src/gprs/gprs_llc.c

/* GPRS LLC protocol implementation as per 3GPP TS 04.64 */

/* (C) 2009-2010 by Harald Welte <laforge@gnumonks.org>
 *
 * 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 <errno.h>
#include <stdint.h>
#include <stdbool.h>

#include <osmocom/core/msgb.h>
#include <osmocom/core/linuxlist.h>
#include <osmocom/core/timer.h>
#include <osmocom/core/talloc.h>
#include <osmocom/core/rate_ctr.h>
#include <osmocom/gprs/gprs_bssgp.h>
#include <osmocom/gsm/gsm_utils.h>

#include <osmocom/sgsn/debug.h>
#include <osmocom/sgsn/gprs_sgsn.h>
#include <osmocom/sgsn/gprs_gmm.h>
#include <osmocom/sgsn/gprs_llc.h>
#include <osmocom/sgsn/crc24.h>
#include <osmocom/sgsn/sgsn.h>
#include <osmocom/sgsn/gprs_llc_xid.h>
#include <osmocom/sgsn/gprs_sndcp_comp.h>
#include <osmocom/sgsn/gprs_sndcp.h>

const struct value_string gprs_llc_llme_state_names[] = {
	{ GPRS_LLMS_UNASSIGNED,	"UNASSIGNED" },
	{ GPRS_LLMS_ASSIGNED,	"ASSIGNED" },
	{ 0, NULL }
};

static struct gprs_llc_llme *llme_alloc(uint32_t tlli);
static int gprs_llc_tx_xid(struct gprs_llc_lle *lle, struct msgb *msg,
			   int command);
static int gprs_llc_tx_dm(struct gprs_llc_lle *lle);
static int gprs_llc_tx_u(struct msgb *msg, uint8_t sapi,
			 int command, enum gprs_llc_u_cmd u_cmd, int pf_bit);

/* BEGIN XID RELATED */

/* Generate XID message */
static int gprs_llc_generate_xid(uint8_t *bytes, int bytes_len,
				 struct gprs_llc_xid_field *l3_xid_field,
				 struct gprs_llc_lle *lle)
{
	/* Note: Called by gprs_ll_xid_req() */

	LLIST_HEAD(xid_fields);

	struct gprs_llc_xid_field xid_version;
	struct gprs_llc_xid_field xid_n201u;
	struct gprs_llc_xid_field xid_n201i;

	xid_version.type = GPRS_LLC_XID_T_VERSION;
	xid_version.data = (uint8_t *) "\x00";
	xid_version.data_len = 1;

	xid_n201u.type = GPRS_LLC_XID_T_N201_U;
	xid_n201u.data = (uint8_t *) "\x05\xf0";
	xid_n201u.data_len = 2;

	xid_n201i.type = GPRS_LLC_XID_T_N201_I;
	xid_n201i.data = (uint8_t *) "\x05\xf0";
	xid_n201i.data_len = 2;

	/* Add locally managed XID Fields */
	llist_add(&xid_version.list, &xid_fields);
	llist_add(&xid_n201u.list, &xid_fields);
	llist_add(&xid_n201i.list, &xid_fields);

	/* Append layer 3 XID field (if present) */
	if (l3_xid_field) {
		/* Enforce layer 3 XID type (just to be sure) */
		l3_xid_field->type = GPRS_LLC_XID_T_L3_PAR;

		/* Add Layer 3 XID field to the list */
		llist_add(&l3_xid_field->list, &xid_fields);
	}

	/* Store generated XID for later reference */
	talloc_free(lle->xid);
	lle->xid = gprs_llc_copy_xid(lle->llme, &xid_fields);

	return gprs_llc_compile_xid(bytes, bytes_len, &xid_fields);
}

/* Generate XID message that will cause the GMM to reset */
static int gprs_llc_generate_xid_for_gmm_reset(uint8_t *bytes,
					       int bytes_len, uint32_t iov_ui,
					       struct gprs_llc_lle *lle)
{
	/* Called by gprs_llgmm_reset() and
	 * gprs_llgmm_reset_oldmsg() */

	LLIST_HEAD(xid_fields);

	struct gprs_llc_xid_field xid_reset;
	struct gprs_llc_xid_field xid_iovui;

	/* First XID component must be RESET */
	xid_reset.type = GPRS_LLC_XID_T_RESET;
	xid_reset.data = NULL;
	xid_reset.data_len = 0;

	/* Add new IOV-UI */
	xid_iovui.type = GPRS_LLC_XID_T_IOV_UI;
	xid_iovui.data = (uint8_t *) & iov_ui;
	xid_iovui.data_len = 4;

	/* Add locally managed XID Fields */
	llist_add(&xid_iovui.list, &xid_fields);
	llist_add(&xid_reset.list, &xid_fields);

	/* Store generated XID for later reference */
	talloc_free(lle->xid);
	lle->xid = gprs_llc_copy_xid(lle->llme, &xid_fields);

	return gprs_llc_compile_xid(bytes, bytes_len, &xid_fields);
}

/* Process an incoming XID confirmation */
static int gprs_llc_process_xid_conf(uint8_t *bytes, int bytes_len,
				     struct gprs_llc_lle *lle)
{
	/* Note: This function handles the response of a network originated
	 * XID-Request. There XID messages reflected by the MS are analyzed
	 * and processed here. The caller is called by rx_llc_xid(). */

	struct llist_head *xid_fields;
	struct gprs_llc_xid_field *xid_field;
	struct gprs_llc_xid_field *xid_field_request;
	struct gprs_llc_xid_field *xid_field_request_l3 = NULL;

	/* Pick layer3 XID from the XID request we have sent last */
	if (lle->xid) {
		llist_for_each_entry(xid_field_request, lle->xid, list) {
			if (xid_field_request->type == GPRS_LLC_XID_T_L3_PAR)
				xid_field_request_l3 = xid_field_request;
		}
	}

	/* Parse and analyze XID-Response */
	xid_fields = gprs_llc_parse_xid(NULL, bytes, bytes_len);

	if (xid_fields) {

		gprs_llc_dump_xid_fields(xid_fields, LOGL_DEBUG);
		llist_for_each_entry(xid_field, xid_fields, list) {

			/* Forward SNDCP-XID fields to Layer 3 (SNDCP) */
			if (xid_field->type == GPRS_LLC_XID_T_L3_PAR &&
			    xid_field_request_l3) {
				sndcp_sn_xid_conf(xid_field,
						  xid_field_request_l3, lle);
			}

			/* Process LLC-XID fields: */
			else {

				/* FIXME: Do something more useful with the
				 * echoed XID-Information. Currently we
				 * just ignore the response completely and
				 * by doing so we blindly accept any changes
				 * the MS might have done to the our XID
				 * inquiry. There is a remainig risk of
				 * malfunction! */
				LOGP(DLLC, LOGL_NOTICE,
				     "Ignoring XID-Field: XID: type %s, data_len=%d, data=%s\n",
				     get_value_string(gprs_llc_xid_type_names,
						      xid_field->type),
				     xid_field->data_len,
				     osmo_hexdump_nospc(xid_field->data,
				     xid_field->data_len));
			}
		}
		talloc_free(xid_fields);
	}

	/* Flush pending XID fields */
	talloc_free(lle->xid);
	lle->xid = NULL;

	return 0;
}

/* Process an incoming XID indication and generate an appropiate response */
static int gprs_llc_process_xid_ind(uint8_t *bytes_request,
				    int bytes_request_len,
				    uint8_t *bytes_response,
				    int bytes_response_maxlen,
				    struct gprs_llc_lle *lle)
{
	/* Note: This function computes the response that is sent back to the
	 * MS when a mobile originated XID is received. The function is
	 * called by rx_llc_xid() */

	int rc = -EINVAL;

	struct llist_head *xid_fields;
	struct llist_head *xid_fields_response;

	struct gprs_llc_xid_field *xid_field;
	struct gprs_llc_xid_field *xid_field_response;

	/* Parse and analyze XID-Request */
	xid_fields =
	    gprs_llc_parse_xid(lle->llme, bytes_request, bytes_request_len);
	if (xid_fields) {
		xid_fields_response = talloc_zero(lle->llme, struct llist_head);
		INIT_LLIST_HEAD(xid_fields_response);
		gprs_llc_dump_xid_fields(xid_fields, LOGL_DEBUG);

		/* Process LLC-XID fields: */
		llist_for_each_entry(xid_field, xid_fields, list) {

			if (xid_field->type != GPRS_LLC_XID_T_L3_PAR) {
				/* FIXME: Check the incoming XID parameters for
				 * for validity. Currently we just blindly
				 * accept all XID fields by just echoing them.
				 * There is a remaining risk of malfunction
				 * when a MS submits values which defer from
				 * the default! */
				LOGP(DLLC, LOGL_NOTICE,
				     "Echoing XID-Field: XID: type %s, data_len=%d, data=%s\n",
				     get_value_string(gprs_llc_xid_type_names,
						      xid_field->type),
				     xid_field->data_len,
				     osmo_hexdump_nospc(xid_field->data,
							xid_field->data_len));
				xid_field_response =
				    gprs_llc_dup_xid_field
				    (lle->llme, xid_field);
				llist_add(&xid_field_response->list,
					  xid_fields_response);
			}
		}

		/* Forward SNDCP-XID fields to Layer 3 (SNDCP) */
		llist_for_each_entry(xid_field, xid_fields, list) {
			if (xid_field->type == GPRS_LLC_XID_T_L3_PAR) {

				xid_field_response =
				    talloc_zero(lle->llme,
						struct gprs_llc_xid_field);
				rc = sndcp_sn_xid_ind(xid_field,
						      xid_field_response, lle);
				if (rc == 0)
					llist_add(&xid_field_response->list,
						  xid_fields_response);
				else
					talloc_free(xid_field_response);
			}
		}

		rc = gprs_llc_compile_xid(bytes_response,
					  bytes_response_maxlen,
					  xid_fields_response);
		talloc_free(xid_fields_response);
		talloc_free(xid_fields);
	}

	return rc;
}

/* Dispatch XID indications and responses comming from the MS */
static void rx_llc_xid(struct gprs_llc_lle *lle,
		       struct gprs_llc_hdr_parsed *gph)
{
	uint8_t response[1024];
	int response_len;

	/* FIXME: 8.5.3.3: check if XID is invalid */
	if (gph->is_cmd) {
		LOGP(DLLC, LOGL_NOTICE,
		     "Received XID indication from MS.\n");

		struct msgb *resp;
		uint8_t *xid;
		resp = msgb_alloc_headroom(4096, 1024, "LLC_XID");

		response_len =
		    gprs_llc_process_xid_ind(gph->data, gph->data_len,
					     response, sizeof(response),
					     lle);
		if (response_len < 0) {
			LOGP(DLLC, LOGL_ERROR,
			     "invalid XID indication received!\n");
		} else {
			xid = msgb_put(resp, response_len);
			memcpy(xid, response, response_len);
		}
		gprs_llc_tx_xid(lle, resp, 0);
	} else {
		LOGP(DLLC, LOGL_NOTICE,
		     "Received XID confirmation from MS.\n");
		gprs_llc_process_xid_conf(gph->data, gph->data_len, lle);
		/* FIXME: if we had sent a XID reset, send
		 * LLGMM-RESET.conf to GMM */
	}
}

/* Set of LL-XID negotiation (See also: TS 101 351, Section 7.2.2.4) */
int gprs_ll_xid_req(struct gprs_llc_lle *lle,
		    struct gprs_llc_xid_field *l3_xid_field)
{
	/* Note: This functions is calle from gprs_sndcp.c */

	uint8_t xid_bytes[1024];;
	int xid_bytes_len;
	uint8_t *xid;
	struct msgb *msg;
	const char *ftype;

	/* Generate XID */
	xid_bytes_len =
	    gprs_llc_generate_xid(xid_bytes, sizeof(xid_bytes), l3_xid_field, lle);

	/* Only perform XID sending if the XID message contains something */
	if (xid_bytes_len > 0) {
		/* Transmit XID bytes */
		msg = msgb_alloc_headroom(4096, 1024, "LLC_XID");
		xid = msgb_put(msg, xid_bytes_len);
		memcpy(xid, xid_bytes, xid_bytes_len);
		if (l3_xid_field)
			ftype = get_value_string(gprs_llc_xid_type_names,
						 l3_xid_field->type);
		else
			ftype = "NULL";
		LOGP(DLLC, LOGL_NOTICE, "Sending XID type %s (%d bytes) request"
		     " to MS...\n", ftype, xid_bytes_len);
		gprs_llc_tx_xid(lle, msg, 1);
	} else {
		LOGP(DLLC, LOGL_ERROR,
		     "XID-Message generation failed, XID not sent!\n");
		return -EINVAL;
	}

	return 0;
}
/* END XID RELATED */




/* Entry function from upper level (LLC), asking us to transmit a BSSGP PDU
 * to a remote MS (identified by TLLI) at a BTS identified by its BVCI and NSEI */
static int _bssgp_tx_dl_ud(struct msgb *msg, struct sgsn_mm_ctx *mmctx)
{
	struct bssgp_dl_ud_par dup;
	const uint8_t qos_profile_default[3] = { 0x00, 0x00, 0x20 };

	memset(&dup, 0, sizeof(dup));
	/* before we have received some identity from the MS, we might
	 * not yet have a MMC context (e.g. XID negotiation of primarly
	 * LLC connection from GMM sapi). */
	if (mmctx) {
		dup.imsi = mmctx->imsi;
		dup.drx_parms = mmctx->drx_parms;
		dup.ms_ra_cap.len = mmctx->ms_radio_access_capa.len;
		dup.ms_ra_cap.v = mmctx->ms_radio_access_capa.buf;

		/* make sure we only send it to the right llme */
		if (!(msgb_tlli(msg) == mmctx->gb.llme->tlli
		      || msgb_tlli(msg) == mmctx->gb.llme->old_tlli)) {
			LOGP(DLLC, LOGL_ERROR,
			     "_bssgp_tx_dl_ud(): Attempt to send Downlink Unitdata to wrong LLME:"
			     " msgb_tlli=0x%x mmctx->gb.llme->tlli=0x%x ->old_tlli=0x%x\n",
			     msgb_tlli(msg), mmctx->gb.llme->tlli, mmctx->gb.llme->old_tlli);
			msgb_free(msg);
			return -EINVAL;
		}
	}
	memcpy(&dup.qos_profile, qos_profile_default,
		sizeof(qos_profile_default));

	return bssgp_tx_dl_ud(msg, 1000, &dup);
}


/* Section 8.9.9 LLC layer parameter default values */
static const struct gprs_llc_params llc_default_params[NUM_SAPIS] = {
	[1] = {
		.t200_201	= 5,
		.n200		= 3,
		.n201_u		= 400,
	},
	[2] = {
		.t200_201	= 5,
		.n200		= 3,
		.n201_u		= 270,
	},
	[3] = {
		.iov_i_exp	= 27,
		.t200_201	= 5,
		.n200		= 3,
		.n201_u		= 500,
		.n201_i		= 1503,
		.mD		= 1520,
		.mU		= 1520,
		.kD		= 16,
		.kU		= 16,
	},
	[5] = {
		.iov_i_exp	= 27,
		.t200_201	= 10,
		.n200		= 3,
		.n201_u		= 500,
		.n201_i		= 1503,
		.mD		= 760,
		.mU		= 760,
		.kD		= 8,
		.kU		= 8,
	},
	[7] = {
		.t200_201	= 20,
		.n200		= 3,
		.n201_u		= 270,
	},
	[8] = {
		.t200_201	= 20,
		.n200		= 3,
		.n201_u		= 270,
	},
	[9] = {
		.iov_i_exp	= 27,
		.t200_201	= 20,
		.n200		= 3,
		.n201_u		= 500,
		.n201_i		= 1503,
		.mD		= 380,
		.mU		= 380,
		.kD		= 4,
		.kU		= 4,
	},
	[11] = {
		.iov_i_exp	= 27,
		.t200_201	= 40,
		.n200		= 3,
		.n201_u		= 500,
		.n201_i		= 1503,
		.mD		= 190,
		.mU		= 190,
		.kD		= 2,
		.kU		= 2,
	},
};

LLIST_HEAD(gprs_llc_llmes);
void *llc_tall_ctx;

/* lookup LLC Entity based on DLCI (TLLI+SAPI tuple) */
static struct gprs_llc_lle *lle_by_tlli_sapi(const uint32_t tlli, uint8_t sapi)
{
	struct gprs_llc_llme *llme;

	llist_for_each_entry(llme, &gprs_llc_llmes, list) {
		if (llme->tlli == tlli || llme->old_tlli == tlli)
			return &llme->lle[sapi];
	}
	return NULL;
}

struct gprs_llc_lle *gprs_lle_get_or_create(const uint32_t tlli, uint8_t sapi)
{
	struct gprs_llc_llme *llme;
	struct gprs_llc_lle *lle;

	lle = lle_by_tlli_sapi(tlli, sapi);
	if (lle)
		return lle;

	LOGP(DLLC, LOGL_NOTICE, "LLC: unknown TLLI 0x%08x, "
		"creating LLME on the fly\n", tlli);
	llme = llme_alloc(tlli);
	lle = &llme->lle[sapi];
	return lle;
}

struct llist_head *gprs_llme_list(void)
{
	return &gprs_llc_llmes;
}

/* lookup LLC Entity for RX based on DLCI (TLLI+SAPI tuple) */
static struct gprs_llc_lle *lle_for_rx_by_tlli_sapi(const uint32_t tlli,
					uint8_t sapi, enum gprs_llc_cmd cmd)
{
	struct gprs_llc_lle *lle;

	/* We already know about this TLLI */
	lle = lle_by_tlli_sapi(tlli, sapi);
	if (lle)
		return lle;

	/* Maybe it is a routing area update but we already know this sapi? */
	if (gprs_tlli_type(tlli) == TLLI_FOREIGN) {
		lle = lle_by_tlli_sapi(tlli, sapi);
		if (lle) {
			LOGP(DLLC, LOGL_NOTICE,
				"LLC RX: Found a local entry for TLLI 0x%08x\n",
				tlli);
			return lle;
		}
	}

	/* 7.2.1.1 LLC belonging to unassigned TLLI+SAPI shall be discarded,
	 * except UID and XID frames with SAPI=1 */
	if (sapi == GPRS_SAPI_GMM &&
		    (cmd == GPRS_LLC_XID || cmd == GPRS_LLC_UI)) {
		struct gprs_llc_llme *llme;
		/* FIXME: don't use the TLLI but the 0xFFFF unassigned? */
		llme = llme_alloc(tlli);
		LOGP(DLLC, LOGL_NOTICE, "LLC RX: unknown TLLI 0x%08x, "
			"creating LLME on the fly\n", tlli);
		lle = &llme->lle[sapi];
		return lle;
	}

	LOGP(DLLC, LOGL_NOTICE,
		"unknown TLLI(0x%08x)/SAPI(%d): Silently dropping\n",
		tlli, sapi);
	return NULL;
}

static void lle_init(struct gprs_llc_llme *llme, uint8_t sapi)
{
	struct gprs_llc_lle *lle = &llme->lle[sapi];

	lle->llme = llme;
	lle->sapi = sapi;
	lle->state = GPRS_LLES_UNASSIGNED;

	/* Initialize according to parameters */
	memcpy(&lle->params, &llc_default_params[sapi], sizeof(lle->params));
}

static struct gprs_llc_llme *llme_alloc(uint32_t tlli)
{
	struct gprs_llc_llme *llme;
	uint32_t i;

	llme = talloc_zero(llc_tall_ctx, struct gprs_llc_llme);
	if (!llme)
		return NULL;

	llme->tlli = tlli;
	llme->old_tlli = TLLI_UNASSIGNED;
	llme->state = GPRS_LLMS_UNASSIGNED;
	llme->age_timestamp = GPRS_LLME_RESET_AGE;
	llme->cksn = GSM_KEY_SEQ_INVAL;

	for (i = 0; i < ARRAY_SIZE(llme->lle); i++)
		lle_init(llme, i);

	llist_add(&llme->list, &gprs_llc_llmes);

	llme->comp.proto = gprs_sndcp_comp_alloc(llme);
	llme->comp.data = gprs_sndcp_comp_alloc(llme);

	return llme;
}

static void llme_free(struct gprs_llc_llme *llme)
{
	gprs_sndcp_comp_free(llme->comp.proto);
	gprs_sndcp_comp_free(llme->comp.data);
	llist_del(&llme->list);
	talloc_free(llme);
}

#if 0
/* FIXME: Unused code... */
static void t200_expired(void *data)
{
	struct gprs_llc_lle *lle = data;

	/* 8.5.1.3: Expiry of T200 */

	if (lle->retrans_ctr >= lle->params.n200) {
		/* FIXME: LLGM-STATUS-IND, LL-RELEASE-IND/CNF */
		lle->state = GPRS_LLES_ASSIGNED_ADM;
	}

	switch (lle->state) {
	case GPRS_LLES_LOCAL_EST:
		/* FIXME: retransmit SABM */
		/* FIXME: re-start T200 */
		lle->retrans_ctr++;
		break;
	case GPRS_LLES_LOCAL_REL:
		/* FIXME: retransmit DISC */
		/* FIXME: re-start T200 */
		lle->retrans_ctr++;
		break;
	default:
		LOGP(DLLC, LOGL_ERROR, "LLC unhandled state: %d\n", lle->state);
		break;
	}

}

static void t201_expired(void *data)
{
	struct gprs_llc_lle *lle = data;

	if (lle->retrans_ctr < lle->params.n200) {
		/* FIXME: transmit apropriate supervisory frame (8.6.4.1) */
		/* FIXME: set timer T201 */
		lle->retrans_ctr++;
	}
}
#endif

int gprs_llc_tx_u(struct msgb *msg, uint8_t sapi, int command,
		  enum gprs_llc_u_cmd u_cmd, int pf_bit)
{
	uint8_t *fcs, *llch;
	uint8_t addr, ctrl;
	uint32_t fcs_calc;

	/* Identifiers from UP: (TLLI, SAPI) + (BVCI, NSEI) */

	/* Address Field */
	addr = sapi & 0xf;
	if (command)
		addr |= 0x40;

	/* 6.3 Figure 8 */
	ctrl = 0xe0 | u_cmd;
	if (pf_bit)
		ctrl |= 0x10;

	/* prepend LLC UI header */
	llch = msgb_push(msg, 2);
	llch[0] = addr;
	llch[1] = ctrl;

	/* append FCS to end of frame */
	fcs = msgb_put(msg, 3);
	fcs_calc = gprs_llc_fcs(llch, fcs - llch);
	fcs[0] = fcs_calc & 0xff;
	fcs[1] = (fcs_calc >> 8) & 0xff;
	fcs[2] = (fcs_calc >> 16) & 0xff;

	/* Identifiers passed down: (BVCI, NSEI) */

	rate_ctr_inc(&sgsn->rate_ctrs->ctr[CTR_LLC_DL_PACKETS]);
	rate_ctr_add(&sgsn->rate_ctrs->ctr[CTR_LLC_DL_BYTES], msg->len);

	/* Send BSSGP-DL-UNITDATA.req */
	return _bssgp_tx_dl_ud(msg, NULL);
}

/* Send XID response to LLE */
static int gprs_llc_tx_xid(struct gprs_llc_lle *lle, struct msgb *msg,
			   int command)
{
	/* copy identifiers from LLE to ensure lower layers can route */
	msgb_tlli(msg) = lle->llme->tlli;
	msgb_bvci(msg) = lle->llme->bvci;
	msgb_nsei(msg) = lle->llme->nsei;

	return gprs_llc_tx_u(msg, lle->sapi, command, GPRS_LLC_U_XID, 1);
}

static int gprs_llc_tx_dm(struct gprs_llc_lle *lle)
{
	struct msgb *msg = msgb_alloc_headroom(4096, 1024, "LLC_DM");

	/* copy identifiers from LLE to ensure lower layers can route */
	msgb_tlli(msg) = lle->llme->tlli;
	msgb_bvci(msg) = lle->llme->bvci;
	msgb_nsei(msg) = lle->llme->nsei;

	return gprs_llc_tx_u(msg, lle->sapi, 0, GPRS_LLC_U_DM_RESP, 1);
}

/* encrypt information field + FCS, if needed! */
static int apply_gea(struct gprs_llc_lle *lle, uint16_t crypt_len, uint16_t nu,
		     uint32_t oc, uint8_t sapi, uint8_t *fcs, uint8_t *data)
{
	uint8_t cipher_out[GSM0464_CIPH_MAX_BLOCK];

	if (lle->llme->algo == GPRS_ALGO_GEA0)
		return -EINVAL;

	/* Compute the 'Input' Paraemeter */
	uint32_t fcs_calc, iv = gprs_cipher_gen_input_ui(lle->llme->iov_ui, sapi,
							 nu, oc);
	/* Compute gamma that we need to XOR with the data */
	int r = gprs_cipher_run(cipher_out, crypt_len, lle->llme->algo,
				lle->llme->kc, iv,
				fcs ? GPRS_CIPH_SGSN2MS : GPRS_CIPH_MS2SGSN);
	if (r < 0) {
		LOGP(DLLC, LOGL_ERROR, "Error producing %s gamma for UI "
		     "frame: %d\n", get_value_string(gprs_cipher_names,
						     lle->llme->algo), r);
		return -ENOMSG;
	}

	if (fcs) {
		/* Mark frame as encrypted and update FCS */
		data[2] |= 0x02;
		fcs_calc = gprs_llc_fcs(data, fcs - data);
		fcs[0] = fcs_calc & 0xff;
		fcs[1] = (fcs_calc >> 8) & 0xff;
		fcs[2] = (fcs_calc >> 16) & 0xff;
		data += 3;
	}

	/* XOR the cipher output with the data */
	for (r = 0; r < crypt_len; r++)
		*(data + r) ^= cipher_out[r];

	return 0;
}

/* Transmit a UI frame over the given SAPI:
   'encryptable' indicates whether particular message can be encrypted according
   to 3GPP TS 24.008 § 4.7.1.2
 */
int gprs_llc_tx_ui(struct msgb *msg, uint8_t sapi, int command,
		   struct sgsn_mm_ctx *mmctx, bool encryptable)
{
	struct gprs_llc_lle *lle;
	uint8_t *fcs, *llch;
	uint8_t addr, ctrl[2];
	uint32_t fcs_calc;
	uint16_t nu = 0;
	uint32_t oc;

	/* Identifiers from UP: (TLLI, SAPI) + (BVCI, NSEI) */

	/* look-up or create the LL Entity for this (TLLI, SAPI) tuple */
	lle = gprs_lle_get_or_create(msgb_tlli(msg), sapi);

	if (msg->len > lle->params.n201_u) {
		LOGP(DLLC, LOGL_ERROR, "Cannot Tx %u bytes (N201-U=%u)\n",
			msg->len, lle->params.n201_u);
		msgb_free(msg);
		return -EFBIG;
	}

	gprs_llme_copy_key(mmctx, lle->llme);

	/* Update LLE's (BVCI, NSEI) tuple */
	lle->llme->bvci = msgb_bvci(msg);
	lle->llme->nsei = msgb_nsei(msg);

	/* Obtain current values for N(u) and OC */
	nu = lle->vu_send;
	oc = lle->oc_ui_send;
	/* Increment V(U) */
	lle->vu_send = (lle->vu_send + 1) % 512;
	/* Increment Overflow Counter, if needed */
	if ((lle->vu_send + 1) / 512)
		lle->oc_ui_send += 512;

	/* Address Field */
	addr = sapi & 0xf;
	if (command)
		addr |= 0x40;

	/* Control Field */
	ctrl[0] = 0xc0;
	ctrl[0] |= nu >> 6;
	ctrl[1] = (nu << 2) & 0xfc;
	ctrl[1] |= 0x01; /* Protected Mode */

	/* prepend LLC UI header */
	llch = msgb_push(msg, 3);
	llch[0] = addr;
	llch[1] = ctrl[0];
	llch[2] = ctrl[1];

	/* append FCS to end of frame */
	fcs = msgb_put(msg, 3);
	fcs_calc = gprs_llc_fcs(llch, fcs - llch);
	fcs[0] = fcs_calc & 0xff;
	fcs[1] = (fcs_calc >> 8) & 0xff;
	fcs[2] = (fcs_calc >> 16) & 0xff;

	if (lle->llme->algo != GPRS_ALGO_GEA0 && encryptable) {
		int rc = apply_gea(lle, fcs - llch, nu, oc, sapi, fcs, llch);
		if (rc < 0) {
			msgb_free(msg);
			return rc;
		}
	}

	rate_ctr_inc(&sgsn->rate_ctrs->ctr[CTR_LLC_DL_PACKETS]);
	rate_ctr_add(&sgsn->rate_ctrs->ctr[CTR_LLC_DL_BYTES], msg->len);

	/* Identifiers passed down: (BVCI, NSEI) */

	/* Send BSSGP-DL-UNITDATA.req */
	return _bssgp_tx_dl_ud(msg, mmctx);
}

static int gprs_llc_hdr_rx(struct gprs_llc_hdr_parsed *gph,
			   struct gprs_llc_lle *lle)
{
	switch (gph->cmd) {
#if 0
	/* we don't fully imoplement ABM, so refuse it properly (OS#3953) */
	case GPRS_LLC_SABM: /* Section 6.4.1.1 */
		lle->v_sent = lle->v_ack = lle->v_recv = 0;
		if (lle->state == GPRS_LLES_ASSIGNED_ADM) {
			/* start re-establishment (8.7.1) */
		}
		lle->state = GPRS_LLES_REMOTE_EST;
		/* FIXME: Send UA */
		lle->state = GPRS_LLES_ABM;
		/* FIXME: process data */
		break;
	case GPRS_LLC_DISC: /* Section 6.4.1.2 */
		/* FIXME: Send UA */
		/* terminate ABM */
		lle->state = GPRS_LLES_ASSIGNED_ADM;
		break;
	case GPRS_LLC_UA: /* Section 6.4.1.3 */
		if (lle->state == GPRS_LLES_LOCAL_EST)
			lle->state = GPRS_LLES_ABM;
		break;
	case GPRS_LLC_DM: /* Section 6.4.1.4: ABM cannot be performed */
		if (lle->state == GPRS_LLES_LOCAL_EST)
			lle->state = GPRS_LLES_ASSIGNED_ADM;
		break;
	case GPRS_LLC_FRMR: /* Section 6.4.1.5 */
		break;
#else
	case GPRS_LLC_SABM:
	case GPRS_LLC_DISC:
		/* send DM to properly signal we don't do ABM */
		gprs_llc_tx_dm(lle);
		break;
#endif
	case GPRS_LLC_XID: /* Section 6.4.1.6 */
		rx_llc_xid(lle, gph);
		break;
	case GPRS_LLC_UI:
		if (gprs_llc_is_retransmit(gph->seq_tx, lle->vu_recv)) {
			LOGP(DLLC, LOGL_NOTICE,
				"TLLI=%08x dropping UI, N(U=%d) not in window V(URV(UR:%d).\n",
				lle->llme ? lle->llme->tlli : -1,
				gph->seq_tx, lle->vu_recv);

			/* HACK: non-standard recovery handling.  If remote LLE
			 * is re-transmitting the same sequence number for
			 * three times, don't discard the frame but pass it on
			 * and 'learn' the new sequence number */
			if (gph->seq_tx != lle->vu_recv_last) {
				lle->vu_recv_last = gph->seq_tx;
				lle->vu_recv_duplicates = 0;
			} else {
				lle->vu_recv_duplicates++;
				if (lle->vu_recv_duplicates < 3)
					return -EIO;
				LOGP(DLLC, LOGL_NOTICE, "TLLI=%08x recovering "
				     "N(U=%d) after receiving %u duplicates\n",
					lle->llme ? lle->llme->tlli : -1,
					gph->seq_tx, lle->vu_recv_duplicates);
			}
		}
		/* Increment the sequence number that we expect in the next frame */
		lle->vu_recv = (gph->seq_tx + 1) % 512;
		/* Increment Overflow Counter */
		if ((gph->seq_tx + 1) / 512)
			lle->oc_ui_recv += 512;
		break;
	case GPRS_LLC_NULL:
		LOGP(DLLC, LOGL_DEBUG, "TLLI=%08x sends us LLC NULL\n", lle->llme ? lle->llme->tlli : -1);
		break;
	default:
		LOGP(DLLC, LOGL_NOTICE, "Unhandled command: %d\n", gph->cmd);
		break;
	}

	return 0;
}

/* receive an incoming LLC PDU (BSSGP-UL-UNITDATA-IND, 7.2.4.2) */
int gprs_llc_rcvmsg(struct msgb *msg, struct tlv_parsed *tv)
{
	struct gprs_llc_hdr *lh = (struct gprs_llc_hdr *) msgb_llch(msg);
	struct gprs_llc_hdr_parsed llhp;
	struct gprs_llc_lle *lle = NULL;
	bool drop_cipherable = false;
	int rc = 0;

	/* Identifiers from DOWN: NSEI, BVCI, TLLI */

	memset(&llhp, 0, sizeof(llhp));
	rc = gprs_llc_hdr_parse(&llhp, (uint8_t *) lh, TLVP_LEN(tv, BSSGP_IE_LLC_PDU));
	if (rc < 0) {
		LOGP(DLLC, LOGL_NOTICE, "Error during LLC header parsing\n");
		return rc;
	}

	switch (gprs_tlli_type(msgb_tlli(msg))) {
	case TLLI_LOCAL:
	case TLLI_FOREIGN:
	case TLLI_RANDOM:
	case TLLI_AUXILIARY:
		break;
	default:
		LOGP(DLLC, LOGL_ERROR,
			"Discarding frame with strange TLLI type\n");
		break;
	}

	/* find the LLC Entity for this TLLI+SAPI tuple */
	lle = lle_for_rx_by_tlli_sapi(msgb_tlli(msg), llhp.sapi, llhp.cmd);
	if (!lle) {
		switch (llhp.sapi) {
		case GPRS_SAPI_SNDCP3:
		case GPRS_SAPI_SNDCP5:
		case GPRS_SAPI_SNDCP9:
		case GPRS_SAPI_SNDCP11:
			/* Ask an upper layer for help. */
			return gsm0408_gprs_force_reattach_oldmsg(msg, NULL);
		default:
			break;
		}
		return 0;
	}
	gprs_llc_hdr_dump(&llhp, lle);
	/* reset age computation */
	lle->llme->age_timestamp = GPRS_LLME_RESET_AGE;

	/* decrypt information field + FCS, if needed! */
	if (llhp.is_encrypted) {
		if (lle->llme->algo != GPRS_ALGO_GEA0) {
			rc = apply_gea(lle, llhp.data_len + 3, llhp.seq_tx,
				       lle->oc_ui_recv, lle->sapi, NULL,
				       llhp.data);
			if (rc < 0)
				return rc;
		llhp.fcs = *(llhp.data + llhp.data_len);
		llhp.fcs |= *(llhp.data + llhp.data_len + 1) << 8;
		llhp.fcs |= *(llhp.data + llhp.data_len + 2) << 16;
		} else {
			LOGP(DLLC, LOGL_NOTICE, "encrypted frame for LLC that "
				"has no KC/Algo! Dropping.\n");
			return 0;
		}
	} else {
		if (lle->llme->algo != GPRS_ALGO_GEA0 &&
		    lle->llme->cksn != GSM_KEY_SEQ_INVAL)
			drop_cipherable = true;
	}

	/* We have to do the FCS check _after_ decryption */
	llhp.fcs_calc = gprs_llc_fcs((uint8_t *)lh, llhp.crc_length);
	if (llhp.fcs != llhp.fcs_calc) {
		LOGP(DLLC, LOGL_INFO, "Dropping frame with invalid FCS\n");
		return -EIO;
	}

	/* Update LLE's (BVCI, NSEI) tuple */
	lle->llme->bvci = msgb_bvci(msg);
	lle->llme->nsei = msgb_nsei(msg);

	/* Receive and Process the actual LLC frame */
	rc = gprs_llc_hdr_rx(&llhp, lle);
	if (rc < 0)
		return rc;

	/* there are many frame types that don't carry user information
	 * and which hence have llhp.data = NULL */
	if (llhp.data)  {
		/* set l3 layer & remove the fcs */
		msg->l3h = llhp.data;
		msgb_l3trim(msg, llhp.data_len);
	}

	rate_ctr_inc(&sgsn->rate_ctrs->ctr[CTR_LLC_UL_PACKETS]);
	rate_ctr_add(&sgsn->rate_ctrs->ctr[CTR_LLC_UL_BYTES], msg->len);

	/* llhp.data is only set when we need to send LL_[UNIT]DATA_IND up */
	if (llhp.cmd == GPRS_LLC_UI && llhp.data && llhp.data_len) {
		switch (llhp.sapi) {
		case GPRS_SAPI_GMM:
			/* send LL_UNITDATA_IND to GMM */
			rc = gsm0408_gprs_rcvmsg_gb(msg, lle->llme,
						    drop_cipherable);
			break;
		case GPRS_SAPI_SNDCP3:
		case GPRS_SAPI_SNDCP5:
		case GPRS_SAPI_SNDCP9:
		case GPRS_SAPI_SNDCP11:
			/* send LL_DATA_IND/LL_UNITDATA_IND to SNDCP */
			rc = sndcp_llunitdata_ind(msg, lle, llhp.data, llhp.data_len);
			break;
		case GPRS_SAPI_SMS:
			/* FIXME */
		case GPRS_SAPI_TOM2:
		case GPRS_SAPI_TOM8:
			/* FIXME: send LL_DATA_IND/LL_UNITDATA_IND to TOM */
		default:
			LOGP(DLLC, LOGL_NOTICE, "Unsupported SAPI %u\n", llhp.sapi);
			rc = -EINVAL;
			break;
		}
	}

	return rc;
}

/* Propagate crypto parameters MM -> LLME */
void gprs_llme_copy_key(struct sgsn_mm_ctx *mm, struct gprs_llc_llme *llme)
{
	if (!mm)
		return;
	if (mm->ciph_algo != GPRS_ALGO_GEA0) {
		llme->algo = mm->ciph_algo;
		if (llme->cksn != mm->auth_triplet.key_seq &&
		    mm->auth_triplet.key_seq != GSM_KEY_SEQ_INVAL) {
			memcpy(llme->kc, mm->auth_triplet.vec.kc,
			       gprs_cipher_key_length(mm->ciph_algo));
			llme->cksn = mm->auth_triplet.key_seq;
		}
	} else
		llme->cksn = GSM_KEY_SEQ_INVAL;
}

/* 04.64 Chapter 7.2.1.1 LLGMM-ASSIGN */
int gprs_llgmm_assign(struct gprs_llc_llme *llme,
		      uint32_t old_tlli, uint32_t new_tlli)
{
	unsigned int i;

	if (old_tlli == TLLI_UNASSIGNED && new_tlli != TLLI_UNASSIGNED) {
		/* TLLI Assignment 8.3.1 */
		/* New TLLI shall be assigned and used when (re)transmitting LLC frames */
		/* If old TLLI != TLLI_UNASSIGNED was assigned to LLME, then TLLI
		 * old is unassigned.  Only TLLI new shall be accepted when
		 * received from peer. */
		if (llme->old_tlli != TLLI_UNASSIGNED) {
			llme->old_tlli = TLLI_UNASSIGNED;
			llme->tlli = new_tlli;
		} else {
			/* If TLLI old == TLLI_UNASSIGNED was assigned to LLME, then this is
			 * TLLI assignmemt according to 8.3.1 */
			llme->old_tlli = TLLI_UNASSIGNED;
			llme->tlli = new_tlli;
			llme->state = GPRS_LLMS_ASSIGNED;
			/* 8.5.3.1 For all LLE's */
			for (i = 0; i < ARRAY_SIZE(llme->lle); i++) {
				struct gprs_llc_lle *l = &llme->lle[i];
				l->vu_send = l->vu_recv = 0;
				l->retrans_ctr = 0;
				l->state = GPRS_LLES_ASSIGNED_ADM;
				/* FIXME Set parameters according to table 9 */
			}
		}
	} else if (old_tlli != TLLI_UNASSIGNED && new_tlli != TLLI_UNASSIGNED) {
		/* TLLI Change 8.3.2 */
		/* Both TLLI Old and TLLI New are assigned; use New when
		 * (re)transmitting.  Accept both Old and New on Rx */
		llme->old_tlli = old_tlli;
		llme->tlli = new_tlli;
		llme->state = GPRS_LLMS_ASSIGNED;
	} else if (old_tlli != TLLI_UNASSIGNED && new_tlli == TLLI_UNASSIGNED) {
		/* TLLI Unassignment 8.3.3) */
		llme->tlli = llme->old_tlli = 0;
		llme->state = GPRS_LLMS_UNASSIGNED;
		for (i = 0; i < ARRAY_SIZE(llme->lle); i++) {
			struct gprs_llc_lle *l = &llme->lle[i];
			l->state = GPRS_LLES_UNASSIGNED;
		}
		llme_free(llme);
	} else
		return -EINVAL;

	return 0;
}

/* TLLI unassignment */
int gprs_llgmm_unassign(struct gprs_llc_llme *llme)
{
	return gprs_llgmm_assign(llme, llme->tlli, TLLI_UNASSIGNED);
}

/* Chapter 7.2.1.2 LLGMM-RESET.req */
int gprs_llgmm_reset(struct gprs_llc_llme *llme)
{
	struct msgb *msg = msgb_alloc_headroom(4096, 1024, "LLC_XID");
	struct gprs_llc_lle *lle = &llme->lle[1];
	uint8_t xid_bytes[1024];
	int xid_bytes_len, rc;
	uint8_t *xid;

	LOGP(DLLC, LOGL_NOTICE, "LLGM Reset\n");

	rc = osmo_get_rand_id((uint8_t *) &llme->iov_ui, 4);
	if (rc < 0) {
		LOGP(DLLC, LOGL_ERROR, "osmo_get_rand_id() failed for LLC XID reset: %s\n", strerror(-rc));
		return rc;
	}

	/* Generate XID message */
	xid_bytes_len = gprs_llc_generate_xid_for_gmm_reset(xid_bytes, sizeof(xid_bytes),
							    llme->iov_ui, lle);
	if (xid_bytes_len < 0)
		return -EINVAL;
	xid = msgb_put(msg, xid_bytes_len);
	memcpy(xid, xid_bytes, xid_bytes_len);

	/* Reset some of the LLC parameters. See GSM 04.64, 8.5.3.1 */
	lle->vu_recv = 0;
	lle->vu_send = 0;
	lle->oc_ui_send = 0;
	lle->oc_ui_recv = 0;

	/* FIXME: Start T200, wait for XID response */
	return gprs_llc_tx_xid(lle, msg, 1);
}

int gprs_llgmm_reset_oldmsg(struct msgb* oldmsg, uint8_t sapi,
			    struct gprs_llc_llme *llme)
{
	struct msgb *msg = msgb_alloc_headroom(4096, 1024, "LLC_XID");
	struct gprs_llc_lle *lle = &llme->lle[sapi];
	uint8_t xid_bytes[1024];
	int xid_bytes_len, rc;
	uint8_t *xid;

	LOGP(DLLC, LOGL_NOTICE, "LLGM Reset\n");

	rc = osmo_get_rand_id((uint8_t *) &llme->iov_ui, 4);
	if (rc < 0) {
		LOGP(DLLC, LOGL_ERROR, "osmo_get_rand_id() failed for LLC XID reset: %s\n", strerror(-rc));
		return rc;
	}

	/* Generate XID message */
	xid_bytes_len = gprs_llc_generate_xid_for_gmm_reset(xid_bytes, sizeof(xid_bytes),
							    llme->iov_ui, lle);
	if (xid_bytes_len < 0)
		return -EINVAL;
	xid = msgb_put(msg, xid_bytes_len);
	memcpy(xid, xid_bytes, xid_bytes_len);

	/* FIXME: Start T200, wait for XID response */

	msgb_tlli(msg) = msgb_tlli(oldmsg);
	msgb_bvci(msg) = msgb_bvci(oldmsg);
	msgb_nsei(msg) = msgb_nsei(oldmsg);

	return gprs_llc_tx_u(msg, sapi, 1, GPRS_LLC_U_XID, 1);
}

int gprs_llc_init(const char *cipher_plugin_path)
{
	return gprs_cipher_load(cipher_plugin_path);
}