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/*
* Copyright (C) 2013-2018 Nikos Mavrogiannopoulos
* Copyright (C) 2018 Red Hat, Inc.
*
* This file is part of GnuTLS.
*
* The GnuTLS is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
* as published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>
*
*/
#include "gnutls_int.h"
#include "auth.h"
#include "errors.h"
#include "num.h"
#include <ext/dumbfw.h>
/* This extension adds additional padding data in the TLS client hello.
* There is an issue with some firewalls [0] rejecting TLS client hello
* data that are between 256 and 511 bytes, and this extension will
* make sure that client hello isn't in this range.
*
* [0]. https://www.ietf.org/mail-archive/web/tls/current/msg10423.html
*/
static int _gnutls_dumbfw_send_params(gnutls_session_t session,
gnutls_buffer_st * extdata);
const hello_ext_entry_st ext_mod_dumbfw = {
.name = "ClientHello Padding",
.tls_id = 21,
.gid = GNUTLS_EXTENSION_DUMBFW,
.client_parse_point = GNUTLS_EXT_APPLICATION,
.server_parse_point = GNUTLS_EXT_APPLICATION,
.validity = GNUTLS_EXT_FLAG_TLS | GNUTLS_EXT_FLAG_CLIENT_HELLO,
.recv_func = NULL,
.send_func = _gnutls_dumbfw_send_params,
.pack_func = NULL,
.unpack_func = NULL,
.deinit_func = NULL,
.cannot_be_overriden = 0
};
static int
_gnutls_dumbfw_send_params(gnutls_session_t session,
gnutls_buffer_st * extdata)
{
int total_size = 0, ret;
uint8_t pad[257];
unsigned pad_size;
ssize_t len = extdata->length - sizeof(mbuffer_st);
if (session->security_parameters.entity == GNUTLS_SERVER ||
session->internals.dumbfw == 0 ||
IS_DTLS(session) != 0 ||
(len < 256 || len >= 512)) {
return 0;
} else {
/* 256 <= extdata->length < 512 */
pad_size = 512 - len;
memset(pad, 0, pad_size);
ret =
gnutls_buffer_append_data(extdata, pad,
pad_size);
if (ret < 0)
return gnutls_assert_val(ret);
total_size += pad_size;
}
return total_size;
}
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