Workaround bug where old hnb_context from same remote addr+port is kept

Under some circumstancies not yet fully known, which seems to
involve bad link quality and high latencies and some specific hNodeB
which reuse its local IP addr+port, it is seen that a 2nd SCTP
connection is created from the same HNB while locally we still keep the
old SCTP connection and its related hnb_context. Hence, when the hNodeB
tries to register again with this new conn, it is rejected all the time
by the HNBGW.

Related: SYS#6113
Change-Id: I33ae901cc37646eca90bf06953e44fcc25f4d6c6

src/osmo-hnbgw/hnbgw_hnbap.c

@@ -395,7 +395,7 @@ static int hnbgw_rx_hnb_deregister(struct hnb_context *ctx, ANY_t *in)
 
 static int hnbgw_rx_hnb_register_req(struct hnb_context *ctx, ANY_t *in)
 {
-	struct hnb_context *hnb;
+	struct hnb_context *hnb, *tmp;
 	HNBAP_HNBRegisterRequestIEs_t ies;
 	int rc;
 	struct osmo_plmn_id plmn;
@@ -422,8 +422,35 @@ static int hnbgw_rx_hnb_register_req(struct hnb_context *ctx, ANY_t *in)
 	ctx->id.mcc = plmn.mcc;
 	ctx->id.mnc = plmn.mnc;
 
-	llist_for_each_entry(hnb, &ctx->gw->hnb_list, list) {
+	llist_for_each_entry_safe(hnb, tmp, &ctx->gw->hnb_list, list) {
 		if (hnb->hnb_registered && ctx != hnb && memcmp(&ctx->id, &hnb->id, sizeof(ctx->id)) == 0) {
+			/* If it's coming from the same remote IP addr+port, then it must be our internal
+			 * fault (bug), and we release the old context to keep going... */
+			struct osmo_fd *other_fd = osmo_stream_srv_get_ofd(hnb->conn);
+			struct osmo_sockaddr other_osa = {};
+			struct osmo_sockaddr cur_osa = {};
+			socklen_t len = sizeof(other_osa);
+			if (getpeername(other_fd->fd, &other_osa.u.sa, &len) < 0) {
+				LOGHNB(ctx, DHNBAP, LOGL_ERROR, "BUG! Found old registered HNB with invalid socket, releasing it\n");
+				hnb_context_release(hnb);
+				continue;
+			}
+			len = sizeof(cur_osa);
+			if (getpeername(ofd->fd, &cur_osa.u.sa, &len) < 0) {
+				LOGHNB(ctx, DHNBAP, LOGL_ERROR, "Error getpeername(): %s\n", strerror(errno));
+				if (osmo_sockaddr_cmp(&cur_osa, &other_osa) == 0) {
+					LOGHNB(ctx, DHNBAP, LOGL_ERROR, "BUG! Found old registered HNB with same remote address, releasing it\n");
+					hnb_context_release(hnb);
+					continue;
+				}
+			} else if (osmo_sockaddr_cmp(&cur_osa, &other_osa) == 0) {
+				LOGHNB(ctx, DHNBAP, LOGL_ERROR, "BUG! Found old registered HNB with same remote address, releasing it\n");
+				hnb_context_release(hnb);
+				continue;
+			} /* else: addresses are different, we continue below */
+
+			/* If new conn registering same HNB is from anoter remote addr+port, let's reject it to avoid
+			 * misconfigurations or someone trying to impersonate an already working HNB: */
 			LOGHNB(ctx, DHNBAP, LOGL_ERROR, "rejecting HNB-REGISTER-REQ with duplicate cell identity "
 				"MCC=%u,MNC=%u,LAC=%u,RAC=%u,SAC=%u,CID=%u from %s\n",
 				ctx->id.mcc, ctx->id.mnc, ctx->id.lac, ctx->id.rac, ctx->id.sac, ctx->id.cid, name);