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WIP: sccp: Send RELRE when CREQ is refused by peer

WIP attempt to make sure the peer drops the conn if it refuses to create
a new conn, perhaps due to conn already established according to peer
state.

Related: SYS#6602
Change-Id: Iea2e6f684a6cdbc978833785704b8cf2cbd4e645
---
M src/sccp_scoc.c
1 file changed, 9 insertions(+), 2 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/libosmo-sigtran refs/changes/51/38551/1

diff --git a/src/sccp_scoc.c b/src/sccp_scoc.c
index 0e1eb34..d14a90e 100644
--- a/src/sccp_scoc.c
+++ b/src/sccp_scoc.c
@@ -1061,6 +1061,7 @@
 	struct sccp_connection *conn = fi->priv;
 	struct osmo_scu_prim *prim = NULL;
 	struct xua_msg *xua = NULL;
+	uint32_t sccp_cause;
 
 	switch (event) {
 	case SCOC_E_SCU_N_DISC_REQ:
@@ -1081,11 +1082,17 @@
 		xua = data;
 		/* stop conn timer */
 		conn_stop_connect_timer(conn);
-		/* release local res + ref (implicit by going to idle) */
+		/* Tx RELRE in case CREQ was refused due to misaligned state
+		 * where peer thinks this conn already exists... (SYS#6602)
+		 * Note: this is a deviation from Figure C.2/Q.714 (sheet 2 of 7)
+		 */
+		sccp_cause = xua_msg_get_u32(xua, SUA_IEI_CAUSE);
+		if (sccp_cause == (SUA_CAUSE_T_REFUSAL | SCCP_REFUSAL_END_USER_FAILURE))
+			xua_gen_relre_and_send(conn, SCCP_RELEASE_CAUSE_REMOTE_PROCEDURE_ERROR, NULL);
 		/* N-DISCONNECT.ind to user */
 		scu_gen_encode_and_send(conn, event, xua, OSMO_SCU_PRIM_N_DISCONNECT,
 					PRIM_OP_INDICATION);
-		/* below implicitly releases resources + local ref */
+		/* below going to idle implicitly releases resources + local ref */
 		osmo_fsm_inst_state_chg(fi, S_IDLE, 0, 0);
 		break;
 	case SCOC_E_RCOC_RLSD_IND:

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