Mon Mar 19 11:30:30 2012

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: 352955 $")
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 static int g_initialized = 0;
00067 
00068 /* SRTP functions */
00069 static int ast_srtp_create(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy);
00070 static void ast_srtp_destroy(struct ast_srtp *srtp);
00071 static int ast_srtp_add_stream(struct ast_srtp *srtp, struct ast_srtp_policy *policy);
00072 static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc, unsigned int to_ssrc);
00073 
00074 static int ast_srtp_unprotect(struct ast_srtp *srtp, void *buf, int *len, int rtcp);
00075 static int ast_srtp_protect(struct ast_srtp *srtp, void **buf, int *len, int rtcp);
00076 static void ast_srtp_set_cb(struct ast_srtp *srtp, const struct ast_srtp_cb *cb, void *data);
00077 static int ast_srtp_get_random(unsigned char *key, size_t len);
00078 
00079 /* Policy functions */
00080 static struct ast_srtp_policy *ast_srtp_policy_alloc(void);
00081 static void ast_srtp_policy_destroy(struct ast_srtp_policy *policy);
00082 static int ast_srtp_policy_set_suite(struct ast_srtp_policy *policy, enum ast_srtp_suite suite);
00083 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);
00084 static void ast_srtp_policy_set_ssrc(struct ast_srtp_policy *policy, unsigned long ssrc, int inbound);
00085 
00086 static struct ast_srtp_res srtp_res = {
00087    .create = ast_srtp_create,
00088    .destroy = ast_srtp_destroy,
00089    .add_stream = ast_srtp_add_stream,
00090    .change_source = ast_srtp_change_source,
00091    .set_cb = ast_srtp_set_cb,
00092    .unprotect = ast_srtp_unprotect,
00093    .protect = ast_srtp_protect,
00094    .get_random = ast_srtp_get_random
00095 };
00096 
00097 static struct ast_srtp_policy_res policy_res = {
00098    .alloc = ast_srtp_policy_alloc,
00099    .destroy = ast_srtp_policy_destroy,
00100    .set_suite = ast_srtp_policy_set_suite,
00101    .set_master_key = ast_srtp_policy_set_master_key,
00102    .set_ssrc = ast_srtp_policy_set_ssrc
00103 };
00104 
00105 static const char *srtp_errstr(int err)
00106 {
00107    switch(err) {
00108    case err_status_ok:
00109       return "nothing to report";
00110    case err_status_fail:
00111       return "unspecified failure";
00112    case err_status_bad_param:
00113       return "unsupported parameter";
00114    case err_status_alloc_fail:
00115       return "couldn't allocate memory";
00116    case err_status_dealloc_fail:
00117       return "couldn't deallocate properly";
00118    case err_status_init_fail:
00119       return "couldn't initialize";
00120    case err_status_terminus:
00121       return "can't process as much data as requested";
00122    case err_status_auth_fail:
00123       return "authentication failure";
00124    case err_status_cipher_fail:
00125       return "cipher failure";
00126    case err_status_replay_fail:
00127       return "replay check failed (bad index)";
00128    case err_status_replay_old:
00129       return "replay check failed (index too old)";
00130    case err_status_algo_fail:
00131       return "algorithm failed test routine";
00132    case err_status_no_such_op:
00133       return "unsupported operation";
00134    case err_status_no_ctx:
00135       return "no appropriate context found";
00136    case err_status_cant_check:
00137       return "unable to perform desired validation";
00138    case err_status_key_expired:
00139       return "can't use key any more";
00140    default:
00141       return "unknown";
00142    }
00143 }
00144 
00145 static int policy_hash_fn(const void *obj, const int flags)
00146 {
00147    const struct ast_srtp_policy *policy = obj;
00148 
00149    return policy->sp.ssrc.type == ssrc_specific ? policy->sp.ssrc.value : policy->sp.ssrc.type;
00150 }
00151 
00152 static int policy_cmp_fn(void *obj, void *arg, int flags)
00153 {
00154    const struct ast_srtp_policy *one = obj, *two = arg;
00155 
00156    return one->sp.ssrc.type == two->sp.ssrc.type && one->sp.ssrc.value == two->sp.ssrc.value;
00157 }
00158 
00159 static struct ast_srtp_policy *find_policy(struct ast_srtp *srtp, const srtp_policy_t *policy, int flags)
00160 {
00161    struct ast_srtp_policy tmp = {
00162       .sp = {
00163          .ssrc.type = policy->ssrc.type,
00164          .ssrc.value = policy->ssrc.value,
00165       },
00166    };
00167 
00168    return ao2_t_find(srtp->policies, &tmp, flags, "Looking for policy");
00169 }
00170 
00171 static struct ast_srtp *res_srtp_new(void)
00172 {
00173    struct ast_srtp *srtp;
00174 
00175    if (!(srtp = ast_calloc(1, sizeof(*srtp)))) {
00176       ast_log(LOG_ERROR, "Unable to allocate memory for srtp\n");
00177       return NULL;
00178    }
00179 
00180    if (!(srtp->policies = ao2_t_container_alloc(5, policy_hash_fn, policy_cmp_fn, "SRTP policy container"))) {
00181       ast_free(srtp);
00182       return NULL;
00183    }
00184    
00185    srtp->warned = 1;
00186 
00187    return srtp;
00188 }
00189 
00190 /*
00191   struct ast_srtp_policy
00192 */
00193 static void srtp_event_cb(srtp_event_data_t *data)
00194 {
00195    switch (data->event) {
00196    case event_ssrc_collision:
00197       ast_debug(1, "SSRC collision\n");
00198       break;
00199    case event_key_soft_limit:
00200       ast_debug(1, "event_key_soft_limit\n");
00201       break;
00202    case event_key_hard_limit:
00203       ast_debug(1, "event_key_hard_limit\n");
00204       break;
00205    case event_packet_index_limit:
00206       ast_debug(1, "event_packet_index_limit\n");
00207       break;
00208    }
00209 }
00210 
00211 static void ast_srtp_policy_set_ssrc(struct ast_srtp_policy *policy,
00212       unsigned long ssrc, int inbound)
00213 {
00214    if (ssrc) {
00215       policy->sp.ssrc.type = ssrc_specific;
00216       policy->sp.ssrc.value = ssrc;
00217    } else {
00218       policy->sp.ssrc.type = inbound ? ssrc_any_inbound : ssrc_any_outbound;
00219    }
00220 }
00221 
00222 static void policy_destructor(void *obj)
00223 {
00224    struct ast_srtp_policy *policy = obj;
00225 
00226    if (policy->sp.key) {
00227       ast_free(policy->sp.key);
00228       policy->sp.key = NULL;
00229    }
00230 }
00231 
00232 static struct ast_srtp_policy *ast_srtp_policy_alloc()
00233 {
00234    struct ast_srtp_policy *tmp;
00235 
00236    if (!(tmp = ao2_t_alloc(sizeof(*tmp), policy_destructor, "Allocating policy"))) {
00237       ast_log(LOG_ERROR, "Unable to allocate memory for srtp_policy\n");
00238    }
00239 
00240    return tmp;
00241 }
00242 
00243 static void ast_srtp_policy_destroy(struct ast_srtp_policy *policy)
00244 {
00245    ao2_t_ref(policy, -1, "Destroying policy");
00246 }
00247 
00248 static int policy_set_suite(crypto_policy_t *p, enum ast_srtp_suite suite)
00249 {
00250    switch (suite) {
00251    case AST_AES_CM_128_HMAC_SHA1_80:
00252       p->cipher_type = AES_128_ICM;
00253       p->cipher_key_len = 30;
00254       p->auth_type = HMAC_SHA1;
00255       p->auth_key_len = 20;
00256       p->auth_tag_len = 10;
00257       p->sec_serv = sec_serv_conf_and_auth;
00258       return 0;
00259 
00260    case AST_AES_CM_128_HMAC_SHA1_32:
00261       p->cipher_type = AES_128_ICM;
00262       p->cipher_key_len = 30;
00263       p->auth_type = HMAC_SHA1;
00264       p->auth_key_len = 20;
00265       p->auth_tag_len = 4;
00266       p->sec_serv = sec_serv_conf_and_auth;
00267       return 0;
00268 
00269    default:
00270       ast_log(LOG_ERROR, "Invalid crypto suite: %d\n", suite);
00271       return -1;
00272    }
00273 }
00274 
00275 static int ast_srtp_policy_set_suite(struct ast_srtp_policy *policy, enum ast_srtp_suite suite)
00276 {
00277    return policy_set_suite(&policy->sp.rtp, suite) | policy_set_suite(&policy->sp.rtcp, suite);
00278 }
00279 
00280 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)
00281 {
00282    size_t size = key_len + salt_len;
00283    unsigned char *master_key;
00284 
00285    if (policy->sp.key) {
00286       ast_free(policy->sp.key);
00287       policy->sp.key = NULL;
00288    }
00289 
00290    if (!(master_key = ast_calloc(1, size))) {
00291       return -1;
00292    }
00293 
00294    memcpy(master_key, key, key_len);
00295    memcpy(master_key + key_len, salt, salt_len);
00296 
00297    policy->sp.key = master_key;
00298 
00299    return 0;
00300 }
00301 
00302 static int ast_srtp_get_random(unsigned char *key, size_t len)
00303 {
00304    return crypto_get_random(key, len) != err_status_ok ? -1: 0;
00305 }
00306 
00307 static void ast_srtp_set_cb(struct ast_srtp *srtp, const struct ast_srtp_cb *cb, void *data)
00308 {
00309    if (!srtp) {
00310       return;
00311    }
00312 
00313    srtp->cb = cb;
00314    srtp->data = data;
00315 }
00316 
00317 /* Vtable functions */
00318 static int ast_srtp_unprotect(struct ast_srtp *srtp, void *buf, int *len, int rtcp)
00319 {
00320    int res = 0;
00321    int i;
00322    int retry = 0;
00323    struct ast_rtp_instance_stats stats = {0,};
00324 
00325 tryagain:
00326 
00327    for (i = 0; i < 2; i++) {
00328       res = rtcp ? srtp_unprotect_rtcp(srtp->session, buf, len) : srtp_unprotect(srtp->session, buf, len);
00329       if (res != err_status_no_ctx) {
00330          break;
00331       }
00332 
00333       if (srtp->cb && srtp->cb->no_ctx) {
00334          if (ast_rtp_instance_get_stats(srtp->rtp, &stats, AST_RTP_INSTANCE_STAT_REMOTE_SSRC)) {
00335             break;
00336          }
00337          if (srtp->cb->no_ctx(srtp->rtp, stats.remote_ssrc, srtp->data) < 0) {
00338             break;
00339          }
00340       } else {
00341          break;
00342       }
00343    }
00344 
00345    if (retry == 0  && res == err_status_replay_old) {
00346       ast_log(LOG_WARNING, "SRTP unprotect: %s\n", srtp_errstr(res));
00347 
00348       if (srtp->session) {
00349          struct ast_srtp_policy *policy;
00350          struct ao2_iterator it;
00351          int policies_count;
00352 
00353          // dealloc first
00354          ast_log(LOG_WARNING, "SRTP destroy before re-create\n");
00355          srtp_dealloc(srtp->session);
00356 
00357          // get the count
00358          policies_count = ao2_container_count(srtp->policies);
00359 
00360          // get the first to build up
00361          it = ao2_iterator_init(srtp->policies, 0);
00362          policy = ao2_iterator_next(&it);
00363 
00364          ast_log(LOG_WARNING, "SRTP try to re-create\n");
00365          if (policy) {
00366             if (srtp_create(&srtp->session, &policy->sp) == err_status_ok) {
00367                ast_log(LOG_WARNING, "SRTP re-created with first policy\n");
00368 
00369                // unref first element
00370                ao2_t_ref(policy, -1, "Unreffing first policy for re-creating srtp session");
00371 
00372                // if we have more than one policy, add them afterwards
00373                if (policies_count > 1) {
00374                   ast_log(LOG_WARNING, "Add all the other %d policies\n",
00375                      policies_count - 1);
00376                   while ((policy = ao2_iterator_next(&it))) {
00377                      srtp_add_stream(srtp->session, &policy->sp);
00378                      ao2_t_ref(policy, -1, "Unreffing n-th policy for re-creating srtp session");
00379                   }
00380                }
00381 
00382                retry++;
00383                ao2_iterator_destroy(&it);
00384                goto tryagain;
00385             }
00386             ao2_t_ref(policy, -1, "Unreffing first policy after srtp_create failed");
00387          }
00388          ao2_iterator_destroy(&it);
00389       }
00390    }
00391 
00392    if (res != err_status_ok && res != err_status_replay_fail ) {
00393       if ((srtp->warned >= 10) && !((srtp->warned - 10) % 100)) {
00394          ast_log(LOG_WARNING, "SRTP unprotect: %s %d\n", srtp_errstr(res), srtp->warned);
00395          srtp->warned = 11;
00396       } else {
00397          srtp->warned++;
00398       }
00399       errno = EAGAIN;
00400       return -1;
00401    }
00402 
00403    return *len;
00404 }
00405 
00406 static int ast_srtp_protect(struct ast_srtp *srtp, void **buf, int *len, int rtcp)
00407 {
00408    int res;
00409    unsigned char *localbuf;
00410 
00411    if ((*len + SRTP_MAX_TRAILER_LEN) > sizeof(srtp->buf)) {
00412       return -1;
00413    }
00414    
00415    localbuf = rtcp ? srtp->rtcpbuf : srtp->buf;
00416 
00417    memcpy(localbuf, *buf, *len);
00418 
00419    if ((res = rtcp ? srtp_protect_rtcp(srtp->session, localbuf, len) : srtp_protect(srtp->session, localbuf, len)) != err_status_ok && res != err_status_replay_fail) {
00420       ast_log(LOG_WARNING, "SRTP protect: %s\n", srtp_errstr(res));
00421       return -1;
00422    }
00423 
00424    *buf = localbuf;
00425    return *len;
00426 }
00427 
00428 static int ast_srtp_create(struct ast_srtp **srtp, struct ast_rtp_instance *rtp, struct ast_srtp_policy *policy)
00429 {
00430    struct ast_srtp *temp;
00431 
00432    if (!(temp = res_srtp_new())) {
00433       return -1;
00434    }
00435 
00436    if (srtp_create(&temp->session, &policy->sp) != err_status_ok) {
00437       return -1;
00438    }
00439 
00440    ast_module_ref(ast_module_info->self);
00441    temp->rtp = rtp;
00442    *srtp = temp;
00443 
00444    ao2_t_link((*srtp)->policies, policy, "Created initial policy");
00445 
00446    return 0;
00447 }
00448 
00449 static void ast_srtp_destroy(struct ast_srtp *srtp)
00450 {
00451    if (srtp->session) {
00452       srtp_dealloc(srtp->session);
00453    }
00454 
00455    ao2_t_callback(srtp->policies, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, NULL, NULL, "Unallocate policy");
00456    ao2_t_ref(srtp->policies, -1, "Destroying container");
00457 
00458    ast_free(srtp);
00459    ast_module_unref(ast_module_info->self);
00460 }
00461 
00462 static int ast_srtp_add_stream(struct ast_srtp *srtp, struct ast_srtp_policy *policy)
00463 {
00464    struct ast_srtp_policy *match;
00465 
00466    if ((match = find_policy(srtp, &policy->sp, OBJ_POINTER))) {
00467       ast_debug(3, "Policy already exists, not re-adding\n");
00468       ao2_t_ref(match, -1, "Unreffing already existing policy");
00469       return -1;
00470    }
00471 
00472    if (srtp_add_stream(srtp->session, &policy->sp) != err_status_ok) {
00473       return -1;
00474    }
00475 
00476    ao2_t_link(srtp->policies, policy, "Added additional stream");
00477 
00478    return 0;
00479 }
00480 
00481 static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc, unsigned int to_ssrc)
00482 {
00483    struct ast_srtp_policy *match;
00484    struct srtp_policy_t sp = {
00485       .ssrc.type = ssrc_specific,
00486       .ssrc.value = from_ssrc,
00487    };
00488    err_status_t status;
00489 
00490    /* If we find a mach, return and unlink it from the container so we
00491     * can change the SSRC (which is part of the hash) and then have
00492     * ast_srtp_add_stream link it back in if all is well */
00493    if ((match = find_policy(srtp, &sp, OBJ_POINTER | OBJ_UNLINK))) {
00494       match->sp.ssrc.value = to_ssrc;
00495       if (ast_srtp_add_stream(srtp, match)) {
00496          ast_log(LOG_WARNING, "Couldn't add stream\n");
00497       } else if ((status = srtp_remove_stream(srtp->session, from_ssrc))) {
00498          ast_debug(3, "Couldn't remove stream (%d)\n", status);
00499       }
00500       ao2_t_ref(match, -1, "Unreffing found policy in change_source");
00501    }
00502 
00503    return 0;
00504 }
00505 
00506 static int res_srtp_init(void)
00507 {
00508    if (g_initialized) {
00509       return 0;
00510    }
00511 
00512    if (srtp_init() != err_status_ok) {
00513       return -1;
00514    }
00515 
00516    srtp_install_event_handler(srtp_event_cb);
00517 
00518    return ast_rtp_engine_register_srtp(&srtp_res, &policy_res);
00519 }
00520 
00521 /*
00522  * Exported functions
00523  */
00524 
00525 static int load_module(void)
00526 {
00527    return res_srtp_init();
00528 }
00529 
00530 static int unload_module(void)
00531 {
00532    ast_rtp_engine_unregister_srtp();
00533    return 0;
00534 }
00535 
00536 AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS | AST_MODFLAG_LOAD_ORDER, "Secure RTP (SRTP)",
00537    .load = load_module,
00538    .unload = unload_module,
00539    .load_pri = AST_MODPRI_CHANNEL_DEPEND,
00540 );

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