From ef38e85542a92b125548c9f7913c6ca25b2fd980 Mon Sep 17 00:00:00 2001
From: Holger Hans Peter Freyther <zecke@selfish.org>
Date: Wed, 6 Apr 2011 11:27:52 +0200
Subject: [PATCH] nat: Remember if the MSC accepted the connection on principle

For the USSD module we only want to handle requests that are
legitimate. This is achieved by looking for the CM Service Accept
or the BSSAP CIPHER MODE COMMAND.
---
 openbsc/include/openbsc/bsc_nat_sccp.h |  1 +
 openbsc/src/osmo-bsc_nat/bsc_nat.c     | 32 ++++++++++++++++++++++++++
 openbsc/src/osmo-bsc_nat/bsc_ussd.c    |  4 ++++
 3 files changed, 37 insertions(+)

diff --git a/openbsc/include/openbsc/bsc_nat_sccp.h b/openbsc/include/openbsc/bsc_nat_sccp.h
index 0ade668c4..4ae640e7f 100644
--- a/openbsc/include/openbsc/bsc_nat_sccp.h
+++ b/openbsc/include/openbsc/bsc_nat_sccp.h
@@ -77,6 +77,7 @@ struct sccp_connections {
 	/* status */
 	int con_type;
 	int con_local;
+	int authorized;
 	int imsi_checked;
 	char *imsi;
 
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat.c b/openbsc/src/osmo-bsc_nat/bsc_nat.c
index 2075ab683..2b62ea691 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat.c
@@ -525,6 +525,36 @@ send_refuse:
 	bsc_write(bsc, refuse, IPAC_PROTO_SCCP);
 }
 
+/*
+ * Update the auth status. This can be either a CIPHER MODE COMAMND or
+ * a CM Serivce Accept. Maybe also LU Accept or such in the future.
+ */
+static void update_con_authorize(struct sccp_connections *con,
+				 struct bsc_nat_parsed *parsed,
+				 struct msgb *msg)
+{
+	if (!con)
+		return;
+	if (con->authorized)
+		return;
+
+	if (parsed->bssap == BSSAP_MSG_BSS_MANAGEMENT &&
+	    parsed->gsm_type == BSS_MAP_MSG_CIPHER_MODE_CMD) {
+		con->authorized = 1;
+	} else if (parsed->bssap == BSSAP_MSG_DTAP) {
+		uint8_t msg_type;
+		uint32_t len;
+		struct gsm48_hdr *hdr48;
+		hdr48 = bsc_unpack_dtap(parsed, msg, &len);
+		if (!hdr48)
+			return;
+
+		msg_type = hdr48->msg_type & 0xbf;
+		if (hdr48->proto_discr == GSM48_PDISC_MM &&
+		    msg_type == GSM48_MT_MM_CM_SERV_ACC)
+			con->authorized = 1;
+	}
+}
 
 static int forward_sccp_to_bts(struct bsc_msc_connection *msc_con, struct msgb *msg)
 {
@@ -601,6 +631,8 @@ static int forward_sccp_to_bts(struct bsc_msc_connection *msc_con, struct msgb *
 		return -1;
 	}
 
+	update_con_authorize(con, parsed, msg);
+
 	bsc_send_data(con->bsc, msg->l2h, msgb_l2len(msg), proto);
 	return 0;
 
diff --git a/openbsc/src/osmo-bsc_nat/bsc_ussd.c b/openbsc/src/osmo-bsc_nat/bsc_ussd.c
index 50c50ed1f..ff1d27a0b 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_ussd.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_ussd.c
@@ -318,6 +318,10 @@ int bsc_check_ussd(struct sccp_connections *con, struct bsc_nat_parsed *parsed,
 	if (!con->imsi)
 		return 0;
 
+	/* We have not verified the IMSI yet */
+	if (!con->authorized)
+		return 0;
+
 	if (!con->bsc->nat->ussd_lst_name)
 		return 0;
 	if (!con->bsc->nat->ussd_query)