dtls.c

   1 /*
   2  * OpenConnect (SSL + DTLS) VPN client
   3  *
   4  * Copyright © 2008-2010 Intel Corporation.
   5  *
   6  * Author: David Woodhouse <dwmw2@infradead.org>
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public License
  10  * version 2.1, as published by the Free Software Foundation.
  11  *
  12  * This program is distributed in the hope that it will be useful, but
  13  * WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with this library; if not, write to:
  19  *
  20  *   Free Software Foundation, Inc.
  21  *   51 Franklin Street, Fifth Floor,
  22  *   Boston, MA 02110-1301 USA
  23  */
  24
  25 #include <errno.h>
  26 #include <sys/types.h>
  27 #include <sys/socket.h>
  28 #include <netdb.h>
  29 #include <unistd.h>
  30 #include <netinet/in.h>
  31 #include <openssl/err.h>
  32 #include <openssl/ssl.h>
  33 #include <fcntl.h>
  34 #include <string.h>
  35
  36 #include "openconnect-internal.h"
  37
  38 static unsigned char nybble(unsigned char n)
  39 {
  40         if      (n >= '0' && n <= '9') return n - '0';
  41         else if (n >= 'A' && n <= 'F') return n - ('A' - 10);
  42         else if (n >= 'a' && n <= 'f') return n - ('a' - 10);
  43         return 0;
  44 }
  45
  46 unsigned char unhex(const char *data)
  47 {
  48         return (nybble(data[0]) << 4) | nybble(data[1]);
  49 }
  50
  51 #ifdef SSL_F_DTLS1_CONNECT
  52 #if 0
  53 /*
  54  * Useful for catching test cases, where we want everything to be
  55  * reproducible.  *NEVER* do this in the wild.
  56  */
  57 time_t time(time_t *t)
  58 {
  59         time_t x = 0x3ab2d948;
  60         if (t) *t = x;
  61         return x;
  62 }
  63
  64 int RAND_pseudo_bytes(char *buf, int len)
  65 {
  66         memset(buf, 0x5a, len);
  67         printf("FAKE PSEUDO RANDOM!\n");
  68         return 1;
  69
  70 }
  71 int RAND_bytes(char *buf, int len)
  72 {
  73         static int foo = 0x5b;
  74         printf("FAKE RANDOM!\n");
  75         memset(buf, foo, len);
  76         return 1;
  77 }
  78 #endif
  79
  80 /*
  81  * The master-secret is generated randomly by the client. The server
  82  * responds with a DTLS Session-ID. These, done over the HTTPS
  83  * connection, are enough to 'resume' a DTLS session, bypassing all
  84  * the normal setup of a normal DTLS connection.
  85  *
  86  * Cisco use a version of the protocol which predates RFC4347, but
  87  * isn't quite the same as the pre-RFC version of the protocol which
  88  * was in OpenSSL 0.9.8e -- it includes backports of some later
  89  * OpenSSL patches.
  90  *
  91  * The openssl/ directory of this source tree should contain both a
  92  * small patch against OpenSSL 0.9.8e to make it support Cisco's
  93  * snapshot of the protocol, and a larger patch against newer OpenSSL
  94  * which gives us an option to use the old protocol again.
  95  *
  96  * Cisco's server also seems to respond to the official version of the
  97  * protocol, with a change in the ChangeCipherSpec packet which implies
  98  * that it does know the difference and isn't just repeating the version
  99  * number seen in the ClientHello. But although I can make the handshake
 100  * complete by hacking tls1_mac() to use the _old_ protocol version
 101  * number when calculating the MAC, the server still seems to be ignoring
 102  * my subsequent data packets. So we use the old protocol, which is what
 103  * their clients use anyway.
 104  */
 105
 106 int connect_dtls_socket(struct openconnect_info *vpninfo)
 107 {
 108         STACK_OF(SSL_CIPHER) *ciphers;
 109         method_const SSL_METHOD *dtls_method;
 110         SSL_CIPHER *dtls_cipher;
 111         SSL *dtls_ssl;
 112         BIO *dtls_bio;
 113         int dtls_fd;
 114
 115         if (!vpninfo->dtls_addr) {
 116                 vpn_progress(vpninfo, PRG_ERR, "No DTLS address\n");
 117                 vpninfo->dtls_attempt_period = 0;
 118                 return -EINVAL;
 119         }
 120
 121         if (!vpninfo->dtls_cipher) {
 122                 /* We probably didn't offer it any ciphers it liked */
 123                 vpn_progress(vpninfo, PRG_ERR, "Server offered no DTLS cipher option\n");
 124                 vpninfo->dtls_attempt_period = 0;
 125                 return -EINVAL;
 126         }
 127
 128         if (vpninfo->proxy) {
 129                 /* XXX: Theoretically, SOCKS5 proxies can do UDP too */
 130                 vpn_progress(vpninfo, PRG_ERR, "No DTLS when connected via proxy\n");
 131                 vpninfo->dtls_attempt_period = 0;
 132                 return -EINVAL;
 133         }
 134
 135         dtls_fd = socket(vpninfo->peer_addr->sa_family, SOCK_DGRAM, IPPROTO_UDP);
 136         if (dtls_fd < 0) {
 137                 perror("Open UDP socket for DTLS:");
 138                 return -EINVAL;
 139         }
 140
 141         if (connect(dtls_fd, vpninfo->dtls_addr, vpninfo->peer_addrlen)) {
 142                 perror("UDP (DTLS) connect:\n");
 143                 close(dtls_fd);
 144                 return -EINVAL;
 145         }
 146
 147         fcntl(dtls_fd, F_SETFD, FD_CLOEXEC);
 148
 149         if (!vpninfo->dtls_ctx) {
 150                 dtls_method = DTLSv1_client_method();
 151                 vpninfo->dtls_ctx = SSL_CTX_new(dtls_method);
 152                 if (!vpninfo->dtls_ctx) {
 153                         vpn_progress(vpninfo, PRG_ERR, "Initialise DTLSv1 CTX failed\n");
 154                         vpninfo->dtls_attempt_period = 0;
 155                         return -EINVAL;
 156                 }
 157
 158                 /* If we don't readahead, then we do short reads and throw
 159                    away the tail of data packets. */
 160                 SSL_CTX_set_read_ahead(vpninfo->dtls_ctx, 1);
 161
 162                 if (!SSL_CTX_set_cipher_list(vpninfo->dtls_ctx, vpninfo->dtls_cipher)) {
 163                         vpn_progress(vpninfo, PRG_ERR, "Set DTLS cipher list failed\n");
 164                         SSL_CTX_free(vpninfo->dtls_ctx);
 165                         vpninfo->dtls_ctx = NULL;
 166                         vpninfo->dtls_attempt_period = 0;
 167                         return -EINVAL;
 168                 }
 169         }
 170
 171         if (!vpninfo->dtls_session) {
 172                 /* We're going to "resume" a session which never existed. Fake it... */
 173                 vpninfo->dtls_session = SSL_SESSION_new();
 174                 if (!vpninfo->dtls_session) {
 175                         vpn_progress(vpninfo, PRG_ERR, "Initialise DTLSv1 session failed\n");
 176                         vpninfo->dtls_attempt_period = 0;
 177                         return -EINVAL;
 178                 }
 179                 vpninfo->dtls_session->ssl_version = 0x0100; // DTLS1_BAD_VER
 180         }
 181
 182         /* Do this every time; it may have changed due to a rekey */
 183         vpninfo->dtls_session->master_key_length = sizeof(vpninfo->dtls_secret);
 184         memcpy(vpninfo->dtls_session->master_key, vpninfo->dtls_secret,
 185                sizeof(vpninfo->dtls_secret));
 186
 187         vpninfo->dtls_session->session_id_length = sizeof(vpninfo->dtls_session_id);
 188         memcpy(vpninfo->dtls_session->session_id, vpninfo->dtls_session_id,
 189                sizeof(vpninfo->dtls_session_id));
 190
 191         dtls_ssl = SSL_new(vpninfo->dtls_ctx);
 192         SSL_set_connect_state(dtls_ssl);
 193
 194         ciphers = SSL_get_ciphers(dtls_ssl);
 195         if (sk_SSL_CIPHER_num(ciphers) != 1) {
 196                 vpn_progress(vpninfo, PRG_ERR, "Not precisely one DTLS cipher\n");
 197                 SSL_CTX_free(vpninfo->dtls_ctx);
 198                 SSL_free(dtls_ssl);
 199                 SSL_SESSION_free(vpninfo->dtls_session);
 200                 vpninfo->dtls_ctx = NULL;
 201                 vpninfo->dtls_session = NULL;
 202                 vpninfo->dtls_attempt_period = 0;
 203                 return -EINVAL;
 204         }
 205         dtls_cipher = sk_SSL_CIPHER_value(ciphers, 0);
 206
 207         /* Set the appropriate cipher on our session to be resumed */
 208         vpninfo->dtls_session->cipher = dtls_cipher;
 209         vpninfo->dtls_session->cipher_id = dtls_cipher->id;
 210
 211         /* Add the generated session to the SSL */
 212         if (!SSL_set_session(dtls_ssl, vpninfo->dtls_session)) {
 213                 vpn_progress(vpninfo, PRG_ERR,
 214                                   "SSL_set_session() failed with old protocol version 0x%x\n"
 215                                   "Are you using a version of OpenSSL older than 0.9.8m?\n"
 216                                   "See http://rt.openssl.org/Ticket/Display.html?id=1751\n"
 217                                   "Use the --no-dtls command line option to avoid this message\n",
 218                                   vpninfo->dtls_session->ssl_version);
 219                 vpninfo->dtls_attempt_period = 0;
 220                 return -EINVAL;
 221         }
 222
 223         /* Go Go Go! */
 224         dtls_bio = BIO_new_socket(dtls_fd, BIO_NOCLOSE);
 225         SSL_set_bio(dtls_ssl, dtls_bio, dtls_bio);
 226
 227 #ifndef SSL_OP_CISCO_ANYCONNECT
 228 #warning Your version of OpenSSL does not seem to support Cisco DTLS compatibility
 229 #define SSL_OP_CISCO_ANYCONNECT 0x8000
 230 #endif
 231         SSL_set_options(dtls_ssl, SSL_OP_CISCO_ANYCONNECT);
 232
 233         /* Set non-blocking */
 234         BIO_set_nbio(SSL_get_rbio(dtls_ssl), 1);
 235         BIO_set_nbio(SSL_get_wbio(dtls_ssl), 1);
 236
 237         fcntl(dtls_fd, F_SETFL, fcntl(dtls_fd, F_GETFL) | O_NONBLOCK);
 238
 239         vpninfo->new_dtls_fd = dtls_fd;
 240         vpninfo->new_dtls_ssl = dtls_ssl;
 241
 242         if (vpninfo->select_nfds <= dtls_fd)
 243                 vpninfo->select_nfds = dtls_fd + 1;
 244
 245         FD_SET(dtls_fd, &vpninfo->select_rfds);
 246         FD_SET(dtls_fd, &vpninfo->select_efds);
 247
 248         time(&vpninfo->new_dtls_started);
 249         return dtls_try_handshake(vpninfo);
 250 }
 251
 252 int dtls_try_handshake(struct openconnect_info *vpninfo)
 253 {
 254         int ret = SSL_do_handshake(vpninfo->new_dtls_ssl);
 255
 256         if (ret == 1) {
 257                 vpn_progress(vpninfo, PRG_INFO, "Established DTLS connection\n");
 258
 259                 if (vpninfo->dtls_ssl) {
 260                         /* We are replacing an old connection */
 261                         SSL_free(vpninfo->dtls_ssl);
 262                         close(vpninfo->dtls_fd);
 263                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 264                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 265                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 266                 }
 267                 vpninfo->dtls_ssl = vpninfo->new_dtls_ssl;
 268                 vpninfo->dtls_fd = vpninfo->new_dtls_fd;
 269
 270                 vpninfo->new_dtls_ssl = NULL;
 271                 vpninfo->new_dtls_fd = -1;
 272
 273                 vpninfo->dtls_times.last_rx = vpninfo->dtls_times.last_tx = time(NULL);
 274
 275                 return 0;
 276         }
 277
 278         ret = SSL_get_error(vpninfo->new_dtls_ssl, ret);
 279         if (ret == SSL_ERROR_WANT_WRITE || ret == SSL_ERROR_WANT_READ) {
 280                 if (time(NULL) < vpninfo->new_dtls_started + 5)
 281                         return 0;
 282                 vpn_progress(vpninfo, PRG_TRACE, "DTLS handshake timed out\n");
 283         }
 284
 285         vpn_progress(vpninfo, PRG_ERR, "DTLS handshake failed: %d\n", ret);
 286         report_ssl_errors(vpninfo);
 287
 288         /* Kill the new (failed) connection... */
 289         SSL_free(vpninfo->new_dtls_ssl);
 290         FD_CLR(vpninfo->new_dtls_fd, &vpninfo->select_rfds);
 291         FD_CLR(vpninfo->new_dtls_fd, &vpninfo->select_efds);
 292         close(vpninfo->new_dtls_fd);
 293         vpninfo->new_dtls_ssl = NULL;
 294         vpninfo->new_dtls_fd = -1;
 295
 296         /* ... and kill the old one too. The only time there'll be a valid
 297            existing session is when it was a rekey, and in that case it's
 298            time for the old one to die. */
 299         if (vpninfo->dtls_ssl) {
 300                 SSL_free(vpninfo->dtls_ssl);
 301                 close(vpninfo->dtls_fd);
 302                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 303                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 304                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 305                 vpninfo->dtls_ssl = NULL;
 306                 vpninfo->dtls_fd = -1;
 307         }
 308
 309         time(&vpninfo->new_dtls_started);
 310         return -EINVAL;
 311 }
 312
 313 static int dtls_restart(struct openconnect_info *vpninfo)
 314 {
 315         if (vpninfo->dtls_ssl) {
 316                 SSL_free(vpninfo->dtls_ssl);
 317                 close(vpninfo->dtls_fd);
 318                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 319                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 320                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 321                 vpninfo->dtls_ssl = NULL;
 322                 vpninfo->dtls_fd = -1;
 323         }
 324
 325         return connect_dtls_socket(vpninfo);
 326 }
 327
 328
 329 int setup_dtls(struct openconnect_info *vpninfo)
 330 {
 331         struct vpn_option *dtls_opt = vpninfo->dtls_options;
 332         int dtls_port = 0;
 333
 334         while (dtls_opt) {
 335                 vpn_progress(vpninfo, PRG_TRACE,
 336                                   "DTLS option %s : %s\n",
 337                                   dtls_opt->option, dtls_opt->value);
 338
 339                 if (!strcmp(dtls_opt->option + 7, "Port")) {
 340                         dtls_port = atol(dtls_opt->value);
 341                 } else if (!strcmp(dtls_opt->option + 7, "Keepalive")) {
 342                         vpninfo->dtls_times.keepalive = atol(dtls_opt->value);
 343                 } else if (!strcmp(dtls_opt->option + 7, "DPD")) {
 344                         int j = atol(dtls_opt->value);
 345                         if (j && (!vpninfo->dtls_times.dpd || j < vpninfo->dtls_times.dpd))
 346                                 vpninfo->dtls_times.dpd = j;
 347                 } else if (!strcmp(dtls_opt->option + 7, "Rekey-Time")) {
 348                         vpninfo->dtls_times.rekey = atol(dtls_opt->value);
 349                 } else if (!strcmp(dtls_opt->option + 7, "CipherSuite")) {
 350                         vpninfo->dtls_cipher = strdup(dtls_opt->value);
 351                 }
 352
 353                 dtls_opt = dtls_opt->next;
 354         }
 355         if (!dtls_port) {
 356                 vpninfo->dtls_attempt_period = 0;
 357                 return -EINVAL;
 358         }
 359
 360         vpninfo->dtls_addr = malloc(vpninfo->peer_addrlen);
 361         if (!vpninfo->dtls_addr) {
 362                 vpninfo->dtls_attempt_period = 0;
 363                 return -ENOMEM;
 364         }
 365         memcpy(vpninfo->dtls_addr, vpninfo->peer_addr, vpninfo->peer_addrlen);
 366
 367         if (vpninfo->peer_addr->sa_family == AF_INET) {
 368                 struct sockaddr_in *sin = (void *)vpninfo->dtls_addr;
 369                 sin->sin_port = htons(dtls_port);
 370         } else if (vpninfo->peer_addr->sa_family == AF_INET6) {
 371                 struct sockaddr_in6 *sin = (void *)vpninfo->dtls_addr;
 372                 sin->sin6_port = htons(dtls_port);
 373         } else {
 374                 vpn_progress(vpninfo, PRG_ERR, "Unknown protocol family %d. Cannot do DTLS\n",
 375                                   vpninfo->peer_addr->sa_family);
 376                 vpninfo->dtls_attempt_period = 0;
 377                 return -EINVAL;
 378         }
 379
 380         if (connect_dtls_socket(vpninfo))
 381                 return -EINVAL;
 382
 383         vpn_progress(vpninfo, PRG_TRACE,
 384                           "DTLS connected. DPD %d, Keepalive %d\n",
 385                           vpninfo->dtls_times.dpd, vpninfo->dtls_times.keepalive);
 386
 387         return 0;
 388 }
 389
 390 int dtls_mainloop(struct openconnect_info *vpninfo, int *timeout)
 391 {
 392         unsigned char buf[2000];
 393         int len;
 394         int work_done = 0;
 395         char magic_pkt;
 396
 397         while ( (len = SSL_read(vpninfo->dtls_ssl, buf, sizeof(buf))) > 0 ) {
 398
 399                 vpn_progress(vpninfo, PRG_TRACE,
 400                                   "Received DTLS packet 0x%02x of %d bytes\n",
 401                                   buf[0], len);
 402
 403                 vpninfo->dtls_times.last_rx = time(NULL);
 404
 405                 switch(buf[0]) {
 406                 case AC_PKT_DATA:
 407                         queue_new_packet(&vpninfo->incoming_queue, buf+1, len-1);
 408                         work_done = 1;
 409                         break;
 410
 411                 case AC_PKT_DPD_OUT:
 412                         vpn_progress(vpninfo, PRG_TRACE, "Got DTLS DPD request\n");
 413
 414                         /* FIXME: What if the packet doesn't get through? */
 415                         magic_pkt = AC_PKT_DPD_RESP;
 416                         if (SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1) != 1)
 417                                 vpn_progress(vpninfo, PRG_ERR, "Failed to send DPD response. Expect disconnect\n");
 418                         continue;
 419
 420                 case AC_PKT_DPD_RESP:
 421                         vpn_progress(vpninfo, PRG_TRACE, "Got DTLS DPD response\n");
 422                         break;
 423
 424                 case AC_PKT_KEEPALIVE:
 425                         vpn_progress(vpninfo, PRG_TRACE, "Got DTLS Keepalive\n");
 426                         break;
 427
 428                 default:
 429                         vpn_progress(vpninfo, PRG_ERR,
 430                                           "Unknown DTLS packet type %02x, len %d\n", buf[0], len);
 431                         if (1) {
 432                                 /* Some versions of OpenSSL have bugs with receiving out-of-order
 433                                  * packets. Not only do they wrongly decide to drop packets if
 434                                  * two packets get swapped in transit, but they also _fail_ to
 435                                  * drop the packet in non-blocking mode; instead they return
 436                                  * the appropriate length of garbage. So don't abort... for now. */
 437                                 break;
 438                         } else {
 439                                 vpninfo->quit_reason = "Unknown packet received";
 440                                 return 1;
 441                         }
 442
 443                 }
 444         }
 445
 446         switch (keepalive_action(&vpninfo->dtls_times, timeout)) {
 447         case KA_REKEY:
 448                 vpn_progress(vpninfo, PRG_INFO, "DTLS rekey due\n");
 449
 450                 /* There ought to be a method of rekeying DTLS without tearing down
 451                    the CSTP session and restarting, but we don't (yet) know it */
 452                 if (cstp_reconnect(vpninfo)) {
 453                         vpn_progress(vpninfo, PRG_ERR, "Reconnect failed\n");
 454                         vpninfo->quit_reason = "CSTP reconnect failed";
 455                         return 1;
 456                 }
 457
 458                 if (dtls_restart(vpninfo)) {
 459                         vpn_progress(vpninfo, PRG_ERR, "DTLS rekey failed\n");
 460                         return 1;
 461                 }
 462                 work_done = 1;
 463                 break;
 464
 465
 466         case KA_DPD_DEAD:
 467                 vpn_progress(vpninfo, PRG_ERR, "DTLS Dead Peer Detection detected dead peer!\n");
 468                 /* Fall back to SSL, and start a new DTLS connection */
 469                 dtls_restart(vpninfo);
 470                 return 1;
 471
 472         case KA_DPD:
 473                 vpn_progress(vpninfo, PRG_TRACE, "Send DTLS DPD\n");
 474
 475                 magic_pkt = AC_PKT_DPD_OUT;
 476                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 477                 /* last_dpd will just have been set */
 478                 vpninfo->dtls_times.last_tx = vpninfo->dtls_times.last_dpd;
 479                 work_done = 1;
 480                 break;
 481
 482         case KA_KEEPALIVE:
 483                 /* No need to send an explicit keepalive
 484                    if we have real data to send */
 485                 if (vpninfo->outgoing_queue)
 486                         break;
 487
 488                 vpn_progress(vpninfo, PRG_TRACE, "Send DTLS Keepalive\n");
 489
 490                 magic_pkt = AC_PKT_KEEPALIVE;
 491                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 492                 time(&vpninfo->dtls_times.last_tx);
 493                 work_done = 1;
 494                 break;
 495
 496         case KA_NONE:
 497                 ;
 498         }
 499
 500         /* Service outgoing packet queue */
 501         while (vpninfo->outgoing_queue) {
 502                 struct pkt *this = vpninfo->outgoing_queue;
 503                 int ret;
 504
 505                 vpninfo->outgoing_queue = this->next;
 506                 vpninfo->outgoing_qlen--;
 507
 508                 /* One byte of header */
 509                 this->hdr[7] = AC_PKT_DATA;
 510
 511                 ret = SSL_write(vpninfo->dtls_ssl, &this->hdr[7], this->len + 1);
 512                 if (ret <= 0) {
 513                         ret = SSL_get_error(vpninfo->dtls_ssl, ret);
 514
 515                         /* If it's a real error, kill the DTLS connection and
 516                            requeue the packet to be sent over SSL */
 517                         if (ret != SSL_ERROR_WANT_READ && ret != SSL_ERROR_WANT_WRITE) {
 518                                 vpn_progress(vpninfo, PRG_ERR,
 519                                                   "DTLS got write error %d. Falling back to SSL\n", ret);
 520                                 report_ssl_errors(vpninfo);
 521                                 dtls_restart(vpninfo);
 522                                 vpninfo->outgoing_queue = this;
 523                                 vpninfo->outgoing_qlen++;
 524                         }
 525                         return 1;
 526                 }
 527                 time(&vpninfo->dtls_times.last_tx);
 528                 vpn_progress(vpninfo, PRG_TRACE,
 529                                   "Sent DTLS packet of %d bytes; SSL_write() returned %d\n",
 530                                   this->len, ret);
 531                 free(this);
 532         }
 533
 534         return work_done;
 535 }
 536 #else /* No DTLS support in OpenSSL */
 537 int setup_dtls(struct openconnect_info *vpninfo)
 538 {
 539         vpn_progress(vpninfo, PRG_ERR, "Built against OpenSSL with no DTLS support\n");
 540         return -EINVAL;
 541 }
 542 #endif
 543