Tue Aug 20 16:34:37 2013

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: 378591 $")
00041 
00042 #include <srtp/srtp.h>
00043 
00044 #include "asterisk/lock.h"
00045 #include "asterisk/sched.h"
00046 #include "asterisk/module.h"
00047 #include "asterisk/options.h"
00048 #include "asterisk/rtp_engine.h"
00049 #include "asterisk/astobj2.h"
00050 
00051 struct ast_srtp {
00052    struct ast_rtp_instance *rtp;
00053    struct ao2_container *policies;
00054    srtp_t session;
00055    const struct ast_srtp_cb *cb;
00056    void *data;
00057    int warned;
00058    unsigned char buf[8192 + AST_FRIENDLY_OFFSET];
00059    unsigned char rtcpbuf[8192 + AST_FRIENDLY_OFFSET];
00060 };
00061 
00062 struct ast_srtp_policy {
00063    srtp_policy_t sp;
00064 };
00065 
00066 /*! Tracks whether or not we've initialized the libsrtp library */
00067 static int g_initialized = 0;
00068 
00069 /* SRTP functions */
00070 static int ast_srtp_create(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy);
00071 static int ast_srtp_replace(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy);
00072 static void ast_srtp_destroy(struct ast_srtp *srtp);
00073 static int ast_srtp_add_stream(struct ast_srtp *srtp, struct ast_srtp_policy *policy);
00074 static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc, unsigned int to_ssrc);
00075 
00076 static int ast_srtp_unprotect(struct ast_srtp *srtp, void *buf, int *len, int rtcp);
00077 static int ast_srtp_protect(struct ast_srtp *srtp, void **buf, int *len, int rtcp);
00078 static void ast_srtp_set_cb(struct ast_srtp *srtp, const struct ast_srtp_cb *cb, void *data);
00079 static int ast_srtp_get_random(unsigned char *key, size_t len);
00080 
00081 /* Policy functions */
00082 static struct ast_srtp_policy *ast_srtp_policy_alloc(void);
00083 static void ast_srtp_policy_destroy(struct ast_srtp_policy *policy);
00084 static int ast_srtp_policy_set_suite(struct ast_srtp_policy *policy, enum ast_srtp_suite suite);
00085 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);
00086 static void ast_srtp_policy_set_ssrc(struct ast_srtp_policy *policy, unsigned long ssrc, int inbound);
00087 
00088 static struct ast_srtp_res srtp_res = {
00089    .create = ast_srtp_create,
00090    .replace = ast_srtp_replace,
00091    .destroy = ast_srtp_destroy,
00092    .add_stream = ast_srtp_add_stream,
00093    .change_source = ast_srtp_change_source,
00094    .set_cb = ast_srtp_set_cb,
00095    .unprotect = ast_srtp_unprotect,
00096    .protect = ast_srtp_protect,
00097    .get_random = ast_srtp_get_random
00098 };
00099 
00100 static struct ast_srtp_policy_res policy_res = {
00101    .alloc = ast_srtp_policy_alloc,
00102    .destroy = ast_srtp_policy_destroy,
00103    .set_suite = ast_srtp_policy_set_suite,
00104    .set_master_key = ast_srtp_policy_set_master_key,
00105    .set_ssrc = ast_srtp_policy_set_ssrc
00106 };
00107 
00108 static const char *srtp_errstr(int err)
00109 {
00110    switch(err) {
00111    case err_status_ok:
00112       return "nothing to report";
00113    case err_status_fail:
00114       return "unspecified failure";
00115    case err_status_bad_param:
00116       return "unsupported parameter";
00117    case err_status_alloc_fail:
00118       return "couldn't allocate memory";
00119    case err_status_dealloc_fail:
00120       return "couldn't deallocate properly";
00121    case err_status_init_fail:
00122       return "couldn't initialize";
00123    case err_status_terminus:
00124       return "can't process as much data as requested";
00125    case err_status_auth_fail:
00126       return "authentication failure";
00127    case err_status_cipher_fail:
00128       return "cipher failure";
00129    case err_status_replay_fail:
00130       return "replay check failed (bad index)";
00131    case err_status_replay_old:
00132       return "replay check failed (index too old)";
00133    case err_status_algo_fail:
00134       return "algorithm failed test routine";
00135    case err_status_no_such_op:
00136       return "unsupported operation";
00137    case err_status_no_ctx:
00138       return "no appropriate context found";
00139    case err_status_cant_check:
00140       return "unable to perform desired validation";
00141    case err_status_key_expired:
00142       return "can't use key any more";
00143    default:
00144       return "unknown";
00145    }
00146 }
00147 
00148 static int policy_hash_fn(const void *obj, const int flags)
00149 {
00150    const struct ast_srtp_policy *policy = obj;
00151 
00152    return policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type;
00153 }
00154 
00155 static int policy_cmp_fn(void *obj, void *arg, int flags)
00156 {
00157    const struct ast_srtp_policy *one = obj, *two = arg;
00158 
00159    return one->sp.ssrc.type == two->sp.ssrc.type && one->sp.ssrc.value == two->sp.ssrc.value;
00160 }
00161 
00162 static struct ast_srtp_policy *find_policy(struct ast_srtp *srtp, const srtp_policy_t *policy, int flags)
00163 {
00164    struct ast_srtp_policy tmp = {
00165       .sp = {
00166          .ssrc.type = policy->ssrc.type,
00167          .ssrc.value = policy->ssrc.value,
00168       },
00169    };
00170 
00171    return ao2_t_find(srtp->policies, &tmp, flags, "Looking for policy");
00172 }
00173 
00174 static struct ast_srtp *res_srtp_new(void)
00175 {
00176    struct ast_srtp *srtp;
00177 
00178    if (!(srtp = ast_calloc(1, sizeof(*srtp)))) {
00179       ast_log(LOG_ERROR, "Unable to allocate memory for srtp\n");
00180       return NULL;
00181    }
00182 
00183    if (!(srtp->policies = ao2_t_container_alloc(5, policy_hash_fn, policy_cmp_fn, "SRTP policy container"))) {
00184       ast_free(srtp);
00185       return NULL;
00186    }
00187    
00188    srtp->warned = 1;
00189 
00190    return srtp;
00191 }
00192 
00193 /*
00194   struct ast_srtp_policy
00195 */
00196 static void srtp_event_cb(srtp_event_data_t *data)
00197 {
00198    switch (data->event) {
00199    case event_ssrc_collision:
00200       ast_debug(1, "SSRC collision\n");
00201       break;
00202    case event_key_soft_limit:
00203       ast_debug(1, "event_key_soft_limit\n");
00204       break;
00205    case event_key_hard_limit:
00206       ast_debug(1, "event_key_hard_limit\n");
00207       break;
00208    case event_packet_index_limit:
00209       ast_debug(1, "event_packet_index_limit\n");
00210       break;
00211    }
00212 }
00213 
00214 static void ast_srtp_policy_set_ssrc(struct ast_srtp_policy *policy,
00215       unsigned long ssrc, int inbound)
00216 {
00217    if (ssrc) {
00218       policy->sp.ssrc.type = ssrc_specific;
00219       policy->sp.ssrc.value = ssrc;
00220    } else {
00221       policy->sp.ssrc.type = inbound ? ssrc_any_inbound : ssrc_any_outbound;
00222    }
00223 }
00224 
00225 static void policy_destructor(void *obj)
00226 {
00227    struct ast_srtp_policy *policy = obj;
00228 
00229    if (policy->sp.key) {
00230       ast_free(policy->sp.key);
00231       policy->sp.key = NULL;
00232    }
00233 }
00234 
00235 static struct ast_srtp_policy *ast_srtp_policy_alloc()
00236 {
00237    struct ast_srtp_policy *tmp;
00238 
00239    if (!(tmp = ao2_t_alloc(sizeof(*tmp), policy_destructor, "Allocating policy"))) {
00240       ast_log(LOG_ERROR, "Unable to allocate memory for srtp_policy\n");
00241    }
00242 
00243    return tmp;
00244 }
00245 
00246 static void ast_srtp_policy_destroy(struct ast_srtp_policy *policy)
00247 {
00248    ao2_t_ref(policy, -1, "Destroying policy");
00249 }
00250 
00251 static int policy_set_suite(crypto_policy_t *p, enum ast_srtp_suite suite)
00252 {
00253    switch (suite) {
00254    case AST_AES_CM_128_HMAC_SHA1_80:
00255       p->cipher_type = AES_128_ICM;
00256       p->cipher_key_len = 30;
00257       p->auth_type = HMAC_SHA1;
00258       p->auth_key_len = 20;
00259       p->auth_tag_len = 10;
00260       p->sec_serv = sec_serv_conf_and_auth;
00261       return 0;
00262 
00263    case AST_AES_CM_128_HMAC_SHA1_32:
00264       p->cipher_type = AES_128_ICM;
00265       p->cipher_key_len = 30;
00266       p->auth_type = HMAC_SHA1;
00267       p->auth_key_len = 20;
00268       p->auth_tag_len = 4;
00269       p->sec_serv = sec_serv_conf_and_auth;
00270       return 0;
00271 
00272    default:
00273       ast_log(LOG_ERROR, "Invalid crypto suite: %d\n", suite);
00274       return -1;
00275    }
00276 }
00277 
00278 static int ast_srtp_policy_set_suite(struct ast_srtp_policy *policy, enum ast_srtp_suite suite)
00279 {
00280    return policy_set_suite(&policy->sp.rtp, suite) | policy_set_suite(&policy->sp.rtcp, suite);
00281 }
00282 
00283 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)
00284 {
00285    size_t size = key_len + salt_len;
00286    unsigned char *master_key;
00287 
00288    if (policy->sp.key) {
00289       ast_free(policy->sp.key);
00290       policy->sp.key = NULL;
00291    }
00292 
00293    if (!(master_key = ast_calloc(1, size))) {
00294       return -1;
00295    }
00296 
00297    memcpy(master_key, key, key_len);
00298    memcpy(master_key + key_len, salt, salt_len);
00299 
00300    policy->sp.key = master_key;
00301 
00302    return 0;
00303 }
00304 
00305 static int ast_srtp_get_random(unsigned char *key, size_t len)
00306 {
00307    return crypto_get_random(key, len) != err_status_ok ? -1: 0;
00308 }
00309 
00310 static void ast_srtp_set_cb(struct ast_srtp *srtp, const struct ast_srtp_cb *cb, void *data)
00311 {
00312    if (!srtp) {
00313       return;
00314    }
00315 
00316    srtp->cb = cb;
00317    srtp->data = data;
00318 }
00319 
00320 /* Vtable functions */
00321 static int ast_srtp_unprotect(struct ast_srtp *srtp, void *buf, int *len, int rtcp)
00322 {
00323    int res = 0;
00324    int i;
00325    int retry = 0;
00326    struct ast_rtp_instance_stats stats = {0,};
00327 
00328 tryagain:
00329 
00330    for (i = 0; i < 2; i++) {
00331       res = rtcp ? srtp_unprotect_rtcp(srtp->session, buf, len) : srtp_unprotect(srtp->session, buf, len);
00332       if (res != err_status_no_ctx) {
00333          break;
00334       }
00335 
00336       if (srtp->cb && srtp->cb->no_ctx) {
00337          if (ast_rtp_instance_get_stats(srtp->rtp, &stats, AST_RTP_INSTANCE_STAT_REMOTE_SSRC)) {
00338             break;
00339          }
00340          if (srtp->cb->no_ctx(srtp->rtp, stats.remote_ssrc, srtp->data) < 0) {
00341             break;
00342          }
00343       } else {
00344          break;
00345       }
00346    }
00347 
00348    if (retry == 0  && res == err_status_replay_old) {
00349       ast_log(AST_LOG_NOTICE, "SRTP unprotect failed with %s, retrying\n", srtp_errstr(res));
00350 
00351       if (srtp->session) {
00352          struct ast_srtp_policy *policy;
00353          struct ao2_iterator it;
00354          int policies_count;
00355 
00356          /* dealloc first */
00357          ast_debug(5, "SRTP destroy before re-create\n");
00358          srtp_dealloc(srtp->session);
00359 
00360          /* get the count */
00361          policies_count = ao2_container_count(srtp->policies);
00362 
00363          /* get the first to build up */
00364          it = ao2_iterator_init(srtp->policies, 0);
00365          policy = ao2_iterator_next(&it);
00366 
00367          ast_debug(5, "SRTP try to re-create\n");
00368          if (policy) {
00369             int res_srtp_create = srtp_create(&srtp->session, &policy->sp);
00370             if (res_srtp_create == err_status_ok) {
00371                ast_debug(5, "SRTP re-created with first policy\n");
00372                ao2_t_ref(policy, -1, "Unreffing first policy for re-creating srtp session");
00373 
00374                /* if we have more than one policy, add them */
00375                if (policies_count > 1) {
00376                   ast_debug(5, "Add all the other %d policies\n",
00377                      policies_count - 1);
00378                   while ((policy = ao2_iterator_next(&it))) {
00379                      srtp_add_stream(srtp->session, &policy->sp);
00380                      ao2_t_ref(policy, -1, "Unreffing n-th policy for re-creating srtp session");
00381                   }
00382                }
00383 
00384                retry++;
00385                ao2_iterator_destroy(&it);
00386                goto tryagain;
00387             }
00388             ast_log(LOG_ERROR, "SRTP session could not be re-created after unprotect failure: %s\n", srtp_errstr(res_srtp_create));
00389 
00390             /* If srtp_create() fails with a previously alloced session, it will have been dealloced before returning. */
00391             srtp->session = NULL;
00392 
00393             ao2_t_ref(policy, -1, "Unreffing first policy after srtp_create failed");
00394          }
00395          ao2_iterator_destroy(&it);
00396       }
00397    }
00398 
00399    if (!srtp->session) {
00400       errno = EINVAL;
00401       return -1;
00402    }
00403 
00404    if (res != err_status_ok && res != err_status_replay_fail ) {
00405       if ((srtp->warned >= 10) && !((srtp->warned - 10) % 100)) {
00406          ast_log(AST_LOG_WARNING, "SRTP unprotect failed with: %s %d\n", srtp_errstr(res), srtp->warned);
00407          srtp->warned = 11;
00408       } else {
00409          srtp->warned++;
00410       }
00411       errno = EAGAIN;
00412       return -1;
00413    }
00414 
00415    return *len;
00416 }
00417 
00418 static int ast_srtp_protect(struct ast_srtp *srtp, void **buf, int *len, int rtcp)
00419 {
00420    int res;
00421    unsigned char *localbuf;
00422 
00423    if ((*len + SRTP_MAX_TRAILER_LEN) > sizeof(srtp->buf)) {
00424       return -1;
00425    }
00426    
00427    localbuf = rtcp ? srtp->rtcpbuf : srtp->buf;
00428 
00429    memcpy(localbuf, *buf, *len);
00430 
00431    if ((res = rtcp ? srtp_protect_rtcp(srtp->session, localbuf, len) : srtp_protect(srtp->session, localbuf, len)) != err_status_ok && res != err_status_replay_fail) {
00432       ast_log(LOG_WARNING, "SRTP protect: %s\n", srtp_errstr(res));
00433       return -1;
00434    }
00435 
00436    *buf = localbuf;
00437    return *len;
00438 }
00439 
00440 static int ast_srtp_create(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy)
00441 {
00442    struct ast_srtp *temp;
00443 
00444    if (!(temp = res_srtp_new())) {
00445       return -1;
00446    }
00447    ast_module_ref(ast_module_info->self);
00448 
00449    /* Any failures after this point can use ast_srtp_destroy to destroy the instance */
00450    if (srtp_create(&temp->session, &policy->sp) != err_status_ok) {
00451       /* Session either wasn't created or was created and dealloced. */
00452       temp->session = NULL;
00453       ast_srtp_destroy(temp);
00454       return -1;
00455    }
00456 
00457    temp->rtp = rtp;
00458    *srtp = temp;
00459 
00460    ao2_t_link((*srtp)->policies, policy, "Created initial policy");
00461 
00462    return 0;
00463 }
00464 
00465 static int ast_srtp_replace(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy)
00466 {
00467    if ((*srtp) != NULL) {
00468       ast_srtp_destroy(*srtp);
00469    }
00470    return ast_srtp_create(srtp, rtp, policy);
00471 }
00472 
00473 static void ast_srtp_destroy(struct ast_srtp *srtp)
00474 {
00475    if (srtp->session) {
00476       srtp_dealloc(srtp->session);
00477    }
00478 
00479    ao2_t_callback(srtp->policies, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, NULL, NULL, "Unallocate policy");
00480    ao2_t_ref(srtp->policies, -1, "Destroying container");
00481 
00482    ast_free(srtp);
00483    ast_module_unref(ast_module_info->self);
00484 }
00485 
00486 static int ast_srtp_add_stream(struct ast_srtp *srtp, struct ast_srtp_policy *policy)
00487 {
00488    struct ast_srtp_policy *match;
00489 
00490    /* For existing streams, replace if its an SSRC stream, or bail if its a wildcard */
00491    if ((match = find_policy(srtp, &policy->sp, OBJ_POINTER))) {
00492       if (policy->sp.ssrc.type != ssrc_specific) {
00493          ast_log(AST_LOG_WARNING, "Cannot replace an existing wildcard policy\n");
00494          ao2_t_ref(match, -1, "Unreffing already existing policy");
00495          return -1;
00496       } else {
00497          if (srtp_remove_stream(srtp->session, match->sp.ssrc.value) != err_status_ok) {
00498             ast_log(AST_LOG_WARNING, "Failed to remove SRTP stream for SSRC %d\n", match->sp.ssrc.value);
00499          }
00500          ao2_t_unlink(srtp->policies, match, "Remove existing match policy");
00501          ao2_t_ref(match, -1, "Unreffing already existing policy");
00502       }
00503    }
00504 
00505    ast_debug(3, "Adding new policy for %s %d\n",
00506       policy->sp.ssrc.type == ssrc_specific ? "SSRC" : "type",
00507       policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type);
00508    if (srtp_add_stream(srtp->session, &policy->sp) != err_status_ok) {
00509       ast_log(AST_LOG_WARNING, "Failed to add SRTP stream for %s %d\n",
00510          policy->sp.ssrc.type == ssrc_specific ? "SSRC" : "type",
00511          policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type);
00512       return -1;
00513    }
00514 
00515    ao2_t_link(srtp->policies, policy, "Added additional stream");
00516 
00517    return 0;
00518 }
00519 
00520 static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc, unsigned int to_ssrc)
00521 {
00522    struct ast_srtp_policy *match;
00523    struct srtp_policy_t sp = {
00524       .ssrc.type = ssrc_specific,
00525       .ssrc.value = from_ssrc,
00526    };
00527    err_status_t status;
00528 
00529    /* If we find a match, return and unlink it from the container so we
00530     * can change the SSRC (which is part of the hash) and then have
00531     * ast_srtp_add_stream link it back in if all is well */
00532    if ((match = find_policy(srtp, &sp, OBJ_POINTER | OBJ_UNLINK))) {
00533       match->sp.ssrc.value = to_ssrc;
00534       if (ast_srtp_add_stream(srtp, match)) {
00535          ast_log(LOG_WARNING, "Couldn't add stream\n");
00536       } else if ((status = srtp_remove_stream(srtp->session, from_ssrc))) {
00537          ast_debug(3, "Couldn't remove stream (%d)\n", status);
00538       }
00539       ao2_t_ref(match, -1, "Unreffing found policy in change_source");
00540    }
00541 
00542    return 0;
00543 }
00544 
00545 static void res_srtp_shutdown(void)
00546 {
00547    srtp_install_event_handler(NULL);
00548    ast_rtp_engine_unregister_srtp();
00549    g_initialized = 0;
00550 }
00551 
00552 static int res_srtp_init(void)
00553 {
00554    if (g_initialized) {
00555       return 0;
00556    }
00557 
00558    if (srtp_init() != err_status_ok) {
00559       ast_log(AST_LOG_WARNING, "Failed to initialize libsrtp\n");
00560       return -1;
00561    }
00562 
00563    srtp_install_event_handler(srtp_event_cb);
00564 
00565    if (ast_rtp_engine_register_srtp(&srtp_res, &policy_res)) {
00566       ast_log(AST_LOG_WARNING, "Failed to register SRTP with rtp engine\n");
00567       res_srtp_shutdown();
00568       return -1;
00569    }
00570 
00571    g_initialized = 1;
00572    return 0;
00573 }
00574 
00575 /*
00576  * Exported functions
00577  */
00578 
00579 static int load_module(void)
00580 {
00581    return res_srtp_init();
00582 }
00583 
00584 static int unload_module(void)
00585 {
00586    res_srtp_shutdown();
00587    return 0;
00588 }
00589 
00590 AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS | AST_MODFLAG_LOAD_ORDER, "Secure RTP (SRTP)",
00591    .load = load_module,
00592    .unload = unload_module,
00593    .load_pri = AST_MODPRI_CHANNEL_DEPEND,
00594 );

Generated on 20 Aug 2013 for Asterisk - The Open Source Telephony Project by  doxygen 1.6.1