dtls.c

   1 /*
   2  * Open AnyConnect (SSL + DTLS) client
   3  *
   4  * © 2008 David Woodhouse <dwmw2@infradead.org>
   5  *
   6  * This library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public License
   8  * as published by the Free Software Foundation; either version 2.1 of
   9  * the License, or (at your option) any later version.
  10  *
  11  * This library is distributed in the hope that it will be useful, but
  12  * WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with this library; if not, write to:
  18  *
  19  *   Free Software Foundation, Inc.
  20  *   51 Franklin Street, Fifth Floor,
  21  *   Boston, MA 02110-1301 USA
  22  */
  23
  24 #include <errno.h>
  25 #include <sys/types.h>
  26 #include <sys/socket.h>
  27 #include <netdb.h>
  28 #include <unistd.h>
  29 #include <openssl/err.h>
  30 #include <fcntl.h>
  31 #include <string.h>
  32
  33 #include "openconnect.h"
  34
  35 #if 0
  36 /*
  37  * Useful for catching test cases, where we want everything to be
  38  * reproducible.  *NEVER* do this in the wild.
  39  */
  40 time_t time(time_t *t)
  41 {
  42         time_t x = 0x3ab2d948;
  43         if (t) *t = x;
  44         return x;
  45 }
  46
  47 int RAND_pseudo_bytes(char *buf, int len)
  48 {
  49         memset(buf, 0x5a, len);
  50         printf("FAKE PSEUDO RANDOM!\n");
  51         return 1;
  52
  53 }
  54 int RAND_bytes(char *buf, int len)
  55 {
  56         static int foo = 0x5b;
  57         printf("FAKE RANDOM!\n");
  58         memset(buf, foo, len);
  59         return 1;
  60 }
  61 #endif
  62
  63 /*
  64  * The master-secret is generated randomly by the client. The server
  65  * responds with a DTLS Session-ID. These, done over the HTTPS
  66  * connection, are enough to 'resume' a DTLS session, bypassing all
  67  * the normal setup of a normal DTLS connection.
  68  *
  69  * Cisco use a version of the protocol which predates RFC4347, but
  70  * isn't quite the same as the pre-RFC version of the protocol which
  71  * was in OpenSSL 0.9.8e -- it includes backports of some later
  72  * OpenSSL patches.
  73  *
  74  * The openssl/ directory of this source tree should contain both a
  75  * small patch against OpenSSL 0.9.8e to make it support Cisco's
  76  * snapshot of the protocol, and a larger patch against newer OpenSSL
  77  * which gives us an option to use the old protocol again.
  78  *
  79  * Cisco's server also seems to respond to the official version of the
  80  * protocol, with a change in the ChangeCipherSpec packet which implies
  81  * that it does know the difference and isn't just repeating the version
  82  * number seen in the ClientHello. But although I can make the handshake
  83  * complete by hacking tls1_mac() to use the _old_ protocol version
  84  * number when calculating the MAC, the server still seems to be ignoring
  85  * my subsequent data packets. So we use the old protocol, which is what
  86  * their clients use anyway.
  87  */
  88
  89 static unsigned char nybble(unsigned char n)
  90 {
  91         if      (n >= '0' && n <= '9') return n - '0';
  92         else if (n >= 'A' && n <= 'F') return n - ('A' - 10);
  93         else if (n >= 'a' && n <= 'f') return n - ('a' - 10);
  94         return 0;
  95 }
  96
  97 static unsigned char hex(const char *data)
  98 {
  99         return (nybble(data[0]) << 4) | nybble(data[1]);
 100 }
 101
 102 int connect_dtls_socket(struct openconnect_info *vpninfo)
 103 {
 104         SSL_METHOD *dtls_method;
 105         SSL_CIPHER *https_cipher;
 106         SSL *dtls_ssl;
 107         BIO *dtls_bio;
 108         int dtls_fd;
 109
 110         dtls_fd = socket(vpninfo->peer_addr->sa_family, SOCK_DGRAM, IPPROTO_UDP);
 111         if (dtls_fd < 0) {
 112                 perror("Open UDP socket for DTLS:");
 113                 return -EINVAL;
 114         }
 115
 116         if (connect(dtls_fd, vpninfo->peer_addr, vpninfo->peer_addrlen)) {
 117                 perror("UDP (DTLS) connect:\n");
 118                 close(dtls_fd);
 119                 return -EINVAL;
 120         }
 121
 122         fcntl(dtls_fd, F_SETFD, FD_CLOEXEC);
 123
 124         https_cipher = SSL_get_current_cipher(vpninfo->https_ssl);
 125
 126         if (!vpninfo->dtls_ctx) {
 127                 dtls_method = DTLSv1_client_method();
 128                 vpninfo->dtls_ctx = SSL_CTX_new(dtls_method);
 129                 if (!vpninfo->dtls_ctx) {
 130                         vpninfo->progress(vpninfo, PRG_ERR, "Initialise DTLSv1 CTX failed\n");
 131                         return -EINVAL;
 132                 }
 133
 134                 /* If we don't readahead, then we do short reads and throw
 135                    away the tail of data packets. */
 136                 SSL_CTX_set_read_ahead(vpninfo->dtls_ctx, 1);
 137         }
 138
 139         if (!vpninfo->dtls_session) {
 140                 /* We're going to "resume" a session which never existed. Fake it... */
 141                 vpninfo->dtls_session = SSL_SESSION_new();
 142                 if (!vpninfo->dtls_session) {
 143                         vpninfo->progress(vpninfo, PRG_ERR, "Initialise DTLSv1 session failed\n");
 144                         return -EINVAL;
 145                 }
 146                 vpninfo->dtls_session->ssl_version = 0x0100; // DTLS1_BAD_VER
 147
 148                 vpninfo->dtls_session->master_key_length = sizeof(vpninfo->dtls_secret);
 149                 memcpy(vpninfo->dtls_session->master_key, vpninfo->dtls_secret,
 150                        sizeof(vpninfo->dtls_secret));
 151
 152                 vpninfo->dtls_session->session_id_length = sizeof(vpninfo->dtls_session_id);
 153                 memcpy(vpninfo->dtls_session->session_id, vpninfo->dtls_session_id,
 154                        sizeof(vpninfo->dtls_session_id));
 155
 156                 vpninfo->dtls_session->cipher = https_cipher;
 157                 vpninfo->dtls_session->cipher_id = https_cipher->id;
 158         }
 159
 160         dtls_ssl = SSL_new(vpninfo->dtls_ctx);
 161         SSL_set_connect_state(dtls_ssl);
 162         SSL_set_cipher_list(dtls_ssl, SSL_CIPHER_get_name(https_cipher));
 163
 164         /* Add the generated session to the SSL */
 165         if (!SSL_set_session(dtls_ssl, vpninfo->dtls_session)) {
 166                 vpninfo->progress(vpninfo, PRG_ERR,
 167                                   "SSL_set_session() failed with old protocol version 0x%x\n"
 168                                   "Your OpenSSL may lack Cisco compatibility support\n"
 169                                   "See http://rt.openssl.org/Ticket/Display.html?id=1751\n"
 170                                   "Use the --no-dtls command line option to avoid this message\n",
 171                                   vpninfo->dtls_session->ssl_version);
 172                 return -EINVAL;
 173         }
 174
 175         /* Go Go Go! */
 176         dtls_bio = BIO_new_socket(dtls_fd, BIO_NOCLOSE);
 177         SSL_set_bio(dtls_ssl, dtls_bio, dtls_bio);
 178
 179 #ifndef __APPLE__
 180         /* XXX Cargo cult programming. Other DTLS code does this, and it might
 181            avoid http://rt.openssl.org/Ticket/Display.html?id=1703 */
 182         BIO_ctrl(dtls_bio, BIO_CTRL_DGRAM_MTU_DISCOVER, 0, NULL);
 183 #endif
 184
 185 #ifndef SSL_OP_CISCO_ANYCONNECT
 186 #define SSL_OP_CISCO_ANYCONNECT 0x8000
 187 #endif
 188         SSL_set_options(dtls_ssl, SSL_OP_CISCO_ANYCONNECT);
 189
 190         /* Set non-blocking */
 191         BIO_set_nbio(SSL_get_rbio(dtls_ssl),1);
 192         BIO_set_nbio(SSL_get_wbio(dtls_ssl),1);
 193
 194         fcntl(dtls_fd, F_SETFL, fcntl(dtls_fd, F_GETFL) | O_NONBLOCK);
 195
 196         vpninfo->new_dtls_fd = dtls_fd;
 197         vpninfo->new_dtls_ssl = dtls_ssl;
 198         vpninfo->pfds[vpninfo->new_dtls_pfd].fd = vpninfo->new_dtls_fd;
 199
 200         time(&vpninfo->new_dtls_started);
 201         return dtls_try_handshake(vpninfo);
 202 }
 203
 204 int dtls_try_handshake(struct openconnect_info *vpninfo)
 205 {
 206         int ret = SSL_do_handshake(vpninfo->new_dtls_ssl);
 207
 208         if (ret == 1) {
 209                 vpninfo->progress(vpninfo, PRG_INFO, "Established DTLS connection\n");
 210
 211                 if (vpninfo->dtls_ssl) {
 212                         /* We are replacing an old connection */
 213                         SSL_free(vpninfo->dtls_ssl);
 214                         close(vpninfo->dtls_fd);
 215                 }
 216                 vpninfo->pfds[vpninfo->dtls_pfd].fd = vpninfo->new_dtls_fd;
 217                 vpninfo->dtls_ssl = vpninfo->new_dtls_ssl;
 218                 vpninfo->dtls_fd = vpninfo->new_dtls_fd;
 219
 220                 vpninfo->pfds[vpninfo->new_dtls_pfd].fd = -1;
 221                 vpninfo->new_dtls_ssl = NULL;
 222                 vpninfo->new_dtls_fd = -1;
 223
 224                 vpninfo->dtls_times.last_rekey = vpninfo->dtls_times.last_rx =
 225                         vpninfo->dtls_times.last_tx = time(NULL);
 226
 227                 return 0;
 228         }
 229
 230         ret = SSL_get_error(vpninfo->new_dtls_ssl, ret);
 231         if (ret == SSL_ERROR_WANT_WRITE || ret == SSL_ERROR_WANT_READ) {
 232                 if (time(NULL) < vpninfo->new_dtls_started + 5)
 233                         return 0;
 234                 vpninfo->progress(vpninfo, PRG_TRACE, "DTLS handshake timed out\n");
 235         }
 236
 237         vpninfo->progress(vpninfo, PRG_ERR, "DTLS handshake failed: %d\n", ret);
 238         ERR_print_errors_fp(stderr);
 239
 240         /* Kill the new (failed) connection... */
 241         SSL_free(vpninfo->new_dtls_ssl);
 242         vpninfo->pfds[vpninfo->new_dtls_pfd].fd = -1;
 243         close(vpninfo->new_dtls_fd);
 244         vpninfo->new_dtls_ssl = NULL;
 245         vpninfo->new_dtls_fd = -1;
 246
 247         /* ... and kill the old one too. The only time there'll be a valid
 248            existing session is when it was a rekey, and in that case it's
 249            time for the old one to die. */
 250         if (vpninfo->dtls_ssl) {
 251                 SSL_free(vpninfo->dtls_ssl);
 252                 close(vpninfo->dtls_fd);
 253                 vpninfo->pfds[vpninfo->dtls_pfd].fd = -1;
 254                 vpninfo->dtls_ssl = NULL;
 255                 vpninfo->dtls_fd = -1;
 256         }
 257
 258         time(&vpninfo->new_dtls_started);
 259         return -EINVAL;
 260 }
 261
 262 static int dtls_restart(struct openconnect_info *vpninfo)
 263 {
 264         if (vpninfo->dtls_ssl) {
 265                 SSL_free(vpninfo->dtls_ssl);
 266                 close(vpninfo->dtls_fd);
 267                 vpninfo->pfds[vpninfo->dtls_pfd].fd = -1;
 268                 vpninfo->dtls_ssl = NULL;
 269                 vpninfo->dtls_fd = -1;
 270         }
 271
 272         return connect_dtls_socket(vpninfo);
 273 }
 274
 275
 276 int setup_dtls(struct openconnect_info *vpninfo)
 277 {
 278         struct vpn_option *dtls_opt = vpninfo->dtls_options;
 279         int sessid_found = 0;
 280         int dtls_port = 0;
 281         int i;
 282
 283         while (dtls_opt) {
 284                 vpninfo->progress(vpninfo, PRG_TRACE,
 285                                   "DTLS option %s : %s\n",
 286                                   dtls_opt->option, dtls_opt->value);
 287
 288                 if (!strcmp(dtls_opt->option, "X-DTLS-Session-ID")) {
 289                         if (strlen(dtls_opt->value) != 64) {
 290                                 vpninfo->progress(vpninfo, PRG_ERR, "X-DTLS-Session-ID not 64 characters\n");
 291                                 vpninfo->progress(vpninfo, PRG_ERR, "Is: %s\n", dtls_opt->value);
 292                                 return -EINVAL;
 293                         }
 294                         for (i = 0; i < 64; i += 2)
 295                                 vpninfo->dtls_session_id[i/2] = hex(dtls_opt->value + i);
 296                         sessid_found = 1;
 297                 } else if (!strcmp(dtls_opt->option + 7, "Port")) {
 298                         dtls_port = atol(dtls_opt->value);
 299                 } else if (!strcmp(dtls_opt->option + 7, "Keepalive")) {
 300                         vpninfo->dtls_times.keepalive = atol(dtls_opt->value);
 301                 } else if (!strcmp(dtls_opt->option + 7, "DPD")) {
 302                         vpninfo->dtls_times.dpd = atol(dtls_opt->value);
 303                 } else if (!strcmp(dtls_opt->option + 7, "Rekey-Time")) {
 304                         vpninfo->dtls_times.rekey = atol(dtls_opt->value);
 305                 }
 306
 307                 dtls_opt = dtls_opt->next;
 308         }
 309         if (!sessid_found || !dtls_port)
 310                 return -EINVAL;
 311
 312         if (vpninfo->peer_addr->sa_family == AF_INET) {
 313                 struct sockaddr_in *sin = (void *)vpninfo->peer_addr;
 314                 sin->sin_port = htons(dtls_port);
 315         } else if (vpninfo->peer_addr->sa_family == AF_INET6) {
 316                 struct sockaddr_in6 *sin = (void *)vpninfo->peer_addr;
 317                 sin->sin6_port = htons(dtls_port);
 318         } else {
 319                 vpninfo->progress(vpninfo, PRG_ERR, "Unknown protocol family %d. Cannot do DTLS\n",
 320                         vpninfo->peer_addr->sa_family);
 321                 return -EINVAL;
 322         }
 323
 324         vpninfo->dtls_pfd = vpn_add_pollfd(vpninfo, -1,
 325                                            POLLIN|POLLHUP|POLLERR);
 326         vpninfo->new_dtls_pfd = vpn_add_pollfd(vpninfo, -1,
 327                                            POLLIN|POLLHUP|POLLERR);
 328
 329         if (connect_dtls_socket(vpninfo))
 330                 return -EINVAL;
 331
 332         vpninfo->progress(vpninfo, PRG_TRACE,
 333                           "DTLS connected. DPD %d, Keepalive %d\n",
 334                           vpninfo->dtls_times.dpd, vpninfo->dtls_times.keepalive);
 335
 336         return 0;
 337 }
 338
 339 int dtls_mainloop(struct openconnect_info *vpninfo, int *timeout)
 340 {
 341         unsigned char buf[2000];
 342         int len;
 343         int work_done = 0;
 344         char magic_pkt;
 345
 346         while ( (len = SSL_read(vpninfo->dtls_ssl, buf, sizeof(buf))) > 0 ) {
 347
 348                 vpninfo->progress(vpninfo, PRG_TRACE,
 349                                   "Received DTLS packet 0x%02x of %d bytes\n",
 350                                   buf[0], len);
 351
 352                 vpninfo->dtls_times.last_rx = time(NULL);
 353
 354                 switch(buf[0]) {
 355                 case AC_PKT_DATA:
 356                         queue_new_packet(&vpninfo->incoming_queue, AF_INET, buf+1, len-1);
 357                         work_done = 1;
 358                         break;
 359
 360                 case AC_PKT_DPD_OUT:
 361                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS DPD request\n");
 362
 363                         /* FIXME: What if the packet doesn't get through? */
 364                         magic_pkt = AC_PKT_DPD_RESP;
 365                         if (SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1) != 1)
 366                                 vpninfo->progress(vpninfo, PRG_ERR, "Failed to send DPD response. Expect disconnect\n");
 367                         continue;
 368
 369                 case AC_PKT_DPD_RESP:
 370                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS DPD response\n");
 371                         break;
 372
 373                 case AC_PKT_KEEPALIVE:
 374                         vpninfo->progress(vpninfo, PRG_TRACE, "Got DTLS Keepalive\n");
 375                         break;
 376
 377                 default:
 378                         vpninfo->progress(vpninfo, PRG_ERR,
 379                                           "Unknown DTLS packet type %02x, len %d\n", buf[0], len);
 380                         if (1) {
 381                                 /* Some versions of OpenSSL have bugs with receiving out-of-order
 382                                  * packets. Not only do they wrongly decide to drop packets if
 383                                  * two packets get swapped in transit, but they also _fail_ to
 384                                  * drop the packet in non-blocking mode; instead they return
 385                                  * the appropriate length of garbage. So don't abort... for now. */
 386                                 break;
 387                         } else {
 388                                 vpninfo->quit_reason = "Unknown packet received";
 389                                 return 1;
 390                         }
 391
 392                 }
 393         }
 394
 395         switch (keepalive_action(&vpninfo->dtls_times, timeout)) {
 396         case KA_REKEY:
 397                 time(&vpninfo->dtls_times.last_rekey);
 398                 vpninfo->progress(vpninfo, PRG_TRACE, "DTLS rekey due\n");
 399                 if (connect_dtls_socket(vpninfo)) {
 400                         vpninfo->progress(vpninfo, PRG_ERR, "DTLS rekey failed\n");
 401                         return 1;
 402                 }
 403                 work_done = 1;
 404                 break;
 405
 406
 407         case KA_DPD_DEAD:
 408                 vpninfo->progress(vpninfo, PRG_ERR, "DTLS Dead Peer Detection detected dead peer!\n");
 409                 /* Fall back to SSL, and start a new DTLS connection */
 410                 dtls_restart(vpninfo);
 411                 return 1;
 412
 413         case KA_DPD:
 414                 vpninfo->progress(vpninfo, PRG_TRACE, "Send DTLS DPD\n");
 415
 416                 magic_pkt = AC_PKT_DPD_OUT;
 417                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 418                 /* last_dpd will just have been set */
 419                 vpninfo->dtls_times.last_tx = vpninfo->dtls_times.last_dpd;
 420                 work_done = 1;
 421                 break;
 422
 423         case KA_KEEPALIVE:
 424                 /* No need to send an explicit keepalive
 425                    if we have real data to send */
 426                 if (vpninfo->outgoing_queue)
 427                         break;
 428
 429                 vpninfo->progress(vpninfo, PRG_TRACE, "Send DTLS Keepalive\n");
 430
 431                 magic_pkt = AC_PKT_KEEPALIVE;
 432                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 433                 time(&vpninfo->dtls_times.last_tx);
 434                 work_done = 1;
 435                 break;
 436
 437         case KA_NONE:
 438                 ;
 439         }
 440
 441         /* Service outgoing packet queue */
 442         while (vpninfo->outgoing_queue) {
 443                 struct pkt *this = vpninfo->outgoing_queue;
 444                 int ret;
 445
 446                 vpninfo->outgoing_queue = this->next;
 447
 448                 /* One byte of header */
 449                 this->hdr[7] = AC_PKT_DATA;
 450
 451                 ret = SSL_write(vpninfo->dtls_ssl, &this->hdr[7], this->len + 1);
 452                 if (ret <= 0) {
 453                         ret = SSL_get_error(vpninfo->dtls_ssl, ret);
 454
 455                         /* If it's a real error, kill the DTLS connection and
 456                            requeue the packet to be sent over SSL */
 457                         if (ret != SSL_ERROR_WANT_READ && ret != SSL_ERROR_WANT_WRITE) {
 458                                 vpninfo->progress(vpninfo, PRG_ERR,
 459                                                   "DTLS got write error %d. Falling back to SSL\n", ret);
 460                                 ERR_print_errors_fp(stderr);
 461                                 dtls_restart(vpninfo);
 462                                 vpninfo->outgoing_queue = this;
 463                         }
 464                         return 1;
 465                 }
 466                 time(&vpninfo->dtls_times.last_tx);
 467                 vpninfo->progress(vpninfo, PRG_TRACE,
 468                                   "Sent DTLS packet of %d bytes; SSL_write() returned %d\n",
 469                                   this->len, ret);
 470         }
 471
 472         return work_done;
 473 }
 474
 475