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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 <sys/param.h>
#include "error/s2n_errno.h"
#include "tls/s2n_connection.h"
#include "tls/s2n_key_update.h"
#include "tls/s2n_tls.h"
#include "utils/s2n_safety.h"
S2N_RESULT s2n_post_handshake_process(struct s2n_connection *conn, struct s2n_stuffer *in, uint8_t message_type)
{
RESULT_ENSURE_REF(conn);
switch (message_type) {
case TLS_KEY_UPDATE:
RESULT_GUARD_POSIX(s2n_key_update_recv(conn, in));
break;
case TLS_SERVER_NEW_SESSION_TICKET:
RESULT_GUARD(s2n_tls13_server_nst_recv(conn, in));
break;
case TLS_HELLO_REQUEST:
RESULT_GUARD(s2n_client_hello_request_recv(conn));
break;
case TLS_CERT_REQ:
/*
* s2n-tls does not support post-handshake authentication.
*
*= https://tools.ietf.org/rfc/rfc8446#section-4.6.2
*# A client that receives a CertificateRequest message without having
*# sent the "post_handshake_auth" extension MUST send an
*# "unexpected_message" fatal alert.
*/
RESULT_BAIL(S2N_ERR_BAD_MESSAGE);
default:
/* All other messages are unexpected */
RESULT_BAIL(S2N_ERR_BAD_MESSAGE);
}
return S2N_RESULT_OK;
}
/*
* Read a handshake message from conn->in.
*
* Handshake messages can be fragmented, meaning that a single message
* may be split between multiple records. conn->in only holds a single
* record at a time, so we may need to call this method multiple
* times to construct the complete message. We store the partial message
* in conn->post_handshake.in between calls.
*/
S2N_RESULT s2n_post_handshake_message_recv(struct s2n_connection *conn)
{
RESULT_ENSURE_REF(conn);
struct s2n_stuffer *in = &conn->in;
struct s2n_stuffer *message = &conn->post_handshake.in;
uint8_t message_type = 0;
uint32_t message_len = 0;
/* We always start reading from the beginning of the message.
* Reset the read progress, but keep the write progress since
* there may already be a partial message stored in `message`.
*/
RESULT_GUARD_POSIX(s2n_stuffer_reread(message));
/* At minimum, the message stuffer needs to have enough space to read the header.
* For small messages like KeyUpdate and HelloRequest, this is all the space we will need.
*/
if (s2n_stuffer_is_freed(message)) {
struct s2n_blob b = { 0 };
RESULT_GUARD_POSIX(s2n_blob_init(&b, conn->post_handshake.header_in,
sizeof(conn->post_handshake.header_in)));
RESULT_GUARD_POSIX(s2n_stuffer_init(message, &b));
}
/* Try to copy the header into the message stuffer.
* The message stuffer may already contain some or all of the header if
* we have read fragments of this message from previous records.
*/
if (s2n_stuffer_data_available(message) < TLS_HANDSHAKE_HEADER_LENGTH) {
uint32_t remaining = TLS_HANDSHAKE_HEADER_LENGTH - s2n_stuffer_data_available(message);
uint32_t to_read = MIN(remaining, s2n_stuffer_data_available(in));
RESULT_GUARD_POSIX(s2n_stuffer_copy(in, message, to_read));
}
RESULT_ENSURE(s2n_stuffer_data_available(message) >= TLS_HANDSHAKE_HEADER_LENGTH, S2N_ERR_IO_BLOCKED);
/* Parse the header */
RESULT_GUARD(s2n_handshake_parse_header(message, &message_type, &message_len));
RESULT_ENSURE(message_len == 0 || s2n_stuffer_data_available(in), S2N_ERR_IO_BLOCKED);
RESULT_ENSURE(message_len <= S2N_MAXIMUM_HANDSHAKE_MESSAGE_LENGTH, S2N_ERR_BAD_MESSAGE);
/* If the message body is not fragmented, just process it directly from conn->in.
* This will be the most common case, and does not require us to allocate any new memory.
*/
if (s2n_stuffer_data_available(message) == 0 && s2n_stuffer_data_available(in) >= message_len) {
struct s2n_stuffer full_message = { 0 };
struct s2n_blob full_message_blob = { 0 };
RESULT_GUARD_POSIX(s2n_blob_init(&full_message_blob, s2n_stuffer_raw_read(in, message_len), message_len));
RESULT_GUARD_POSIX(s2n_stuffer_init(&full_message, &full_message_blob));
RESULT_GUARD_POSIX(s2n_stuffer_skip_write(&full_message, message_len));
RESULT_GUARD(s2n_post_handshake_process(conn, &full_message, message_type));
return S2N_RESULT_OK;
}
/* If the message body is fragmented, then the current fragment will be wiped from conn->in
* in order to read the next record. So the message stuffer needs enough space to store
* the full message as we reconstruct it from multiple records.
* For large messages like NewSessionTicket, this will require allocating new memory.
*/
if (s2n_stuffer_space_remaining(message) < message_len) {
/* We want to avoid servers allocating memory in response to post-handshake messages
* to avoid a potential DDOS / resource exhaustion attack.
*
* Currently, s2n-tls servers only support the KeyUpdate message,
* which should never require additional memory to parse.
*/
RESULT_ENSURE(conn->mode == S2N_CLIENT, S2N_ERR_BAD_MESSAGE);
uint32_t total_size = message_len + TLS_HANDSHAKE_HEADER_LENGTH;
if (message->alloced) {
RESULT_GUARD_POSIX(s2n_stuffer_resize(message, total_size));
} else {
/* Manually convert our static stuffer to a growable stuffer */
RESULT_GUARD_POSIX(s2n_stuffer_growable_alloc(message, total_size));
RESULT_GUARD_POSIX(s2n_stuffer_write_bytes(message, conn->post_handshake.header_in, TLS_HANDSHAKE_HEADER_LENGTH));
RESULT_GUARD_POSIX(s2n_stuffer_skip_read(message, TLS_HANDSHAKE_HEADER_LENGTH));
}
}
/* Try to copy the message body into the message stuffer.
* The message stuffer may already contain some of the message body if
* we have already read fragments from previous records.
*/
if (s2n_stuffer_data_available(message) < message_len) {
uint32_t remaining = message_len - s2n_stuffer_data_available(message);
uint32_t to_read = MIN(remaining, s2n_stuffer_data_available(in));
RESULT_GUARD_POSIX(s2n_stuffer_copy(in, message, to_read));
}
RESULT_ENSURE(s2n_stuffer_data_available(message) == message_len, S2N_ERR_IO_BLOCKED);
/* Now that the full message body is available, process it. */
RESULT_GUARD(s2n_post_handshake_process(conn, message, message_type));
return S2N_RESULT_OK;
}
S2N_RESULT s2n_post_handshake_recv(struct s2n_connection *conn)
{
RESULT_ENSURE_REF(conn);
while (s2n_stuffer_data_available(&conn->in)) {
RESULT_GUARD(s2n_post_handshake_message_recv(conn));
RESULT_GUARD_POSIX(s2n_stuffer_wipe(&conn->post_handshake.in));
}
return S2N_RESULT_OK;
}
S2N_RESULT s2n_post_handshake_write_records(struct s2n_connection *conn, s2n_blocked_status *blocked)
{
struct s2n_stuffer *message = &conn->handshake.io;
/* Flush any existing records before we write a new handshake record.
* We do not support buffering multiple handshake records.
*/
if (s2n_stuffer_data_available(message)) {
RESULT_GUARD_POSIX(s2n_flush(conn, blocked));
}
RESULT_GUARD(s2n_handshake_message_send(conn, TLS_HANDSHAKE, blocked));
RESULT_GUARD_POSIX(s2n_stuffer_wipe(message));
return S2N_RESULT_OK;
}
int s2n_post_handshake_send(struct s2n_connection *conn, s2n_blocked_status *blocked)
{
POSIX_ENSURE_REF(conn);
/* Currently, we only support TLS1.3 post-handshake messages. */
if (conn->actual_protocol_version < S2N_TLS13) {
return S2N_SUCCESS;
}
POSIX_GUARD_RESULT(s2n_post_handshake_write_records(conn, blocked));
POSIX_GUARD(s2n_key_update_send(conn, blocked));
POSIX_GUARD_RESULT(s2n_tls13_server_nst_send(conn, blocked));
POSIX_GUARD(s2n_stuffer_resize(&conn->handshake.io, 0));
return S2N_SUCCESS;
}
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