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