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