nat: Parse the id response, extract the IMSI, compare it
Add a test case and also add a basic check that we got some
size checks correct. The next step is to act on the result.
diff --git a/openbsc/src/nat/bsc_nat_utils.c b/openbsc/src/nat/bsc_nat_utils.c
index 7387b51..a591737 100644
--- a/openbsc/src/nat/bsc_nat_utils.c
+++ b/openbsc/src/nat/bsc_nat_utils.c
@@ -369,6 +369,35 @@
return auth_imsi(bsc, mi_string);
}
+static int _dt_check_id_resp(struct bsc_connection *bsc,
+ uint8_t *data, unsigned int length,
+ struct sccp_connections *con)
+{
+ char mi_string[GSM48_MI_SIZE];
+ uint8_t mi_type;
+ int ret;
+
+ if (length < 2) {
+ LOGP(DNAT, LOGL_ERROR, "mi does not fit.\n");
+ return -1;
+ }
+
+ if (data[0] < length - 1) {
+ LOGP(DNAT, LOGL_ERROR, "mi length too big.\n");
+ return -2;
+ }
+
+ mi_type = data[1] & GSM_MI_TYPE_MASK;
+ gsm48_mi_to_string(mi_string, sizeof(mi_string), &data[1], data[0]);
+
+ if (mi_type != GSM_MI_TYPE_IMSI)
+ return 0;
+
+ ret = auth_imsi(bsc, mi_string);
+ con->imsi_checked = 1;
+ return ret;
+}
+
/* Filter out CR data... */
int bsc_nat_filter_sccp_cr(struct bsc_connection *bsc, struct msgb *msg, struct bsc_nat_parsed *parsed, int *con_type)
{
@@ -434,10 +463,38 @@
int bsc_nat_filter_dt(struct bsc_connection *bsc, struct msgb *msg,
struct sccp_connections *con, struct bsc_nat_parsed *parsed)
{
+ uint32_t len;
+ struct gsm48_hdr *hdr48;
+
if (con->imsi_checked)
return 0;
- return 0;
+ /* only care about DTAP messages */
+ if (parsed->bssap != BSSAP_MSG_DTAP)
+ return 0;
+
+ /* gsm_type is actually the size of the dtap */
+ len = parsed->gsm_type;
+ if (len < msgb_l3len(msg) - 3) {
+ LOGP(DNAT, LOGL_ERROR, "Not enough space for DTAP.\n");
+ return -1;
+ }
+
+ if (len < sizeof(*hdr48)) {
+ LOGP(DNAT, LOGL_ERROR, "GSM48 header does not fit.\n");
+ return -1;
+ }
+
+ msg->l4h = &msg->l3h[3];
+ hdr48 = (struct gsm48_hdr *) msg->l4h;
+
+ if (hdr48->proto_discr == GSM48_PDISC_MM &&
+ (hdr48->msg_type & 0xbf) == GSM48_MT_MM_ID_RESP) {
+ return _dt_check_id_resp(bsc, &hdr48->data[0], len - sizeof(*hdr48), con);
+ } else {
+ printf("%d %x\n", hdr48->proto_discr, hdr48->msg_type);
+ return 0;
+ }
}
void bsc_parse_reg(void *ctx, regex_t *reg, char **imsi, int argc, const char **argv)