nat: Implement the matching of certain USSD messages
Have various checks, check if the IMSI should be handled,
if there is a USSD query set and then decode and compare
the value.
diff --git a/openbsc/src/nat/bsc_ussd.c b/openbsc/src/nat/bsc_ussd.c
index 1812cf7..c4e30d8 100644
--- a/openbsc/src/nat/bsc_ussd.c
+++ b/openbsc/src/nat/bsc_ussd.c
@@ -24,9 +24,71 @@
#include <openbsc/bsc_nat.h>
#include <openbsc/bsc_nat_sccp.h>
+#include <osmocore/protocol/gsm_08_08.h>
+
+#include <osmocore/gsm0480.h>
+
+#include <string.h>
+
int bsc_check_ussd(struct sccp_connections *con, struct bsc_nat_parsed *parsed,
struct msgb *msg)
{
- return 0;
+ uint32_t len;
+ uint8_t msg_type;
+ struct gsm48_hdr *hdr48;
+ struct bsc_nat_acc_lst *lst;
+ struct ussd_request req;
+
+ /*
+ * various checks to avoid the decoding work. Right now we only want to
+ * decode if the connection was created for USSD, we do have a USSD access
+ * list, a query, a IMSI and such...
+ */
+ if (con->con_type != NAT_CON_TYPE_SSA)
+ return 0;
+
+ if (!con->imsi)
+ return 0;
+
+ if (!con->bsc->nat->ussd_lst_name)
+ return 0;
+ if (!con->bsc->nat->ussd_query)
+ return 0;
+
+ if (parsed->bssap != BSSAP_MSG_DTAP)
+ return 0;
+
+ if (strlen(con->imsi) > GSM_IMSI_LENGTH)
+ return 0;
+
+ hdr48 = bsc_unpack_dtap(parsed, msg, &len);
+ if (!hdr48)
+ return 0;
+
+ msg_type = hdr48->msg_type & 0xbf;
+ if (hdr48->proto_discr != GSM48_PDISC_NC_SS || msg_type != GSM0480_MTYPE_REGISTER)
+ return 0;
+
+ /* now check if it is a IMSI we care about */
+ lst = bsc_nat_acc_lst_find(con->bsc->nat, con->bsc->nat->ussd_lst_name);
+ if (!lst)
+ return 0;
+
+ if (bsc_nat_lst_check_allow(lst, con->imsi) != 0)
+ return 0;
+
+ /* now decode the message and see if we really want to handle it */
+ memset(&req, 0, sizeof(req));
+ if (gsm0480_decode_ussd_request(hdr48, len, &req) != 1)
+ return 0;
+ if (req.text[0] == 0xff)
+ return 0;
+
+ if (strcmp(req.text, con->bsc->nat->ussd_query) != 0)
+ return 0;
+
+ /* found a USSD query for our subscriber */
+ LOGP(DNAT, LOGL_NOTICE, "Found USSD query for %s\n", con->imsi);
+ return 1;
}