gprs: Let GSUP parser functions return GMM causes on errors

Currently the GSUP message handling function in gprs_subscriber.c and
the functions in gprs_gsup_messages.c are not consistent with respect
to the return codes if an error happens. Albeit all error return
codes are negative, the semantics of the absolute value are not
clearly defined. In addition, some return codes are not passed to the
calling function.

This path changes these functions to always return a negated GMM
cause value in case of errors. Return values of called parser
functions are not longer ignored.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/gprs/gprs_gsup_messages.c b/openbsc/src/gprs/gprs_gsup_messages.c
index f47ad55..1dad74f 100644
--- a/openbsc/src/gprs/gprs_gsup_messages.c
+++ b/openbsc/src/gprs/gprs_gsup_messages.c
@@ -74,7 +74,7 @@
 
 		rc = gprs_shift_tlv(&data, &data_len, &tag, &value, &value_len);
 		if (rc < 0)
-			return rc;
+			return -GMM_CAUSE_PROTO_ERR_UNSPEC;
 
 		iei = tag;
 
@@ -116,7 +116,7 @@
 	while (data_len > 0) {
 		rc = gprs_shift_tlv(&data, &data_len, &tag, &value, &value_len);
 		if (rc < 0)
-			return rc;
+			return -GMM_CAUSE_PROTO_ERR_UNSPEC;
 
 		iei = tag;
 
diff --git a/openbsc/src/gprs/gprs_subscriber.c b/openbsc/src/gprs/gprs_subscriber.c
index fd16fa3..136ac28 100644
--- a/openbsc/src/gprs/gprs_subscriber.c
+++ b/openbsc/src/gprs/gprs_subscriber.c
@@ -339,7 +339,8 @@
 	rc = gprs_gsup_decode(data, data_len, &gsup_msg);
 	if (rc < 0) {
 		LOGP(DGPRS, LOGL_ERROR,
-		     "decoding GSUP message fails with error code %d\n", -rc);
+		     "decoding GSUP message fails with error '%s' (%d)\n",
+		     get_value_string(gsm48_gmm_cause_names, -rc), -rc);
 		return rc;
 	}
 
@@ -369,19 +370,19 @@
 		break;
 
 	case GPRS_GSUP_MSGT_SEND_AUTH_INFO_RESULT:
-		gprs_subscr_handle_gsup_auth_res(subscr, &gsup_msg);
+		rc = gprs_subscr_handle_gsup_auth_res(subscr, &gsup_msg);
 		break;
 
 	case GPRS_GSUP_MSGT_SEND_AUTH_INFO_ERROR:
-		gprs_subscr_handle_gsup_auth_err(subscr, &gsup_msg);
+		rc = gprs_subscr_handle_gsup_auth_err(subscr, &gsup_msg);
 		break;
 
 	case GPRS_GSUP_MSGT_UPDATE_LOCATION_RESULT:
-		gprs_subscr_handle_gsup_upd_loc_res(subscr, &gsup_msg);
+		rc = gprs_subscr_handle_gsup_upd_loc_res(subscr, &gsup_msg);
 		break;
 
 	case GPRS_GSUP_MSGT_UPDATE_LOCATION_ERROR:
-		gprs_subscr_handle_gsup_upd_loc_err(subscr, &gsup_msg);
+		rc = gprs_subscr_handle_gsup_upd_loc_err(subscr, &gsup_msg);
 		break;
 
 	case GPRS_GSUP_MSGT_PURGE_MS_ERROR:
diff --git a/openbsc/tests/sgsn/sgsn_test.c b/openbsc/tests/sgsn/sgsn_test.c
index ef8661b..6980a90 100644
--- a/openbsc/tests/sgsn/sgsn_test.c
+++ b/openbsc/tests/sgsn/sgsn_test.c
@@ -28,6 +28,7 @@
 #include <osmocom/gprs/gprs_bssgp.h>
 
 #include <osmocom/gsm/gsm_utils.h>
+#include <openbsc/gsm_04_08_gprs.h>
 
 #include <osmocom/core/application.h>
 #include <osmocom/core/msgb.h>
@@ -438,7 +439,7 @@
 
 	/* Inject SendAuthInfoErr GSUP message */
 	rc = rx_gsup_message(send_auth_info_err, sizeof(send_auth_info_err));
-	OSMO_ASSERT(rc >= 0);
+	OSMO_ASSERT(rc == -GMM_CAUSE_GPRS_NOTALLOWED);
 	OSMO_ASSERT(last_updated_subscr == s1);
 
 	/* Check triplets */
@@ -456,7 +457,7 @@
 
 	/* Inject UpdateLocErr GSUP message */
 	rc = rx_gsup_message(update_location_err, sizeof(update_location_err));
-	OSMO_ASSERT(rc >= 0);
+	OSMO_ASSERT(rc == -GMM_CAUSE_GPRS_NOTALLOWED);
 	OSMO_ASSERT(last_updated_subscr == s1);
 
 	/* Check authorization */