SMS over GSUP: correctly route GSUP responses to MT SMS

When OsmoMSC is used with OsmoHLR rather than a GSUP-to-MAP gateway,
MT-forwardSM.req GSUP messages delivering MT SMS will be coming from
a separate SMSC relayed via OsmoHLR, rather than from OsmoHLR itself.
When we reply to these messages, in order for these replies to reach
the MT-sending SMSC via OsmoHLR, we need to save source_name from
the request and regurgitate it into destination_name in our response
messages.  Implement this logic.

Related: OS#6135
Change-Id: I436e333035b8f6e27f86a49fe293ea48ea07a013

4 files changed, 28 insertions, 3 deletions

diff --git a/include/osmocom/msc/gsm_04_11.h b/include/osmocom/msc/gsm_04_11.h
index 19aaa3a5e..17a31ecdd 100644
--- a/include/osmocom/msc/gsm_04_11.h
+++ b/include/osmocom/msc/gsm_04_11.h
@@ -28,7 +28,8 @@ int gsm411_send_sms(struct gsm_network *net,
 int gsm411_send_rp_data(struct gsm_network *net, struct vlr_subscr *vsub,
 			size_t sm_rp_oa_len, const uint8_t *sm_rp_oa,
 			size_t sm_rp_ud_len, const uint8_t *sm_rp_ud,
-			bool sm_rp_mmts_ind);
+			bool sm_rp_mmts_ind, const uint8_t *gsup_source_name,
+			size_t gsup_source_name_len);
 
 void gsm411_sapi_n_reject(struct msc_a *msc_a);
 
diff --git a/include/osmocom/msc/transaction.h b/include/osmocom/msc/transaction.h
index a5a2e84ea..aa529e494 100644
--- a/include/osmocom/msc/transaction.h
+++ b/include/osmocom/msc/transaction.h
@@ -149,6 +149,9 @@ struct gsm_trans {
 			bool sm_rp_mmts_ind;
 
 			struct gsm_sms *sms;
+
+			uint8_t *gsup_source_name;
+			size_t gsup_source_name_len;
 		} sms;
 		struct {
 			/**
diff --git a/src/libmsc/gsm_04_11.c b/src/libmsc/gsm_04_11.c
index adc9d88c8..aa87a192a 100644
--- a/src/libmsc/gsm_04_11.c
+++ b/src/libmsc/gsm_04_11.c
@@ -1230,7 +1230,8 @@ int gsm411_send_sms(struct gsm_network *net,
 int gsm411_send_rp_data(struct gsm_network *net, struct vlr_subscr *vsub,
 			size_t sm_rp_oa_len, const uint8_t *sm_rp_oa,
 			size_t sm_rp_ud_len, const uint8_t *sm_rp_ud,
-			bool sm_rp_mmts_ind)
+			bool sm_rp_mmts_ind, const uint8_t *gsup_source_name,
+			size_t gsup_source_name_len)
 {
 	struct gsm_trans *trans;
 	struct msgb *msg;
@@ -1245,6 +1246,17 @@ int gsm411_send_rp_data(struct gsm_network *net, struct vlr_subscr *vsub,
 	if (trans->msc_a != NULL)
 		gsm411_handle_mmts_ind(trans);
 
+	/* Save GSUP source_name for subsequent response messages */
+	if (gsup_source_name && gsup_source_name_len) {
+		trans->sms.gsup_source_name = talloc_memdup(trans, gsup_source_name,
+							    gsup_source_name_len);
+		if (!trans->sms.gsup_source_name) {
+			trans_free(trans);
+			return -ENOMEM;
+		}
+		trans->sms.gsup_source_name_len = gsup_source_name_len;
+	}
+
 	/* Allocate a message buffer for to be encoded SMS */
 	msg = gsm411_msgb_alloc();
 	if (!msg) {
diff --git a/src/libmsc/gsm_04_11_gsup.c b/src/libmsc/gsm_04_11_gsup.c
index 0f1891280..6225c6c4f 100644
--- a/src/libmsc/gsm_04_11_gsup.c
+++ b/src/libmsc/gsm_04_11_gsup.c
@@ -198,6 +198,10 @@ int gsm411_gsup_mt_fwd_sm_res(struct gsm_trans *trans, uint8_t sm_rp_mr)
 	gsup_sm_msg_init(&gsup_msg, OSMO_GSUP_MSGT_MT_FORWARD_SM_RESULT,
 		trans->vsub->imsi, &sm_rp_mr);
 
+	/* Ensure routing through OsmoHLR to the MT-sending SMSC */
+	gsup_msg.destination_name = trans->sms.gsup_source_name;
+	gsup_msg.destination_name_len = trans->sms.gsup_source_name_len;
+
 	return gsup_client_mux_tx(trans->net->gcm, &gsup_msg);
 }
 
@@ -215,6 +219,10 @@ int gsm411_gsup_mt_fwd_sm_err(struct gsm_trans *trans,
 	gsup_sm_msg_init(&gsup_msg, OSMO_GSUP_MSGT_MT_FORWARD_SM_ERROR,
 		trans->vsub->imsi, &sm_rp_mr);
 
+	/* Ensure routing through OsmoHLR to the MT-sending SMSC */
+	gsup_msg.destination_name = trans->sms.gsup_source_name;
+	gsup_msg.destination_name_len = trans->sms.gsup_source_name_len;
+
 	/* SM-RP-Cause value */
 	gsup_msg.sm_rp_cause = &cause;
 
@@ -259,7 +267,8 @@ static int gsm411_gsup_mt_handler(struct gsm_network *net, struct vlr_subscr *vs
 	rc = gsm411_send_rp_data(net, vsub,
 		gsup_msg->sm_rp_oa_len, gsup_msg->sm_rp_oa,
 		gsup_msg->sm_rp_ui_len, gsup_msg->sm_rp_ui,
-		sm_rp_mmts_ind);
+		sm_rp_mmts_ind, gsup_msg->source_name,
+		gsup_msg->source_name_len);
 	if (rc) {
 		LOGP(DLSMS, LOGL_NOTICE, "Failed to send MT SMS, "
 			"ignoring MT-forwardSM-Req message...\n");