bus: Prevent redundant down event on rekeyed CHILD_SA delete timeout

If a CHILD_SA is rekeyed using a CREATE_CHILD_SA request, a subsequent
DELETE for the old CHILD_SA may time out. Before sending this DELETE,
a CHILD_REKEYED state CHILD_SA set from child_rekey::process_i() is
immediately set to CHILD_DELETING from child_delete::build_i(). If the
IKE_SA dies due to a retransmission timeout of this DELETE, a redundant
child-down event is issued for the rekeyed CHILD_SA that has already seen a
child-rekey event.

A reproducer shows the following log and events:

    [CFG] vici rekey CHILD_SA #533
    [IKE] establishing CHILD_SA XXX{534} reqid 20
    [ENC] generating CREATE_CHILD_SA request 0 [ N(REKEY_SA) SA No KE TSi TSr ]
    [ENC] parsed CREATE_CHILD_SA response 0 [ SA No TSi TSr ]
    [IKE] rekeyed CHILD_SA XXX{533} with SPIs ca997de6_i cd27d4fe_o with XXX{534} with SPIs ced1cd01_i c460a7c9_o
     Event: child-rekey
      [OLD SA] state: REKEYING, spi-in: ca997de6
      [NEW SA] state: INSTALLED, spi-in: ced1cd01
    [IKE] closing CHILD_SA XXX{533} with SPIs ca997de6_i (352 bytes) cd27d4fe_o (264 bytes) and TS 0.0.0.0/0 === 10.11.9.40/29
    [IKE] sending DELETE for ESP CHILD_SA with SPI ca997de6
    [ENC] generating INFORMATIONAL request 1 [ D ]
    [IKE] retransmit 1 of request with message ID 1
    [IKE] retransmit 2 of request with message ID 1
    [IKE] retransmit 3 of request with message ID 1
    [IKE] retransmit 4 of request with message ID 1
    [IKE] giving up after 4 retransmits
     Event: child-updown
      [SA] state: DELETING, spi-in: ca997de6
     Event: child-updown
      [SA] state: INSTALLED, spi-in: ced1cd01

To prevent the redundant child-down event for the successfully rekeyed CHILD_SA,
check if a DELETING CHILD_SA has already removed its outbound state due to
having been rekeyed before issuing the child-down event.

Add a new exchange test exercising that a delete timeout after rekeying does
not cause a duplicate child-down event.

src/libcharon/bus/bus.c

@@ -830,11 +830,23 @@ METHOD(bus_t, ike_updown, void,
 		enumerator = ike_sa->create_child_sa_enumerator(ike_sa);
 		while (enumerator->enumerate(enumerator, (void**)&child_sa))
 		{
-			if (child_sa->get_state(child_sa) != CHILD_REKEYED &&
-				child_sa->get_state(child_sa) != CHILD_DELETED)
+			switch (child_sa->get_state(child_sa))
 			{
-				child_updown(this, child_sa, FALSE);
+				case CHILD_REKEYED:
+				case CHILD_DELETED:
+					continue;
+				case CHILD_DELETING:
+					if (child_sa->get_outbound_state(child_sa) ==
+						CHILD_OUTBOUND_NONE)
+					{
+						/* deleting CHILD_SA has been rekeyed, omit event */
+						continue;
+					}
+					break;
+				default:
+					break;
 			}
+			child_updown(this, child_sa, FALSE);
 		}
 		enumerator->destroy(enumerator);
 	}

src/libcharon/tests/suites/test_child_rekey.c

@@ -1089,6 +1089,64 @@ START_TEST(test_regular_responder_incorrect_delete)
 }
 END_TEST
 
+/**
+ * Check that a delete timeout after rekeying does not cause a duplicate
+ * child-down event for the rekeyed SA.
+ */
+START_TEST(test_regular_delete_timeout)
+{
+	ike_sa_t *a, *b;
+	message_t *msg;
+	status_t s;
+
+	exchange_test_helper->establish_sa(exchange_test_helper, &a, &b, NULL);
+	initiate_rekey(a, 1);
+	assert_ipsec_sas_installed(a, 1, 2);
+
+	/* this should never get called as this results in a successful rekeying */
+	assert_hook_not_called(child_updown);
+
+	/* CREATE_CHILD_SA { N(REKEY_SA), SA, Ni, [KEi,] TSi, TSr } --> */
+	assert_hook_not_called(child_rekey);
+	assert_notify(IN, REKEY_SA);
+	exchange_test_helper->process_message(exchange_test_helper, b, NULL);
+	assert_child_sa_state(b, 2, CHILD_REKEYED, CHILD_OUTBOUND_INSTALLED);
+	assert_child_sa_state(b, 4, CHILD_INSTALLED, CHILD_OUTBOUND_REGISTERED);
+	assert_ipsec_sas_installed(b, 1, 2, 4);
+	assert_hook();
+
+	/* <-- CREATE_CHILD_SA { SA, Nr, [KEr,] TSi, TSr } */
+	assert_hook_rekey(child_rekey, 1, 3);
+	assert_no_notify(IN, REKEY_SA);
+	exchange_test_helper->process_message(exchange_test_helper, a, NULL);
+	assert_child_sa_state(a, 3, CHILD_INSTALLED, CHILD_OUTBOUND_INSTALLED);
+	assert_ipsec_sas_installed(a, 1, 3, 4);
+	assert_hook();
+	assert_hook();
+
+	/* trigger retransmits until the request times out */
+	assert_hook_updown(child_updown, FALSE);
+	msg = exchange_test_helper->sender->dequeue(exchange_test_helper->sender);
+	while (msg)
+	{
+		charon->bus->set_sa(charon->bus, a);
+		s = a->retransmit(a, msg->get_message_id(msg));
+		charon->bus->set_sa(charon->bus, NULL);
+		msg->destroy(msg);
+		if (s == DESTROY_ME)
+		{
+			break;
+		}
+		msg = exchange_test_helper->sender->dequeue(
+												exchange_test_helper->sender);
+	}
+	assert_hook();
+
+	call_ikesa(a, destroy);
+	call_ikesa(b, destroy);
+}
+END_TEST
+
 /**
  * Both peers initiate the CHILD_SA rekeying concurrently and should handle
  * the collision properly depending on the nonces.
@@ -4368,6 +4426,7 @@ Suite *child_rekey_suite_create()
 	tcase_add_test(tc, test_regular_responder_delete);
 	tcase_add_test(tc, test_regular_responder_lost_sa);
 	tcase_add_test(tc, test_regular_responder_incorrect_delete);
+	tcase_add_test(tc, test_regular_delete_timeout);
 	suite_add_tcase(s, tc);
 
 	tc = tcase_create("collisions rekey");