res_pjsip_nat.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2013, Digium, Inc.
 *
 * Joshua Colp <jcolp@digium.com>
 *
 * 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 routable 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 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 ast_sip_transport *, transport, NULL, ao2_cleanup);
    RAII_VAR(struct ast_sip_transport_state *, transport_state, NULL, ao2_cleanup);
    struct ast_sip_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 (ast_sip_set_request_transport_details(&details, tdata, 0)) {
        return PJ_SUCCESS;
    }
 
    uri = ast_sip_get_contact_sip_uri(tdata);
    via = pjsip_msg_find_hdr(tdata->msg, PJSIP_H_VIA, NULL);
 
    if (!(transport_state = ast_sip_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 = ast_sip_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",
);