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 #define SSL_OP_CISCO_ANYCONNECT 0x8000
 215 #endif
 216         SSL_set_options(dtls_ssl, SSL_OP_CISCO_ANYCONNECT);
 217
 218         /* Set non-blocking */
 219         BIO_set_nbio(SSL_get_rbio(dtls_ssl), 1);
 220         BIO_set_nbio(SSL_get_wbio(dtls_ssl), 1);
 221
 222         fcntl(dtls_fd, F_SETFL, fcntl(dtls_fd, F_GETFL) | O_NONBLOCK);
 223
 224         vpninfo->new_dtls_fd = dtls_fd;
 225         vpninfo->new_dtls_ssl = dtls_ssl;
 226
 227         if (vpninfo->select_nfds <= dtls_fd)
 228                 vpninfo->select_nfds = dtls_fd + 1;
 229
 230         FD_SET(dtls_fd, &vpninfo->select_rfds);
 231         FD_SET(dtls_fd, &vpninfo->select_efds);
 232
 233         time(&vpninfo->new_dtls_started);
 234         return dtls_try_handshake(vpninfo);
 235 }
 236
 237 int dtls_try_handshake(struct openconnect_info *vpninfo)
 238 {
 239         int ret = SSL_do_handshake(vpninfo->new_dtls_ssl);
 240
 241         if (ret == 1) {
 242                 vpninfo->progress(vpninfo, PRG_INFO, "Established DTLS connection\n");
 243
 244                 if (vpninfo->dtls_ssl) {
 245                         /* We are replacing an old connection */
 246                         SSL_free(vpninfo->dtls_ssl);
 247                         close(vpninfo->dtls_fd);
 248                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 249                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 250                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 251                 }
 252                 vpninfo->dtls_ssl = vpninfo->new_dtls_ssl;
 253                 vpninfo->dtls_fd = vpninfo->new_dtls_fd;
 254
 255                 vpninfo->new_dtls_ssl = NULL;
 256                 vpninfo->new_dtls_fd = -1;
 257
 258                 vpninfo->dtls_times.last_rekey = vpninfo->dtls_times.last_rx =
 259                         vpninfo->dtls_times.last_tx = time(NULL);
 260
 261                 return 0;
 262         }
 263
 264         ret = SSL_get_error(vpninfo->new_dtls_ssl, ret);
 265         if (ret == SSL_ERROR_WANT_WRITE || ret == SSL_ERROR_WANT_READ) {
 266                 if (time(NULL) < vpninfo->new_dtls_started + 5)
 267                         return 0;
 268                 vpninfo->progress(vpninfo, PRG_TRACE, "DTLS handshake timed out\n");
 269         }
 270
 271         vpninfo->progress(vpninfo, PRG_ERR, "DTLS handshake failed: %d\n", ret);
 272         report_ssl_errors(vpninfo);
 273
 274         /* Kill the new (failed) connection... */
 275         SSL_free(vpninfo->new_dtls_ssl);
 276         FD_CLR(vpninfo->new_dtls_fd, &vpninfo->select_rfds);
 277         FD_CLR(vpninfo->new_dtls_fd, &vpninfo->select_efds);
 278         close(vpninfo->new_dtls_fd);
 279         vpninfo->new_dtls_ssl = NULL;
 280         vpninfo->new_dtls_fd = -1;
 281
 282         /* ... and kill the old one too. The only time there'll be a valid
 283            existing session is when it was a rekey, and in that case it's
 284            time for the old one to die. */
 285         if (vpninfo->dtls_ssl) {
 286                 SSL_free(vpninfo->dtls_ssl);
 287                 close(vpninfo->dtls_fd);
 288                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 289                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 290                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 291                 vpninfo->dtls_ssl = NULL;
 292                 vpninfo->dtls_fd = -1;
 293         }
 294
 295         time(&vpninfo->new_dtls_started);
 296         return -EINVAL;
 297 }
 298
 299 static int dtls_restart(struct openconnect_info *vpninfo)
 300 {
 301         if (vpninfo->dtls_ssl) {
 302                 SSL_free(vpninfo->dtls_ssl);
 303                 close(vpninfo->dtls_fd);
 304                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 305                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 306                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 307                 vpninfo->dtls_ssl = NULL;
 308                 vpninfo->dtls_fd = -1;
 309         }
 310
 311         return connect_dtls_socket(vpninfo);
 312 }
 313
 314
 315 int setup_dtls(struct openconnect_info *vpninfo)
 316 {
 317         struct vpn_option *dtls_opt = vpninfo->dtls_options;
 318         int sessid_found = 0;
 319         int dtls_port = 0;
 320         int i;
 321
 322         while (dtls_opt) {
 323                 vpninfo->progress(vpninfo, PRG_TRACE,
 324                                   "DTLS option %s : %s\n",
 325                                   dtls_opt->option, dtls_opt->value);
 326
 327                 if (!strcmp(dtls_opt->option, "X-DTLS-Session-ID")) {
 328                         if (strlen(dtls_opt->value) != 64) {
 329                                 vpninfo->progress(vpninfo, PRG_ERR, "X-DTLS-Session-ID not 64 characters\n");
 330                                 vpninfo->progress(vpninfo, PRG_ERR, "Is: %s\n", dtls_opt->value);
 331                                 return -EINVAL;
 332                         }
 333                         for (i = 0; i < 64; i += 2)
 334                                 vpninfo->dtls_session_id[i/2] = hex(dtls_opt->value + i);
 335                         sessid_found = 1;
 336                 } else if (!strcmp(dtls_opt->option + 7, "Port")) {
 337                         dtls_port = atol(dtls_opt->value);
 338                 } else if (!strcmp(dtls_opt->option + 7, "Keepalive")) {
 339                         vpninfo->dtls_times.keepalive = atol(dtls_opt->value);
 340                 } else if (!strcmp(dtls_opt->option + 7, "DPD")) {
 341                         vpninfo->dtls_times.dpd = atol(dtls_opt->value);
 342                 } else if (!strcmp(dtls_opt->option + 7, "Rekey-Time")) {
 343                         vpninfo->dtls_times.rekey = atol(dtls_opt->value);
 344                 } else if (!strcmp(dtls_opt->option + 7, "CipherSuite")) {
 345                         vpninfo->dtls_cipher = strdup(dtls_opt->value);
 346                 }
 347
 348                 dtls_opt = dtls_opt->next;
 349         }
 350         if (!sessid_found || !dtls_port)
 351                 return -EINVAL;
 352
 353         if (vpninfo->peer_addr->sa_family == AF_INET) {
 354                 struct sockaddr_in *sin = (void *)vpninfo->peer_addr;
 355                 sin->sin_port = htons(dtls_port);
 356         } else if (vpninfo->peer_addr->sa_family == AF_INET6) {
 357                 struct sockaddr_in6 *sin = (void *)vpninfo->peer_addr;
 358                 sin->sin6_port = htons(dtls_port);
 359         } else {
 360                 vpninfo->progress(vpninfo, PRG_ERR, "Unknown protocol family %d. Cannot do DTLS\n",
 361                         vpninfo->peer_addr->sa_family);
 362                 return -EINVAL;
 363         }
 364
 365
 366         if (connect_dtls_socket(vpninfo))
 367                 return -EINVAL;
 368
 369         vpninfo->progress(vpninfo, PRG_TRACE,
 370                           "DTLS connected. DPD %d, Keepalive %d\n",
 371                           vpninfo->dtls_times.dpd, vpninfo->dtls_times.keepalive);
 372
 373         return 0;
 374 }
 375
 376 int dtls_mainloop(struct openconnect_info *vpninfo, int *timeout)
 377 {
 378         unsigned char buf[2000];
 379         int len;
 380         int work_done = 0;
 381         char magic_pkt;
 382
 383         while ( (len = SSL_read(vpninfo->dtls_ssl, buf, sizeof(buf))) > 0 ) {
 384
 385                 vpninfo->progress(vpninfo, PRG_TRACE,
 386                                   "Received DTLS packet 0x%02x of %d bytes\n",
 387                                   buf[0], len);
 388
 389                 vpninfo->dtls_times.last_rx = time(NULL);
 390
 391                 switch(buf[0]) {
 392                 case AC_PKT_DATA:
 393                         queue_new_packet(&vpninfo->incoming_queue, AF_INET, buf+1, len-1);
 394                         work_done = 1;
 395                         break;
 396
 397                 case AC_PKT_DPD_OUT:
 398                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS DPD request\n");
 399
 400                         /* FIXME: What if the packet doesn't get through? */
 401                         magic_pkt = AC_PKT_DPD_RESP;
 402                         if (SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1) != 1)
 403                                 vpninfo->progress(vpninfo, PRG_ERR, "Failed to send DPD response. Expect disconnect\n");
 404                         continue;
 405
 406                 case AC_PKT_DPD_RESP:
 407                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS DPD response\n");
 408                         break;
 409
 410                 case AC_PKT_KEEPALIVE:
 411                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS Keepalive\n");
 412                         break;
 413
 414                 default:
 415                         vpninfo->progress(vpninfo, PRG_ERR,
 416                                           "Unknown DTLS packet type %02x, len %d\n", buf[0], len);
 417                         if (1) {
 418                                 /* Some versions of OpenSSL have bugs with receiving out-of-order
 419                                  * packets. Not only do they wrongly decide to drop packets if
 420                                  * two packets get swapped in transit, but they also _fail_ to
 421                                  * drop the packet in non-blocking mode; instead they return
 422                                  * the appropriate length of garbage. So don't abort... for now. */
 423                                 break;
 424                         } else {
 425                                 vpninfo->quit_reason = "Unknown packet received";
 426                                 return 1;
 427                         }
 428
 429                 }
 430         }
 431
 432         switch (keepalive_action(&vpninfo->dtls_times, timeout)) {
 433         case KA_REKEY:
 434                 time(&vpninfo->dtls_times.last_rekey);
 435                 vpninfo->progress(vpninfo, PRG_TRACE, "DTLS rekey due\n");
 436                 if (connect_dtls_socket(vpninfo)) {
 437                         vpninfo->progress(vpninfo, PRG_ERR, "DTLS rekey failed\n");
 438                         return 1;
 439                 }
 440                 work_done = 1;
 441                 break;
 442
 443
 444         case KA_DPD_DEAD:
 445                 vpninfo->progress(vpninfo, PRG_ERR, "DTLS Dead Peer Detection detected dead peer!\n");
 446                 /* Fall back to SSL, and start a new DTLS connection */
 447                 dtls_restart(vpninfo);
 448                 return 1;
 449
 450         case KA_DPD:
 451                 vpninfo->progress(vpninfo, PRG_TRACE, "Send DTLS DPD\n");
 452
 453                 magic_pkt = AC_PKT_DPD_OUT;
 454                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 455                 /* last_dpd will just have been set */
 456                 vpninfo->dtls_times.last_tx = vpninfo->dtls_times.last_dpd;
 457                 work_done = 1;
 458                 break;
 459
 460         case KA_KEEPALIVE:
 461                 /* No need to send an explicit keepalive
 462                    if we have real data to send */
 463                 if (vpninfo->outgoing_queue)
 464                         break;
 465
 466                 vpninfo->progress(vpninfo, PRG_TRACE, "Send DTLS Keepalive\n");
 467
 468                 magic_pkt = AC_PKT_KEEPALIVE;
 469                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 470                 time(&vpninfo->dtls_times.last_tx);
 471                 work_done = 1;
 472                 break;
 473
 474         case KA_NONE:
 475                 ;
 476         }
 477
 478         /* Service outgoing packet queue */
 479         while (vpninfo->outgoing_queue) {
 480                 struct pkt *this = vpninfo->outgoing_queue;
 481                 int ret;
 482
 483                 vpninfo->outgoing_queue = this->next;
 484                 vpninfo->outgoing_qlen--;
 485
 486                 /* FIXME: Don't know how to handle IPv6 yet */
 487                 if (this->type != AF_INET)
 488                         continue;
 489
 490                 /* One byte of header */
 491                 this->hdr[7] = AC_PKT_DATA;
 492
 493                 ret = SSL_write(vpninfo->dtls_ssl, &this->hdr[7], this->len + 1);
 494                 if (ret <= 0) {
 495                         ret = SSL_get_error(vpninfo->dtls_ssl, ret);
 496
 497                         /* If it's a real error, kill the DTLS connection and
 498                            requeue the packet to be sent over SSL */
 499                         if (ret != SSL_ERROR_WANT_READ && ret != SSL_ERROR_WANT_WRITE) {
 500                                 vpninfo->progress(vpninfo, PRG_ERR,
 501                                                   "DTLS got write error %d. Falling back to SSL\n", ret);
 502                                 report_ssl_errors(vpninfo);
 503                                 dtls_restart(vpninfo);
 504                                 vpninfo->outgoing_queue = this;
 505                                 vpninfo->outgoing_qlen++;
 506                         }
 507                         return 1;
 508                 }
 509                 time(&vpninfo->dtls_times.last_tx);
 510                 vpninfo->progress(vpninfo, PRG_TRACE,
 511                                   "Sent DTLS packet of %d bytes; SSL_write() returned %d\n",
 512                                   this->len, ret);
 513                 free(this);
 514         }
 515
 516         return work_done;
 517 }
 518 #else /* No DTLS support in OpenSSL */
 519 int setup_dtls(struct openconnect_info *vpninfo)
 520 {
 521         vpninfo->progress(vpninfo, PRG_ERR, "Built against OpenSSL with no DTLS support\n");
 522         return -EINVAL;
 523 }
 524 #endif
 525