path: root/src/libmsc/gsm_09_11.c

/* (C) 2008-2009 by Harald Welte <laforge@gnumonks.org>
 * (C) 2008, 2009 by Holger Hans Peter Freyther <zecke@selfish.org>
 * (C) 2009 by Mike Haben <michael.haben@btinternet.com>
 * (C) 2018 by Vadim Yanitskiy <axilirator@gmail.com>
 *
 * All Rights Reserved
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

/**
 * MSC-specific handling of call independent Supplementary
 * Services messages (NC_SS) according to GSM TS 09.11
 * "Signalling interworking for supplementary services".
 */

#include <stdio.h>
#include <errno.h>
#include <stdbool.h>

#include <osmocom/core/utils.h>
#include <osmocom/core/msgb.h>
#include <osmocom/gsm/tlv.h>

#include <osmocom/msc/gsm_04_80.h>
#include <osmocom/msc/gsm_subscriber.h>
#include <osmocom/msc/debug.h>
#include <osmocom/msc/osmo_msc.h>
#include <osmocom/msc/vlr.h>
#include <osmocom/msc/gsm_04_08.h>
#include <osmocom/msc/transaction.h>
#include <osmocom/msc/gsup_client.h>
#include <osmocom/msc/msc_ifaces.h>

/* FIXME: choose a proper range */
static uint32_t new_callref = 0x20000001;

/* Entry point for call independent MO SS messages */
int gsm0911_rcv_nc_ss(struct gsm_subscriber_connection *conn, struct msgb *msg)
{
	struct gsm48_hdr *gh = msgb_l3(msg);
	struct osmo_gsup_message gsup_msg;
	struct gsm_trans *trans;
	struct msgb *gsup_msgb;
	uint16_t facility_ie_len;
	uint8_t *facility_ie;
	uint8_t pdisc, tid;
	uint8_t msg_type;
	int rc;

	pdisc = gsm48_hdr_pdisc(gh);
	msg_type = gsm48_hdr_msg_type(gh);
	tid = gsm48_hdr_trans_id_flip_ti(gh);

	/* Associate logging messages with this subscriber */
	log_set_context(LOG_CTX_VLR_SUBSCR, conn->vsub);

	DEBUGP(DMM, "Received SS/USSD data (trans_id=%x, msg_type=%s)\n",
		tid, gsm48_pdisc_msgtype_name(pdisc, msg_type));

	/* Reuse existing transaction, or create a new one */
	trans = trans_find_by_id(conn, pdisc, tid);
	if (!trans) {
		/**
		 * According to GSM TS 04.80, section 2.4.2 "Register
		 * (mobile station to network direction)", the REGISTER
		 * message is sent by the mobile station to the network
		 * to assign a new transaction identifier for call independent
		 * supplementary service control and to request or acknowledge
		 * a supplementary service.
		 */
		if (msg_type != GSM0480_MTYPE_REGISTER) {
			LOGP(DMM, LOGL_ERROR, "Unexpected message (msg_type=%s), "
				"transaction is not allocated yet\n",
				gsm48_pdisc_msgtype_name(pdisc, msg_type));
			gsm48_tx_simple(conn,
				GSM48_PDISC_NC_SS | (tid << 4),
				GSM0480_MTYPE_RELEASE_COMPLETE);
			return -EINVAL;
		}

		DEBUGP(DMM, " -> (new transaction)\n");
		trans = trans_alloc(conn->network, conn->vsub,
			pdisc, tid, new_callref++);
		if (!trans) {
			DEBUGP(DMM, " -> No memory for trans\n");
			gsm48_tx_simple(conn,
				GSM48_PDISC_NC_SS | (tid << 4),
				GSM0480_MTYPE_RELEASE_COMPLETE);
			return -ENOMEM;
		}

		trans->conn = msc_subscr_conn_get(conn, MSC_CONN_USE_TRANS_NC_SS);
		trans->dlci = OMSC_LINKID_CB(msg);
		cm_service_request_concludes(conn, msg);
	}

	/* Attempt to extract Facility IE */
	rc = gsm0480_extract_ie_by_tag(gh, msgb_l3len(msg),
		&facility_ie, &facility_ie_len, GSM0480_IE_FACILITY);
	if (rc) {
		LOGP(DMM, LOGL_ERROR, "GSM 04.80 message parsing error, "
			"couldn't extract Facility IE\n");
		goto error;
	}

	/* Facility IE is optional for RELEASE COMPLETE */
	if (msg_type != GSM0480_MTYPE_RELEASE_COMPLETE) {
		if (!facility_ie || facility_ie_len < 2) {
			LOGP(DMM, LOGL_ERROR, "GSM 04.80 message parsing error, "
				"missing mandatory Facility IE\n");
			rc = -EINVAL;
			goto error;
		}
	}

	/* Compose a mew GSUP message */
	memset(&gsup_msg, 0x00, sizeof(gsup_msg));
	gsup_msg.message_type = OSMO_GSUP_MSGT_PROC_SS_REQUEST;
	gsup_msg.session_id = trans->callref;

	/**
	 * Perform A-interface to GSUP-interface mapping,
	 * according to GSM TS 09.11, table 4.2.
	 */
	switch (msg_type) {
	case GSM0480_MTYPE_REGISTER:
		gsup_msg.session_state = OSMO_GSUP_SESSION_STATE_BEGIN;
		break;
	case GSM0480_MTYPE_FACILITY:
		gsup_msg.session_state = OSMO_GSUP_SESSION_STATE_CONTINUE;
		break;
	case GSM0480_MTYPE_RELEASE_COMPLETE:
		gsup_msg.session_state = OSMO_GSUP_SESSION_STATE_END;
		break;
	}

	/* Fill in the (optional) message payload */
	if (facility_ie) {
		gsup_msg.ss_info_len = facility_ie_len;
		gsup_msg.ss_info = facility_ie;
	}

	/* Fill in subscriber's IMSI */
	OSMO_STRLCPY_ARRAY(gsup_msg.imsi, conn->vsub->imsi);

	/* Allocate GSUP message buffer */
	gsup_msgb = gsup_client_msgb_alloc();
	if (!gsup_msgb) {
		LOGP(DMM, LOGL_ERROR, "Couldn't allocate GSUP message\n");
		rc = -ENOMEM;
		goto error;
	}

	/* Encode GSUP message */
	rc = osmo_gsup_encode(gsup_msgb, &gsup_msg);
	if (rc) {
		LOGP(DMM, LOGL_ERROR, "Couldn't encode GSUP message\n");
		goto error;
	}

	/* Finally send */
	rc = gsup_client_send(conn->network->vlr->gsup_client, gsup_msgb);
	if (rc) {
		LOGP(DMM, LOGL_ERROR, "Couldn't send GSUP message\n");
		goto error;
	}

	/* Don't release connection, wait for response */
	msc_subscr_conn_communicating(conn);

	return 0;

error:
	/* Abort transaction on DTAP-interface */
	gsm0480_send_ussd_reject(conn, tid, -1,
		GSM_0480_PROBLEM_CODE_TAG_GENERAL,
		GSM_0480_GEN_PROB_CODE_UNRECOGNISED);
	if (trans)
		trans_free(trans);

	/* TODO: abort transaction on GSUP interface if any */
	return rc;
}

int gsm0911_gsup_handler(struct vlr_subscr *vsub,
			 struct osmo_gsup_message *gsup_msg)
{
	struct vlr_instance *vlr;
	struct gsm_network *net;
	struct gsm_trans *trans;
	struct gsm48_hdr *gh;
	struct msgb *ss_msg;
	bool trans_end;

	/* Associate logging messages with this subscriber */
	log_set_context(LOG_CTX_VLR_SUBSCR, vsub);

	/* Obtain pointer to vlr_instance */
	vlr = vsub->vlr;
	OSMO_ASSERT(vlr);

	/* Obtain pointer to gsm_network */
	net = (struct gsm_network *) vlr->user_ctx;
	OSMO_ASSERT(net);

	/* Handle errors */
	if (OSMO_GSUP_IS_MSGT_ERROR(gsup_msg->message_type)) {
		/* FIXME: handle this error somehow! */
		return 0;
	}

	/* Attempt to find DTAP-transaction */
	trans = trans_find_by_callref(net, gsup_msg->session_id);
	if (!trans) {
		/* FIXME: network-originated sessions are not supported yet */
		LOGP(DMM, LOGL_ERROR, "Network-originated sessions "
			"are not supported, dropping request...\n");
		return -ENOTSUP;
	}

	/* Allocate and prepare a new MT message */
	ss_msg = gsm48_msgb_alloc_name("GSM 04.08 SS/USSD");
	gh = (struct gsm48_hdr *) msgb_push(ss_msg, sizeof(*gh));
	gh->proto_discr  = GSM48_PDISC_NC_SS;
	gh->proto_discr |= trans->transaction_id << 4;

	/**
	 * Perform GSUP-interface to A-interface mapping,
	 * according to GSM TS 09.11, table 4.1.
	 *
	 * TODO: see (note 3), both CONTINUE and END may
	 * be also mapped to REGISTER if a new transaction
	 * has to be established.
	 */
	switch (gsup_msg->session_state) {
	case OSMO_GSUP_SESSION_STATE_BEGIN:
		gh->msg_type = GSM0480_MTYPE_REGISTER;
		break;
	case OSMO_GSUP_SESSION_STATE_CONTINUE:
		gh->msg_type = GSM0480_MTYPE_FACILITY;
		break;
	case OSMO_GSUP_SESSION_STATE_END:
		gh->msg_type = GSM0480_MTYPE_RELEASE_COMPLETE;
		break;

	/* Missing or incorrect session state */
	case OSMO_GSUP_SESSION_STATE_NONE:
	default:
		LOGP(DMM, LOGL_ERROR, "Unexpected session state %d\n",
			gsup_msg->session_state);
		/* FIXME: send ERROR back to the HLR */
		msgb_free(ss_msg);
		return -EINVAL;
	}

	/* Facility IE is optional only for RELEASE COMPLETE */
	if (gh->msg_type != GSM0480_MTYPE_RELEASE_COMPLETE) {
		if (!gsup_msg->ss_info || gsup_msg->ss_info_len < 2) {
			LOGP(DMM, LOGL_ERROR, "Missing mandatory Facility IE "
				"for mapped 0x%02x message\n", gh->msg_type);
			/* FIXME: send ERROR back to the HLR */
			msgb_free(ss_msg);
			return -EINVAL;
		}
	}

	/* Append Facility IE if preset */
	if (gsup_msg->ss_info && gsup_msg->ss_info_len > 2) {
		/* Facility IE carries LV, others carry TLV */
		if (gh->msg_type == GSM0480_MTYPE_FACILITY)
			msgb_lv_put(ss_msg, gsup_msg->ss_info_len, gsup_msg->ss_info);
		else
			msgb_tlv_put(ss_msg, GSM0480_IE_FACILITY,
				gsup_msg->ss_info_len, gsup_msg->ss_info);
	}

	/* Should we release the transaction? */
	trans_end = (gh->msg_type == GSM0480_MTYPE_RELEASE_COMPLETE);

	/* Sent to the MS, give ownership of ss_msg */
	msc_tx_dtap(trans->conn, ss_msg);

	/* Release transaction if required */
	if (trans_end)
		trans_free(trans);

	return 0;
}