res_pjsip_nat.c

Go to the documentation of this file.

/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2013, Digium, Inc.
 *
 * Joshua Colp <[email protected]>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*** MODULEINFO
   <depend>pjproject</depend>
   <depend>res_pjsip</depend>
   <depend>res_pjsip_session</depend>
   <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include <pjsip.h>
#include <pjsip_ua.h>

#include "asterisk/res_pjsip.h"
#include "asterisk/res_pjsip_session.h"
#include "asterisk/module.h"
#include "asterisk/acl.h"

/*! URI parameter for original host/port */
#define AST_SIP_X_AST_ORIG_HOST "x-ast-orig-host"
#define AST_SIP_X_AST_ORIG_HOST_LEN 15

#define is_sip_uri(uri) \
   (PJSIP_URI_SCHEME_IS_SIP(uri) || PJSIP_URI_SCHEME_IS_SIPS(uri))

static void save_orig_contact_host(pjsip_rx_data *rdata, pjsip_sip_uri *uri)
{
   pjsip_param *x_orig_host;
   pj_str_t p_value;
#define COLON_LEN 1
#define MAX_PORT_LEN 5

   if (rdata->msg_info.msg->type != PJSIP_REQUEST_MSG ||
      rdata->msg_info.msg->line.req.method.id != PJSIP_REGISTER_METHOD) {
      return;
   }

   ast_debug(1, "Saving contact '%.*s:%d'\n",
      (int)uri->host.slen, uri->host.ptr, uri->port);

   x_orig_host = PJ_POOL_ALLOC_T(rdata->tp_info.pool, pjsip_param);
   x_orig_host->name = pj_strdup3(rdata->tp_info.pool, AST_SIP_X_AST_ORIG_HOST);
   p_value.slen = pj_strlen(&uri->host) + COLON_LEN + MAX_PORT_LEN;
   p_value.ptr = (char*)pj_pool_alloc(rdata->tp_info.pool, p_value.slen + 1);
   p_value.slen = snprintf(p_value.ptr, p_value.slen + 1, "%.*s:%d", (int)uri->host.slen, uri->host.ptr, uri->port);
   pj_strassign(&x_orig_host->value, &p_value);
   pj_list_insert_before(&uri->other_param, x_orig_host);

   return;
}

static void rewrite_uri(pjsip_rx_data *rdata, pjsip_sip_uri *uri, pj_pool_t *pool)
{

   if (pj_strcmp2(&uri->host, rdata->pkt_info.src_name) != 0) {
      save_orig_contact_host(rdata, uri);
   }

   pj_strdup2(pool, &uri->host, rdata->pkt_info.src_name);
   uri->port = rdata->pkt_info.src_port;
   if (!strcasecmp("WSS", rdata->tp_info.transport->type_name)) {
      /* WSS is special, we don't want to overwrite the URI at all as it needs to be ws */
   } else if (strcasecmp("udp", rdata->tp_info.transport->type_name)) {
      uri->transport_param = pj_str(rdata->tp_info.transport->type_name);
   } else {
      uri->transport_param.slen = 0;
   }
}

/*
 * Update the Record-Route headers in the request or response and in the dialog
 * object if exists.
 *
 * When NAT is in use, the address of the next hop in the SIP may be incorrect.
 * To address this  asterisk uses two strategies in parallel:
 *  1. intercept the messages at the transaction level and rewrite the
 *     messages before arriving at the dialog layer
 *  2. after the application processing, update the dialog object with the
 *     correct information
 *
 * The first strategy has a limitation that the SIP message may not have all
 * the information required to determine if the next hop is in the route set
 * or in the contact. Causing risk that asterisk will update the Contact on
 * receipt of an in-dialog message despite there being a route set saved in
 * the dialog.
 *
 * The second strategy has a limitation that not all UAC layers have interfaces
 * available to invoke this module after dialog creation.  (pjsip_sesion does
 * but pjsip_pubsub does not), thus this strategy can't update the dialog in
 * all cases needed.
 *
 * The ideal solution would be to implement an "incomming_request" event
 * in pubsub module that can then pass the dialog object to this module
 * on SUBSCRIBE, this module then should add itself as a listener to the dialog
 * for the subsequent requests and responses & then be able to properly update
 * the dialog object for all required events.
 */

static int rewrite_route_set(pjsip_rx_data *rdata, pjsip_dialog *dlg)
{
   pjsip_rr_hdr *rr = NULL;
   pjsip_sip_uri *uri;
   int res = -1;
   int ignore_rr = 0;
   int pubsub = 0;

   if (rdata->msg_info.msg->type == PJSIP_RESPONSE_MSG) {
      pjsip_hdr *iter;
      for (iter = rdata->msg_info.msg->hdr.prev; iter != &rdata->msg_info.msg->hdr; iter = iter->prev) {
         if (iter->type == PJSIP_H_RECORD_ROUTE) {
            rr = (pjsip_rr_hdr *)iter;
            break;
         }
      }
   } else if (pjsip_method_cmp(&rdata->msg_info.msg->line.req.method, &pjsip_register_method)) {
      rr = pjsip_msg_find_hdr(rdata->msg_info.msg, PJSIP_H_RECORD_ROUTE, NULL);
   } else {
      /**
       * Record-Route header has no meaning in REGISTER requests
       * and should be ignored
       */
      ignore_rr = 1;
   }

   if (!pjsip_method_cmp(&rdata->msg_info.cseq->method, &pjsip_subscribe_method) ||
      !pjsip_method_cmp(&rdata->msg_info.cseq->method, &pjsip_notify_method)) {
      /**
       * There is currently no good way to get the dlg object for a pubsub dialog
       * so we will just look at the rr & contact of the current message and
       * hope for the best
       */
      pubsub = 1;
   }

   if (rr) {
      uri = pjsip_uri_get_uri(&rr->name_addr);
      rewrite_uri(rdata, uri, rdata->tp_info.pool);
      res = 0;
   }

   if (dlg && !pj_list_empty(&dlg->route_set) && !dlg->route_set_frozen) {
      pjsip_routing_hdr *route = dlg->route_set.next;
      uri = pjsip_uri_get_uri(&route->name_addr);
      rewrite_uri(rdata, uri, dlg->pool);
      res = 0;
   }

   if (!dlg && !rr && !ignore_rr  && !pubsub && rdata->msg_info.to->tag.slen){
      /**
       * Even if this message doesn't have any route headers
       * the dialog may, so wait until a later invocation that
       * has a dialog reference to make sure there isn't a
       * previously saved routset in the dialog before deciding
       * the contact needs to be modified
       */
      res = 0;
   }

   return res;
}

static int rewrite_contact(pjsip_rx_data *rdata, pjsip_dialog *dlg)
{
   pjsip_contact_hdr *contact;

   contact = pjsip_msg_find_hdr(rdata->msg_info.msg, PJSIP_H_CONTACT, NULL);
   if (contact && !contact->star && (PJSIP_URI_SCHEME_IS_SIP(contact->uri) || PJSIP_URI_SCHEME_IS_SIPS(contact->uri))) {
      pjsip_sip_uri *uri = pjsip_uri_get_uri(contact->uri);

      rewrite_uri(rdata, uri, rdata->tp_info.pool);

      if (dlg && pj_list_empty(&dlg->route_set) && (!dlg->remote.contact
         || pjsip_uri_cmp(PJSIP_URI_IN_REQ_URI, dlg->remote.contact->uri, contact->uri))) {
         dlg->remote.contact = (pjsip_contact_hdr*)pjsip_hdr_clone(dlg->pool, contact);
         dlg->target = dlg->remote.contact->uri;
      }
      return 0;
   }

   return -1;
}

static pj_bool_t handle_rx_message(struct ast_sip_endpoint *endpoint, pjsip_rx_data *rdata)
{
   pjsip_dialog *dlg = pjsip_rdata_get_dlg(rdata);

   if (!endpoint) {
      return PJ_FALSE;
   }

   if (endpoint->nat.rewrite_contact) {
      /* rewrite_contact is intended to ensure we send requests/responses to
       * a routeable address when NAT is involved. The URI that dictates where
       * we send requests/responses can be determined either by Record-Route
       * headers or by the Contact header if no Record-Route headers are present.
       * We therefore will attempt to rewrite a Record-Route header first, and if
       * none are present, we fall back to rewriting the Contact header instead.
       */
      if (rewrite_route_set(rdata, dlg)) {
         rewrite_contact(rdata, dlg);
      }
   }

   if (endpoint->nat.force_rport) {
      rdata->msg_info.via->rport_param = rdata->pkt_info.src_port;
   }

   return PJ_FALSE;
}

static pj_bool_t nat_on_rx_message(pjsip_rx_data *rdata)
{
   pj_bool_t res;
   struct ast_sip_endpoint *endpoint;

   endpoint = ast_pjsip_rdata_get_endpoint(rdata);
   res = handle_rx_message(endpoint, rdata);
   ao2_cleanup(endpoint);
   return res;
}

/*! \brief Structure which contains information about a transport */
struct request_transport_details {
   /*! \brief Type of transport */
   enum ast_transport type;
   /*! \brief Potential pointer to the transport itself, if UDP */
   pjsip_transport *transport;
   /*! \brief Potential pointer to the transport factory itself, if TCP/TLS */
   pjsip_tpfactory *factory;
   /*! \brief Local address for transport */
   pj_str_t local_address;
   /*! \brief Local port for transport */
   int local_port;
};

/*! \brief Callback function for finding the transport the request is going out on */
static int find_transport_state_in_use(void *obj, void *arg, int flags)
{
   struct ast_sip_transport_state *transport_state = obj;
   struct request_transport_details *details = arg;

   /* If an explicit transport or factory matches then this is what is in use, if we are unavailable
    * to compare based on that we make sure that the type is the same and the source IP address/port are the same
    */
   if (transport_state && ((details->transport && details->transport == transport_state->transport) ||
      (details->factory && details->factory == transport_state->factory) ||
      ((details->type == transport_state->type) && (transport_state->factory) &&
         !pj_strcmp(&transport_state->factory->addr_name.host, &details->local_address) &&
         transport_state->factory->addr_name.port == details->local_port))) {
      return CMP_MATCH;
   }

   return 0;
}

/*! \brief Helper function which returns the SIP URI of a Contact header */
static pjsip_sip_uri *nat_get_contact_sip_uri(pjsip_tx_data *tdata)
{
   pjsip_contact_hdr *contact = pjsip_msg_find_hdr(tdata->msg, PJSIP_H_CONTACT, NULL);

   if (!contact || (!PJSIP_URI_SCHEME_IS_SIP(contact->uri) && !PJSIP_URI_SCHEME_IS_SIPS(contact->uri))) {
      return NULL;
   }

   return pjsip_uri_get_uri(contact->uri);
}

/*! \brief Structure which contains hook details */
struct nat_hook_details {
   /*! \brief Outgoing message itself */
   pjsip_tx_data *tdata;
   /*! \brief Chosen transport */
   struct ast_sip_transport *transport;
};

/*! \brief Callback function for invoking hooks */
static int nat_invoke_hook(void *obj, void *arg, int flags)
{
   struct ast_sip_nat_hook *hook = obj;
   struct nat_hook_details *details = arg;

   if (hook->outgoing_external_message) {
      hook->outgoing_external_message(details->tdata, details->transport);
   }

   return 0;
}

static void restore_orig_contact_host(pjsip_tx_data *tdata)
{
   pjsip_contact_hdr *contact;
   pj_str_t x_name = { AST_SIP_X_AST_ORIG_HOST, AST_SIP_X_AST_ORIG_HOST_LEN };
   pjsip_param *x_orig_host;
   pjsip_sip_uri *uri;
   pjsip_hdr *hdr;

   if (tdata->msg->type == PJSIP_REQUEST_MSG) {
      if (is_sip_uri(tdata->msg->line.req.uri)) {
         uri = pjsip_uri_get_uri(tdata->msg->line.req.uri);
         while ((x_orig_host = pjsip_param_find(&uri->other_param, &x_name))) {
            pj_list_erase(x_orig_host);
         }
      }
      for (hdr = tdata->msg->hdr.next; hdr != &tdata->msg->hdr; hdr = hdr->next) {
         if (hdr->type == PJSIP_H_TO) {
            if (is_sip_uri(((pjsip_fromto_hdr *) hdr)->uri)) {
               uri = pjsip_uri_get_uri(((pjsip_fromto_hdr *) hdr)->uri);
               while ((x_orig_host = pjsip_param_find(&uri->other_param, &x_name))) {
                  pj_list_erase(x_orig_host);
               }
            }
         }
      }
   }

   if (tdata->msg->type != PJSIP_RESPONSE_MSG) {
      return;
   }

   contact = pjsip_msg_find_hdr(tdata->msg, PJSIP_H_CONTACT, NULL);
   while (contact) {
      pjsip_sip_uri *contact_uri = pjsip_uri_get_uri(contact->uri);
      x_orig_host = pjsip_param_find(&contact_uri->other_param, &x_name);

      if (x_orig_host) {
         char host_port[x_orig_host->value.slen + 1];
         char *sep;

         ast_debug(1, "Restoring contact %.*s:%d  to %.*s\n", (int)contact_uri->host.slen,
            contact_uri->host.ptr, contact_uri->port,
            (int)x_orig_host->value.slen, x_orig_host->value.ptr);

         strncpy(host_port, x_orig_host->value.ptr, x_orig_host->value.slen);
         host_port[x_orig_host->value.slen] = '\0';
         sep = strchr(host_port, ':');
         if (sep) {
            *sep = '\0';
            sep++;
            pj_strdup2(tdata->pool, &contact_uri->host, host_port);
            contact_uri->port = strtol(sep, NULL, 10);
         }
         pj_list_erase(x_orig_host);
      }
      contact = pjsip_msg_find_hdr(tdata->msg, PJSIP_H_CONTACT, contact->next);
   }
}

static pj_status_t process_nat(pjsip_tx_data *tdata)
{
   RAII_VAR(struct ao2_container *, transport_states, NULL, ao2_cleanup);
   RAII_VAR(struct ast_sip_transport *, transport, NULL, ao2_cleanup);
   RAII_VAR(struct ast_sip_transport_state *, transport_state, NULL, ao2_cleanup);
   struct request_transport_details details = { 0, };
   pjsip_via_hdr *via = NULL;
   struct ast_sockaddr addr = { { 0, } };
   pjsip_sip_uri *uri = NULL;
   RAII_VAR(struct ao2_container *, hooks, NULL, ao2_cleanup);

   /* If a transport selector is in use we know the transport or factory, so explicitly find it */
   if (tdata->tp_sel.type == PJSIP_TPSELECTOR_TRANSPORT) {
      details.transport = tdata->tp_sel.u.transport;
   } else if (tdata->tp_sel.type == PJSIP_TPSELECTOR_LISTENER) {
      details.factory = tdata->tp_sel.u.listener;
   } else if (tdata->tp_info.transport->key.type == PJSIP_TRANSPORT_UDP || tdata->tp_info.transport->key.type == PJSIP_TRANSPORT_UDP6) {
      /* Connectionless uses the same transport for all requests */
      details.type = AST_TRANSPORT_UDP;
      details.transport = tdata->tp_info.transport;
   } else {
      if (tdata->tp_info.transport->key.type == PJSIP_TRANSPORT_TCP) {
         details.type = AST_TRANSPORT_TCP;
      } else if (tdata->tp_info.transport->key.type == PJSIP_TRANSPORT_TLS) {
         details.type = AST_TRANSPORT_TLS;
      } else {
         /* Unknown transport type, we can't map and thus can't apply NAT changes */
         return PJ_SUCCESS;
      }

      if ((uri = nat_get_contact_sip_uri(tdata))) {
         details.local_address = uri->host;
         details.local_port = uri->port;
      } else if ((tdata->msg->type == PJSIP_REQUEST_MSG) &&
         (via = pjsip_msg_find_hdr(tdata->msg, PJSIP_H_VIA, NULL))) {
         details.local_address = via->sent_by.host;
         details.local_port = via->sent_by.port;
      } else {
         return PJ_SUCCESS;
      }

      if (!details.local_port) {
         details.local_port = (details.type == AST_TRANSPORT_TLS) ? 5061 : 5060;
      }
   }

   if (!(transport_states = ast_sip_get_transport_states())) {
      return PJ_SUCCESS;
   }

   if (!(transport_state = ao2_callback(transport_states, 0, find_transport_state_in_use, &details))) {
      return PJ_SUCCESS;
   }

   if (!(transport = ast_sorcery_retrieve_by_id(ast_sip_get_sorcery(), "transport", transport_state->id))) {
      return PJ_SUCCESS;
   }

   if (transport_state->localnet) {
      ast_sockaddr_parse(&addr, tdata->tp_info.dst_name, PARSE_PORT_FORBID);
      ast_sockaddr_set_port(&addr, tdata->tp_info.dst_port);

      /* See if where we are sending this request is local or not, and if not that we can get a Contact URI to modify */
      if (ast_sip_transport_is_local(transport_state, &addr)) {
         ast_debug(5, "Request is being sent to local address, skipping NAT manipulation\n");
         return PJ_SUCCESS;
      }
   }

   if (!ast_sockaddr_isnull(&transport_state->external_signaling_address)) {
      pjsip_cseq_hdr *cseq = PJSIP_MSG_CSEQ_HDR(tdata->msg);

      /* Update the Contact header with the external address. We only do this if
       * a CSeq is not present (which should not happen - but we are extra safe),
       * if a request is being sent, or if a response is sent that is not a response
       * to a REGISTER. We specifically don't do this for a response to a REGISTER
       * as the Contact headers would contain the registered Contacts, and not our
       * own Contact.
       */
      if (!cseq || tdata->msg->type == PJSIP_REQUEST_MSG ||
         pjsip_method_cmp(&cseq->method, &pjsip_register_method)) {
         /* We can only rewrite the URI when one is present */
         if (uri || (uri = nat_get_contact_sip_uri(tdata))) {
            pj_strdup2(tdata->pool, &uri->host, ast_sockaddr_stringify_host(&transport_state->external_signaling_address));
            if (transport->external_signaling_port) {
               uri->port = transport->external_signaling_port;
               ast_debug(4, "Re-wrote Contact URI port to %d\n", uri->port);
            }
         }
      }

      /* Update the via header if relevant */
      if ((tdata->msg->type == PJSIP_REQUEST_MSG) && (via || (via = pjsip_msg_find_hdr(tdata->msg, PJSIP_H_VIA, NULL)))) {
         pj_strdup2(tdata->pool, &via->sent_by.host, ast_sockaddr_stringify_host(&transport_state->external_signaling_address));
         if (transport->external_signaling_port) {
            via->sent_by.port = transport->external_signaling_port;
         }
      }
   }

   /* Invoke any additional hooks that may be registered */
   if ((hooks = ast_sorcery_retrieve_by_fields(ast_sip_get_sorcery(), "nat_hook", AST_RETRIEVE_FLAG_MULTIPLE | AST_RETRIEVE_FLAG_ALL, NULL))) {
      struct nat_hook_details hook_details = {
         .tdata = tdata,
         .transport = transport,
      };
      ao2_callback(hooks, 0, nat_invoke_hook, &hook_details);
   }

   return PJ_SUCCESS;
}

static pj_status_t nat_on_tx_message(pjsip_tx_data *tdata) {
   pj_status_t rc;

   rc = process_nat(tdata);
   restore_orig_contact_host(tdata);

   return rc;
}


static pjsip_module nat_module = {
   .name = { "NAT", 3 },
   .id = -1,
   .priority = PJSIP_MOD_PRIORITY_TSX_LAYER - 2,
   .on_rx_request = nat_on_rx_message,
   .on_rx_response = nat_on_rx_message,
   .on_tx_request = nat_on_tx_message,
   .on_tx_response = nat_on_tx_message,
};

/*! \brief Function called when an INVITE goes out */
static int nat_incoming_invite_request(struct ast_sip_session *session, struct pjsip_rx_data *rdata)
{
   if (session->inv_session->state == PJSIP_INV_STATE_INCOMING) {
      pjsip_dlg_add_usage(session->inv_session->dlg, &nat_module, NULL);
   }

   return 0;
}

/*! \brief Function called when an INVITE response comes in */
static void nat_incoming_invite_response(struct ast_sip_session *session, struct pjsip_rx_data *rdata)
{
   handle_rx_message(session->endpoint, rdata);
}

/*! \brief Function called when an INVITE comes in */
static void nat_outgoing_invite_request(struct ast_sip_session *session, struct pjsip_tx_data *tdata)
{
   if (session->inv_session->state == PJSIP_INV_STATE_NULL) {
      pjsip_dlg_add_usage(session->inv_session->dlg, &nat_module, NULL);
   }
}

/*! \brief Supplement for adding NAT functionality to dialog */
static struct ast_sip_session_supplement nat_supplement = {
   .method = "INVITE",
   .priority = AST_SIP_SUPPLEMENT_PRIORITY_FIRST + 1,
   .incoming_request = nat_incoming_invite_request,
   .outgoing_request = nat_outgoing_invite_request,
   .incoming_response = nat_incoming_invite_response,
};


static int unload_module(void)
{
   ast_sip_session_unregister_supplement(&nat_supplement);
   ast_sip_unregister_service(&nat_module);
   return 0;
}

static int load_module(void)
{
   if (ast_sip_register_service(&nat_module)) {
      ast_log(LOG_ERROR, "Could not register NAT module for incoming and outgoing requests\n");
      return AST_MODULE_LOAD_DECLINE;
   }

   ast_sip_session_register_supplement(&nat_supplement);

   return AST_MODULE_LOAD_SUCCESS;
}

AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_LOAD_ORDER, "PJSIP NAT Support",
   .support_level = AST_MODULE_SUPPORT_CORE,
   .load = load_module,
   .unload = unload_module,
   .load_pri = AST_MODPRI_APP_DEPEND,
   .requires = "res_pjsip,res_pjsip_session",
);