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 <fcntl.h>
  33 #include <string.h>
  34
  35 #include "openconnect.h"
  36
  37 #if 0
  38 /*
  39  * Useful for catching test cases, where we want everything to be
  40  * reproducible.  *NEVER* do this in the wild.
  41  */
  42 time_t time(time_t *t)
  43 {
  44         time_t x = 0x3ab2d948;
  45         if (t) *t = x;
  46         return x;
  47 }
  48
  49 int RAND_pseudo_bytes(char *buf, int len)
  50 {
  51         memset(buf, 0x5a, len);
  52         printf("FAKE PSEUDO RANDOM!\n");
  53         return 1;
  54
  55 }
  56 int RAND_bytes(char *buf, int len)
  57 {
  58         static int foo = 0x5b;
  59         printf("FAKE RANDOM!\n");
  60         memset(buf, foo, len);
  61         return 1;
  62 }
  63 #endif
  64
  65 /*
  66  * The master-secret is generated randomly by the client. The server
  67  * responds with a DTLS Session-ID. These, done over the HTTPS
  68  * connection, are enough to 'resume' a DTLS session, bypassing all
  69  * the normal setup of a normal DTLS connection.
  70  *
  71  * Cisco use a version of the protocol which predates RFC4347, but
  72  * isn't quite the same as the pre-RFC version of the protocol which
  73  * was in OpenSSL 0.9.8e -- it includes backports of some later
  74  * OpenSSL patches.
  75  *
  76  * The openssl/ directory of this source tree should contain both a
  77  * small patch against OpenSSL 0.9.8e to make it support Cisco's
  78  * snapshot of the protocol, and a larger patch against newer OpenSSL
  79  * which gives us an option to use the old protocol again.
  80  *
  81  * Cisco's server also seems to respond to the official version of the
  82  * protocol, with a change in the ChangeCipherSpec packet which implies
  83  * that it does know the difference and isn't just repeating the version
  84  * number seen in the ClientHello. But although I can make the handshake
  85  * complete by hacking tls1_mac() to use the _old_ protocol version
  86  * number when calculating the MAC, the server still seems to be ignoring
  87  * my subsequent data packets. So we use the old protocol, which is what
  88  * their clients use anyway.
  89  */
  90
  91 static unsigned char nybble(unsigned char n)
  92 {
  93         if      (n >= '0' && n <= '9') return n - '0';
  94         else if (n >= 'A' && n <= 'F') return n - ('A' - 10);
  95         else if (n >= 'a' && n <= 'f') return n - ('a' - 10);
  96         return 0;
  97 }
  98
  99 static unsigned char hex(const char *data)
 100 {
 101         return (nybble(data[0]) << 4) | nybble(data[1]);
 102 }
 103
 104 int connect_dtls_socket(struct openconnect_info *vpninfo)
 105 {
 106         STACK_OF(SSL_CIPHER) *ciphers;
 107         SSL_METHOD *dtls_method;
 108         SSL_CIPHER *dtls_cipher;
 109         SSL *dtls_ssl;
 110         BIO *dtls_bio;
 111         int dtls_fd;
 112
 113         if (!vpninfo->dtls_cipher) {
 114                 /* We probably didn't offer it any ciphers it liked */
 115                 vpninfo->progress(vpninfo, PRG_ERR, "Server offered no DTLS cipher option\n");
 116                 return -EINVAL;
 117         }
 118
 119         dtls_fd = socket(vpninfo->peer_addr->sa_family, SOCK_DGRAM, IPPROTO_UDP);
 120         if (dtls_fd < 0) {
 121                 perror("Open UDP socket for DTLS:");
 122                 return -EINVAL;
 123         }
 124
 125         if (connect(dtls_fd, vpninfo->peer_addr, vpninfo->peer_addrlen)) {
 126                 perror("UDP (DTLS) connect:\n");
 127                 close(dtls_fd);
 128                 return -EINVAL;
 129         }
 130
 131         fcntl(dtls_fd, F_SETFD, FD_CLOEXEC);
 132
 133         if (!vpninfo->dtls_ctx) {
 134                 dtls_method = DTLSv1_client_method();
 135                 vpninfo->dtls_ctx = SSL_CTX_new(dtls_method);
 136                 if (!vpninfo->dtls_ctx) {
 137                         vpninfo->progress(vpninfo, PRG_ERR, "Initialise DTLSv1 CTX failed\n");
 138                         vpninfo->dtls_attempt_period = 0;
 139                         return -EINVAL;
 140                 }
 141
 142                 /* If we don't readahead, then we do short reads and throw
 143                    away the tail of data packets. */
 144                 SSL_CTX_set_read_ahead(vpninfo->dtls_ctx, 1);
 145
 146                 if (!SSL_CTX_set_cipher_list(vpninfo->dtls_ctx, vpninfo->dtls_cipher)) {
 147                         vpninfo->progress(vpninfo, PRG_ERR, "Set DTLS cipher list failed\n");
 148                         SSL_CTX_free(vpninfo->dtls_ctx);
 149                         vpninfo->dtls_ctx = NULL;
 150                         vpninfo->dtls_attempt_period = 0;
 151                         return -EINVAL;
 152                 }
 153         }
 154
 155         if (!vpninfo->dtls_session) {
 156                 /* We're going to "resume" a session which never existed. Fake it... */
 157                 vpninfo->dtls_session = SSL_SESSION_new();
 158                 if (!vpninfo->dtls_session) {
 159                         vpninfo->progress(vpninfo, PRG_ERR, "Initialise DTLSv1 session failed\n");
 160                         vpninfo->dtls_attempt_period = 0;
 161                         return -EINVAL;
 162                 }
 163                 vpninfo->dtls_session->ssl_version = 0x0100; // DTLS1_BAD_VER
 164
 165                 vpninfo->dtls_session->master_key_length = sizeof(vpninfo->dtls_secret);
 166                 memcpy(vpninfo->dtls_session->master_key, vpninfo->dtls_secret,
 167                        sizeof(vpninfo->dtls_secret));
 168
 169                 vpninfo->dtls_session->session_id_length = sizeof(vpninfo->dtls_session_id);
 170                 memcpy(vpninfo->dtls_session->session_id, vpninfo->dtls_session_id,
 171                        sizeof(vpninfo->dtls_session_id));
 172         }
 173
 174         dtls_ssl = SSL_new(vpninfo->dtls_ctx);
 175         SSL_set_connect_state(dtls_ssl);
 176
 177         ciphers = SSL_get_ciphers(dtls_ssl);
 178         if (sk_SSL_CIPHER_num(ciphers) != 1) {
 179                 vpninfo->progress(vpninfo, PRG_ERR, "Not precisely one DTLS cipher\n");
 180                 SSL_CTX_free(vpninfo->dtls_ctx);
 181                 SSL_free(dtls_ssl);
 182                 SSL_SESSION_free(vpninfo->dtls_session);
 183                 vpninfo->dtls_ctx = NULL;
 184                 vpninfo->dtls_session = NULL;
 185                 vpninfo->dtls_attempt_period = 0;
 186                 return -EINVAL;
 187         }
 188         dtls_cipher = sk_SSL_CIPHER_value(ciphers, 0);
 189
 190         /* Set the appropriate cipher on our session to be resumed */
 191         vpninfo->dtls_session->cipher = dtls_cipher;
 192         vpninfo->dtls_session->cipher_id = dtls_cipher->id;
 193
 194         /* Add the generated session to the SSL */
 195         if (!SSL_set_session(dtls_ssl, vpninfo->dtls_session)) {
 196                 vpninfo->progress(vpninfo, PRG_ERR,
 197                                   "SSL_set_session() failed with old protocol version 0x%x\n"
 198                                   "Your OpenSSL may lack Cisco compatibility support\n"
 199                                   "See http://rt.openssl.org/Ticket/Display.html?id=1751\n"
 200                                   "Use the --no-dtls command line option to avoid this message\n",
 201                                   vpninfo->dtls_session->ssl_version);
 202                 vpninfo->dtls_attempt_period = 0;
 203                 return -EINVAL;
 204         }
 205
 206         /* Go Go Go! */
 207         dtls_bio = BIO_new_socket(dtls_fd, BIO_NOCLOSE);
 208         SSL_set_bio(dtls_ssl, dtls_bio, dtls_bio);
 209
 210 #ifndef SSL_OP_CISCO_ANYCONNECT
 211 #define SSL_OP_CISCO_ANYCONNECT 0x8000
 212 #endif
 213         SSL_set_options(dtls_ssl, SSL_OP_CISCO_ANYCONNECT);
 214
 215         /* Set non-blocking */
 216         BIO_set_nbio(SSL_get_rbio(dtls_ssl), 1);
 217         BIO_set_nbio(SSL_get_wbio(dtls_ssl), 1);
 218
 219         fcntl(dtls_fd, F_SETFL, fcntl(dtls_fd, F_GETFL) | O_NONBLOCK);
 220
 221         vpninfo->new_dtls_fd = dtls_fd;
 222         vpninfo->new_dtls_ssl = dtls_ssl;
 223
 224         if (vpninfo->select_nfds <= dtls_fd)
 225                 vpninfo->select_nfds = dtls_fd + 1;
 226
 227         FD_SET(dtls_fd, &vpninfo->select_rfds);
 228         FD_SET(dtls_fd, &vpninfo->select_efds);
 229
 230         time(&vpninfo->new_dtls_started);
 231         return dtls_try_handshake(vpninfo);
 232 }
 233
 234 int dtls_try_handshake(struct openconnect_info *vpninfo)
 235 {
 236         int ret = SSL_do_handshake(vpninfo->new_dtls_ssl);
 237
 238         if (ret == 1) {
 239                 vpninfo->progress(vpninfo, PRG_INFO, "Established DTLS connection\n");
 240
 241                 if (vpninfo->dtls_ssl) {
 242                         /* We are replacing an old connection */
 243                         SSL_free(vpninfo->dtls_ssl);
 244                         close(vpninfo->dtls_fd);
 245                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 246                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 247                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 248                 }
 249                 vpninfo->dtls_ssl = vpninfo->new_dtls_ssl;
 250                 vpninfo->dtls_fd = vpninfo->new_dtls_fd;
 251
 252                 vpninfo->new_dtls_ssl = NULL;
 253                 vpninfo->new_dtls_fd = -1;
 254
 255                 vpninfo->dtls_times.last_rekey = vpninfo->dtls_times.last_rx =
 256                         vpninfo->dtls_times.last_tx = time(NULL);
 257
 258                 return 0;
 259         }
 260
 261         ret = SSL_get_error(vpninfo->new_dtls_ssl, ret);
 262         if (ret == SSL_ERROR_WANT_WRITE || ret == SSL_ERROR_WANT_READ) {
 263                 if (time(NULL) < vpninfo->new_dtls_started + 5)
 264                         return 0;
 265                 vpninfo->progress(vpninfo, PRG_TRACE, "DTLS handshake timed out\n");
 266         }
 267
 268         vpninfo->progress(vpninfo, PRG_ERR, "DTLS handshake failed: %d\n", ret);
 269         report_ssl_errors(vpninfo);
 270
 271         /* Kill the new (failed) connection... */
 272         SSL_free(vpninfo->new_dtls_ssl);
 273         FD_CLR(vpninfo->new_dtls_fd, &vpninfo->select_rfds);
 274         FD_CLR(vpninfo->new_dtls_fd, &vpninfo->select_efds);
 275         close(vpninfo->new_dtls_fd);
 276         vpninfo->new_dtls_ssl = NULL;
 277         vpninfo->new_dtls_fd = -1;
 278
 279         /* ... and kill the old one too. The only time there'll be a valid
 280            existing session is when it was a rekey, and in that case it's
 281            time for the old one to die. */
 282         if (vpninfo->dtls_ssl) {
 283                 SSL_free(vpninfo->dtls_ssl);
 284                 close(vpninfo->dtls_fd);
 285                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 286                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 287                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 288                 vpninfo->dtls_ssl = NULL;
 289                 vpninfo->dtls_fd = -1;
 290         }
 291
 292         time(&vpninfo->new_dtls_started);
 293         return -EINVAL;
 294 }
 295
 296 static int dtls_restart(struct openconnect_info *vpninfo)
 297 {
 298         if (vpninfo->dtls_ssl) {
 299                 SSL_free(vpninfo->dtls_ssl);
 300                 close(vpninfo->dtls_fd);
 301                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 302                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 303                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 304                 vpninfo->dtls_ssl = NULL;
 305                 vpninfo->dtls_fd = -1;
 306         }
 307
 308         return connect_dtls_socket(vpninfo);
 309 }
 310
 311
 312 int setup_dtls(struct openconnect_info *vpninfo)
 313 {
 314         struct vpn_option *dtls_opt = vpninfo->dtls_options;
 315         int sessid_found = 0;
 316         int dtls_port = 0;
 317         int i;
 318
 319         while (dtls_opt) {
 320                 vpninfo->progress(vpninfo, PRG_TRACE,
 321                                   "DTLS option %s : %s\n",
 322                                   dtls_opt->option, dtls_opt->value);
 323
 324                 if (!strcmp(dtls_opt->option, "X-DTLS-Session-ID")) {
 325                         if (strlen(dtls_opt->value) != 64) {
 326                                 vpninfo->progress(vpninfo, PRG_ERR, "X-DTLS-Session-ID not 64 characters\n");
 327                                 vpninfo->progress(vpninfo, PRG_ERR, "Is: %s\n", dtls_opt->value);
 328                                 return -EINVAL;
 329                         }
 330                         for (i = 0; i < 64; i += 2)
 331                                 vpninfo->dtls_session_id[i/2] = hex(dtls_opt->value + i);
 332                         sessid_found = 1;
 333                 } else if (!strcmp(dtls_opt->option + 7, "Port")) {
 334                         dtls_port = atol(dtls_opt->value);
 335                 } else if (!strcmp(dtls_opt->option + 7, "Keepalive")) {
 336                         vpninfo->dtls_times.keepalive = atol(dtls_opt->value);
 337                 } else if (!strcmp(dtls_opt->option + 7, "DPD")) {
 338                         vpninfo->dtls_times.dpd = atol(dtls_opt->value);
 339                 } else if (!strcmp(dtls_opt->option + 7, "Rekey-Time")) {
 340                         vpninfo->dtls_times.rekey = atol(dtls_opt->value);
 341                 } else if (!strcmp(dtls_opt->option + 7, "CipherSuite")) {
 342                         vpninfo->dtls_cipher = dtls_opt->value;
 343                 }
 344
 345                 dtls_opt = dtls_opt->next;
 346         }
 347         if (!sessid_found || !dtls_port)
 348                 return -EINVAL;
 349
 350         if (vpninfo->peer_addr->sa_family == AF_INET) {
 351                 struct sockaddr_in *sin = (void *)vpninfo->peer_addr;
 352                 sin->sin_port = htons(dtls_port);
 353         } else if (vpninfo->peer_addr->sa_family == AF_INET6) {
 354                 struct sockaddr_in6 *sin = (void *)vpninfo->peer_addr;
 355                 sin->sin6_port = htons(dtls_port);
 356         } else {
 357                 vpninfo->progress(vpninfo, PRG_ERR, "Unknown protocol family %d. Cannot do DTLS\n",
 358                         vpninfo->peer_addr->sa_family);
 359                 return -EINVAL;
 360         }
 361
 362
 363         if (connect_dtls_socket(vpninfo))
 364                 return -EINVAL;
 365
 366         vpninfo->progress(vpninfo, PRG_TRACE,
 367                           "DTLS connected. DPD %d, Keepalive %d\n",
 368                           vpninfo->dtls_times.dpd, vpninfo->dtls_times.keepalive);
 369
 370         return 0;
 371 }
 372
 373 int dtls_mainloop(struct openconnect_info *vpninfo, int *timeout)
 374 {
 375         unsigned char buf[2000];
 376         int len;
 377         int work_done = 0;
 378         char magic_pkt;
 379
 380         while ( (len = SSL_read(vpninfo->dtls_ssl, buf, sizeof(buf))) > 0 ) {
 381
 382                 vpninfo->progress(vpninfo, PRG_TRACE,
 383                                   "Received DTLS packet 0x%02x of %d bytes\n",
 384                                   buf[0], len);
 385
 386                 vpninfo->dtls_times.last_rx = time(NULL);
 387
 388                 switch(buf[0]) {
 389                 case AC_PKT_DATA:
 390                         queue_new_packet(&vpninfo->incoming_queue, AF_INET, buf+1, len-1);
 391                         work_done = 1;
 392                         break;
 393
 394                 case AC_PKT_DPD_OUT:
 395                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS DPD request\n");
 396
 397                         /* FIXME: What if the packet doesn't get through? */
 398                         magic_pkt = AC_PKT_DPD_RESP;
 399                         if (SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1) != 1)
 400                                 vpninfo->progress(vpninfo, PRG_ERR, "Failed to send DPD response. Expect disconnect\n");
 401                         continue;
 402
 403                 case AC_PKT_DPD_RESP:
 404                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS DPD response\n");
 405                         break;
 406
 407                 case AC_PKT_KEEPALIVE:
 408                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS Keepalive\n");
 409                         break;
 410
 411                 default:
 412                         vpninfo->progress(vpninfo, PRG_ERR,
 413                                           "Unknown DTLS packet type %02x, len %d\n", buf[0], len);
 414                         if (1) {
 415                                 /* Some versions of OpenSSL have bugs with receiving out-of-order
 416                                  * packets. Not only do they wrongly decide to drop packets if
 417                                  * two packets get swapped in transit, but they also _fail_ to
 418                                  * drop the packet in non-blocking mode; instead they return
 419                                  * the appropriate length of garbage. So don't abort... for now. */
 420                                 break;
 421                         } else {
 422                                 vpninfo->quit_reason = "Unknown packet received";
 423                                 return 1;
 424                         }
 425
 426                 }
 427         }
 428
 429         switch (keepalive_action(&vpninfo->dtls_times, timeout)) {
 430         case KA_REKEY:
 431                 time(&vpninfo->dtls_times.last_rekey);
 432                 vpninfo->progress(vpninfo, PRG_TRACE, "DTLS rekey due\n");
 433                 if (connect_dtls_socket(vpninfo)) {
 434                         vpninfo->progress(vpninfo, PRG_ERR, "DTLS rekey failed\n");
 435                         return 1;
 436                 }
 437                 work_done = 1;
 438                 break;
 439
 440
 441         case KA_DPD_DEAD:
 442                 vpninfo->progress(vpninfo, PRG_ERR, "DTLS Dead Peer Detection detected dead peer!\n");
 443                 /* Fall back to SSL, and start a new DTLS connection */
 444                 dtls_restart(vpninfo);
 445                 return 1;
 446
 447         case KA_DPD:
 448                 vpninfo->progress(vpninfo, PRG_TRACE, "Send DTLS DPD\n");
 449
 450                 magic_pkt = AC_PKT_DPD_OUT;
 451                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 452                 /* last_dpd will just have been set */
 453                 vpninfo->dtls_times.last_tx = vpninfo->dtls_times.last_dpd;
 454                 work_done = 1;
 455                 break;
 456
 457         case KA_KEEPALIVE:
 458                 /* No need to send an explicit keepalive
 459                    if we have real data to send */
 460                 if (vpninfo->outgoing_queue)
 461                         break;
 462
 463                 vpninfo->progress(vpninfo, PRG_TRACE, "Send DTLS Keepalive\n");
 464
 465                 magic_pkt = AC_PKT_KEEPALIVE;
 466                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 467                 time(&vpninfo->dtls_times.last_tx);
 468                 work_done = 1;
 469                 break;
 470
 471         case KA_NONE:
 472                 ;
 473         }
 474
 475         /* Service outgoing packet queue */
 476         while (vpninfo->outgoing_queue) {
 477                 struct pkt *this = vpninfo->outgoing_queue;
 478                 int ret;
 479
 480                 vpninfo->outgoing_queue = this->next;
 481                 vpninfo->outgoing_qlen--;
 482
 483                 /* FIXME: Don't know how to handle IPv6 yet */
 484                 if (this->type != AF_INET)
 485                         continue;
 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
 516