dtls.c

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