ipa: Patch DPC/OPC information into SCCP Calling/Called Party Address

When we receive a SCCPlite message from an IPA peer, it may simply
contain a SSN number but no point codes.  Similarly to creating a fake
MTP routing label from override DPC and routing key OPC, we can also
add that point code information to the SCCP header.  This way the rest
of the SS7 network can handle the message and route it accordingly.

Change-Id: I4a2ff063e3c060641b3fd181a1cd600da3ec568b

1 files changed, 92 insertions, 15 deletions

diff --git a/src/ipa.c b/src/ipa.c
index 36fbd38..2671896 100644
--- a/src/ipa.c
+++ b/src/ipa.c
@@ -38,8 +38,10 @@
 #include <osmocom/sigtran/xua_msg.h>
 
 #include <osmocom/sigtran/mtp_sap.h>
+#include <osmocom/sigtran/sccp_sap.h>
 #include <osmocom/sigtran/osmo_ss7.h>
 #include <osmocom/sigtran/protocol/m3ua.h>
+#include <osmocom/sigtran/protocol/sua.h>
 #include <osmocom/sigtran/protocol/mtp.h>
 
 #include "xua_internal.h"
@@ -134,11 +136,74 @@ static struct osmo_ss7_as *find_as_for_asp(struct osmo_ss7_asp *asp)
 	return NULL;
 }
 
+/* Patch a SCCP message and add point codes to Called/Calling Party (if missing) */
+static struct msgb *patch_sccp_with_pc(struct osmo_ss7_asp *asp, struct msgb *sccp_msg_in,
+					uint32_t opc, uint32_t dpc)
+{
+	struct osmo_sccp_addr addr;
+	struct msgb *sccp_msg_out;
+	struct xua_msg *sua;
+	int rc;
+
+	/* start by converting SCCP to SUA */
+	sua = osmo_sccp_to_xua(sccp_msg_in);
+	if (!sua) {
+		LOGPASP(asp, DLSS7, LOGL_ERROR, "Couldn't convert SCCP to SUA: %s\n",
+			msgb_hexdump(sccp_msg_in));
+		msgb_free(sccp_msg_in);
+		return NULL;
+	}
+	/* free the input message and work with SUA version instead */
+	msgb_free(sccp_msg_in);
+
+	rc = sua_addr_parse(&addr, sua, SUA_IEI_DEST_ADDR);
+	switch (rc) {
+	case 0:
+		if (addr.presence & OSMO_SCCP_ADDR_T_PC)
+			break;
+		/* if there's no point code in dest_addr, add one */
+		addr.presence |= OSMO_SCCP_ADDR_T_PC;
+		addr.pc = dpc;
+		xua_msg_free_tag(sua, SUA_IEI_DEST_ADDR);
+		xua_msg_add_sccp_addr(sua, SUA_IEI_DEST_ADDR, &addr);
+		break;
+	case -ENODEV: /* no destination address in message */
+		break;
+	default: /* some other error */
+		xua_msg_free(sua);
+		return NULL;
+	}
+
+	rc = sua_addr_parse(&addr, sua, SUA_IEI_SRC_ADDR);
+	switch (rc) {
+	case 0:
+		if (addr.presence & OSMO_SCCP_ADDR_T_PC)
+			break;
+		/* if there's no point code in src_addr, add one */
+		addr.presence |= OSMO_SCCP_ADDR_T_PC;
+		addr.pc = opc;
+		xua_msg_free_tag(sua, SUA_IEI_SRC_ADDR);
+		xua_msg_add_sccp_addr(sua, SUA_IEI_SRC_ADDR, &addr);
+		break;
+	case -ENODEV: /* no source address in message */
+		break;
+	default: /* some other error */
+		xua_msg_free(sua);
+		return NULL;
+	}
+
+	/* re-encode SUA to SCCP and return */
+	sccp_msg_out = osmo_sua_to_sccp(sua);
+	xua_msg_free(sua);
+	return sccp_msg_out;
+}
+
 static int ipa_rx_msg_sccp(struct osmo_ss7_asp *asp, struct msgb *msg)
 {
 	struct m3ua_data_hdr data_hdr;
 	struct xua_msg *xua = xua_msg_alloc();
 	struct osmo_ss7_as *as = find_as_for_asp(asp);
+	uint32_t opc, dpc;
 
 	if (!as) {
 		LOGPASP(asp, DLSS7, LOGL_ERROR, "Rx message for IPA ASP without AS?!\n");
@@ -150,13 +215,15 @@ static int ipa_rx_msg_sccp(struct osmo_ss7_asp *asp, struct msgb *msg)
 	msgb_pull_to_l2(msg);
 
 	/* We have received an IPA-encapsulated SCCP message, without
-	 * any MTP routing label.  This means we have no real idea where
-	 * it came from, nor where it goes to.  We could simply treat it
-	 * as being for the local point code, but then this means that
-	 * we would have to implement SCCP connection coupling in order
-	 * to route the connections to any other point code.  The reason
-	 * for this is the lack of addressing information inside the
-	 * non-CR/CC connection oriented messages.
+	 * any MTP routing label.  Furthermore, the SCCP Called/Calling
+	 * Party are SSN-only, with no GT or PC.  This means we have no
+	 * real idea where it came from, nor where it goes to.  We could
+	 * simply treat it as being for the local point code, but then
+	 * this means that we would have to implement SCCP connection
+	 * coupling in order to route the connections to any other point
+	 * code.  The reason for this is the lack of addressing
+	 * information inside the non-CR/CC connection oriented
+	 * messages.
 	 *
 	 * The only other alternative we have is to simply have a
 	 * STP (server) side configuration that specifies which point
@@ -166,23 +233,33 @@ static int ipa_rx_msg_sccp(struct osmo_ss7_asp *asp, struct msgb *msg)
 	 * to us.  This is all quite ugly, but then what can we do :/
 	 */
 
-	memset(&data_hdr, 0, sizeof(data_hdr));
-	data_hdr.si = MTP_SI_SCCP;
+	/* First, determine the DPC and OPC to use */
 	if (asp->cfg.is_server) {
 		/* Source: the PC of the routing key */
-		data_hdr.opc = osmo_htonl(as->cfg.routing_key.pc);
+		opc = as->cfg.routing_key.pc;
 		/* Destination: Based on VTY config */
-		data_hdr.dpc = osmo_htonl(as->cfg.pc_override.dpc);
+		dpc = as->cfg.pc_override.dpc;
 	} else {
 		/* Source: Based on VTY config */
-		data_hdr.opc = osmo_htonl(as->cfg.pc_override.dpc);
+		opc = as->cfg.pc_override.dpc;
 		/* Destination: PC of the routing key */
-		data_hdr.dpc = osmo_htonl(as->cfg.routing_key.pc);
+		dpc = as->cfg.routing_key.pc;
 	}
+
+	/* Second, patch this into the SCCP message */
+	msg = patch_sccp_with_pc(asp, msg, opc, dpc);
+
+	/* Third, create a MTP3/M3UA label with those point codes */
+	memset(&data_hdr, 0, sizeof(data_hdr));
+	data_hdr.si = MTP_SI_SCCP;
+	data_hdr.opc = osmo_htonl(opc);
+	data_hdr.dpc = osmo_htonl(dpc);
+	/* Create M3UA message in XUA structure */
 	xua = m3ua_xfer_from_data(&data_hdr, msgb_l2(msg), msgb_l2len(msg));
-	xua->mtp.opc = osmo_ntohl(data_hdr.opc);
-	xua->mtp.dpc = osmo_ntohl(data_hdr.dpc);
+	/* Update xua->mtp with values from data_hdr */
+	m3ua_dh_to_xfer_param(&xua->mtp, &data_hdr);
 
+	/* Pass on as if we had received it from an M3UA ASP */
 	return m3ua_hmdc_rx_from_l2(asp->inst, xua);
 }