openbsc/src/osmo-bsc_nat/bsc_nat_filter.c

/*
 * Access filtering
 */
/*
 * (C) 2010-2012 by Holger Hans Peter Freyther <zecke@selfish.org>
 * (C) 2010-2012 by On-Waves
 * 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/>.
 *
 */

#include <openbsc/bsc_nat.h>
#include <openbsc/bsc_nat_sccp.h>
#include <openbsc/bsc_msc.h>
#include <openbsc/gsm_data.h>
#include <openbsc/debug.h>
#include <openbsc/ipaccess.h>

#include <osmocom/core/linuxlist.h>
#include <osmocom/core/talloc.h>
#include <osmocom/gsm/gsm0808.h>

#include <osmocom/gsm/protocol/gsm_08_08.h>
#include <osmocom/gsm/protocol/gsm_04_11.h>

#include <osmocom/sccp/sccp.h>

static int lst_check_deny(struct bsc_nat_acc_lst *lst, const char *mi_string)
{
	struct bsc_nat_acc_lst_entry *entry;

	llist_for_each_entry(entry, &lst->fltr_list, list) {
		if (!entry->imsi_deny)
			continue;
		if (regexec(&entry->imsi_deny_re, mi_string, 0, NULL, 0) == 0)
			return 0;
	}

	return 1;
}

/* apply white/black list */
static int auth_imsi(struct bsc_connection *bsc, const char *mi_string)
{
	/*
	 * Now apply blacklist/whitelist of the BSC and the NAT.
	 * 1.) Allow directly if the IMSI is allowed at the BSC
	 * 2.) Reject if the IMSI is not allowed at the BSC
	 * 3.) Reject if the IMSI not allowed at the global level.
	 * 4.) Allow directly if the IMSI is allowed at the global level
	 */
	struct bsc_nat_acc_lst *nat_lst = NULL;
	struct bsc_nat_acc_lst *bsc_lst = NULL;

	bsc_lst = bsc_nat_acc_lst_find(bsc->nat, bsc->cfg->acc_lst_name);
	nat_lst = bsc_nat_acc_lst_find(bsc->nat, bsc->nat->acc_lst_name);


	if (bsc_lst) {
		/* 1. BSC allow */
		if (bsc_nat_lst_check_allow(bsc_lst, mi_string) == 0)
			return 1;

		/* 2. BSC deny */
		if (lst_check_deny(bsc_lst, mi_string) == 0) {
			LOGP(DNAT, LOGL_ERROR,
			     "Filtering %s by imsi_deny on bsc nr: %d.\n", mi_string, bsc->cfg->nr);
			rate_ctr_inc(&bsc_lst->stats->ctr[ACC_LIST_BSC_FILTER]);
			return -2;
		}

	}

	/* 3. NAT deny */
	if (nat_lst) {
		if (lst_check_deny(nat_lst, mi_string) == 0) {
			LOGP(DNAT, LOGL_ERROR,
			     "Filtering %s by nat imsi_deny on bsc nr: %d.\n", mi_string, bsc->cfg->nr);
			rate_ctr_inc(&nat_lst->stats->ctr[ACC_LIST_NAT_FILTER]);
			return -3;
		}
	}

	return 1;
}

static int _cr_check_loc_upd(struct bsc_connection *bsc,
			     uint8_t *data, unsigned int length,
			     char **imsi)
{
	uint8_t mi_type;
	struct gsm48_loc_upd_req *lu;
	char mi_string[GSM48_MI_SIZE];

	if (length < sizeof(*lu)) {
		LOGP(DNAT, LOGL_ERROR,
		     "LU does not fit. Length is %d \n", length);
		return -1;
	}

	lu = (struct gsm48_loc_upd_req *) data;
	mi_type = lu->mi[0] & GSM_MI_TYPE_MASK;

	/*
	 * We can only deal with the IMSI. This will fail for a phone that
	 * will send the TMSI of a previous network to us.
	 */
	if (mi_type != GSM_MI_TYPE_IMSI)
		return 0;

	gsm48_mi_to_string(mi_string, sizeof(mi_string), lu->mi, lu->mi_len);
	*imsi = talloc_strdup(bsc, mi_string);
	return auth_imsi(bsc, mi_string);
}

static int _cr_check_cm_serv_req(struct bsc_connection *bsc,
				 uint8_t *data, unsigned int length,
				 int *con_type, char **imsi)
{
	static const uint32_t classmark_offset =
				offsetof(struct gsm48_service_request, classmark);

	char mi_string[GSM48_MI_SIZE];
	uint8_t mi_type;
	int rc;
	struct gsm48_service_request *req;

	/* unfortunately in Phase1 the classmark2 length is variable */

	if (length < sizeof(*req)) {
		LOGP(DNAT, LOGL_ERROR,
		     "CM Serv Req does not fit. Length is %d\n", length);
		return -1;
	}

	req = (struct gsm48_service_request *) data;
	if (req->cm_service_type == 0x8)
		*con_type = NAT_CON_TYPE_SSA;
	rc = gsm48_extract_mi((uint8_t *) &req->classmark,
			      length - classmark_offset, mi_string, &mi_type);
	if (rc < 0) {
		LOGP(DNAT, LOGL_ERROR, "Failed to parse the classmark2/mi. error: %d\n", rc);
		return -1;
	}

	/* we have to let the TMSI or such pass */
	if (mi_type != GSM_MI_TYPE_IMSI)
		return 0;

	*imsi = talloc_strdup(bsc, mi_string);
	return auth_imsi(bsc, mi_string);
}

static int _cr_check_pag_resp(struct bsc_connection *bsc,
			      uint8_t *data, unsigned int length,
			      char **imsi)
{
	struct gsm48_pag_resp *resp;
	char mi_string[GSM48_MI_SIZE];
	uint8_t mi_type;

	if (length < sizeof(*resp)) {
		LOGP(DNAT, LOGL_ERROR, "PAG RESP does not fit. Length was %d.\n", length);
		return -1;
	}

	resp = (struct gsm48_pag_resp *) data;
	if (gsm48_paging_extract_mi(resp, length, mi_string, &mi_type) < 0) {
		LOGP(DNAT, LOGL_ERROR, "Failed to extract the MI.\n");
		return -1;
	}

	/* we need to let it pass for now */
	if (mi_type != GSM_MI_TYPE_IMSI)
		return 0;

	*imsi = talloc_strdup(bsc, mi_string);
	return auth_imsi(bsc, mi_string);
}

static int _dt_check_id_resp(struct bsc_connection *bsc,
			     uint8_t *data, unsigned int length,
			     struct sccp_connections *con)
{
	char mi_string[GSM48_MI_SIZE];
	uint8_t mi_type;
	int ret;

	if (length < 2) {
		LOGP(DNAT, LOGL_ERROR, "mi does not fit.\n");
		return -1;
	}

	if (data[0] < length - 1) {
		LOGP(DNAT, LOGL_ERROR, "mi length too big.\n");
		return -2;
	}

	mi_type = data[1] & GSM_MI_TYPE_MASK;
	gsm48_mi_to_string(mi_string, sizeof(mi_string), &data[1], data[0]);

	if (mi_type != GSM_MI_TYPE_IMSI)
		return 0;

	ret = auth_imsi(bsc, mi_string);
	con->imsi_checked = 1;
	con->imsi = talloc_strdup(con, mi_string);
	return ret;
}


/* Filter out CR data... */
int bsc_nat_filter_sccp_cr(struct bsc_connection *bsc, struct msgb *msg,
			struct bsc_nat_parsed *parsed, int *con_type,
			char **imsi, struct bsc_nat_reject_cause *cause)
{
	struct tlv_parsed tp;
	struct gsm48_hdr *hdr48;
	int hdr48_len;
	int len;
	uint8_t msg_type, proto;

	*con_type = NAT_CON_TYPE_NONE;
	cause->cm_reject_cause = GSM48_REJECT_PLMN_NOT_ALLOWED;
	cause->lu_reject_cause = GSM48_REJECT_PLMN_NOT_ALLOWED;
	*imsi = NULL;

	if (parsed->gsm_type != BSS_MAP_MSG_COMPLETE_LAYER_3) {
		LOGP(DNAT, LOGL_ERROR,
		     "Rejecting CR message due wrong GSM Type %d\n", parsed->gsm_type);
		return -1;
	}

	/* the parsed has had some basic l3 length check */
	len = msg->l3h[1];
	if (msgb_l3len(msg) - 3 < len) {
		LOGP(DNAT, LOGL_ERROR,
		     "The CR Data has not enough space...\n");
		return -1;
	}

	msg->l4h = &msg->l3h[3];
	len -= 1;

	tlv_parse(&tp, gsm0808_att_tlvdef(), msg->l4h, len, 0, 0);

	if (!TLVP_PRESENT(&tp, GSM0808_IE_LAYER_3_INFORMATION)) {
		LOGP(DNAT, LOGL_ERROR, "CR Data does not contain layer3 information.\n");
		return -1;
	}

	hdr48_len = TLVP_LEN(&tp, GSM0808_IE_LAYER_3_INFORMATION);

	if (hdr48_len < sizeof(*hdr48)) {
		LOGP(DNAT, LOGL_ERROR, "GSM48 header does not fit.\n");
		return -1;
	}

	hdr48 = (struct gsm48_hdr *) TLVP_VAL(&tp, GSM0808_IE_LAYER_3_INFORMATION);

	proto = hdr48->proto_discr & 0x0f;
	msg_type = hdr48->msg_type & 0xbf;
	if (proto == GSM48_PDISC_MM &&
	    msg_type == GSM48_MT_MM_LOC_UPD_REQUEST) {
		*con_type = NAT_CON_TYPE_LU;
		return _cr_check_loc_upd(bsc, &hdr48->data[0], hdr48_len - sizeof(*hdr48), imsi);
	} else if (proto == GSM48_PDISC_MM &&
		  msg_type == GSM48_MT_MM_CM_SERV_REQ) {
		*con_type = NAT_CON_TYPE_CM_SERV_REQ;
		return _cr_check_cm_serv_req(bsc, &hdr48->data[0],
					     hdr48_len - sizeof(*hdr48),
					     con_type, imsi);
	} else if (proto == GSM48_PDISC_RR &&
		   msg_type == GSM48_MT_RR_PAG_RESP) {
		*con_type = NAT_CON_TYPE_PAG_RESP;
		return _cr_check_pag_resp(bsc, &hdr48->data[0], hdr48_len - sizeof(*hdr48), imsi);
	} else {
		/* We only want to filter the above, let other things pass */
		*con_type = NAT_CON_TYPE_OTHER;
		return 0;
	}
}

int bsc_nat_filter_dt(struct bsc_connection *bsc, struct msgb *msg,
		struct sccp_connections *con, struct bsc_nat_parsed *parsed,
		struct bsc_nat_reject_cause *cause)
{
	uint32_t len;
	uint8_t msg_type, proto;
	struct gsm48_hdr *hdr48;

	cause->cm_reject_cause = GSM48_REJECT_PLMN_NOT_ALLOWED;
	cause->lu_reject_cause = GSM48_REJECT_PLMN_NOT_ALLOWED;

	if (con->imsi_checked)
		return 0;

	/* only care about DTAP messages */
	if (parsed->bssap != BSSAP_MSG_DTAP)
		return 0;

	hdr48 = bsc_unpack_dtap(parsed, msg, &len);
	if (!hdr48)
		return -1;

	proto = hdr48->proto_discr & 0x0f;
	msg_type = hdr48->msg_type & 0xbf;
	if (proto == GSM48_PDISC_MM &&
	    msg_type == GSM48_MT_MM_ID_RESP) {
		return _dt_check_id_resp(bsc, &hdr48->data[0], len - sizeof(*hdr48), con);
	} else {
		return 0;
	}
}