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Asterisk developer's documentation


res_srtp.c

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00001 /*
00002  * Asterisk -- An open source telephony toolkit.
00003  *
00004  * Copyright (C) 2005, Mikael Magnusson
00005  *
00006  * Mikael Magnusson <mikma@users.sourceforge.net>
00007  *
00008  * See http://www.asterisk.org for more information about
00009  * the Asterisk project. Please do not directly contact
00010  * any of the maintainers of this project for assistance;
00011  * the project provides a web site, mailing lists and IRC
00012  * channels for your use.
00013  *
00014  * This program is free software, distributed under the terms of
00015  * the GNU General Public License Version 2. See the LICENSE file
00016  * at the top of the source tree.
00017  *
00018  * Builds on libSRTP http://srtp.sourceforge.net
00019  */
00020 
00021 /*! \file res_srtp.c
00022  *
00023  * \brief Secure RTP (SRTP)
00024  *
00025  * Secure RTP (SRTP)
00026  * Specified in RFC 3711.
00027  *
00028  * \author Mikael Magnusson <mikma@users.sourceforge.net>
00029  */
00030 
00031 /*** MODULEINFO
00032    <depend>srtp</depend>
00033    <support_level>core</support_level>
00034 ***/
00035 
00036 /* See https://wiki.asterisk.org/wiki/display/AST/Secure+Calling */
00037 
00038 #include "asterisk.h"
00039 
00040 ASTERISK_FILE_VERSION(__FILE__, "$Revision: 426140 $")
00041 
00042 #include <srtp/srtp.h>
00043 #include <srtp/crypto_kernel.h>
00044 
00045 #include "asterisk/lock.h"
00046 #include "asterisk/sched.h"
00047 #include "asterisk/module.h"
00048 #include "asterisk/options.h"
00049 #include "asterisk/rtp_engine.h"
00050 #include "asterisk/astobj2.h"
00051 
00052 struct ast_srtp {
00053    struct ast_rtp_instance *rtp;
00054    struct ao2_container *policies;
00055    srtp_t session;
00056    const struct ast_srtp_cb *cb;
00057    void *data;
00058    int warned;
00059    unsigned char buf[8192 + AST_FRIENDLY_OFFSET];
00060    unsigned char rtcpbuf[8192 + AST_FRIENDLY_OFFSET];
00061 };
00062 
00063 struct ast_srtp_policy {
00064    srtp_policy_t sp;
00065 };
00066 
00067 /*! Tracks whether or not we've initialized the libsrtp library */
00068 static int g_initialized = 0;
00069 
00070 /* SRTP functions */
00071 static int ast_srtp_create(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy);
00072 static int ast_srtp_replace(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy);
00073 static void ast_srtp_destroy(struct ast_srtp *srtp);
00074 static int ast_srtp_add_stream(struct ast_srtp *srtp, struct ast_srtp_policy *policy);
00075 static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc, unsigned int to_ssrc);
00076 
00077 static int ast_srtp_unprotect(struct ast_srtp *srtp, void *buf, int *len, int rtcp);
00078 static int ast_srtp_protect(struct ast_srtp *srtp, void **buf, int *len, int rtcp);
00079 static void ast_srtp_set_cb(struct ast_srtp *srtp, const struct ast_srtp_cb *cb, void *data);
00080 static int ast_srtp_get_random(unsigned char *key, size_t len);
00081 
00082 /* Policy functions */
00083 static struct ast_srtp_policy *ast_srtp_policy_alloc(void);
00084 static void ast_srtp_policy_destroy(struct ast_srtp_policy *policy);
00085 static int ast_srtp_policy_set_suite(struct ast_srtp_policy *policy, enum ast_srtp_suite suite);
00086 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);
00087 static void ast_srtp_policy_set_ssrc(struct ast_srtp_policy *policy, unsigned long ssrc, int inbound);
00088 
00089 static struct ast_srtp_res srtp_res = {
00090    .create = ast_srtp_create,
00091    .replace = ast_srtp_replace,
00092    .destroy = ast_srtp_destroy,
00093    .add_stream = ast_srtp_add_stream,
00094    .change_source = ast_srtp_change_source,
00095    .set_cb = ast_srtp_set_cb,
00096    .unprotect = ast_srtp_unprotect,
00097    .protect = ast_srtp_protect,
00098    .get_random = ast_srtp_get_random
00099 };
00100 
00101 static struct ast_srtp_policy_res policy_res = {
00102    .alloc = ast_srtp_policy_alloc,
00103    .destroy = ast_srtp_policy_destroy,
00104    .set_suite = ast_srtp_policy_set_suite,
00105    .set_master_key = ast_srtp_policy_set_master_key,
00106    .set_ssrc = ast_srtp_policy_set_ssrc
00107 };
00108 
00109 static const char *srtp_errstr(int err)
00110 {
00111    switch(err) {
00112    case err_status_ok:
00113       return "nothing to report";
00114    case err_status_fail:
00115       return "unspecified failure";
00116    case err_status_bad_param:
00117       return "unsupported parameter";
00118    case err_status_alloc_fail:
00119       return "couldn't allocate memory";
00120    case err_status_dealloc_fail:
00121       return "couldn't deallocate properly";
00122    case err_status_init_fail:
00123       return "couldn't initialize";
00124    case err_status_terminus:
00125       return "can't process as much data as requested";
00126    case err_status_auth_fail:
00127       return "authentication failure";
00128    case err_status_cipher_fail:
00129       return "cipher failure";
00130    case err_status_replay_fail:
00131       return "replay check failed (bad index)";
00132    case err_status_replay_old:
00133       return "replay check failed (index too old)";
00134    case err_status_algo_fail:
00135       return "algorithm failed test routine";
00136    case err_status_no_such_op:
00137       return "unsupported operation";
00138    case err_status_no_ctx:
00139       return "no appropriate context found";
00140    case err_status_cant_check:
00141       return "unable to perform desired validation";
00142    case err_status_key_expired:
00143       return "can't use key any more";
00144    default:
00145       return "unknown";
00146    }
00147 }
00148 
00149 static int policy_hash_fn(const void *obj, const int flags)
00150 {
00151    const struct ast_srtp_policy *policy = obj;
00152 
00153    return policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type;
00154 }
00155 
00156 static int policy_cmp_fn(void *obj, void *arg, int flags)
00157 {
00158    const struct ast_srtp_policy *one = obj, *two = arg;
00159 
00160    return one->sp.ssrc.type == two->sp.ssrc.type && one->sp.ssrc.value == two->sp.ssrc.value;
00161 }
00162 
00163 static struct ast_srtp_policy *find_policy(struct ast_srtp *srtp, const srtp_policy_t *policy, int flags)
00164 {
00165    struct ast_srtp_policy tmp = {
00166       .sp = {
00167          .ssrc.type = policy->ssrc.type,
00168          .ssrc.value = policy->ssrc.value,
00169       },
00170    };
00171 
00172    return ao2_t_find(srtp->policies, &tmp, flags, "Looking for policy");
00173 }
00174 
00175 static struct ast_srtp *res_srtp_new(void)
00176 {
00177    struct ast_srtp *srtp;
00178 
00179    if (!(srtp = ast_calloc(1, sizeof(*srtp)))) {
00180       ast_log(LOG_ERROR, "Unable to allocate memory for srtp\n");
00181       return NULL;
00182    }
00183 
00184    if (!(srtp->policies = ao2_t_container_alloc(5, policy_hash_fn, policy_cmp_fn, "SRTP policy container"))) {
00185       ast_free(srtp);
00186       return NULL;
00187    }
00188    
00189    srtp->warned = 1;
00190 
00191    return srtp;
00192 }
00193 
00194 /*
00195   struct ast_srtp_policy
00196 */
00197 static void srtp_event_cb(srtp_event_data_t *data)
00198 {
00199    switch (data->event) {
00200    case event_ssrc_collision:
00201       ast_debug(1, "SSRC collision\n");
00202       break;
00203    case event_key_soft_limit:
00204       ast_debug(1, "event_key_soft_limit\n");
00205       break;
00206    case event_key_hard_limit:
00207       ast_debug(1, "event_key_hard_limit\n");
00208       break;
00209    case event_packet_index_limit:
00210       ast_debug(1, "event_packet_index_limit\n");
00211       break;
00212    }
00213 }
00214 
00215 static void ast_srtp_policy_set_ssrc(struct ast_srtp_policy *policy,
00216       unsigned long ssrc, int inbound)
00217 {
00218    if (ssrc) {
00219       policy->sp.ssrc.type = ssrc_specific;
00220       policy->sp.ssrc.value = ssrc;
00221    } else {
00222       policy->sp.ssrc.type = inbound ? ssrc_any_inbound : ssrc_any_outbound;
00223    }
00224 }
00225 
00226 static void policy_destructor(void *obj)
00227 {
00228    struct ast_srtp_policy *policy = obj;
00229 
00230    if (policy->sp.key) {
00231       ast_free(policy->sp.key);
00232       policy->sp.key = NULL;
00233    }
00234 }
00235 
00236 static struct ast_srtp_policy *ast_srtp_policy_alloc()
00237 {
00238    struct ast_srtp_policy *tmp;
00239 
00240    if (!(tmp = ao2_t_alloc(sizeof(*tmp), policy_destructor, "Allocating policy"))) {
00241       ast_log(LOG_ERROR, "Unable to allocate memory for srtp_policy\n");
00242    }
00243 
00244    return tmp;
00245 }
00246 
00247 static void ast_srtp_policy_destroy(struct ast_srtp_policy *policy)
00248 {
00249    ao2_t_ref(policy, -1, "Destroying policy");
00250 }
00251 
00252 static int policy_set_suite(crypto_policy_t *p, enum ast_srtp_suite suite)
00253 {
00254    switch (suite) {
00255    case AST_AES_CM_128_HMAC_SHA1_80:
00256       p->cipher_type = AES_128_ICM;
00257       p->cipher_key_len = 30;
00258       p->auth_type = HMAC_SHA1;
00259       p->auth_key_len = 20;
00260       p->auth_tag_len = 10;
00261       p->sec_serv = sec_serv_conf_and_auth;
00262       return 0;
00263 
00264    case AST_AES_CM_128_HMAC_SHA1_32:
00265       p->cipher_type = AES_128_ICM;
00266       p->cipher_key_len = 30;
00267       p->auth_type = HMAC_SHA1;
00268       p->auth_key_len = 20;
00269       p->auth_tag_len = 4;
00270       p->sec_serv = sec_serv_conf_and_auth;
00271       return 0;
00272 
00273    default:
00274       ast_log(LOG_ERROR, "Invalid crypto suite: %u\n", suite);
00275       return -1;
00276    }
00277 }
00278 
00279 static int ast_srtp_policy_set_suite(struct ast_srtp_policy *policy, enum ast_srtp_suite suite)
00280 {
00281    return policy_set_suite(&policy->sp.rtp, suite) | policy_set_suite(&policy->sp.rtcp, suite);
00282 }
00283 
00284 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)
00285 {
00286    size_t size = key_len + salt_len;
00287    unsigned char *master_key;
00288 
00289    if (policy->sp.key) {
00290       ast_free(policy->sp.key);
00291       policy->sp.key = NULL;
00292    }
00293 
00294    if (!(master_key = ast_calloc(1, size))) {
00295       return -1;
00296    }
00297 
00298    memcpy(master_key, key, key_len);
00299    memcpy(master_key + key_len, salt, salt_len);
00300 
00301    policy->sp.key = master_key;
00302 
00303    return 0;
00304 }
00305 
00306 static int ast_srtp_get_random(unsigned char *key, size_t len)
00307 {
00308    return crypto_get_random(key, len) != err_status_ok ? -1: 0;
00309 }
00310 
00311 static void ast_srtp_set_cb(struct ast_srtp *srtp, const struct ast_srtp_cb *cb, void *data)
00312 {
00313    if (!srtp) {
00314       return;
00315    }
00316 
00317    srtp->cb = cb;
00318    srtp->data = data;
00319 }
00320 
00321 /* Vtable functions */
00322 static int ast_srtp_unprotect(struct ast_srtp *srtp, void *buf, int *len, int rtcp)
00323 {
00324    int res = 0;
00325    int i;
00326    int retry = 0;
00327    struct ast_rtp_instance_stats stats = {0,};
00328 
00329 tryagain:
00330 
00331    for (i = 0; i < 2; i++) {
00332       res = rtcp ? srtp_unprotect_rtcp(srtp->session, buf, len) : srtp_unprotect(srtp->session, buf, len);
00333       if (res != err_status_no_ctx) {
00334          break;
00335       }
00336 
00337       if (srtp->cb && srtp->cb->no_ctx) {
00338          if (ast_rtp_instance_get_stats(srtp->rtp, &stats, AST_RTP_INSTANCE_STAT_REMOTE_SSRC)) {
00339             break;
00340          }
00341          if (srtp->cb->no_ctx(srtp->rtp, stats.remote_ssrc, srtp->data) < 0) {
00342             break;
00343          }
00344       } else {
00345          break;
00346       }
00347    }
00348 
00349    if (retry == 0  && res == err_status_replay_old) {
00350       ast_log(AST_LOG_NOTICE, "SRTP unprotect failed with %s, retrying\n", srtp_errstr(res));
00351 
00352       if (srtp->session) {
00353          struct ast_srtp_policy *policy;
00354          struct ao2_iterator it;
00355          int policies_count;
00356 
00357          /* dealloc first */
00358          ast_debug(5, "SRTP destroy before re-create\n");
00359          srtp_dealloc(srtp->session);
00360 
00361          /* get the count */
00362          policies_count = ao2_container_count(srtp->policies);
00363 
00364          /* get the first to build up */
00365          it = ao2_iterator_init(srtp->policies, 0);
00366          policy = ao2_iterator_next(&it);
00367 
00368          ast_debug(5, "SRTP try to re-create\n");
00369          if (policy) {
00370             int res_srtp_create = srtp_create(&srtp->session, &policy->sp);
00371             if (res_srtp_create == err_status_ok) {
00372                ast_debug(5, "SRTP re-created with first policy\n");
00373                ao2_t_ref(policy, -1, "Unreffing first policy for re-creating srtp session");
00374 
00375                /* if we have more than one policy, add them */
00376                if (policies_count > 1) {
00377                   ast_debug(5, "Add all the other %d policies\n",
00378                      policies_count - 1);
00379                   while ((policy = ao2_iterator_next(&it))) {
00380                      srtp_add_stream(srtp->session, &policy->sp);
00381                      ao2_t_ref(policy, -1, "Unreffing n-th policy for re-creating srtp session");
00382                   }
00383                }
00384 
00385                retry++;
00386                ao2_iterator_destroy(&it);
00387                goto tryagain;
00388             }
00389             ast_log(LOG_ERROR, "SRTP session could not be re-created after unprotect failure: %s\n", srtp_errstr(res_srtp_create));
00390 
00391             /* If srtp_create() fails with a previously alloced session, it will have been dealloced before returning. */
00392             srtp->session = NULL;
00393 
00394             ao2_t_ref(policy, -1, "Unreffing first policy after srtp_create failed");
00395          }
00396          ao2_iterator_destroy(&it);
00397       }
00398    }
00399 
00400    if (!srtp->session) {
00401       errno = EINVAL;
00402       return -1;
00403    }
00404 
00405    if (res != err_status_ok && res != err_status_replay_fail ) {
00406       if ((srtp->warned >= 10) && !((srtp->warned - 10) % 100)) {
00407          ast_log(AST_LOG_WARNING, "SRTP unprotect failed with: %s %d\n", srtp_errstr(res), srtp->warned);
00408          srtp->warned = 11;
00409       } else {
00410          srtp->warned++;
00411       }
00412       errno = EAGAIN;
00413       return -1;
00414    }
00415 
00416    return *len;
00417 }
00418 
00419 static int ast_srtp_protect(struct ast_srtp *srtp, void **buf, int *len, int rtcp)
00420 {
00421    int res;
00422    unsigned char *localbuf;
00423 
00424    if ((*len + SRTP_MAX_TRAILER_LEN) > sizeof(srtp->buf)) {
00425       return -1;
00426    }
00427    
00428    localbuf = rtcp ? srtp->rtcpbuf : srtp->buf;
00429 
00430    memcpy(localbuf, *buf, *len);
00431 
00432    if ((res = rtcp ? srtp_protect_rtcp(srtp->session, localbuf, len) : srtp_protect(srtp->session, localbuf, len)) != err_status_ok && res != err_status_replay_fail) {
00433       ast_log(LOG_WARNING, "SRTP protect: %s\n", srtp_errstr(res));
00434       return -1;
00435    }
00436 
00437    *buf = localbuf;
00438    return *len;
00439 }
00440 
00441 static int ast_srtp_create(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy)
00442 {
00443    struct ast_srtp *temp;
00444 
00445    if (!(temp = res_srtp_new())) {
00446       return -1;
00447    }
00448    ast_module_ref(ast_module_info->self);
00449 
00450    /* Any failures after this point can use ast_srtp_destroy to destroy the instance */
00451    if (srtp_create(&temp->session, &policy->sp) != err_status_ok) {
00452       /* Session either wasn't created or was created and dealloced. */
00453       temp->session = NULL;
00454       ast_srtp_destroy(temp);
00455       return -1;
00456    }
00457 
00458    temp->rtp = rtp;
00459    *srtp = temp;
00460 
00461    ao2_t_link((*srtp)->policies, policy, "Created initial policy");
00462 
00463    return 0;
00464 }
00465 
00466 static int ast_srtp_replace(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy)
00467 {
00468    if ((*srtp) != NULL) {
00469       ast_srtp_destroy(*srtp);
00470    }
00471    return ast_srtp_create(srtp, rtp, policy);
00472 }
00473 
00474 static void ast_srtp_destroy(struct ast_srtp *srtp)
00475 {
00476    if (srtp->session) {
00477       srtp_dealloc(srtp->session);
00478    }
00479 
00480    ao2_t_callback(srtp->policies, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, NULL, NULL, "Unallocate policy");
00481    ao2_t_ref(srtp->policies, -1, "Destroying container");
00482 
00483    ast_free(srtp);
00484    ast_module_unref(ast_module_info->self);
00485 }
00486 
00487 static int ast_srtp_add_stream(struct ast_srtp *srtp, struct ast_srtp_policy *policy)
00488 {
00489    struct ast_srtp_policy *match;
00490 
00491    /* For existing streams, replace if its an SSRC stream, or bail if its a wildcard */
00492    if ((match = find_policy(srtp, &policy->sp, OBJ_POINTER))) {
00493       if (policy->sp.ssrc.type != ssrc_specific) {
00494          ast_log(AST_LOG_WARNING, "Cannot replace an existing wildcard policy\n");
00495          ao2_t_ref(match, -1, "Unreffing already existing policy");
00496          return -1;
00497       } else {
00498          if (srtp_remove_stream(srtp->session, match->sp.ssrc.value) != err_status_ok) {
00499             ast_log(AST_LOG_WARNING, "Failed to remove SRTP stream for SSRC %u\n", match->sp.ssrc.value);
00500          }
00501          ao2_t_unlink(srtp->policies, match, "Remove existing match policy");
00502          ao2_t_ref(match, -1, "Unreffing already existing policy");
00503       }
00504    }
00505 
00506    ast_debug(3, "Adding new policy for %s %u\n",
00507       policy->sp.ssrc.type == ssrc_specific ? "SSRC" : "type",
00508       policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type);
00509    if (srtp_add_stream(srtp->session, &policy->sp) != err_status_ok) {
00510       ast_log(AST_LOG_WARNING, "Failed to add SRTP stream for %s %u\n",
00511          policy->sp.ssrc.type == ssrc_specific ? "SSRC" : "type",
00512          policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type);
00513       return -1;
00514    }
00515 
00516    ao2_t_link(srtp->policies, policy, "Added additional stream");
00517 
00518    return 0;
00519 }
00520 
00521 static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc, unsigned int to_ssrc)
00522 {
00523    struct ast_srtp_policy *match;
00524    struct srtp_policy_t sp = {
00525       .ssrc.type = ssrc_specific,
00526       .ssrc.value = from_ssrc,
00527    };
00528    err_status_t status;
00529 
00530    /* If we find a match, return and unlink it from the container so we
00531     * can change the SSRC (which is part of the hash) and then have
00532     * ast_srtp_add_stream link it back in if all is well */
00533    if ((match = find_policy(srtp, &sp, OBJ_POINTER | OBJ_UNLINK))) {
00534       match->sp.ssrc.value = to_ssrc;
00535       if (ast_srtp_add_stream(srtp, match)) {
00536          ast_log(LOG_WARNING, "Couldn't add stream\n");
00537       } else if ((status = srtp_remove_stream(srtp->session, from_ssrc))) {
00538          ast_debug(3, "Couldn't remove stream (%u)\n", status);
00539       }
00540       ao2_t_ref(match, -1, "Unreffing found policy in change_source");
00541    }
00542 
00543    return 0;
00544 }
00545 
00546 static void res_srtp_shutdown(void)
00547 {
00548    srtp_install_event_handler(NULL);
00549    ast_rtp_engine_unregister_srtp();
00550 #ifdef HAVE_SRTP_SHUTDOWN
00551    srtp_shutdown();
00552 #endif
00553    g_initialized = 0;
00554 }
00555 
00556 static int res_srtp_init(void)
00557 {
00558    if (g_initialized) {
00559       return 0;
00560    }
00561 
00562    if (srtp_init() != err_status_ok) {
00563       ast_log(AST_LOG_WARNING, "Failed to initialize libsrtp\n");
00564       return -1;
00565    }
00566 
00567    srtp_install_event_handler(srtp_event_cb);
00568 
00569    if (ast_rtp_engine_register_srtp(&srtp_res, &policy_res)) {
00570       ast_log(AST_LOG_WARNING, "Failed to register SRTP with rtp engine\n");
00571       res_srtp_shutdown();
00572       return -1;
00573    }
00574 
00575    g_initialized = 1;
00576    return 0;
00577 }
00578 
00579 /*
00580  * Exported functions
00581  */
00582 
00583 static int load_module(void)
00584 {
00585    return res_srtp_init();
00586 }
00587 
00588 static int unload_module(void)
00589 {
00590    res_srtp_shutdown();
00591    return 0;
00592 }
00593 
00594 AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS | AST_MODFLAG_LOAD_ORDER, "Secure RTP (SRTP)",
00595    .load = load_module,
00596    .unload = unload_module,
00597    .load_pri = AST_MODPRI_CHANNEL_DEPEND,
00598 );

Generated on 7 Aug 2019 for Asterisk - The Open Source Telephony Project by  doxygen 1.6.1