TLS_RANDOM_DATA_LEN);
/* Parse raw, collected client hello */
uint8_t client_protocol_version[S2N_TLS_PROTOCOL_VERSION_LEN] = { 0 };
POSIX_GUARD_RESULT(s2n_client_hello_parse_raw(&conn->client_hello,
client_protocol_version, conn->handshake_params.client_random));
/* Protocol version in the ClientHello is fixed at 0x0303(TLS 1.2) for
* future versions of TLS. Therefore, we will negotiate down if a client sends
* an unexpected value above 0x0303.
*/
conn->client_protocol_version = MIN((client_protocol_version[0] * 10) + client_protocol_version[1], S2N_TLS12);
conn->client_hello_version = conn->client_protocol_version;
/* Copy the session id to the connection. */
conn->session_id_len = conn->client_hello.session_id.size;
POSIX_CHECKED_MEMCPY(conn->session_id, conn->client_hello.session_id.data, conn->session_id_len);
POSIX_GUARD_RESULT(s2n_client_hello_verify_for_retry(conn,
&previous_hello_retry, &conn->client_hello, previous_client_random));
return S2N_SUCCESS;
}
static S2N_RESULT s2n_client_hello_parse_message_impl(struct s2n_client_hello **result,
const uint8_t *raw_message, uint32_t raw_message_size)
{
RESULT_ENSURE_REF(result);
DEFER_CLEANUP(struct s2n_blob mem = { 0 }, s2n_free);
RESULT_GUARD_POSIX(s2n_alloc(&mem, sizeof(struct s2n_client_hello)));
RESULT_GUARD_POSIX(s2n_blob_zero(&mem));
DEFER_CLEANUP(struct s2n_client_hello *client_hello = NULL, s2n_client_hello_free);
client_hello = (struct s2n_client_hello *) (void *) mem.data;
client_hello->alloced = true;
ZERO_TO_DISABLE_DEFER_CLEANUP(mem);
DEFER_CLEANUP(struct s2n_stuffer in = { 0 }, s2n_stuffer_free);
RESULT_GUARD_POSIX(s2n_stuffer_alloc(&in, raw_message_size));
RESULT_GUARD_POSIX(s2n_stuffer_write_bytes(&in, raw_message, raw_message_size));
uint8_t message_type = 0;
uint32_t message_len = 0;
RESULT_GUARD(s2n_handshake_parse_header(&in, &message_type, &message_len));
RESULT_ENSURE(message_type == TLS_CLIENT_HELLO, S2N_ERR_BAD_MESSAGE);
RESULT_ENSURE(message_len == s2n_stuffer_data_available(&in), S2N_ERR_BAD_MESSAGE);
RESULT_GUARD_POSIX(s2n_collect_client_hello(client_hello, &in));
RESULT_ENSURE(s2n_stuffer_data_available(&in) == 0, S2N_ERR_BAD_MESSAGE);
uint8_t protocol_version[S2N_TLS_PROTOCOL_VERSION_LEN] = { 0 };
uint8_t random[S2N_TLS_RANDOM_DATA_LEN] = { 0 };
RESULT_GUARD(s2n_client_hello_parse_raw(client_hello, protocol_version, random));
*result = client_hello;
ZERO_TO_DISABLE_DEFER_CLEANUP(client_hello);
return S2N_RESULT_OK;
}
struct s2n_client_hello *s2n_client_hello_parse_message(const uint8_t *raw_message, uint32_t raw_message_size)
{
struct s2n_client_hello *result = NULL;
PTR_GUARD_RESULT(s2n_client_hello_parse_message_impl(&result, raw_message, raw_message_size));
return result;
}
int s2n_process_client_hello(struct s2n_connection *conn)
{
POSIX_ENSURE_REF(conn);
POSIX_ENSURE_REF(conn->secure);
POSIX_ENSURE_REF(conn->secure->cipher_suite);
/* Client hello is parsed and config is finalized.
* Negotiate protocol version, cipher suite, ALPN, select a cert, etc. */
struct s2n_client_hello *client_hello = &conn->client_hello;
const struct s2n_security_policy *security_policy = NULL;
POSIX_GUARD(s2n_connection_get_security_policy(conn, &security_policy));
if (!s2n_connection_supports_tls13(conn) || !s2n_security_policy_supports_tls13(security_policy)) {
conn->server_protocol_version = MIN(conn->server_protocol_version, S2N_TLS12);
conn->actual_protocol_version = MIN(conn->server_protocol_version, S2N_TLS12);
}
/* Set default key exchange curve.
* This is going to be our fallback if the client has no preference.
*
* P-256 is our preferred fallback option because the TLS1.3 RFC requires
* all implementations to support it:
*
* https://tools.ietf.org/rfc/rfc8446#section-9.1
* A TLS-compliant application MUST support key exchange with secp256r1 (NIST P-256)
* and SHOULD support key exchange with X25519 [RFC7748]
*
*= https://www.rfc-editor.org/rfc/rfc4492#section-4
*# A client that proposes ECC cipher suites may choose not to include these extensions.
*# In this case, the server is free to choose any one of the elliptic curves or point formats listed in Section 5.
*
*/
const struct s2n_ecc_preferences *ecc_pref = NULL;
POSIX_GUARD(s2n_connection_get_ecc_preferences(conn, &ecc_pref));
POSIX_ENSURE_REF(ecc_pref);
POSIX_ENSURE_GT(ecc_pref->count, 0);
if (s2n_ecc_preferences_includes_curve(ecc_pref, TLS_EC_CURVE_SECP_256_R1)) {
conn->kex_params.server_ecc_evp_params.negotiated_curve = &s2n_ecc_curve_secp256r1;
} else {
/* If P-256 isn't allowed by the current security policy, instead choose
* the first / most preferred curve.
*/
conn->kex_params.server_ecc_evp_params.negotiated_curve = ecc_pref->ecc_curves[0];
}
POSIX_GUARD(s2n_extension_list_process(S2N_EXTENSION_LIST_CLIENT_HELLO, conn, &conn->client_hello.extensions));
/* After parsing extensions, select a curve and corresponding keyshare to use */
if (conn->actual_protocol_version >= S2N_TLS13) {
POSIX_GUARD(s2n_extensions_server_key_share_select(conn));
}
/* for pre TLS 1.3 connections, protocol selection is not done in supported_versions extensions, so do it here */
if (conn->actual_protocol_version < S2N_TLS13) {
conn->actual_protocol_version = MIN(conn->server_protocol_version, conn->client_protocol_version);
}
if (conn->client_protocol_version < security_policy->minimum_protocol_version) {
POSIX_GUARD(s2n_queue_reader_unsupported_protocol_version_alert(conn));
POSIX_BAIL(S2N_ERR_PROTOCOL_VERSION_UNSUPPORTED);
}
if (s2n_connection_is_quic_enabled(conn)) {
POSIX_ENSURE(conn->actual_protocol_version >= S2N_TLS13, S2N_ERR_PROTOCOL_VERSION_UNSUPPORTED);
}
/* Find potential certificate matches before we choose the cipher. */
POSIX_GUARD(s2n_conn_find_name_matching_certs(conn));
/* Save the previous cipher suite */
uint8_t previous_cipher_suite_iana[S2N_TLS_CIPHER_SUITE_LEN] = { 0 };
POSIX_CHECKED_MEMCPY(previous_cipher_suite_iana, conn->secure->cipher_suite->iana_value, S2N_TLS_CIPHER_SUITE_LEN);
/* Now choose the ciphers we have certs for. */
POSIX_GUARD(s2n_set_cipher_as_tls_server(conn, client_hello->cipher_suites.data,
client_hello->cipher_suites.size / 2));
/* Check if this is the second client hello in a hello retry handshake */
if (s2n_is_hello_retry_handshake(conn) && conn->handshake.message_number > 0) {
/**
*= https://www.rfc-editor.org/rfc/rfc8446#4.1.4
*# Servers MUST ensure that they negotiate the
*# same cipher suite when receiving a conformant updated ClientHello (if
*# the server selects the cipher suite as the first step in the
*# negotiation, then this will happen automatically).
**/
POSIX_ENSURE(s2n_constant_time_equals(previous_cipher_suite_iana, conn->secure->cipher_suite->iana_value,
S2N_TLS_CIPHER_SUITE_LEN),
S2N_ERR_BAD_MESSAGE);
}
/* If we're using a PSK, we don't need to choose a signature algorithm or certificate,
* because no additional auth is required. */
if (conn->psk_params.chosen_psk != NULL) {
return S2N_SUCCESS;
}
/* And set the signature and hash algorithm used for key exchange signatures */
POSIX_GUARD_RESULT(s2n_signature_algorithm_select(conn));
/* And finally, set the certs specified by the final auth + sig_alg combo. */
POSIX_GUARD(s2n_select_certs_for_server_auth(conn, &conn->handshake_params.our_chain_and_key));
return S2N_SUCCESS;
}
static S2N_RESULT s2n_client_hello_process_cb_response(struct s2n_connection *conn, int rc)
{
if (rc < 0) {
goto fail;
}
switch (conn->config->client_hello_cb_mode) {
case S2N_CLIENT_HELLO_CB_BLOCKING: {
if (rc) {
conn->server_name_used = 1;
}
return S2N_RESULT_OK;
}
case S2N_CLIENT_HELLO_CB_NONBLOCKING: {
if (conn->client_hello.callback_async_done) {
return S2N_RESULT_OK;
}
conn->client_hello.callback_async_blocked = 1;
RESULT_BAIL(S2N_ERR_ASYNC_BLOCKED);
}
}
fail:
/* rc < 0 */
RESULT_GUARD_POSIX(s2n_queue_reader_handshake_failure_alert(conn));
RESULT_BAIL(S2N_ERR_CANCELLED);
}
int s2n_client_hello_recv(struct s2n_connection *conn)
{
POSIX_ENSURE(!conn->client_hello.callback_async_blocked, S2N_ERR_ASYNC_BLOCKED);
/* Only parse the ClientHello once */
if (!conn->client_hello.parsed) {
POSIX_GUARD(s2n_parse_client_hello(conn));
/* Mark the collected client hello as available when parsing is done and before the client hello callback */
conn->client_hello.parsed = true;
}
/* Only invoke the ClientHello callback once.
* This means that we do NOT invoke the callback again on the second ClientHello
* in a TLS1.3 retry handshake. We explicitly check for a retry because the
* callback state may have been cleared while parsing the second ClientHello.
*/
if (!conn->client_hello.callback_invoked && !IS_HELLO_RETRY_HANDSHAKE(conn)) {
/* Mark the client hello callback as invoked to avoid calling it again. */
conn->client_hello.callback_invoked = true;
/* Do NOT move this null check. A test exists to assert that a server connection can get
* as far as the client hello callback without using its config. To do this we need a
* specific error for a null config just before the client hello callback. The test's
* assertions are weakened if this check is moved. */
POSIX_ENSURE(conn->config, S2N_ERR_CONFIG_NULL_BEFORE_CH_CALLBACK);
/* Call client_hello_cb if exists, letting application to modify s2n_connection or swap s2n_config */
if (conn->config->client_hello_cb) {
int rc = conn->config->client_hello_cb(conn, conn->config->client_hello_cb_ctx);
POSIX_GUARD_RESULT(s2n_client_hello_process_cb_response(conn, rc));
}
}
if (conn->client_hello_version != S2N_SSLv2) {
POSIX_GUARD(s2n_process_client_hello(conn));
}
return 0;
}
S2N_RESULT s2n_cipher_suite_validate_available(struct s2n_connection *conn, struct s2n_cipher_suite *cipher)
{
RESULT_ENSURE_REF(conn);
RESULT_ENSURE_REF(cipher);
RESULT_ENSURE_EQ(cipher->available, true);
RESULT_ENSURE_LTE(cipher->minimum_required_tls_version, conn->client_protocol_version);
if (s2n_connection_is_quic_enabled(conn)) {
RESULT_ENSURE_GTE(cipher->minimum_required_tls_version, S2N_TLS13);
}
return S2N_RESULT_OK;
}
int s2n_client_hello_send(struct s2n_connection *conn)
{
POSIX_ENSURE_REF(conn);
const struct s2n_security_policy *security_policy = NULL;
POSIX_GUARD(s2n_connection_get_security_policy(conn, &security_policy));
const struct s2n_cipher_preferences *cipher_preferences = security_policy->cipher_preferences;
POSIX_ENSURE_REF(cipher_preferences);
if (!s2n_connection_supports_tls13(conn) || !s2n_security_policy_supports_tls13(security_policy)) {
conn->client_protocol_version = MIN(conn->client_protocol_version, S2N_TLS12);
conn->actual_protocol_version = MIN(conn->actual_protocol_version, S2N_TLS12);
}
struct s2n_stuffer *out = &conn->handshake.io;
uint8_t client_protocol_version[S2N_TLS_PROTOCOL_VERSION_LEN] = { 0 };
uint8_t reported_protocol_version = MIN(conn->client_protocol_version, S2N_TLS12);
client_protocol_version[0] = reported_protocol_version / 10;
client_protocol_version[1] = reported_protocol_version % 10;
conn->client_hello_version = reported_protocol_version;
POSIX_GUARD(s2n_stuffer_write_bytes(out, client_protocol_version, S2N_TLS_PROTOCOL_VERSION_LEN));
struct s2n_blob client_random = { 0 };
POSIX_GUARD(s2n_blob_init(&client_random, conn->handshake_params.client_random, S2N_TLS_RANDOM_DATA_LEN));
if (!s2n_is_hello_retry_handshake(conn)) {
/* Only generate the random data for our first client hello.
* If we retry, we'll reuse the value. */
POSIX_GUARD_RESULT(s2n_get_public_random_data(&client_random));
}
POSIX_GUARD(s2n_stuffer_write(out, &client_random));
POSIX_GUARD_RESULT(s2n_generate_client_session_id(conn));
POSIX_GUARD(s2n_stuffer_write_uint8(out, conn->session_id_len));
if (conn->session_id_len > 0) {
POSIX_GUARD(s2n_stuffer_write_bytes(out, conn->session_id, conn->session_id_len));
}
/* Reserve space for size of the list of available ciphers */
struct s2n_stuffer_reservation available_cipher_suites_size;
POSIX_GUARD(s2n_stuffer_reserve_uint16(out, &available_cipher_suites_size));
/* Now, write the IANA values of every available cipher suite in our list */
struct s2n_cipher_suite *cipher = NULL;
bool tls12_is_possible = false;
for (size_t i = 0; i < security_policy->cipher_preferences->count; i++) {
cipher = cipher_preferences->suites[i];
if (s2n_result_is_error(s2n_cipher_suite_validate_available(conn, cipher))) {
continue;
}
if (cipher->minimum_required_tls_version < S2N_TLS13) {
tls12_is_possible = true;
}
POSIX_GUARD(s2n_stuffer_write_bytes(out, cipher->iana_value, S2N_TLS_CIPHER_SUITE_LEN));
}
/**
* For initial handshakes:
*= https://www.rfc-editor.org/rfc/rfc5746#3.4
*# o The client MUST include either an empty "renegotiation_info"
*# extension, or the TLS_EMPTY_RENEGOTIATION_INFO_SCSV signaling
*# cipher suite value in the ClientHello. Including both is NOT
*# RECOMMENDED.
* For maximum backwards compatibility, we choose to use the TLS_EMPTY_RENEGOTIATION_INFO_SCSV cipher suite
* rather than the "renegotiation_info" extension.
*
* For renegotiation handshakes:
*= https://www.rfc-editor.org/rfc/rfc5746#3.5
*# The SCSV MUST NOT be included.
*/
if (tls12_is_possible && !s2n_handshake_is_renegotiation(conn)) {
uint8_t renegotiation_info_scsv[S2N_TLS_CIPHER_SUITE_LEN] = { TLS_EMPTY_RENEGOTIATION_INFO_SCSV };
POSIX_GUARD(s2n_stuffer_write_bytes(out, renegotiation_info_scsv, S2N_TLS_CIPHER_SUITE_LEN));
}
/* Write size of the list of available ciphers */
uint32_t ciphers_size = 0;
POSIX_GUARD(s2n_stuffer_get_vector_size(&available_cipher_suites_size, &ciphers_size));
POSIX_ENSURE(ciphers_size > 0, S2N_ERR_INVALID_CIPHER_PREFERENCES);
POSIX_GUARD(s2n_stuffer_write_reservation(&available_cipher_suites_size, ciphers_size));
/* Zero compression methods */
POSIX_GUARD(s2n_stuffer_write_uint8(out, 1));
POSIX_GUARD(s2n_stuffer_write_uint8(out, 0));
/* Write the extensions */
POSIX_GUARD(s2n_extension_list_send(S2N_EXTENSION_LIST_CLIENT_HELLO, conn, out));
/* Once the message is complete, finish calculating the PSK binders.
*
* The PSK binders require all the sizes in the ClientHello to be written correctly,
* including the extension size and extension list size, and therefore have
* to be calculated AFTER we finish writing the entire extension list. */
POSIX_GUARD_RESULT(s2n_finish_psk_extension(conn));
/* If early data was not requested as part of the ClientHello, it never will be. */
if (conn->early_data_state == S2N_UNKNOWN_EARLY_DATA_STATE) {
POSIX_GUARD_RESULT(s2n_connection_set_early_data_state(conn, S2N_EARLY_DATA_NOT_REQUESTED));
}
return S2N_SUCCESS;
}
/*
* s2n-tls does NOT support SSLv2. However, it does support SSLv2 ClientHellos.
* Clients may send SSLv2 ClientHellos advertising higher protocol versions for
* backwards compatibility reasons. See https://tools.ietf.org/rfc/rfc2246 Appendix E.
*
* In this case, conn->client_hello_version will be SSLv2, but conn->client_protocol_version
* will likely be higher.
*
* See http://www-archive.mozilla.org/projects/security/pki/nss/ssl/draft02.html Section 2.5
* for a description of the expected SSLv2 format.
* Alternatively, the TLS1.0 RFC includes a more modern description of the format:
* https://tools.ietf.org/rfc/rfc2246 Appendix E.1
*/
int s2n_sslv2_client_hello_recv(struct s2n_connection *conn)
{
struct s2n_client_hello *client_hello = &conn->client_hello;
client_hello->sslv2 = true;
struct s2n_stuffer in_stuffer = { 0 };
POSIX_GUARD(s2n_stuffer_init(&in_stuffer, &client_hello->raw_message));
POSIX_GUARD(s2n_stuffer_skip_write(&in_stuffer, client_hello->raw_message.size));
struct s2n_stuffer *in = &in_stuffer;
const struct s2n_security_policy *security_policy = NULL;
POSIX_GUARD(s2n_connection_get_security_policy(conn, &security_policy));
if (conn->client_protocol_version < security_policy->minimum_protocol_version) {
POSIX_GUARD(s2n_queue_reader_unsupported_protocol_version_alert(conn));
POSIX_BAIL(S2N_ERR_PROTOCOL_VERSION_UNSUPPORTED);
}
conn->actual_protocol_version = MIN(conn->client_protocol_version, conn->server_protocol_version);
/* We start 5 bytes into the record */
uint16_t cipher_suites_length = 0;
POSIX_GUARD(s2n_stuffer_read_uint16(in, &cipher_suites_length));
POSIX_ENSURE(cipher_suites_length > 0, S2N_ERR_BAD_MESSAGE);
POSIX_ENSURE(cipher_suites_length % S2N_SSLv2_CIPHER_SUITE_LEN == 0, S2N_ERR_BAD_MESSAGE);
uint16_t session_id_length = 0;
POSIX_GUARD(s2n_stuffer_read_uint16(in, &session_id_length));
uint16_t challenge_length = 0;
POSIX_GUARD(s2n_stuffer_read_uint16(in, &challenge_length));
S2N_ERROR_IF(challenge_length > S2N_TLS_RANDOM_DATA_LEN, S2N_ERR_BAD_MESSAGE);
client_hello->cipher_suites.size = cipher_suites_length;
client_hello->cipher_suites.data = s2n_stuffer_raw_read(in, cipher_suites_length);
POSIX_ENSURE_REF(client_hello->cipher_suites.data);
/* Find potential certificate matches before we choose the cipher. */
POSIX_GUARD(s2n_conn_find_name_matching_certs(conn));
POSIX_GUARD(s2n_set_cipher_as_sslv2_server(conn, client_hello->cipher_suites.data,
client_hello->cipher_suites.size / S2N_SSLv2_CIPHER_SUITE_LEN));
POSIX_GUARD_RESULT(s2n_signature_algorithm_select(conn));
POSIX_GUARD(s2n_select_certs_for_server_auth(conn, &conn->handshake_params.our_chain_and_key));
S2N_ERROR_IF(session_id_length > s2n_stuffer_data_available(in), S2N_ERR_BAD_MESSAGE);
POSIX_GUARD(s2n_blob_init(&client_hello->session_id, s2n_stuffer_raw_read(in, session_id_length), session_id_length));
if (session_id_length > 0 && session_id_length <= S2N_TLS_SESSION_ID_MAX_LEN) {
POSIX_CHECKED_MEMCPY(conn->session_id, client_hello->session_id.data, session_id_length);
conn->session_id_len = (uint8_t) session_id_length;
}
struct s2n_blob b = { 0 };
POSIX_GUARD(s2n_blob_init(&b, conn->handshake_params.client_random, S2N_TLS_RANDOM_DATA_LEN));
b.data += S2N_TLS_RANDOM_DATA_LEN - challenge_length;
b.size -= S2N_TLS_RANDOM_DATA_LEN - challenge_length;
POSIX_GUARD(s2n_stuffer_read(in, &b));
return 0;
}
int s2n_client_hello_get_parsed_extension(s2n_tls_extension_type extension_type,
s2n_parsed_extensions_list *parsed_extension_list, s2n_parsed_extension **parsed_extension)
{
POSIX_ENSURE_REF(parsed_extension_list);
POSIX_ENSURE_REF(parsed_extension);
s2n_extension_type_id extension_type_id = 0;
POSIX_GUARD(s2n_extension_supported_iana_value_to_id(extension_type, &extension_type_id));
s2n_parsed_extension *found_parsed_extension = &parsed_extension_list->parsed_extensions[extension_type_id];
POSIX_ENSURE(found_parsed_extension->extension.data, S2N_ERR_EXTENSION_NOT_RECEIVED);
POSIX_ENSURE(found_parsed_extension->extension_type == extension_type, S2N_ERR_INVALID_PARSED_EXTENSIONS);
*parsed_extension = found_parsed_extension;
return S2N_SUCCESS;
}
ssize_t s2n_client_hello_get_extension_length(struct s2n_client_hello *ch, s2n_tls_extension_type extension_type)
{
POSIX_ENSURE_REF(ch);
s2n_parsed_extension *parsed_extension = NULL;
if (s2n_client_hello_get_parsed_extension(extension_type, &ch->extensions, &parsed_extension) != S2N_SUCCESS) {
return 0;
}
return parsed_extension->extension.size;
}
ssize_t s2n_client_hello_get_extension_by_id(struct s2n_client_hello *ch, s2n_tls_extension_type extension_type, uint8_t *out, uint32_t max_length)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(out);
s2n_parsed_extension *parsed_extension = NULL;
if (s2n_client_hello_get_parsed_extension(extension_type, &ch->extensions, &parsed_extension) != S2N_SUCCESS) {
return 0;
}
uint32_t len = min_size(&parsed_extension->extension, max_length);
POSIX_CHECKED_MEMCPY(out, parsed_extension->extension.data, len);
return len;
}
int s2n_client_hello_get_session_id_length(struct s2n_client_hello *ch, uint32_t *out_length)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(out_length);
*out_length = ch->session_id.size;
return S2N_SUCCESS;
}
int s2n_client_hello_get_session_id(struct s2n_client_hello *ch, uint8_t *out, uint32_t *out_length, uint32_t max_length)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(out);
POSIX_ENSURE_REF(out_length);
uint32_t len = min_size(&ch->session_id, max_length);
POSIX_CHECKED_MEMCPY(out, ch->session_id.data, len);
*out_length = len;
return S2N_SUCCESS;
}
int s2n_client_hello_get_compression_methods_length(struct s2n_client_hello *ch, uint32_t *out_length)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(out_length);
*out_length = ch->compression_methods.size;
return S2N_SUCCESS;
}
int s2n_client_hello_get_compression_methods(struct s2n_client_hello *ch, uint8_t *list, uint32_t list_length, uint32_t *out_length)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(list);
POSIX_ENSURE_REF(out_length);
POSIX_ENSURE(list_length >= ch->compression_methods.size, S2N_ERR_INSUFFICIENT_MEM_SIZE);
POSIX_CHECKED_MEMCPY(list, ch->compression_methods.data, ch->compression_methods.size);
*out_length = ch->compression_methods.size;
return S2N_SUCCESS;
}
int s2n_client_hello_get_legacy_protocol_version(struct s2n_client_hello *ch, uint8_t *out)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(out);
*out = ch->legacy_version;
return S2N_SUCCESS;
}
int s2n_client_hello_get_legacy_record_version(struct s2n_client_hello *ch, uint8_t *out)
{
POSIX_ENSURE_REF(ch);
POSIX_ENSURE_REF(out);
POSIX_ENSURE(ch->record_version_recorded, S2N_ERR_INVALID_ARGUMENT);
*out = ch->legacy_record_version;
return S2N_SUCCESS;
}
S2N_RESULT s2n_client_hello_get_raw_extension(uint16_t extension_iana,
struct s2n_blob *raw_extensions, struct s2n_blob *extension)
{
RESULT_ENSURE_REF(raw_extensions);
RESULT_ENSURE_REF(extension);
*extension = (struct s2n_blob){ 0 };
struct s2n_stuffer raw_extensions_stuffer = { 0 };
RESULT_GUARD_POSIX(s2n_stuffer_init(&raw_extensions_stuffer, raw_extensions));
RESULT_GUARD_POSIX(s2n_stuffer_skip_write(&raw_extensions_stuffer, raw_extensions->size));