dtls.c

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