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gnutls-dtls.c
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gnutls-dtls.c
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/*
* OpenConnect (SSL + DTLS) VPN client
*
* Copyright © 2008-2016 Intel Corporation.
*
* Author: David Woodhouse <dwmw2@infradead.org>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
* version 2.1, as published by the Free Software Foundation.
*
* This program 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.
*/
#include <config.h>
#include <errno.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#ifndef _WIN32
#include <netinet/in.h>
#include <sys/socket.h>
#endif
#include <gnutls/dtls.h>
#include "gnutls.h"
#if GNUTLS_VERSION_NUMBER < 0x030200
# define GNUTLS_DTLS1_2 202
#endif
#if GNUTLS_VERSION_NUMBER < 0x030400
# define GNUTLS_CIPHER_CHACHA20_POLY1305 23
#endif
/* sets the DTLS MTU and returns the actual tunnel MTU */
unsigned dtls_set_mtu(struct openconnect_info *vpninfo, unsigned mtu)
{
gnutls_dtls_set_mtu(vpninfo->dtls_ssl, mtu);
return gnutls_dtls_get_data_mtu(vpninfo->dtls_ssl);
}
struct {
const char *name;
gnutls_protocol_t version;
gnutls_cipher_algorithm_t cipher;
gnutls_kx_algorithm_t kx;
gnutls_mac_algorithm_t mac;
const char *prio;
const char *min_gnutls_version;
} gnutls_dtls_ciphers[] = {
{ "DHE-RSA-AES128-SHA", GNUTLS_DTLS0_9, GNUTLS_CIPHER_AES_128_CBC, GNUTLS_KX_DHE_RSA, GNUTLS_MAC_SHA1,
"NONE:+VERS-DTLS0.9:+COMP-NULL:+AES-128-CBC:+SHA1:+DHE-RSA:%COMPAT", "3.0.0" },
{ "DHE-RSA-AES256-SHA", GNUTLS_DTLS0_9, GNUTLS_CIPHER_AES_256_CBC, GNUTLS_KX_DHE_RSA, GNUTLS_MAC_SHA1,
"NONE:+VERS-DTLS0.9:+COMP-NULL:+AES-256-CBC:+SHA1:+DHE-RSA:%COMPAT", "3.0.0" },
{ "AES128-SHA", GNUTLS_DTLS0_9, GNUTLS_CIPHER_AES_128_CBC, GNUTLS_KX_RSA, GNUTLS_MAC_SHA1,
"NONE:+VERS-DTLS0.9:+COMP-NULL:+AES-128-CBC:+SHA1:+RSA:%COMPAT", "3.0.0" },
{ "AES256-SHA", GNUTLS_DTLS0_9, GNUTLS_CIPHER_AES_256_CBC, GNUTLS_KX_RSA, GNUTLS_MAC_SHA1,
"NONE:+VERS-DTLS0.9:+COMP-NULL:+AES-256-CBC:+SHA1:+RSA:%COMPAT", "3.0.0" },
{ "DES-CBC3-SHA", GNUTLS_DTLS0_9, GNUTLS_CIPHER_3DES_CBC, GNUTLS_KX_RSA, GNUTLS_MAC_SHA1,
"NONE:+VERS-DTLS0.9:+COMP-NULL:+3DES-CBC:+SHA1:+RSA:%COMPAT", "3.0.0" },
{ "OC-DTLS1_2-AES128-GCM", GNUTLS_DTLS1_2, GNUTLS_CIPHER_AES_128_GCM, GNUTLS_KX_RSA, GNUTLS_MAC_AEAD,
"NONE:+VERS-DTLS1.2:+COMP-NULL:+AES-128-GCM:+AEAD:+RSA:%COMPAT:+SIGN-ALL", "3.2.7" },
{ "OC-DTLS1_2-AES256-GCM", GNUTLS_DTLS1_2, GNUTLS_CIPHER_AES_256_GCM, GNUTLS_KX_RSA, GNUTLS_MAC_AEAD,
"NONE:+VERS-DTLS1.2:+COMP-NULL:+AES-256-GCM:+AEAD:+RSA:%COMPAT:+SIGN-ALL", "3.2.7" },
{ "OC2-DTLS1_2-CHACHA20-POLY1305", GNUTLS_DTLS1_2, GNUTLS_CIPHER_CHACHA20_POLY1305, GNUTLS_KX_PSK, GNUTLS_MAC_AEAD,
"NONE:+VERS-DTLS1.2:+COMP-NULL:+CHACHA20-POLY1305:+AEAD:+PSK:%COMPAT:+SIGN-ALL", "3.4.8" },
/* NB. We agreed that any new cipher suites probably shouldn't use
* Cisco's session resume hack (which ties us to a specific version
* of DTLS). Instead, we'll use GNUTLS_KX_PSK and let it negotiate
* the session properly. We might want to wait for
* draft-jay-tls-psk-identity-extension before we do that. */
};
#if GNUTLS_VERSION_NUMBER < 0x030009
void append_dtls_ciphers(struct openconnect_info *vpninfo, struct oc_text_buf *buf)
{
int i, first = 1;
for (i = 0; i < sizeof(gnutls_dtls_ciphers) / sizeof(gnutls_dtls_ciphers[0]); i++) {
if (gnutls_check_version(gnutls_dtls_ciphers[i].min_gnutls_version)) {
buf_append(buf, "%s%s", first ? "" : ":",
gnutls_dtls_ciphers[i].name);
first = 0;
}
}
#else
void append_dtls_ciphers(struct openconnect_info *vpninfo, struct oc_text_buf *buf)
{
/* only enable the ciphers that would have been negotiated in the TLS channel */
unsigned i, j, first = 1;
int ret;
unsigned idx;
gnutls_cipher_algorithm_t cipher;
gnutls_mac_algorithm_t mac;
gnutls_priority_t cache;
uint32_t used = 0;
buf_append(buf, "PSK-NEGOTIATE");
first = 0;
ret = gnutls_priority_init(&cache, vpninfo->gnutls_prio, NULL);
if (ret < 0) {
buf->error = -EIO;
return;
}
for (j=0; ; j++) {
ret = gnutls_priority_get_cipher_suite_index(cache, j, &idx);
if (ret == GNUTLS_E_UNKNOWN_CIPHER_SUITE)
continue;
else if (ret < 0)
break;
if (gnutls_cipher_suite_info(idx, NULL, NULL, &cipher, &mac, NULL) != NULL) {
for (i = 0; i < sizeof(gnutls_dtls_ciphers)/sizeof(gnutls_dtls_ciphers[0]); i++) {
if (used & (1 << i))
continue;
if (gnutls_dtls_ciphers[i].mac == mac && gnutls_dtls_ciphers[i].cipher == cipher) {
buf_append(buf, "%s%s", first ? "" : ":",
gnutls_dtls_ciphers[i].name);
first = 0;
used |= (1 << i);
break;
}
}
}
}
gnutls_priority_deinit(cache);
}
#endif
/* This enables a DTLS protocol negotiation. The new negotiation is as follows:
*
* If the client's X-DTLS-CipherSuite contains the "PSK-NEGOTIATE" keyword,
* the server will reply with "X-DTLS-CipherSuite: PSK-NEGOTIATE" and will
* enable DTLS-PSK negotiation on the DTLS channel. This allows the protocol
* to use new DTLS versions, as well as new DTLS ciphersuites, as long as
* they are also permitted by the system crypto policy in use.
*
* That change still requires to client to pretend it is resuming by setting
* in the TLS ClientHello the session ID provided by the X-DTLS-Session-ID
* header. That is, because there is no TLS extension we can use to set an
* identifier in the client hello (draft-jay-tls-psk-identity-extension
* could be used in the future). The session is not actually resumed.
*/
static int start_dtls_psk_handshake(struct openconnect_info *vpninfo, int dtls_fd)
{
gnutls_session_t dtls_ssl;
gnutls_datum_t key;
struct oc_text_buf *prio;
int err;
if (!vpninfo->https_sess) {
vpn_progress(vpninfo, PRG_INFO,
_("Deferring DTLS resumption until CSTP generates a PSK\n"));
return -EAGAIN;
}
prio = buf_alloc();
buf_append(prio, "%s:-VERS-TLS-ALL:+VERS-DTLS-ALL:-KX-ALL:+PSK", vpninfo->gnutls_prio);
if (buf_error(prio)) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to generate DTLS priority string\n"));
vpninfo->dtls_attempt_period = 0;
return buf_free(prio);
}
err = gnutls_init(&dtls_ssl, GNUTLS_CLIENT|GNUTLS_DATAGRAM|GNUTLS_NONBLOCK|GNUTLS_NO_EXTENSIONS);
if (err) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to initialize DTLS: %s\n"),
gnutls_strerror(err));
goto fail;
}
gnutls_session_set_ptr(dtls_ssl, (void *) vpninfo);
err = gnutls_priority_set_direct(dtls_ssl, prio->data, NULL);
if (err) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to set DTLS priority: '%s': %s\n"),
prio->data, gnutls_strerror(err));
goto fail;
}
gnutls_transport_set_ptr(dtls_ssl,
(gnutls_transport_ptr_t)(intptr_t)dtls_fd);
/* set PSK credentials */
err = gnutls_psk_allocate_client_credentials(&vpninfo->psk_cred);
if (err < 0) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to allocate credentials: %s\n"),
gnutls_strerror(err));
goto fail;
}
/* generate key */
/* we should have used gnutls_prf_rfc5705() but since we don't use
* the RFC5705 context, the output is identical with gnutls_prf(). The
* latter is available in much earlier versions of gnutls. */
err = gnutls_prf(vpninfo->https_sess, PSK_LABEL_SIZE, PSK_LABEL,
0, 0, 0, PSK_KEY_SIZE, (char*)vpninfo->dtls_secret);
if (err < 0) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to generate DTLS key: %s\n"),
gnutls_strerror(err));
goto fail;
}
key.data = vpninfo->dtls_secret;
key.size = PSK_KEY_SIZE;
/* we set an arbitrary username here. We cannot take advantage of the
* username field to send our ID to the server, since the username in TLS-PSK
* is sent after the server-hello. */
err = gnutls_psk_set_client_credentials(vpninfo->psk_cred, "psk", &key, 0);
if (err < 0) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to set DTLS key: %s\n"),
gnutls_strerror(err));
goto fail;
}
err = gnutls_credentials_set(dtls_ssl, GNUTLS_CRD_PSK, vpninfo->psk_cred);
if (err) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to set DTLS PSK credentials: %s\n"),
gnutls_strerror(err));
goto fail;
}
buf_free(prio);
vpninfo->dtls_ssl = dtls_ssl;
return 0;
fail:
buf_free(prio);
gnutls_deinit(dtls_ssl);
gnutls_psk_free_client_credentials(vpninfo->psk_cred);
vpninfo->psk_cred = NULL;
vpninfo->dtls_attempt_period = 0;
return -EINVAL;
}
int start_dtls_handshake(struct openconnect_info *vpninfo, int dtls_fd)
{
gnutls_session_t dtls_ssl;
gnutls_datum_t master_secret, session_id;
int err;
int cipher;
if (strcmp(vpninfo->dtls_cipher, "PSK-NEGOTIATE") == 0)
return start_dtls_psk_handshake(vpninfo, dtls_fd);
for (cipher = 0; cipher < sizeof(gnutls_dtls_ciphers)/sizeof(gnutls_dtls_ciphers[0]); cipher++) {
if (gnutls_check_version(gnutls_dtls_ciphers[cipher].min_gnutls_version) == NULL)
continue;
if (!strcmp(vpninfo->dtls_cipher, gnutls_dtls_ciphers[cipher].name))
goto found_cipher;
}
vpn_progress(vpninfo, PRG_ERR, _("Unknown DTLS parameters for requested CipherSuite '%s'\n"),
vpninfo->dtls_cipher);
vpninfo->dtls_attempt_period = 0;
return -EINVAL;
found_cipher:
gnutls_init(&dtls_ssl, GNUTLS_CLIENT|GNUTLS_DATAGRAM|GNUTLS_NONBLOCK);
gnutls_session_set_ptr(dtls_ssl, (void *) vpninfo);
err = gnutls_priority_set_direct(dtls_ssl,
gnutls_dtls_ciphers[cipher].prio,
NULL);
if (err) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to set DTLS priority: %s\n"),
gnutls_strerror(err));
gnutls_deinit(dtls_ssl);
vpninfo->dtls_attempt_period = 0;
return -EINVAL;
}
gnutls_transport_set_ptr(dtls_ssl,
(gnutls_transport_ptr_t)(intptr_t)dtls_fd);
gnutls_record_disable_padding(dtls_ssl);
master_secret.data = vpninfo->dtls_secret;
master_secret.size = sizeof(vpninfo->dtls_secret);
session_id.data = vpninfo->dtls_session_id;
session_id.size = sizeof(vpninfo->dtls_session_id);
err = gnutls_session_set_premaster(dtls_ssl, GNUTLS_CLIENT, gnutls_dtls_ciphers[cipher].version,
gnutls_dtls_ciphers[cipher].kx, gnutls_dtls_ciphers[cipher].cipher,
gnutls_dtls_ciphers[cipher].mac, GNUTLS_COMP_NULL,
&master_secret, &session_id);
if (err) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to set DTLS session parameters: %s\n"),
gnutls_strerror(err));
gnutls_deinit(dtls_ssl);
vpninfo->dtls_attempt_period = 0;
return -EINVAL;
}
vpninfo->dtls_ssl = dtls_ssl;
return 0;
}
int dtls_try_handshake(struct openconnect_info *vpninfo)
{
int err = gnutls_handshake(vpninfo->dtls_ssl);
char *str;
if (!err) {
if (!strcmp(vpninfo->dtls_cipher, "PSK-NEGOTIATE")) {
/* For PSK-NEGOTIATE, we have to determine the tunnel MTU
* for ourselves based on the base MTU */
int data_mtu = vpninfo->cstp_basemtu;
if (vpninfo->peer_addr->sa_family == IPPROTO_IPV6)
data_mtu -= 40; /* IPv6 header */
else
data_mtu -= 20; /* Legacy IP header */
data_mtu -= 8; /* UDP header */
if (data_mtu < 0) {
vpn_progress(vpninfo, PRG_ERR,
_("Peer MTU %d too small to allow DTLS\n"),
vpninfo->cstp_basemtu);
goto nodtls;
}
/* Reduce it by one because that's the payload header *inside*
* the encryption */
data_mtu = dtls_set_mtu(vpninfo, data_mtu) - 1;
if (data_mtu < vpninfo->ip_info.mtu) {
vpn_progress(vpninfo, PRG_INFO,
_("DTLS MTU reduced to %d\n"),
data_mtu);
vpninfo->ip_info.mtu = data_mtu;
}
} else {
if (!gnutls_session_is_resumed(vpninfo->dtls_ssl)) {
/* Someone attempting to hijack the DTLS session?
* A real server would never allow a full session
* establishment instead of the agreed resume. */
vpn_progress(vpninfo, PRG_ERR,
_("DTLS session resume failed; possible MITM attack. Disabling DTLS.\n"));
nodtls:
dtls_close(vpninfo);
vpninfo->dtls_attempt_period = 0;
vpninfo->dtls_state = DTLS_DISABLED;
return -EIO;
}
/* Make sure GnuTLS's idea of the MTU is sufficient to take
a full VPN MTU (with 1-byte header) in a data record. */
err = gnutls_dtls_set_data_mtu(vpninfo->dtls_ssl, vpninfo->ip_info.mtu + 1);
if (err) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to set DTLS MTU: %s\n"),
gnutls_strerror(err));
goto error;
}
}
vpninfo->dtls_state = DTLS_CONNECTED;
str = get_gnutls_cipher(vpninfo->dtls_ssl);
if (str) {
const char *c;
vpn_progress(vpninfo, PRG_INFO,
_("Established DTLS connection (using GnuTLS). Ciphersuite %s.\n"),
str);
gnutls_free(str);
c = openconnect_get_dtls_compression(vpninfo);
if (c) {
vpn_progress(vpninfo, PRG_INFO,
_("DTLS connection compression using %s.\n"), c);
}
}
vpninfo->dtls_times.last_rekey = vpninfo->dtls_times.last_rx =
vpninfo->dtls_times.last_tx = time(NULL);
dtls_detect_mtu(vpninfo);
/* XXX: For OpenSSL we explicitly prevent retransmits here. */
return 0;
}
if (err == GNUTLS_E_AGAIN || err == GNUTLS_E_INTERRUPTED) {
if (time(NULL) < vpninfo->new_dtls_started + 12)
return 0;
vpn_progress(vpninfo, PRG_DEBUG, _("DTLS handshake timed out\n"));
}
vpn_progress(vpninfo, PRG_ERR, _("DTLS handshake failed: %s\n"),
gnutls_strerror(err));
if (err == GNUTLS_E_PUSH_ERROR)
vpn_progress(vpninfo, PRG_ERR,
_("(Is a firewall preventing you from sending UDP packets?)\n"));
error:
dtls_close(vpninfo);
vpninfo->dtls_state = DTLS_SLEEPING;
time(&vpninfo->new_dtls_started);
return -EINVAL;
}
void dtls_shutdown(struct openconnect_info *vpninfo)
{
dtls_close(vpninfo);
}
void dtls_ssl_free(struct openconnect_info *vpninfo)
{
gnutls_deinit(vpninfo->dtls_ssl);
if (vpninfo->psk_cred) {
gnutls_psk_free_client_credentials(vpninfo->psk_cred);
vpninfo->psk_cred = NULL;
}
}