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                                 int res_srtp_create = srtp_create(&srtp->session, &policy->sp);
 370                                 if (res_srtp_create == err_status_ok) {
 371                                         ast_debug(5, "SRTP re-created with first policy\n");
 372                                         ao2_t_ref(policy, -1, "Unreffing first policy for re-creating srtp session");
 373
 374                                         /* if we have more than one policy, add them */
 375                                         if (policies_count > 1) {
 376                                                 ast_debug(5, "Add all the other %d policies\n",
 377                                                         policies_count - 1);
 378                                                 while ((policy = ao2_iterator_next(&it))) {
 379                                                         srtp_add_stream(srtp->session, &policy->sp);
 380                                                         ao2_t_ref(policy, -1, "Unreffing n-th policy for re-creating srtp session");
 381                                                 }
 382                                         }
 383
 384                                         retry++;
 385                                         ao2_iterator_destroy(&it);
 386                                         goto tryagain;
 387                                 }
 388                                 ast_log(LOG_ERROR, "SRTP session could not be re-created after unprotect failure: %s\n", srtp_errstr(res_srtp_create));
 389
 390                                 /* If srtp_create() fails with a previously alloced session, it will have been dealloced before returning. */
 391                                 srtp->session = NULL;
 392
 393                                 ao2_t_ref(policy, -1, "Unreffing first policy after srtp_create failed");
 394                         }
 395                         ao2_iterator_destroy(&it);
 396                 }
 397         }
 398
 399         if (!srtp->session) {
 400                 errno = EINVAL;
 401                 return -1;
 402         }
 403
 404         if (res != err_status_ok && res != err_status_replay_fail ) {
 405                 if ((srtp->warned >= 10) && !((srtp->warned - 10) % 100)) {
 406                         ast_log(AST_LOG_WARNING, "SRTP unprotect failed with: %s %d\n", srtp_errstr(res), srtp->warned);
 407                         srtp->warned = 11;
 408                 } else {
 409                         srtp->warned++;
 410                 }
 411                 errno = EAGAIN;
 412                 return -1;
 413         }
 414
 415         return *len;
 416 }
 417
 418 static int ast_srtp_protect(struct ast_srtp *srtp, void **buf, int *len, int rtcp)
 419 {
 420         int res;
 421         unsigned char *localbuf;
 422
 423         if ((*len + SRTP_MAX_TRAILER_LEN) > sizeof(srtp->buf)) {
 424                 return -1;
 425         }
 426
 427         localbuf = rtcp ? srtp->rtcpbuf : srtp->buf;
 428
 429         memcpy(localbuf, *buf, *len);
 430
 431         if ((res = rtcp ? srtp_protect_rtcp(srtp->session, localbuf, len) : srtp_protect(srtp->session, localbuf, len)) != err_status_ok && res != err_status_replay_fail) {
 432                 ast_log(LOG_WARNING, "SRTP protect: %s\n", srtp_errstr(res));
 433                 return -1;
 434         }
 435
 436         *buf = localbuf;
 437         return *len;
 438 }
 439
 440 static int ast_srtp_create(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy)
 441 {
 442         struct ast_srtp *temp;
 443
 444         if (!(temp = res_srtp_new())) {
 445                 return -1;
 446         }
 447         ast_module_ref(ast_module_info->self);
 448
 449         /* Any failures after this point can use ast_srtp_destroy to destroy the instance */
 450         if (srtp_create(&temp->session, &policy->sp) != err_status_ok) {
 451                 /* Session either wasn't created or was created and dealloced. */
 452                 temp->session = NULL;
 453                 ast_srtp_destroy(temp);
 454                 return -1;
 455         }
 456
 457         temp->rtp = rtp;
 458         *srtp = temp;
 459
 460         ao2_t_link((*srtp)->policies, policy, "Created initial policy");
 461
 462         return 0;
 463 }
 464
 465 static int ast_srtp_replace(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy)
 466 {
 467         if ((*srtp) != NULL) {
 468                 ast_srtp_destroy(*srtp);
 469         }
 470         return ast_srtp_create(srtp, rtp, policy);
 471 }
 472
 473 static void ast_srtp_destroy(struct ast_srtp *srtp)
 474 {
 475         if (srtp->session) {
 476                 srtp_dealloc(srtp->session);
 477         }
 478
 479         ao2_t_callback(srtp->policies, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, NULL, NULL, "Unallocate policy");
 480         ao2_t_ref(srtp->policies, -1, "Destroying container");
 481
 482         ast_free(srtp);
 483         ast_module_unref(ast_module_info->self);
 484 }
 485
 486 static int ast_srtp_add_stream(struct ast_srtp *srtp, struct ast_srtp_policy *policy)
 487 {
 488         struct ast_srtp_policy *match;
 489
 490         /* For existing streams, replace if its an SSRC stream, or bail if its a wildcard */
 491         if ((match = find_policy(srtp, &policy->sp, OBJ_POINTER))) {
 492                 if (policy->sp.ssrc.type != ssrc_specific) {
 493                         ast_log(AST_LOG_WARNING, "Cannot replace an existing wildcard policy\n");
 494                         ao2_t_ref(match, -1, "Unreffing already existing policy");
 495                         return -1;
 496                 } else {
 497                         if (srtp_remove_stream(srtp->session, match->sp.ssrc.value) != err_status_ok) {
 498                                 ast_log(AST_LOG_WARNING, "Failed to remove SRTP stream for SSRC %d\n", match->sp.ssrc.value);
 499                         }
 500                         ao2_t_unlink(srtp->policies, match, "Remove existing match policy");
 501                         ao2_t_ref(match, -1, "Unreffing already existing policy");
 502                 }
 503         }
 504
 505         ast_debug(3, "Adding new policy for %s %d\n",
 506                 policy->sp.ssrc.type == ssrc_specific ? "SSRC" : "type",
 507                 policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type);
 508         if (srtp_add_stream(srtp->session, &policy->sp) != err_status_ok) {
 509                 ast_log(AST_LOG_WARNING, "Failed to add SRTP stream for %s %d\n",
 510                         policy->sp.ssrc.type == ssrc_specific ? "SSRC" : "type",
 511                         policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type);
 512                 return -1;
 513         }
 514
 515         ao2_t_link(srtp->policies, policy, "Added additional stream");
 516
 517         return 0;
 518 }
 519
 520 static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc, unsigned int to_ssrc)
 521 {
 522         struct ast_srtp_policy *match;
 523         struct srtp_policy_t sp = {
 524                 .ssrc.type = ssrc_specific,
 525                 .ssrc.value = from_ssrc,
 526         };
 527         err_status_t status;
 528
 529         /* If we find a match, return and unlink it from the container so we
 530          * can change the SSRC (which is part of the hash) and then have
 531          * ast_srtp_add_stream link it back in if all is well */
 532         if ((match = find_policy(srtp, &sp, OBJ_POINTER | OBJ_UNLINK))) {
 533                 match->sp.ssrc.value = to_ssrc;
 534                 if (ast_srtp_add_stream(srtp, match)) {
 535                         ast_log(LOG_WARNING, "Couldn't add stream\n");
 536                 } else if ((status = srtp_remove_stream(srtp->session, from_ssrc))) {
 537                         ast_debug(3, "Couldn't remove stream (%d)\n", status);
 538                 }
 539                 ao2_t_ref(match, -1, "Unreffing found policy in change_source");
 540         }
 541
 542         return 0;
 543 }
 544
 545 static void res_srtp_shutdown(void)
 546 {
 547         srtp_install_event_handler(NULL);
 548         ast_rtp_engine_unregister_srtp();
 549         g_initialized = 0;
 550 }
 551
 552 static int res_srtp_init(void)
 553 {
 554         if (g_initialized) {
 555                 return 0;
 556         }
 557
 558         if (srtp_init() != err_status_ok) {
 559                 ast_log(AST_LOG_WARNING, "Failed to initialize libsrtp\n");
 560                 return -1;
 561         }
 562
 563         srtp_install_event_handler(srtp_event_cb);
 564
 565         if (ast_rtp_engine_register_srtp(&srtp_res, &policy_res)) {
 566                 ast_log(AST_LOG_WARNING, "Failed to register SRTP with rtp engine\n");
 567                 res_srtp_shutdown();
 568                 return -1;
 569         }
 570
 571         g_initialized = 1;
 572         return 0;
 573 }
 574
 575 /*
 576  * Exported functions
 577  */
 578
 579 static int load_module(void)
 580 {
 581         return res_srtp_init();
 582 }
 583
 584 static int unload_module(void)
 585 {
 586         res_srtp_shutdown();
 587         return 0;
 588 }
 589
 590 AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS | AST_MODFLAG_LOAD_ORDER, "Secure RTP (SRTP)",
 591         .load = load_module,
 592         .unload = unload_module,
 593         .load_pri = AST_MODPRI_CHANNEL_DEPEND,
 594 );