sgsn_rim: forward message based on RIM ROUTING ADDRESS

At the moment we parse the RAN TRANSPARENT CONTAINER to look at the
destination RIM ROUTING INFORMATION. This is not correct. The SGSN
should not decode the RAN TRANSPARENT CONTAINER and use the RIM ROUTING
ADDRESS / RIM ROUTING ADDRESS DISCRIMINATOR IE to make the routing
decision.

Related: OS#6095
Depends: libosmocore.git Ibca1f08906c4ffeecdae80d4e91c6c7b05fe4f8a
Change-Id: Ifd2b915ed2f05130cff8ee77714b82005c17de3d
---
M include/osmocom/sgsn/sgsn_rim.h
M src/sgsn/sgsn_libgtp.c
M src/sgsn/sgsn_rim.c
3 files changed, 83 insertions(+), 14 deletions(-)

diff --git a/include/osmocom/sgsn/sgsn_rim.h b/include/osmocom/sgsn/sgsn_rim.h
index f43b09a..fc87b46 100644
--- a/include/osmocom/sgsn/sgsn_rim.h
+++ b/include/osmocom/sgsn/sgsn_rim.h
@@ -3,4 +3,4 @@
 struct sgsn_mme_ctx;
 
 int sgsn_rim_rx_from_gb(struct osmo_bssgp_prim *bp, struct msgb *msg);
-int sgsn_rim_rx_from_gtp(struct bssgp_ran_information_pdu *pdu);
+int sgsn_rim_rx_from_gtp(struct msgb *msg, struct bssgp_rim_routing_info *rim_routing_address);
diff --git a/src/sgsn/sgsn_libgtp.c b/src/sgsn/sgsn_libgtp.c
index 156f730..0b6da62 100644
--- a/src/sgsn/sgsn_libgtp.c
+++ b/src/sgsn/sgsn_libgtp.c
@@ -695,9 +695,46 @@
 
 	LOGMME(mme, DGTP, LOGL_INFO, "Rx GTP RAN Information Relay\n");
 
+	int rc;
 	unsigned int len = 0;
-	struct msgb *msg = msgb_alloc(4096, "gtpcv1_ran_info");
-	struct bssgp_ran_information_pdu pdu;
+	struct msgb *msg = bssgp_msgb_alloc();
+
+	uint8_t rim_ra_encoded[256];
+	unsigned int rim_ra_encoded_len = 0;
+	struct bssgp_rim_routing_info rim_ra;
+
+	unsigned int rim_ra_discr_encoded_len = 0;
+	uint8_t rim_ra_discr;
+
+	/* Read RIM Routing Address Discriminator (optional) */
+	rc = gtpie_gettlv(ie, GTPIE_RIM_RA_DISCR, 0, &rim_ra_discr_encoded_len, &rim_ra_discr,
+			  sizeof(rim_ra_discr));
+	if (rc || rim_ra_discr_encoded_len <= 0) {
+		LOGMME(mme, DGTP, LOGL_NOTICE, "Rx GTP RAN Information Relay: No RIM Routing Address Discriminator IE found!\n");
+
+		/* It is not an error when the RIM ROUTING ADDRESS DISCRIMINATOR IE is missing. The RIM ROUTING ADDRESS
+		 * DISCRIMINATOR IE is an optional IE. When it is missing, the RIM Routing Address shall be processed
+		 * as an RNC address ("0001")  See also: 3GPP TS 29.060 */
+		rim_ra_discr = BSSGP_RIM_ROUTING_INFO_UTRAN;
+	}
+
+	/* Read RIM Routing Address (optional) */
+	rc = gtpie_gettlv(ie, GTPIE_RIM_ROUT_ADDR, 0, &rim_ra_encoded_len, rim_ra_encoded, sizeof(rim_ra_encoded));
+	if (rc || rim_ra_encoded_len <= 0) {
+		LOGMME(mme, DGTP, LOGL_ERROR, "Rx GTP RAN Information Relay: No RIM Routing Address IE found!\n");
+
+		/* TODO: The (usually included) RIM ROUTING ADDRESS field is an optional field. However, we cannot
+		 * proceed without a destination address. A possible way to fix this would be a default route that
+		 * can be configured via the VTY. */
+		goto ret_error;
+	} else {
+		rc = bssgp_parse_rim_ra(&rim_ra, rim_ra_encoded, rim_ra_encoded_len, rim_ra_discr);
+		if (rc < 0) {
+			LOGMME(mme, DGTP, LOGL_ERROR,
+			       "Rx GTP RAN Information Relay: Failed parsing RIM Routing Address/RIM Routing Address Discriminator IE!\n");
+			goto ret_error;
+		}
+	}
 
 	if (gtpie_gettlv(ie, GTPIE_RAN_T_CONTAIN, 0, &len, msgb_data(msg), 4096) || len <= 0) {
 		LOGMME(mme, DGTP, LOGL_ERROR, "Rx GTP RAN Information Relay: No Transparent Container IE found!\n");
@@ -706,13 +743,8 @@
 	msgb_put(msg, len);
 	msgb_bssgph(msg) = msg->data;
 	msgb_nsei(msg) = 0;
-	if (bssgp_parse_rim_pdu(&pdu, msg) < 0) {
-		LOGMME(mme, DGTP, LOGL_ERROR, "Rx GTP RAN Information Relay: Failed parsing Transparent Container IE!\n");
-		goto ret_error;
-	}
 
-	msgb_free(msg);
-	return sgsn_rim_rx_from_gtp(&pdu);
+	return sgsn_rim_rx_from_gtp(msg, &rim_ra);
 
 ret_error:
 	msgb_free(msg);
diff --git a/src/sgsn/sgsn_rim.c b/src/sgsn/sgsn_rim.c
index c6f8dcd..40e1f90 100644
--- a/src/sgsn/sgsn_rim.c
+++ b/src/sgsn/sgsn_rim.c
@@ -33,6 +33,23 @@
 	return bssgp_tx_rim(pdu, bvc_ctx->nsei);
 }
 
+static int sgsn_bssgp_fwd_rim_to_geran_encoded(struct msgb *msg, struct bssgp_rim_routing_info *rim_routing_address)
+{
+	struct bssgp_bvc_ctx *bvc_ctx;
+	OSMO_ASSERT(rim_routing_address->discr == BSSGP_RIM_ROUTING_INFO_GERAN);
+
+	/* Resolve RIM ROUTING ADDRESS to a BVC context */
+	bvc_ctx = btsctx_by_raid_cid(&rim_routing_address->geran.raid, rim_routing_address->geran.cid);
+	if (!bvc_ctx) {
+		LOGP(DRIM, LOGL_ERROR, "Unable to find NSEI for destination cell %s\n",
+		       bssgp_rim_ri_name(rim_routing_address));
+		return -EINVAL;
+	}
+
+	/* Forward PDU to the NSEI of the resolved BVC context */
+	return bssgp_tx_rim_encoded(msg, bvc_ctx->nsei);
+}
+
 static int sgsn_bssgp_fwd_rim_to_eutran(const struct bssgp_ran_information_pdu *pdu)
 {
 	struct sgsn_mme_ctx *mme;
@@ -91,17 +108,20 @@
 }
 
 /* Receive a RIM PDU from GTPv1C (EUTRAN) */
-int sgsn_rim_rx_from_gtp(struct bssgp_ran_information_pdu *pdu)
+int sgsn_rim_rx_from_gtp(struct msgb *msg, struct bssgp_rim_routing_info *rim_routing_address)
 {
-	if (pdu->routing_info_dest.discr != BSSGP_RIM_ROUTING_INFO_GERAN) {
+	/* TODO: In this code path, we currently only support RIM message forwarding to GERAN (BSSGP). However, it
+	 * technically also be possible to route a message back to GTP (BSSGP_RIM_ROUTING_INFO_EUTRAN) or to
+	 * IuPS (BSSGP_RIM_ROUTING_INFO_UTRAN) */
+	if (rim_routing_address->discr != BSSGP_RIM_ROUTING_INFO_GERAN) {
 		LOGP(DRIM, LOGL_ERROR, "Rx GTP RAN Information Relay: Expected dst %s, got %s\n",
 		     bssgp_rim_routing_info_discr_str(BSSGP_RIM_ROUTING_INFO_GERAN),
-		     bssgp_rim_routing_info_discr_str(pdu->routing_info_dest.discr));
+		     bssgp_rim_routing_info_discr_str(rim_routing_address->discr));
 		return -EINVAL;
 	}
 
 	LOGP(DRIM, LOGL_INFO, "Rx GTP RAN Information Relay for dest cell %s\n",
-	     bssgp_rim_ri_name(&pdu->routing_info_dest));
+	     bssgp_rim_ri_name(rim_routing_address));
 
-	return sgsn_bssgp_fwd_rim_to_geran(pdu);
+	return sgsn_bssgp_fwd_rim_to_geran_encoded(msg, rim_routing_address);
 }

