[nat] Intercept the PAGING message and then forward it to the BSCs with that LAC

* Provide access to the GSM0808 TLV attributes so we can use it in
  the nat code.
* Read the PAGING message, if it is paged by LAC we go through each
  LAC and then attempt to find the proper BSC connection and then
  send the message to that BSC.

1 files changed, 41 insertions, 1 deletions

diff --git a/openbsc/src/nat/bsc_nat.c b/openbsc/src/nat/bsc_nat.c
index 588a9e247..e4db47f0b 100644
--- a/openbsc/src/nat/bsc_nat.c
+++ b/openbsc/src/nat/bsc_nat.c
@@ -270,7 +270,7 @@ static void initialize_msc_if_needed()
 
 static int forward_sccp_to_bts(struct msgb *msg)
 {
-	struct bsc_connection *bsc;
+	struct bsc_connection *bsc = NULL;
 	struct bsc_nat_parsed *parsed;
 	int rc;
 
@@ -316,6 +316,46 @@ static int forward_sccp_to_bts(struct msgb *msg)
 	return write(bsc->bsc_fd.fd, msg->data, msg->len);
 
 send_to_all:
+	/*
+	 * Filter Paging from the network. We do not want to send a PAGING
+	 * Command to every BSC in our network. We will analys the PAGING
+	 * message and then send it to the authenticated messages...
+	 */
+	if (parsed->ipa_proto == IPAC_PROTO_SCCP && parsed->gsm_type == BSS_MAP_MSG_PAGING) {
+		int data_length;
+		const u_int8_t *data;
+		struct tlv_parsed tp;
+		int i = 0;
+
+		tlv_parse(&tp, gsm0808_att_tlvdef(), msg->l3h + 3, msgb_l3len(msg) - 3, 0, 0);
+		if (!TLVP_PRESENT(&tp, GSM0808_IE_CELL_IDENTIFIER_LIST)) {
+			LOGP(DNAT, LOGL_ERROR, "No CellIdentifier List inside paging msg.\n");
+			goto exit;
+		}
+
+		data_length = TLVP_LEN(&tp, GSM0808_IE_CELL_IDENTIFIER_LIST);
+		data = TLVP_VAL(&tp, GSM0808_IE_CELL_IDENTIFIER_LIST);
+		if (data[0] !=  CELL_IDENT_LAC) {
+			LOGP(DNAT, LOGL_ERROR, "Unhandled cell ident discrminator: %c\n", data[0]);
+			goto exit;
+		}
+
+		/* go through each LAC and forward the message */
+		for (i = 1; i < data_length - 1; i += 2) {
+			unsigned int _lac = ntohs(*(unsigned int *) &data[i]);
+			llist_for_each_entry(bsc, &nat->bsc_connections, list_entry) {
+				if (!bsc->authenticated || _lac != bsc->lac)
+					continue;
+
+				rc = write(bsc->bsc_fd.fd, msg->data, msg->len);
+				if (rc < msg->len)
+					LOGP(DNAT, LOGL_ERROR,
+					     "Failed to write message to BTS: %d\n", rc);
+			}
+		}
+
+		goto exit;
+	}
 	/* currently send this to every BSC connected */
 	llist_for_each_entry(bsc, &nat->bsc_connections, list_entry) {
 		if (!bsc->authenticated)