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         SSL_METHOD *dtls_method;
 107         SSL_CIPHER *https_cipher;
 108         SSL *dtls_ssl;
 109         BIO *dtls_bio;
 110         int dtls_fd;
 111
 112         dtls_fd = socket(vpninfo->peer_addr->sa_family, SOCK_DGRAM, IPPROTO_UDP);
 113         if (dtls_fd < 0) {
 114                 perror("Open UDP socket for DTLS:");
 115                 return -EINVAL;
 116         }
 117
 118         if (connect(dtls_fd, vpninfo->peer_addr, vpninfo->peer_addrlen)) {
 119                 perror("UDP (DTLS) connect:\n");
 120                 close(dtls_fd);
 121                 return -EINVAL;
 122         }
 123
 124         fcntl(dtls_fd, F_SETFD, FD_CLOEXEC);
 125
 126         https_cipher = SSL_get_current_cipher(vpninfo->https_ssl);
 127
 128         if (!vpninfo->dtls_ctx) {
 129                 dtls_method = DTLSv1_client_method();
 130                 vpninfo->dtls_ctx = SSL_CTX_new(dtls_method);
 131                 if (!vpninfo->dtls_ctx) {
 132                         vpninfo->progress(vpninfo, PRG_ERR, "Initialise DTLSv1 CTX failed\n");
 133                         return -EINVAL;
 134                 }
 135
 136                 /* If we don't readahead, then we do short reads and throw
 137                    away the tail of data packets. */
 138                 SSL_CTX_set_read_ahead(vpninfo->dtls_ctx, 1);
 139         }
 140
 141         if (!vpninfo->dtls_session) {
 142                 /* We're going to "resume" a session which never existed. Fake it... */
 143                 vpninfo->dtls_session = SSL_SESSION_new();
 144                 if (!vpninfo->dtls_session) {
 145                         vpninfo->progress(vpninfo, PRG_ERR, "Initialise DTLSv1 session failed\n");
 146                         return -EINVAL;
 147                 }
 148                 vpninfo->dtls_session->ssl_version = 0x0100; // DTLS1_BAD_VER
 149
 150                 vpninfo->dtls_session->master_key_length = sizeof(vpninfo->dtls_secret);
 151                 memcpy(vpninfo->dtls_session->master_key, vpninfo->dtls_secret,
 152                        sizeof(vpninfo->dtls_secret));
 153
 154                 vpninfo->dtls_session->session_id_length = sizeof(vpninfo->dtls_session_id);
 155                 memcpy(vpninfo->dtls_session->session_id, vpninfo->dtls_session_id,
 156                        sizeof(vpninfo->dtls_session_id));
 157
 158                 vpninfo->dtls_session->cipher = https_cipher;
 159                 vpninfo->dtls_session->cipher_id = https_cipher->id;
 160         }
 161
 162         dtls_ssl = SSL_new(vpninfo->dtls_ctx);
 163         SSL_set_connect_state(dtls_ssl);
 164         SSL_set_cipher_list(dtls_ssl, SSL_CIPHER_get_name(https_cipher));
 165
 166         /* Add the generated session to the SSL */
 167         if (!SSL_set_session(dtls_ssl, vpninfo->dtls_session)) {
 168                 vpninfo->progress(vpninfo, PRG_ERR,
 169                                   "SSL_set_session() failed with old protocol version 0x%x\n"
 170                                   "Your OpenSSL may lack Cisco compatibility support\n"
 171                                   "See http://rt.openssl.org/Ticket/Display.html?id=1751\n"
 172                                   "Use the --no-dtls command line option to avoid this message\n",
 173                                   vpninfo->dtls_session->ssl_version);
 174                 vpninfo->dtls_attempt_period = 0;
 175                 return -EINVAL;
 176         }
 177
 178         /* Go Go Go! */
 179         dtls_bio = BIO_new_socket(dtls_fd, BIO_NOCLOSE);
 180         SSL_set_bio(dtls_ssl, dtls_bio, dtls_bio);
 181
 182 #ifndef SSL_OP_CISCO_ANYCONNECT
 183 #define SSL_OP_CISCO_ANYCONNECT 0x8000
 184 #endif
 185         SSL_set_options(dtls_ssl, SSL_OP_CISCO_ANYCONNECT);
 186
 187         /* Set non-blocking */
 188         BIO_set_nbio(SSL_get_rbio(dtls_ssl),1);
 189         BIO_set_nbio(SSL_get_wbio(dtls_ssl),1);
 190
 191         fcntl(dtls_fd, F_SETFL, fcntl(dtls_fd, F_GETFL) | O_NONBLOCK);
 192
 193         vpninfo->new_dtls_fd = dtls_fd;
 194         vpninfo->new_dtls_ssl = dtls_ssl;
 195
 196         if (vpninfo->select_nfds <= dtls_fd)
 197                 vpninfo->select_nfds = dtls_fd + 1;
 198
 199         FD_SET(dtls_fd, &vpninfo->select_rfds);
 200         FD_SET(dtls_fd, &vpninfo->select_efds);
 201
 202         time(&vpninfo->new_dtls_started);
 203         return dtls_try_handshake(vpninfo);
 204 }
 205
 206 int dtls_try_handshake(struct openconnect_info *vpninfo)
 207 {
 208         int ret = SSL_do_handshake(vpninfo->new_dtls_ssl);
 209
 210         if (ret == 1) {
 211                 vpninfo->progress(vpninfo, PRG_INFO, "Established DTLS connection\n");
 212
 213                 if (vpninfo->dtls_ssl) {
 214                         /* We are replacing an old connection */
 215                         SSL_free(vpninfo->dtls_ssl);
 216                         close(vpninfo->dtls_fd);
 217                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 218                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 219                         FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 220                 }
 221                 vpninfo->dtls_ssl = vpninfo->new_dtls_ssl;
 222                 vpninfo->dtls_fd = vpninfo->new_dtls_fd;
 223
 224                 vpninfo->new_dtls_ssl = NULL;
 225                 vpninfo->new_dtls_fd = -1;
 226
 227                 vpninfo->dtls_times.last_rekey = vpninfo->dtls_times.last_rx =
 228                         vpninfo->dtls_times.last_tx = time(NULL);
 229
 230                 return 0;
 231         }
 232
 233         ret = SSL_get_error(vpninfo->new_dtls_ssl, ret);
 234         if (ret == SSL_ERROR_WANT_WRITE || ret == SSL_ERROR_WANT_READ) {
 235                 if (time(NULL) < vpninfo->new_dtls_started + 5)
 236                         return 0;
 237                 vpninfo->progress(vpninfo, PRG_TRACE, "DTLS handshake timed out\n");
 238         }
 239
 240         vpninfo->progress(vpninfo, PRG_ERR, "DTLS handshake failed: %d\n", ret);
 241         ERR_print_errors_fp(stderr);
 242
 243         /* Kill the new (failed) connection... */
 244         SSL_free(vpninfo->new_dtls_ssl);
 245         FD_CLR(vpninfo->new_dtls_fd, &vpninfo->select_rfds);
 246         FD_CLR(vpninfo->new_dtls_fd, &vpninfo->select_efds);
 247         close(vpninfo->new_dtls_fd);
 248         vpninfo->new_dtls_ssl = NULL;
 249         vpninfo->new_dtls_fd = -1;
 250
 251         /* ... and kill the old one too. The only time there'll be a valid
 252            existing session is when it was a rekey, and in that case it's
 253            time for the old one to die. */
 254         if (vpninfo->dtls_ssl) {
 255                 SSL_free(vpninfo->dtls_ssl);
 256                 close(vpninfo->dtls_fd);
 257                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 258                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 259                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 260                 vpninfo->dtls_ssl = NULL;
 261                 vpninfo->dtls_fd = -1;
 262         }
 263
 264         time(&vpninfo->new_dtls_started);
 265         return -EINVAL;
 266 }
 267
 268 static int dtls_restart(struct openconnect_info *vpninfo)
 269 {
 270         if (vpninfo->dtls_ssl) {
 271                 SSL_free(vpninfo->dtls_ssl);
 272                 close(vpninfo->dtls_fd);
 273                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_rfds);
 274                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_wfds);
 275                 FD_CLR(vpninfo->dtls_fd, &vpninfo->select_efds);
 276                 vpninfo->dtls_ssl = NULL;
 277                 vpninfo->dtls_fd = -1;
 278         }
 279
 280         return connect_dtls_socket(vpninfo);
 281 }
 282
 283
 284 int setup_dtls(struct openconnect_info *vpninfo)
 285 {
 286         struct vpn_option *dtls_opt = vpninfo->dtls_options;
 287         int sessid_found = 0;
 288         int dtls_port = 0;
 289         int i;
 290
 291         while (dtls_opt) {
 292                 vpninfo->progress(vpninfo, PRG_TRACE,
 293                                   "DTLS option %s : %s\n",
 294                                   dtls_opt->option, dtls_opt->value);
 295
 296                 if (!strcmp(dtls_opt->option, "X-DTLS-Session-ID")) {
 297                         if (strlen(dtls_opt->value) != 64) {
 298                                 vpninfo->progress(vpninfo, PRG_ERR, "X-DTLS-Session-ID not 64 characters\n");
 299                                 vpninfo->progress(vpninfo, PRG_ERR, "Is: %s\n", dtls_opt->value);
 300                                 return -EINVAL;
 301                         }
 302                         for (i = 0; i < 64; i += 2)
 303                                 vpninfo->dtls_session_id[i/2] = hex(dtls_opt->value + i);
 304                         sessid_found = 1;
 305                 } else if (!strcmp(dtls_opt->option + 7, "Port")) {
 306                         dtls_port = atol(dtls_opt->value);
 307                 } else if (!strcmp(dtls_opt->option + 7, "Keepalive")) {
 308                         vpninfo->dtls_times.keepalive = atol(dtls_opt->value);
 309                 } else if (!strcmp(dtls_opt->option + 7, "DPD")) {
 310                         vpninfo->dtls_times.dpd = atol(dtls_opt->value);
 311                 } else if (!strcmp(dtls_opt->option + 7, "Rekey-Time")) {
 312                         vpninfo->dtls_times.rekey = atol(dtls_opt->value);
 313                 }
 314
 315                 dtls_opt = dtls_opt->next;
 316         }
 317         if (!sessid_found || !dtls_port)
 318                 return -EINVAL;
 319
 320         if (vpninfo->peer_addr->sa_family == AF_INET) {
 321                 struct sockaddr_in *sin = (void *)vpninfo->peer_addr;
 322                 sin->sin_port = htons(dtls_port);
 323         } else if (vpninfo->peer_addr->sa_family == AF_INET6) {
 324                 struct sockaddr_in6 *sin = (void *)vpninfo->peer_addr;
 325                 sin->sin6_port = htons(dtls_port);
 326         } else {
 327                 vpninfo->progress(vpninfo, PRG_ERR, "Unknown protocol family %d. Cannot do DTLS\n",
 328                         vpninfo->peer_addr->sa_family);
 329                 return -EINVAL;
 330         }
 331
 332
 333         if (connect_dtls_socket(vpninfo))
 334                 return -EINVAL;
 335
 336         vpninfo->progress(vpninfo, PRG_TRACE,
 337                           "DTLS connected. DPD %d, Keepalive %d\n",
 338                           vpninfo->dtls_times.dpd, vpninfo->dtls_times.keepalive);
 339
 340         return 0;
 341 }
 342
 343 int dtls_mainloop(struct openconnect_info *vpninfo, int *timeout)
 344 {
 345         unsigned char buf[2000];
 346         int len;
 347         int work_done = 0;
 348         char magic_pkt;
 349
 350         while ( (len = SSL_read(vpninfo->dtls_ssl, buf, sizeof(buf))) > 0 ) {
 351
 352                 vpninfo->progress(vpninfo, PRG_TRACE,
 353                                   "Received DTLS packet 0x%02x of %d bytes\n",
 354                                   buf[0], len);
 355
 356                 vpninfo->dtls_times.last_rx = time(NULL);
 357
 358                 switch(buf[0]) {
 359                 case AC_PKT_DATA:
 360                         queue_new_packet(&vpninfo->incoming_queue, AF_INET, buf+1, len-1);
 361                         work_done = 1;
 362                         break;
 363
 364                 case AC_PKT_DPD_OUT:
 365                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS DPD request\n");
 366
 367                         /* FIXME: What if the packet doesn't get through? */
 368                         magic_pkt = AC_PKT_DPD_RESP;
 369                         if (SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1) != 1)
 370                                 vpninfo->progress(vpninfo, PRG_ERR, "Failed to send DPD response. Expect disconnect\n");
 371                         continue;
 372
 373                 case AC_PKT_DPD_RESP:
 374                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS DPD response\n");
 375                         break;
 376
 377                 case AC_PKT_KEEPALIVE:
 378                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS Keepalive\n");
 379                         break;
 380
 381                 default:
 382                         vpninfo->progress(vpninfo, PRG_ERR,
 383                                           "Unknown DTLS packet type %02x, len %d\n", buf[0], len);
 384                         if (1) {
 385                                 /* Some versions of OpenSSL have bugs with receiving out-of-order
 386                                  * packets. Not only do they wrongly decide to drop packets if
 387                                  * two packets get swapped in transit, but they also _fail_ to
 388                                  * drop the packet in non-blocking mode; instead they return
 389                                  * the appropriate length of garbage. So don't abort... for now. */
 390                                 break;
 391                         } else {
 392                                 vpninfo->quit_reason = "Unknown packet received";
 393                                 return 1;
 394                         }
 395
 396                 }
 397         }
 398
 399         switch (keepalive_action(&vpninfo->dtls_times, timeout)) {
 400         case KA_REKEY:
 401                 time(&vpninfo->dtls_times.last_rekey);
 402                 vpninfo->progress(vpninfo, PRG_TRACE, "DTLS rekey due\n");
 403                 if (connect_dtls_socket(vpninfo)) {
 404                         vpninfo->progress(vpninfo, PRG_ERR, "DTLS rekey failed\n");
 405                         return 1;
 406                 }
 407                 work_done = 1;
 408                 break;
 409
 410
 411         case KA_DPD_DEAD:
 412                 vpninfo->progress(vpninfo, PRG_ERR, "DTLS Dead Peer Detection detected dead peer!\n");
 413                 /* Fall back to SSL, and start a new DTLS connection */
 414                 dtls_restart(vpninfo);
 415                 return 1;
 416
 417         case KA_DPD:
 418                 vpninfo->progress(vpninfo, PRG_TRACE, "Send DTLS DPD\n");
 419
 420                 magic_pkt = AC_PKT_DPD_OUT;
 421                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 422                 /* last_dpd will just have been set */
 423                 vpninfo->dtls_times.last_tx = vpninfo->dtls_times.last_dpd;
 424                 work_done = 1;
 425                 break;
 426
 427         case KA_KEEPALIVE:
 428                 /* No need to send an explicit keepalive
 429                    if we have real data to send */
 430                 if (vpninfo->outgoing_queue)
 431                         break;
 432
 433                 vpninfo->progress(vpninfo, PRG_TRACE, "Send DTLS Keepalive\n");
 434
 435                 magic_pkt = AC_PKT_KEEPALIVE;
 436                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 437                 time(&vpninfo->dtls_times.last_tx);
 438                 work_done = 1;
 439                 break;
 440
 441         case KA_NONE:
 442                 ;
 443         }
 444
 445         /* Service outgoing packet queue */
 446         while (vpninfo->outgoing_queue) {
 447                 struct pkt *this = vpninfo->outgoing_queue;
 448                 int ret;
 449
 450                 vpninfo->outgoing_queue = this->next;
 451                 vpninfo->outgoing_qlen--;
 452
 453                 /* One byte of header */
 454                 this->hdr[7] = AC_PKT_DATA;
 455
 456                 ret = SSL_write(vpninfo->dtls_ssl, &this->hdr[7], this->len + 1);
 457                 if (ret <= 0) {
 458                         ret = SSL_get_error(vpninfo->dtls_ssl, ret);
 459
 460                         /* If it's a real error, kill the DTLS connection and
 461                            requeue the packet to be sent over SSL */
 462                         if (ret != SSL_ERROR_WANT_READ && ret != SSL_ERROR_WANT_WRITE) {
 463                                 vpninfo->progress(vpninfo, PRG_ERR,
 464                                                   "DTLS got write error %d. Falling back to SSL\n", ret);
 465                                 ERR_print_errors_fp(stderr);
 466                                 dtls_restart(vpninfo);
 467                                 vpninfo->outgoing_queue = this;
 468                                 vpninfo->outgoing_qlen++;
 469                         }
 470                         return 1;
 471                 }
 472                 time(&vpninfo->dtls_times.last_tx);
 473                 vpninfo->progress(vpninfo, PRG_TRACE,
 474                                   "Sent DTLS packet of %d bytes; SSL_write() returned %d\n",
 475                                   this->len, ret);
 476                 free(this);
 477         }
 478
 479         return work_done;
 480 }
 481
 482