res/res_srtp.c

   1 /*
   2  * Asterisk -- An open source telephony toolkit.
   3  *
   4  * Copyright (C) 2005, Mikael Magnusson
   5  *
   6  * Mikael Magnusson <mikma@users.sourceforge.net>
   7  *
   8  * See http://www.asterisk.org for more information about
   9  * the Asterisk project. Please do not directly contact
  10  * any of the maintainers of this project for assistance;
  11  * the project provides a web site, mailing lists and IRC
  12  * channels for your use.
  13  *
  14  * This program is free software, distributed under the terms of
  15  * the GNU General Public License Version 2. See the LICENSE file
  16  * at the top of the source tree.
  17  *
  18  * Builds on libSRTP http://srtp.sourceforge.net
  19  */
  20
  21 /*! \file res_srtp.c
  22  *
  23  * \brief Secure RTP (SRTP)
  24  *
  25  * Secure RTP (SRTP)
  26  * Specified in RFC 3711.
  27  *
  28  * \author Mikael Magnusson <mikma@users.sourceforge.net>
  29  */
  30
  31 /*** MODULEINFO
  32         <depend>srtp</depend>
  33         <support_level>core</support_level>
  34 ***/
  35
  36 /* See https://wiki.asterisk.org/wiki/display/AST/Secure+Calling */
  37
  38 #include "asterisk.h"
  39
  40 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
  41
  42 #include <srtp/srtp.h>
  43
  44 #include "asterisk/lock.h"
  45 #include "asterisk/sched.h"
  46 #include "asterisk/module.h"
  47 #include "asterisk/options.h"
  48 #include "asterisk/rtp_engine.h"
  49 #include "asterisk/astobj2.h"
  50
  51 struct ast_srtp {
  52         struct ast_rtp_instance *rtp;
  53         struct ao2_container *policies;
  54         srtp_t session;
  55         const struct ast_srtp_cb *cb;
  56         void *data;
  57         int warned;
  58         unsigned char buf[8192 + AST_FRIENDLY_OFFSET];
  59         unsigned char rtcpbuf[8192 + AST_FRIENDLY_OFFSET];
  60 };
  61
  62 struct ast_srtp_policy {
  63         srtp_policy_t sp;
  64 };
  65
  66 /*! Tracks whether or not we've initialized the libsrtp library */
  67 static int g_initialized = 0;
  68
  69 /* SRTP functions */
  70 static int ast_srtp_create(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy);
  71 static int ast_srtp_replace(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy);
  72 static void ast_srtp_destroy(struct ast_srtp *srtp);
  73 static int ast_srtp_add_stream(struct ast_srtp *srtp, struct ast_srtp_policy *policy);
  74 static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc, unsigned int to_ssrc);
  75
  76 static int ast_srtp_unprotect(struct ast_srtp *srtp, void *buf, int *len, int rtcp);
  77 static int ast_srtp_protect(struct ast_srtp *srtp, void **buf, int *len, int rtcp);
  78 static void ast_srtp_set_cb(struct ast_srtp *srtp, const struct ast_srtp_cb *cb, void *data);
  79 static int ast_srtp_get_random(unsigned char *key, size_t len);
  80
  81 /* Policy functions */
  82 static struct ast_srtp_policy *ast_srtp_policy_alloc(void);
  83 static void ast_srtp_policy_destroy(struct ast_srtp_policy *policy);
  84 static int ast_srtp_policy_set_suite(struct ast_srtp_policy *policy, enum ast_srtp_suite suite);
  85 static int ast_srtp_policy_set_master_key(struct ast_srtp_policy *policy, const unsigned char *key, size_t key_len, const unsigned char *salt, size_t salt_len);
  86 static void ast_srtp_policy_set_ssrc(struct ast_srtp_policy *policy, unsigned long ssrc, int inbound);
  87
  88 static struct ast_srtp_res srtp_res = {
  89         .create = ast_srtp_create,
  90         .replace = ast_srtp_replace,
  91         .destroy = ast_srtp_destroy,
  92         .add_stream = ast_srtp_add_stream,
  93         .change_source = ast_srtp_change_source,
  94         .set_cb = ast_srtp_set_cb,
  95         .unprotect = ast_srtp_unprotect,
  96         .protect = ast_srtp_protect,
  97         .get_random = ast_srtp_get_random
  98 };
  99
 100 static struct ast_srtp_policy_res policy_res = {
 101         .alloc = ast_srtp_policy_alloc,
 102         .destroy = ast_srtp_policy_destroy,
 103         .set_suite = ast_srtp_policy_set_suite,
 104         .set_master_key = ast_srtp_policy_set_master_key,
 105         .set_ssrc = ast_srtp_policy_set_ssrc
 106 };
 107
 108 static const char *srtp_errstr(int err)
 109 {
 110         switch(err) {
 111         case err_status_ok:
 112                 return "nothing to report";
 113         case err_status_fail:
 114                 return "unspecified failure";
 115         case err_status_bad_param:
 116                 return "unsupported parameter";
 117         case err_status_alloc_fail:
 118                 return "couldn't allocate memory";
 119         case err_status_dealloc_fail:
 120                 return "couldn't deallocate properly";
 121         case err_status_init_fail:
 122                 return "couldn't initialize";
 123         case err_status_terminus:
 124                 return "can't process as much data as requested";
 125         case err_status_auth_fail:
 126                 return "authentication failure";
 127         case err_status_cipher_fail:
 128                 return "cipher failure";
 129         case err_status_replay_fail:
 130                 return "replay check failed (bad index)";
 131         case err_status_replay_old:
 132                 return "replay check failed (index too old)";
 133         case err_status_algo_fail:
 134                 return "algorithm failed test routine";
 135         case err_status_no_such_op:
 136                 return "unsupported operation";
 137         case err_status_no_ctx:
 138                 return "no appropriate context found";
 139         case err_status_cant_check:
 140                 return "unable to perform desired validation";
 141         case err_status_key_expired:
 142                 return "can't use key any more";
 143         default:
 144                 return "unknown";
 145         }
 146 }
 147
 148 static int policy_hash_fn(const void *obj, const int flags)
 149 {
 150         const struct ast_srtp_policy *policy = obj;
 151
 152         return policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type;
 153 }
 154
 155 static int policy_cmp_fn(void *obj, void *arg, int flags)
 156 {
 157         const struct ast_srtp_policy *one = obj, *two = arg;
 158
 159         return one->sp.ssrc.type == two->sp.ssrc.type && one->sp.ssrc.value == two->sp.ssrc.value;
 160 }
 161
 162 static struct ast_srtp_policy *find_policy(struct ast_srtp *srtp, const srtp_policy_t *policy, int flags)
 163 {
 164         struct ast_srtp_policy tmp = {
 165                 .sp = {
 166                         .ssrc.type = policy->ssrc.type,
 167                         .ssrc.value = policy->ssrc.value,
 168                 },
 169         };
 170
 171         return ao2_t_find(srtp->policies, &tmp, flags, "Looking for policy");
 172 }
 173
 174 static struct ast_srtp *res_srtp_new(void)
 175 {
 176         struct ast_srtp *srtp;
 177
 178         if (!(srtp = ast_calloc(1, sizeof(*srtp)))) {
 179                 ast_log(LOG_ERROR, "Unable to allocate memory for srtp\n");
 180                 return NULL;
 181         }
 182
 183         if (!(srtp->policies = ao2_t_container_alloc(5, policy_hash_fn, policy_cmp_fn, "SRTP policy container"))) {
 184                 ast_free(srtp);
 185                 return NULL;
 186         }
 187
 188         srtp->warned = 1;
 189
 190         return srtp;
 191 }
 192
 193 /*
 194   struct ast_srtp_policy
 195 */
 196 static void srtp_event_cb(srtp_event_data_t *data)
 197 {
 198         switch (data->event) {
 199         case event_ssrc_collision:
 200                 ast_debug(1, "SSRC collision\n");
 201                 break;
 202         case event_key_soft_limit:
 203                 ast_debug(1, "event_key_soft_limit\n");
 204                 break;
 205         case event_key_hard_limit:
 206                 ast_debug(1, "event_key_hard_limit\n");
 207                 break;
 208         case event_packet_index_limit:
 209                 ast_debug(1, "event_packet_index_limit\n");
 210                 break;
 211         }
 212 }
 213
 214 static void ast_srtp_policy_set_ssrc(struct ast_srtp_policy *policy,
 215                 unsigned long ssrc, int inbound)
 216 {
 217         if (ssrc) {
 218                 policy->sp.ssrc.type = ssrc_specific;
 219                 policy->sp.ssrc.value = ssrc;
 220         } else {
 221                 policy->sp.ssrc.type = inbound ? ssrc_any_inbound : ssrc_any_outbound;
 222         }
 223 }
 224
 225 static void policy_destructor(void *obj)
 226 {
 227         struct ast_srtp_policy *policy = obj;
 228
 229         if (policy->sp.key) {
 230                 ast_free(policy->sp.key);
 231                 policy->sp.key = NULL;
 232         }
 233 }
 234
 235 static struct ast_srtp_policy *ast_srtp_policy_alloc()
 236 {
 237         struct ast_srtp_policy *tmp;
 238
 239         if (!(tmp = ao2_t_alloc(sizeof(*tmp), policy_destructor, "Allocating policy"))) {
 240                 ast_log(LOG_ERROR, "Unable to allocate memory for srtp_policy\n");
 241         }
 242
 243         return tmp;
 244 }
 245
 246 static void ast_srtp_policy_destroy(struct ast_srtp_policy *policy)
 247 {
 248         ao2_t_ref(policy, -1, "Destroying policy");
 249 }
 250
 251 static int policy_set_suite(crypto_policy_t *p, enum ast_srtp_suite suite)
 252 {
 253         switch (suite) {
 254         case AST_AES_CM_128_HMAC_SHA1_80:
 255                 p->cipher_type = AES_128_ICM;
 256                 p->cipher_key_len = 30;
 257                 p->auth_type = HMAC_SHA1;
 258                 p->auth_key_len = 20;
 259                 p->auth_tag_len = 10;
 260                 p->sec_serv = sec_serv_conf_and_auth;
 261                 return 0;
 262
 263         case AST_AES_CM_128_HMAC_SHA1_32:
 264                 p->cipher_type = AES_128_ICM;
 265                 p->cipher_key_len = 30;
 266                 p->auth_type = HMAC_SHA1;
 267                 p->auth_key_len = 20;
 268                 p->auth_tag_len = 4;
 269                 p->sec_serv = sec_serv_conf_and_auth;
 270                 return 0;
 271
 272         default:
 273                 ast_log(LOG_ERROR, "Invalid crypto suite: %d\n", suite);
 274                 return -1;
 275         }
 276 }
 277
 278 static int ast_srtp_policy_set_suite(struct ast_srtp_policy *policy, enum ast_srtp_suite suite)
 279 {
 280         return policy_set_suite(&policy->sp.rtp, suite) | policy_set_suite(&policy->sp.rtcp, suite);
 281 }
 282
 283 static int ast_srtp_policy_set_master_key(struct ast_srtp_policy *policy, const unsigned char *key, size_t key_len, const unsigned char *salt, size_t salt_len)
 284 {
 285         size_t size = key_len + salt_len;
 286         unsigned char *master_key;
 287
 288         if (policy->sp.key) {
 289                 ast_free(policy->sp.key);
 290                 policy->sp.key = NULL;
 291         }
 292
 293         if (!(master_key = ast_calloc(1, size))) {
 294                 return -1;
 295         }
 296
 297         memcpy(master_key, key, key_len);
 298         memcpy(master_key + key_len, salt, salt_len);
 299
 300         policy->sp.key = master_key;
 301
 302         return 0;
 303 }
 304
 305 static int ast_srtp_get_random(unsigned char *key, size_t len)
 306 {
 307         return crypto_get_random(key, len) != err_status_ok ? -1: 0;
 308 }
 309
 310 static void ast_srtp_set_cb(struct ast_srtp *srtp, const struct ast_srtp_cb *cb, void *data)
 311 {
 312         if (!srtp) {
 313                 return;
 314         }
 315
 316         srtp->cb = cb;
 317         srtp->data = data;
 318 }
 319
 320 /* Vtable functions */
 321 static int ast_srtp_unprotect(struct ast_srtp *srtp, void *buf, int *len, int rtcp)
 322 {
 323         int res = 0;
 324         int i;
 325         int retry = 0;
 326         struct ast_rtp_instance_stats stats = {0,};
 327
 328 tryagain:
 329
 330         for (i = 0; i < 2; i++) {
 331                 res = rtcp ? srtp_unprotect_rtcp(srtp->session, buf, len) : srtp_unprotect(srtp->session, buf, len);
 332                 if (res != err_status_no_ctx) {
 333                         break;
 334                 }
 335
 336                 if (srtp->cb && srtp->cb->no_ctx) {
 337                         if (ast_rtp_instance_get_stats(srtp->rtp, &stats, AST_RTP_INSTANCE_STAT_REMOTE_SSRC)) {
 338                                 break;
 339                         }
 340                         if (srtp->cb->no_ctx(srtp->rtp, stats.remote_ssrc, srtp->data) < 0) {
 341                                 break;
 342                         }
 343                 } else {
 344                         break;
 345                 }
 346         }
 347
 348         if (retry == 0  && res == err_status_replay_old) {
 349                 ast_log(AST_LOG_NOTICE, "SRTP unprotect failed with %s, retrying\n", srtp_errstr(res));
 350
 351                 if (srtp->session) {
 352                         struct ast_srtp_policy *policy;
 353                         struct ao2_iterator it;
 354                         int policies_count;
 355
 356                         /* dealloc first */
 357                         ast_debug(5, "SRTP destroy before re-create\n");
 358                         srtp_dealloc(srtp->session);
 359
 360                         /* get the count */
 361                         policies_count = ao2_container_count(srtp->policies);
 362
 363                         /* get the first to build up */
 364                         it = ao2_iterator_init(srtp->policies, 0);
 365                         policy = ao2_iterator_next(&it);
 366
 367                         ast_debug(5, "SRTP try to re-create\n");
 368                         if (policy) {
 369                                 if (srtp_create(&srtp->session, &policy->sp) == err_status_ok) {
 370                                         ast_debug(5, "SRTP re-created with first policy\n");
 371                                         ao2_t_ref(policy, -1, "Unreffing first policy for re-creating srtp session");
 372
 373                                         /* if we have more than one policy, add them */
 374                                         if (policies_count > 1) {
 375                                                 ast_debug(5, "Add all the other %d policies\n",
 376                                                         policies_count - 1);
 377                                                 while ((policy = ao2_iterator_next(&it))) {
 378                                                         srtp_add_stream(srtp->session, &policy->sp);
 379                                                         ao2_t_ref(policy, -1, "Unreffing n-th policy for re-creating srtp session");
 380                                                 }
 381                                         }
 382
 383                                         retry++;
 384                                         ao2_iterator_destroy(&it);
 385                                         goto tryagain;
 386                                 } else {
 387                                         srtp->session = NULL;
 388                                 }
 389                                 ao2_t_ref(policy, -1, "Unreffing first policy after srtp_create failed");
 390                         }
 391                         ao2_iterator_destroy(&it);
 392                 }
 393         }
 394
 395         if (res != err_status_ok && res != err_status_replay_fail ) {
 396                 if ((srtp->warned >= 10) && !((srtp->warned - 10) % 100)) {
 397                         ast_log(AST_LOG_WARNING, "SRTP unprotect failed with: %s %d\n", srtp_errstr(res), srtp->warned);
 398                         srtp->warned = 11;
 399                 } else {
 400                         srtp->warned++;
 401                 }
 402                 errno = EAGAIN;
 403                 return -1;
 404         }
 405
 406         return *len;
 407 }
 408
 409 static int ast_srtp_protect(struct ast_srtp *srtp, void **buf, int *len, int rtcp)
 410 {
 411         int res;
 412         unsigned char *localbuf;
 413
 414         if ((*len + SRTP_MAX_TRAILER_LEN) > sizeof(srtp->buf)) {
 415                 return -1;
 416         }
 417
 418         localbuf = rtcp ? srtp->rtcpbuf : srtp->buf;
 419
 420         memcpy(localbuf, *buf, *len);
 421
 422         if ((res = rtcp ? srtp_protect_rtcp(srtp->session, localbuf, len) : srtp_protect(srtp->session, localbuf, len)) != err_status_ok && res != err_status_replay_fail) {
 423                 ast_log(LOG_WARNING, "SRTP protect: %s\n", srtp_errstr(res));
 424                 return -1;
 425         }
 426
 427         *buf = localbuf;
 428         return *len;
 429 }
 430
 431 static int ast_srtp_create(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy)
 432 {
 433         struct ast_srtp *temp;
 434
 435         if (!(temp = res_srtp_new())) {
 436                 return -1;
 437         }
 438         ast_module_ref(ast_module_info->self);
 439
 440         /* Any failures after this point can use ast_srtp_destroy to destroy the instance */
 441         if (srtp_create(&temp->session, &policy->sp) != err_status_ok) {
 442                 /* Session either wasn't created or was created and dealloced. */
 443                 temp->session = NULL;
 444                 ast_srtp_destroy(temp);
 445                 return -1;
 446         }
 447
 448         temp->rtp = rtp;
 449         *srtp = temp;
 450
 451         ao2_t_link((*srtp)->policies, policy, "Created initial policy");
 452
 453         return 0;
 454 }
 455
 456 static int ast_srtp_replace(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy)
 457 {
 458         if ((*srtp) != NULL) {
 459                 ast_srtp_destroy(*srtp);
 460         }
 461         return ast_srtp_create(srtp, rtp, policy);
 462 }
 463
 464 static void ast_srtp_destroy(struct ast_srtp *srtp)
 465 {
 466         if (srtp->session) {
 467                 srtp_dealloc(srtp->session);
 468         }
 469
 470         ao2_t_callback(srtp->policies, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, NULL, NULL, "Unallocate policy");
 471         ao2_t_ref(srtp->policies, -1, "Destroying container");
 472
 473         ast_free(srtp);
 474         ast_module_unref(ast_module_info->self);
 475 }
 476
 477 static int ast_srtp_add_stream(struct ast_srtp *srtp, struct ast_srtp_policy *policy)
 478 {
 479         struct ast_srtp_policy *match;
 480
 481         /* For existing streams, replace if its an SSRC stream, or bail if its a wildcard */
 482         if ((match = find_policy(srtp, &policy->sp, OBJ_POINTER))) {
 483                 if (policy->sp.ssrc.type != ssrc_specific) {
 484                         ast_log(AST_LOG_WARNING, "Cannot replace an existing wildcard policy\n");
 485                         ao2_t_ref(match, -1, "Unreffing already existing policy");
 486                         return -1;
 487                 } else {
 488                         if (srtp_remove_stream(srtp->session, match->sp.ssrc.value) != err_status_ok) {
 489                                 ast_log(AST_LOG_WARNING, "Failed to remove SRTP stream for SSRC %d\n", match->sp.ssrc.value);
 490                         }
 491                         ao2_t_unlink(srtp->policies, match, "Remove existing match policy");
 492                         ao2_t_ref(match, -1, "Unreffing already existing policy");
 493                 }
 494         }
 495
 496         ast_debug(3, "Adding new policy for %s %d\n",
 497                 policy->sp.ssrc.type == ssrc_specific ? "SSRC" : "type",
 498                 policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type);
 499         if (srtp_add_stream(srtp->session, &policy->sp) != err_status_ok) {
 500                 ast_log(AST_LOG_WARNING, "Failed to add SRTP stream for %s %d\n",
 501                         policy->sp.ssrc.type == ssrc_specific ? "SSRC" : "type",
 502                         policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type);
 503                 return -1;
 504         }
 505
 506         ao2_t_link(srtp->policies, policy, "Added additional stream");
 507
 508         return 0;
 509 }
 510
 511 static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc, unsigned int to_ssrc)
 512 {
 513         struct ast_srtp_policy *match;
 514         struct srtp_policy_t sp = {
 515                 .ssrc.type = ssrc_specific,
 516                 .ssrc.value = from_ssrc,
 517         };
 518         err_status_t status;
 519
 520         /* If we find a match, return and unlink it from the container so we
 521          * can change the SSRC (which is part of the hash) and then have
 522          * ast_srtp_add_stream link it back in if all is well */
 523         if ((match = find_policy(srtp, &sp, OBJ_POINTER | OBJ_UNLINK))) {
 524                 match->sp.ssrc.value = to_ssrc;
 525                 if (ast_srtp_add_stream(srtp, match)) {
 526                         ast_log(LOG_WARNING, "Couldn't add stream\n");
 527                 } else if ((status = srtp_remove_stream(srtp->session, from_ssrc))) {
 528                         ast_debug(3, "Couldn't remove stream (%d)\n", status);
 529                 }
 530                 ao2_t_ref(match, -1, "Unreffing found policy in change_source");
 531         }
 532
 533         return 0;
 534 }
 535
 536 static void res_srtp_shutdown(void)
 537 {
 538         srtp_install_event_handler(NULL);
 539         ast_rtp_engine_unregister_srtp();
 540         g_initialized = 0;
 541 }
 542
 543 static int res_srtp_init(void)
 544 {
 545         if (g_initialized) {
 546                 return 0;
 547         }
 548
 549         if (srtp_init() != err_status_ok) {
 550                 ast_log(AST_LOG_WARNING, "Failed to initialize libsrtp\n");
 551                 return -1;
 552         }
 553
 554         srtp_install_event_handler(srtp_event_cb);
 555
 556         if (ast_rtp_engine_register_srtp(&srtp_res, &policy_res)) {
 557                 ast_log(AST_LOG_WARNING, "Failed to register SRTP with rtp engine\n");
 558                 res_srtp_shutdown();
 559                 return -1;
 560         }
 561
 562         g_initialized = 1;
 563         return 0;
 564 }
 565
 566 /*
 567  * Exported functions
 568  */
 569
 570 static int load_module(void)
 571 {
 572         return res_srtp_init();
 573 }
 574
 575 static int unload_module(void)
 576 {
 577         res_srtp_shutdown();
 578         return 0;
 579 }
 580
 581 AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS | AST_MODFLAG_LOAD_ORDER, "Secure RTP (SRTP)",
 582         .load = load_module,
 583         .unload = unload_module,
 584         .load_pri = AST_MODPRI_CHANNEL_DEPEND,
 585 );