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.
  54  */
  55
  56 static unsigned char nybble(unsigned char n)
  57 {
  58         if      (n >= '0' && n <= '9') return n - '0';
  59         else if (n >= 'A' && n <= 'F') return n - ('A' - 10);
  60         else if (n >= 'a' && n <= 'f') return n - ('a' - 10);
  61         return 0;
  62 }
  63
  64 static unsigned char hex(const char *data)
  65 {
  66         return (nybble(data[0]) << 4) | nybble(data[1]);
  67 }
  68
  69 static int connect_dtls_socket(struct anyconnect_info *vpninfo, SSL **ret_ssl,
  70                                int *ret_fd)
  71 {
  72         SSL_METHOD *dtls_method;
  73         SSL_CIPHER *https_cipher;
  74         SSL *dtls_ssl;
  75         BIO *dtls_bio;
  76         int dtls_fd;
  77         int ret;
  78
  79         dtls_fd = socket(vpninfo->peer_addr->sa_family, SOCK_DGRAM, IPPROTO_UDP);
  80         if (dtls_fd < 0) {
  81                 perror("Open UDP socket for DTLS:");
  82                 return -EINVAL;
  83         }
  84
  85         if (connect(dtls_fd, vpninfo->peer_addr, vpninfo->peer_addrlen)) {
  86                 perror("UDP (DTLS) connect:\n");
  87                 close(dtls_fd);
  88                 return -EINVAL;
  89         }
  90
  91         fcntl(dtls_fd, F_SETFD, FD_CLOEXEC);
  92
  93         https_cipher = SSL_get_current_cipher(vpninfo->https_ssl);
  94
  95         if (!vpninfo->dtls_ctx) {
  96                 dtls_method = DTLSv1_client_method();
  97                 vpninfo->dtls_ctx = SSL_CTX_new(dtls_method);
  98                 if (!vpninfo->dtls_ctx) {
  99                         fprintf(stderr, "Initialise DTLSv1 CTX failed\n");
 100                         return -EINVAL;
 101                 }
 102
 103                 /* If we don't readahead, then we do short reads and throw
 104                    away the tail of data packets. */
 105                 SSL_CTX_set_read_ahead(vpninfo->dtls_ctx, 1);
 106         }
 107
 108         if (!vpninfo->dtls_session) {
 109                 /* We're going to "resume" a session which never existed. Fake it... */
 110                 vpninfo->dtls_session = SSL_SESSION_new();
 111                 if (!vpninfo->dtls_session) {
 112                         fprintf(stderr, "Initialise DTLSv1 session failed\n");
 113                         return -EINVAL;
 114                 }
 115                 vpninfo->dtls_session->ssl_version = 0x0100; // DTLS1_BAD_VER
 116
 117                 vpninfo->dtls_session->master_key_length = sizeof(vpninfo->dtls_secret);
 118                 memcpy(vpninfo->dtls_session->master_key, vpninfo->dtls_secret,
 119                        sizeof(vpninfo->dtls_secret));
 120
 121                 vpninfo->dtls_session->session_id_length = sizeof(vpninfo->dtls_session_id);
 122                 memcpy(vpninfo->dtls_session->session_id, vpninfo->dtls_session_id,
 123                        sizeof(vpninfo->dtls_session_id));
 124
 125                 vpninfo->dtls_session->cipher = https_cipher;
 126                 vpninfo->dtls_session->cipher_id = https_cipher->id;
 127         }
 128
 129         dtls_ssl = SSL_new(vpninfo->dtls_ctx);
 130         SSL_set_connect_state(dtls_ssl);
 131         SSL_set_cipher_list(dtls_ssl, SSL_CIPHER_get_name(https_cipher));
 132
 133         /* Add the generated session to the SSL */
 134         if (!SSL_set_session(dtls_ssl, vpninfo->dtls_session)) {
 135                 printf("SSL_set_session() failed with old protocol version 0x%x\n",
 136                        vpninfo->dtls_session->ssl_version);
 137                 printf("Your OpenSSL may lack Cisco compatibility support\n");
 138                 printf("See http://rt.openssl.org/Ticket/Display.html?id=1751\n");
 139                 printf("Use the --no-dtls command line option to avoid this message\n");
 140                 return -EINVAL;
 141         }
 142
 143         /* Go Go Go! */
 144         dtls_bio = BIO_new_socket(dtls_fd, BIO_NOCLOSE);
 145         SSL_set_bio(dtls_ssl, dtls_bio, dtls_bio);
 146
 147         /* XXX Cargo cult programming. Other DTLS code does this, and it might
 148            avoid http://rt.openssl.org/Ticket/Display.html?id=1703 */
 149         BIO_ctrl(dtls_bio, BIO_CTRL_DGRAM_MTU_DISCOVER, 0, NULL);
 150
 151 #ifndef SSL_OP_CISCO_ANYCONNECT
 152 #define SSL_OP_CISCO_ANYCONNECT 0x8000
 153 #endif
 154         SSL_set_options(dtls_ssl, SSL_OP_CISCO_ANYCONNECT);
 155         ret = SSL_do_handshake(dtls_ssl);
 156
 157         if (ret != 1) {
 158                 fprintf(stderr, "DTLS connection returned %d\n", ret);
 159                 if (ret < 0)
 160                         fprintf(stderr, "DTLS handshake error: %d\n", SSL_get_error(dtls_ssl, ret));
 161                 ERR_print_errors_fp(stderr);
 162                 SSL_free(dtls_ssl);
 163                 SSL_CTX_free(vpninfo->dtls_ctx);
 164                 vpninfo->dtls_ctx = NULL;
 165                 close(dtls_fd);
 166                 return -EINVAL;
 167         }
 168
 169         BIO_set_nbio(SSL_get_rbio(dtls_ssl),1);
 170         BIO_set_nbio(SSL_get_wbio(dtls_ssl),1);
 171
 172         fcntl(dtls_fd, F_SETFL, fcntl(dtls_fd, F_GETFL) | O_NONBLOCK);
 173
 174         vpninfo->dtls_times.last_rekey = vpninfo->dtls_times.last_rx =
 175                 vpninfo->dtls_times.last_tx = time(NULL);
 176
 177         *ret_fd = dtls_fd;
 178         *ret_ssl = dtls_ssl;
 179
 180         return 0;
 181 }
 182
 183 static int dtls_rekey(struct anyconnect_info *vpninfo)
 184 {
 185         SSL *dtls_ssl;
 186         int dtls_fd;
 187
 188         /* To rekey, we just 'resume' the session again */
 189         if (connect_dtls_socket(vpninfo, &dtls_ssl, &dtls_fd)) {
 190                 /* Fall back to SSL */
 191                 SSL_free(vpninfo->dtls_ssl);
 192                 close(vpninfo->dtls_fd);
 193                 vpninfo->pfds[vpninfo->dtls_pfd].fd = -1;
 194                 vpninfo->dtls_ssl = NULL;
 195                 vpninfo->dtls_fd = -1;
 196                 return -EINVAL;
 197         }
 198
 199         vpninfo->pfds[vpninfo->dtls_pfd].fd = dtls_fd;
 200
 201         SSL_free(vpninfo->dtls_ssl);
 202         close(vpninfo->dtls_fd);
 203
 204         vpninfo->dtls_ssl = dtls_ssl;
 205         vpninfo->dtls_fd = dtls_fd;
 206
 207         return 0;
 208 }
 209
 210 int setup_dtls(struct anyconnect_info *vpninfo)
 211 {
 212         struct vpn_option *dtls_opt = vpninfo->dtls_options;
 213         int sessid_found = 0;
 214         int dtls_port = 0;
 215         int i;
 216
 217         while (dtls_opt) {
 218                 if (verbose)
 219                         printf("DTLS option %s : %s\n", dtls_opt->option, dtls_opt->value);
 220
 221                 if (!strcmp(dtls_opt->option, "X-DTLS-Session-ID")) {
 222                         if (strlen(dtls_opt->value) != 64) {
 223                                 fprintf(stderr, "X-DTLS-Session-ID not 64 characters\n");
 224                                 fprintf(stderr, "Is: %s\n", dtls_opt->value);
 225                                 return -EINVAL;
 226                         }
 227                         for (i = 0; i < 64; i += 2)
 228                                 vpninfo->dtls_session_id[i/2] = hex(dtls_opt->value + i);
 229                         sessid_found = 1;
 230                 } else if (!strcmp(dtls_opt->option + 7, "Port")) {
 231                         dtls_port = atol(dtls_opt->value);
 232                 } else if (!strcmp(dtls_opt->option + 7, "Keepalive")) {
 233                         vpninfo->dtls_times.keepalive = atol(dtls_opt->value);
 234                 } else if (!strcmp(dtls_opt->option + 7, "DPD")) {
 235                         vpninfo->dtls_times.dpd = 10;//atol(dtls_opt->value);
 236                 } else if (!strcmp(dtls_opt->option + 7, "Rekey-Time")) {
 237                         vpninfo->dtls_times.rekey = atol(dtls_opt->value);
 238                 }
 239
 240                 dtls_opt = dtls_opt->next;
 241         }
 242         if (!sessid_found || !dtls_port)
 243                 return -EINVAL;
 244
 245         if (vpninfo->peer_addr->sa_family == AF_INET) {
 246                 struct sockaddr_in *sin = (void *)vpninfo->peer_addr;
 247                 sin->sin_port = htons(dtls_port);
 248         } else if (vpninfo->peer_addr->sa_family == AF_INET6) {
 249                 struct sockaddr_in6 *sin = (void *)vpninfo->peer_addr;
 250                 sin->sin6_port = htons(dtls_port);
 251         } else {
 252                 fprintf(stderr, "Unknown protocol family %d. Cannot do DTLS\n",
 253                         vpninfo->peer_addr->sa_family);
 254                 return -EINVAL;
 255         }
 256
 257         if (connect_dtls_socket(vpninfo, &vpninfo->dtls_ssl, &vpninfo->dtls_fd))
 258                 return -EINVAL;
 259
 260         vpninfo->dtls_pfd = vpn_add_pollfd(vpninfo, vpninfo->dtls_fd,
 261                                            POLLIN|POLLHUP|POLLERR);
 262
 263         if (verbose)
 264                 printf("DTLS connected. DPD %d, Keepalive %d\n",
 265                        vpninfo->dtls_times.dpd, vpninfo->dtls_times.keepalive);
 266
 267         return 0;
 268 }
 269
 270 int dtls_mainloop(struct anyconnect_info *vpninfo, int *timeout)
 271 {
 272         unsigned char buf[2000];
 273         int len;
 274         int work_done = 0;
 275         char magic_pkt;
 276
 277         while ( (len = SSL_read(vpninfo->dtls_ssl, buf, sizeof(buf))) > 0 ) {
 278                 if (verbose)
 279                         printf("Received DTLS packet 0x%02x of %d bytes\n",
 280                                buf[0], len);
 281
 282                 //vpninfo->dtls_times.last_rx = time(NULL);
 283
 284                 switch(buf[0]) {
 285                 case AC_PKT_DATA:
 286                         queue_new_packet(&vpninfo->incoming_queue, AF_INET, buf+1, len-1);
 287                         work_done = 1;
 288                         break;
 289
 290                 case AC_PKT_DPD_OUT:
 291                         if (verbose)
 292                                 printf("Got DTLS DPD request\n");
 293
 294                         /* FIXME: What if the packet doesn't get through? */
 295                         magic_pkt = AC_PKT_DPD_RESP;
 296                         if (SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1) != 1)
 297                                 fprintf(stderr, "Failed to send DPD response. Expect disconnect\n");
 298                         continue;
 299
 300                 case AC_PKT_DPD_RESP:
 301                         if (verbose)
 302                                 printf("Got DTLS DPD response\n");
 303                         break;
 304
 305                 case AC_PKT_KEEPALIVE:
 306                         if (verbose)
 307                                 printf("Got DTLS Keepalive\n");
 308                         break;
 309
 310                 default:
 311                         fprintf(stderr, "Unknown DTLS packet type %02x\n", buf[0]);
 312                         vpninfo->quit_reason = "Unknown packet received";
 313                         return 1;
 314                 }
 315         }
 316
 317         if (verbose)
 318                 printf("Process DTLS keepalive...\n");
 319         switch (keepalive_action(&vpninfo->dtls_times, timeout)) {
 320         case KA_REKEY:
 321                 if (verbose)
 322                         printf("DTLS rekey due\n");
 323                 if (dtls_rekey(vpninfo)) {
 324                         fprintf(stderr, "DTLS rekey failed\n");
 325                         return 1;
 326                 }
 327                 work_done = 1;
 328                 break;
 329
 330
 331         case KA_DPD_DEAD:
 332                 fprintf(stderr, "DTLS Dead Peer Detection detected dead peer!\n");
 333                 if (dtls_rekey(vpninfo)) {
 334                         fprintf(stderr, "DTLS reconnect failed\n");
 335                         return 1;
 336                 }
 337                 work_done = 1;
 338                 break;
 339
 340         case KA_DPD:
 341                 if (verbose)
 342                         printf("Send DTLS DPD\n");
 343
 344                 magic_pkt = AC_PKT_DPD_OUT;
 345                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 346                 /* last_dpd will just have been set */
 347                 vpninfo->dtls_times.last_tx = vpninfo->dtls_times.last_dpd;
 348                 work_done = 1;
 349                 break;
 350
 351         case KA_KEEPALIVE:
 352                 /* No need to send an explicit keepalive
 353                    if we have real data to send */
 354                 if (vpninfo->outgoing_queue)
 355                         break;
 356
 357                 if (verbose)
 358                         printf("Send DTLS Keepalive\n");
 359
 360                 magic_pkt = AC_PKT_KEEPALIVE;
 361                 SSL_write(vpninfo->dtls_ssl, &magic_pkt, 1);
 362                 time(&vpninfo->dtls_times.last_tx);
 363                 work_done = 1;
 364                 break;
 365
 366         case KA_NONE:
 367                 ;
 368         }
 369
 370         /* Service outgoing packet queue */
 371         while (vpninfo->outgoing_queue) {
 372                 struct pkt *this = vpninfo->outgoing_queue;
 373                 int ret;
 374
 375                 vpninfo->outgoing_queue = this->next;
 376
 377                 /* One byte of header */
 378                 this->hdr[7] = AC_PKT_DATA;
 379
 380                 ret = SSL_write(vpninfo->dtls_ssl, &this->hdr[7], this->len + 1);
 381                 time(&vpninfo->dtls_times.last_tx);
 382                 if (verbose) {
 383                         printf("Sent DTLS packet of %d bytes; SSL_write() returned %d\n",
 384                                this->len, ret);
 385                 }
 386         }
 387
 388         return work_done;
 389 }
 390
 391