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         dtls_method = DTLSv1_client_method();
  94         dtls_ctx = SSL_CTX_new(dtls_method);
  95         SSL_CTX_set_read_ahead(dtls_ctx, 1);
  96         https_cipher = SSL_get_current_cipher(vpninfo->https_ssl);
  97
  98         dtls_ssl = SSL_new(dtls_ctx);
  99         SSL_set_connect_state(dtls_ssl);
 100         SSL_set_cipher_list(dtls_ssl, SSL_CIPHER_get_name(https_cipher));
 101
 102         if (verbose)
 103                 printf("SSL_SESSION is %zd bytes\n", sizeof(*dtls_session));
 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         /* Having faked a session, add it to the CTX and the SSL */
 121         if (!SSL_set_session(dtls_ssl, dtls_session)) {
 122                 printf("SSL_set_session() failed with old protocol version 0x%x\n", dtls_session->ssl_version);
 123                 printf("Trying the official version %x\n", 0xfeff);
 124                 dtls_session->ssl_version = 0xfeff;
 125                 if (!SSL_set_session(dtls_ssl, dtls_session)) {
 126                         printf("SSL_set_session() failed still. Is your build ABI-compatible with your libssl?\n");
 127                         return -EINVAL;
 128                 }
 129         }
 130         if (!SSL_CTX_add_session(dtls_ctx, dtls_session))
 131                 printf("SSL_CTX_add_session() failed\n");
 132
 133
 134         /* Go Go Go! */
 135         dtls_bio = BIO_new_socket(dtls_fd, BIO_NOCLOSE);
 136         SSL_set_bio(dtls_ssl, dtls_bio, dtls_bio);
 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         *ret_fd = dtls_fd;
 156         *ret_ssl = dtls_ssl;
 157
 158         return 0;
 159 }
 160
 161 static int dtls_rekey(struct anyconnect_info *vpninfo)
 162 {
 163         printf("FIXME: Implement DTLS rekey\n");
 164         return -EINVAL;
 165 }
 166
 167 int setup_dtls(struct anyconnect_info *vpninfo)
 168 {
 169         struct vpn_option *dtls_opt = vpninfo->dtls_options;
 170         int sessid_found = 0;
 171         int dtls_port = 0;
 172         int i;
 173
 174         while (dtls_opt) {
 175                 if (verbose)
 176                         printf("DTLS option %s : %s\n", dtls_opt->option, dtls_opt->value);
 177
 178                 if (!strcmp(dtls_opt->option, "X-DTLS-Session-ID")) {
 179                         if (strlen(dtls_opt->value) != 64) {
 180                                 fprintf(stderr, "X-DTLS-Session-ID not 64 characters\n");
 181                                 fprintf(stderr, "Is: %s\n", dtls_opt->value);
 182                                 return -EINVAL;
 183                         }
 184                         for (i = 0; i < 64; i += 2)
 185                                 vpninfo->dtls_session_id[i/2] = hex(dtls_opt->value + i);
 186                         sessid_found = 1;
 187                 } else if (!strcmp(dtls_opt->option + 7, "Port")) {
 188                         dtls_port = atol(dtls_opt->value);
 189                 } else if (!strcmp(dtls_opt->option + 7, "Keepalive")) {
 190                         vpninfo->dtls_keepalive = atol(dtls_opt->value);
 191                 } else if (!strcmp(dtls_opt->option + 7, "DPD")) {
 192                         vpninfo->dtls_dpd = atol(dtls_opt->value);
 193                 } else if (!strcmp(dtls_opt->option + 7, "Rekey-Time")) {
 194                         vpninfo->dtls_rekey = atol(dtls_opt->value);
 195                 }
 196
 197                 dtls_opt = dtls_opt->next;
 198         }
 199         if (!sessid_found || !dtls_port)
 200                 return -EINVAL;
 201
 202         if (vpninfo->peer_addr->sa_family == AF_INET) {
 203                 struct sockaddr_in *sin = (void *)vpninfo->peer_addr;
 204                 sin->sin_port = htons(dtls_port);
 205         } else if (vpninfo->peer_addr->sa_family == AF_INET6) {
 206                 struct sockaddr_in6 *sin = (void *)vpninfo->peer_addr;
 207                 sin->sin6_port = htons(dtls_port);
 208         } else {
 209                 fprintf(stderr, "Unknown protocol family %d. Cannot do DTLS\n",
 210                         vpninfo->peer_addr->sa_family);
 211                 return -EINVAL;
 212         }
 213
 214         if (connect_dtls_socket(vpninfo, &vpninfo->dtls_ssl, &vpninfo->dtls_fd))
 215                 return -EINVAL;
 216
 217         BIO_set_nbio(SSL_get_rbio(vpninfo->dtls_ssl),1);
 218         BIO_set_nbio(SSL_get_wbio(vpninfo->dtls_ssl),1);
 219
 220         fcntl(vpninfo->dtls_fd, F_SETFL, fcntl(vpninfo->dtls_fd, F_GETFL) | O_NONBLOCK);
 221
 222         vpn_add_pollfd(vpninfo, vpninfo->dtls_fd, POLLIN|POLLHUP|POLLERR);
 223         vpninfo->last_dtls_rekey = vpninfo->last_dtls_rx =
 224                 vpninfo->last_dtls_tx = time(NULL);
 225
 226         if (verbose)
 227                 printf("DTLS connected. DPD %d, Keepalive %d\n",
 228                        vpninfo->dtls_dpd, vpninfo->dtls_keepalive);
 229
 230         return 0;
 231 }
 232
 233 int dtls_mainloop(struct anyconnect_info *vpninfo, int *timeout)
 234 {
 235         char buf[2000];
 236         int len;
 237         int work_done = 0;
 238
 239         while ( (len = SSL_read(vpninfo->dtls_ssl, buf, sizeof(buf))) > 0 ) {
 240                 if (verbose) {
 241                         printf("Received DTLS packet of %d bytes\n", len);
 242                         printf("Packet starts %02x %02x %02x %02x %02x %02x %02x %02x\n",
 243                                buf[0], buf[1], buf[2], buf[3], buf[4], buf[5], buf[6], buf[7]);
 244                 }
 245                 vpninfo->last_dtls_rx = time(NULL);
 246                 switch(buf[0]) {
 247                 case 0:
 248                         queue_new_packet(&vpninfo->incoming_queue, AF_INET, buf+1, len-1);
 249                         work_done = 1;
 250                         break;
 251
 252                 case 4: /* DPD response */
 253                         if (verbose)
 254                                 printf("Got DTLS DPD response\n");
 255                         break;
 256
 257                 default:
 258                         fprintf(stderr, "Unknown DTLS packet type %02x\n", buf[0]);
 259                         vpninfo->quit_reason = "Unknown packet received";
 260                         return 1;
 261                 }
 262         }
 263         while (vpninfo->outgoing_queue) {
 264                 struct pkt *this = vpninfo->outgoing_queue;
 265                 int ret;
 266
 267                 vpninfo->outgoing_queue = this->next;
 268
 269                 buf[0] = 0;
 270                 memcpy(buf + 1, this->data, this->len);
 271
 272                 ret = SSL_write(vpninfo->dtls_ssl, buf, this->len + 1);
 273                 vpninfo->last_dtls_tx = time(NULL);
 274                 if (verbose) {
 275                         printf("Sent DTLS packet of %d bytes; SSL_write() returned %d\n",
 276                                this->len, ret);
 277                 }
 278         }
 279
 280         /* DPD is bidirectional -- PKT 3 out, PKT 4 back */
 281         if (vpninfo->dtls_dpd) {
 282                 time_t now = time(NULL);
 283                 time_t due = vpninfo->last_dtls_rx + vpninfo->dtls_dpd;
 284                 time_t overdue = vpninfo->last_dtls_rx + (5 * vpninfo->dtls_dpd);
 285
 286                 /* If we already have DPD outstanding, don't flood */
 287                 if (vpninfo->last_dtls_dpd > vpninfo->last_dtls_rx)
 288                         due = vpninfo->last_dtls_dpd + vpninfo->dtls_dpd;
 289
 290                 if (now > overdue) {
 291                         fprintf(stderr, "DTLS Dead Peer Detection detected dead peer!\n");
 292                         /* Fall back to SSL */
 293                         SSL_free(vpninfo->dtls_ssl);
 294                         close(vpninfo->dtls_fd);
 295                         vpninfo->dtls_ssl = NULL;
 296                         vpninfo->dtls_fd = -1;
 297                         return 1;
 298                 }
 299                 if (now >= due) {
 300                         static unsigned char dtls_dpd_pkt[1] = { 3 };
 301                         /* Haven't heard anything from the other end for a while.
 302                            Check if it's still there */
 303                         /* FIXME: If isn't, we should act on that */
 304                         SSL_write(vpninfo->dtls_ssl, dtls_dpd_pkt, 1);
 305                         vpninfo->last_dtls_tx = now;
 306
 307                         due = now + vpninfo->dtls_dpd;
 308                         if (verbose)
 309                                 printf("Sent DTLS DPD\n");
 310                 }
 311
 312                 if (verbose)
 313                         printf("Next DTLS DPD due in %ld seconds\n", (due - now));
 314                 if (*timeout > (due - now) * 1000)
 315                         *timeout = (due - now) * 1000;
 316         }
 317
 318         /* Keepalive is just client -> server */
 319         if (vpninfo->dtls_keepalive) {
 320                 time_t now = time(NULL);
 321                 time_t due = vpninfo->last_dtls_tx + vpninfo->dtls_keepalive;
 322
 323                 if (now >= due) {
 324                         static unsigned char dtls_keepalive_pkt[1] = { 7 };
 325
 326                         /* Send something (which is discarded), to keep
 327                            the connection alive. */
 328                         SSL_write(vpninfo->dtls_ssl, dtls_keepalive_pkt, 1);
 329                         vpninfo->last_dtls_tx = now;
 330
 331                         due = now + vpninfo->dtls_keepalive;
 332                         if (verbose)
 333                                 printf("Sent DTLS Keepalive\n");
 334                 }
 335
 336                 if (verbose)
 337                         printf("Next DTLS Keepalive due in %ld seconds\n", (due - now));
 338                 if (*timeout > (due - now) * 1000)
 339                         *timeout = (due - now) * 1000;
 340         }
 341
 342         if (vpninfo->dtls_rekey) {
 343                 time_t now = time(NULL);
 344                 time_t due = vpninfo->last_dtls_rekey + vpninfo->dtls_rekey;
 345
 346                 if (now > due) {
 347                         if (verbose)
 348                                 printf("DTLS rekey due\n");
 349                         if (dtls_rekey(vpninfo)) {
 350                                 fprintf(stderr, "DTLS rekey failed\n");
 351                                 /* Fall back to SSL */
 352                                 SSL_free(vpninfo->dtls_ssl);
 353                                 close(vpninfo->dtls_fd);
 354                                 vpninfo->dtls_ssl = NULL;
 355                                 vpninfo->dtls_fd = -1;
 356                                 return 1;
 357                         }
 358                         vpninfo->last_dtls_rekey = time(NULL);
 359                         due = vpninfo->last_dtls_rekey + vpninfo->dtls_rekey;
 360                 }
 361                 if (verbose)
 362                         printf("Next DTLS rekey due in %ld seconds\n", (due - now));
 363                 if (*timeout > (due - now) * 1000)
 364                         *timeout = (due - now) * 1000;
 365         }
 366
 367         /* FIXME: Keepalive */
 368         return work_done;
 369 }
 370
 371