Correctly fail back downstream-failed blinded HTLCs as intro

lightning/src/ln/blinded_payment_tests.rs

@@ -235,3 +235,60 @@ fn do_forward_checks_failure(check: ForwardCheckFail) {
 	expect_payment_failed_conditions(&nodes[0], payment_hash, false,
 		PaymentFailedConditions::new().expected_htlc_error_data(INVALID_ONION_BLINDING, &[0; 32]));
 }
+
+#[test]
+fn failed_backwards_to_intro_node() {
+	// Ensure the intro node will error backwards properly even if the downstream node did not blind
+	// their error.
+	let chanmon_cfgs = create_chanmon_cfgs(3);
+	let node_cfgs = create_node_cfgs(3, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(3, &node_cfgs, &[None, None, None]);
+	let mut nodes = create_network(3, &node_cfgs, &node_chanmgrs);
+	create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 0);
+	let chan_upd_1_2 = create_announced_chan_between_nodes_with_value(&nodes, 1, 2, 1_000_000, 0).0.contents;
+
+	let amt_msat = 5000;
+	let (_, payment_hash, payment_secret) = get_payment_preimage_hash(&nodes[2], Some(amt_msat), None);
+	let route_params = get_blinded_route_parameters(amt_msat, payment_secret,
+		nodes.iter().skip(1).map(|n| n.node.get_our_node_id()).collect(), &[&chan_upd_1_2],
+		&chanmon_cfgs[2].keys_manager);
+
+	nodes[0].node.send_payment(payment_hash, RecipientOnionFields::spontaneous_empty(), PaymentId(payment_hash.0), route_params, Retry::Attempts(0)).unwrap();
+	check_added_monitors(&nodes[0], 1);
+
+	let mut events = nodes[0].node.get_and_clear_pending_msg_events();
+	assert_eq!(events.len(), 1);
+	let ev = remove_first_msg_event_to_node(&nodes[1].node.get_our_node_id(), &mut events);
+	let mut payment_event = SendEvent::from_event(ev);
+
+	nodes[1].node.handle_update_add_htlc(&nodes[0].node.get_our_node_id(), &payment_event.msgs[0]);
+	check_added_monitors!(nodes[1], 0);
+	do_commitment_signed_dance(&nodes[1], &nodes[0], &payment_event.commitment_msg, false, false);
+	expect_pending_htlcs_forwardable!(nodes[1]);
+	check_added_monitors!(&nodes[1], 1);
+
+	let mut events = nodes[1].node.get_and_clear_pending_msg_events();
+	assert_eq!(events.len(), 1);
+	let ev = remove_first_msg_event_to_node(&nodes[2].node.get_our_node_id(), &mut events);
+	let mut payment_event = SendEvent::from_event(ev);
+
+	// Ensure the final node fails to handle the HTLC.
+	payment_event.msgs[0].onion_routing_packet.hop_data[0] ^= 1;
+	nodes[2].node.handle_update_add_htlc(&nodes[1].node.get_our_node_id(), &payment_event.msgs[0]);
+	check_added_monitors!(nodes[2], 0);
+	do_commitment_signed_dance(&nodes[2], &nodes[1], &payment_event.commitment_msg, true, true);
+	nodes[2].node.process_pending_htlc_forwards();
+
+	let mut updates = get_htlc_update_msgs!(nodes[2], nodes[1].node.get_our_node_id());
+	let mut update_malformed = &mut updates.update_fail_malformed_htlcs[0];
+	// Ensure the final hop does not correctly blind their error.
+	update_malformed.sha256_of_onion = [1; 32];
+	nodes[1].node.handle_update_fail_malformed_htlc(&nodes[2].node.get_our_node_id(), update_malformed);
+	do_commitment_signed_dance(&nodes[1], &nodes[2], &updates.commitment_signed, true, false);
+
+	let mut updates = get_htlc_update_msgs!(nodes[1], nodes[0].node.get_our_node_id());
+	nodes[0].node.handle_update_fail_htlc(&nodes[1].node.get_our_node_id(), &updates.update_fail_htlcs[0]);
+	do_commitment_signed_dance(&nodes[0], &nodes[1], &updates.commitment_signed, false, false);
+	expect_payment_failed_conditions(&nodes[0], payment_hash, false,
+		PaymentFailedConditions::new().expected_htlc_error_data(INVALID_ONION_BLINDING, &[0; 32]));
+}

lightning/src/ln/channelmanager.rs

@@ -5381,9 +5381,23 @@ where
 					&self.pending_events, &self.logger)
 				{ self.push_pending_forwards_ev(); }
 			},
-			HTLCSource::PreviousHopData(HTLCPreviousHopData { ref short_channel_id, ref htlc_id, ref incoming_packet_shared_secret, ref phantom_shared_secret, ref outpoint, .. }) => {
-				log_trace!(self.logger, "Failing HTLC with payment_hash {} backwards from us with {:?}", &payment_hash, onion_error);
-				let err_packet = onion_error.get_encrypted_failure_packet(incoming_packet_shared_secret, phantom_shared_secret);
+			HTLCSource::PreviousHopData(HTLCPreviousHopData {
+				ref short_channel_id, ref htlc_id, ref incoming_packet_shared_secret,
+				ref phantom_shared_secret, ref outpoint, ref blinded, ..
+			}) => {
+				log_trace!(self.logger, "Failing {}HTLC with payment_hash {} backwards from us: {:?}",
+					if blinded.is_some() { "blinded " } else { "" }, &payment_hash, onion_error);
+				let err_packet = match blinded {
+					Some(Blinded::IntroNode) => {
+						let blinded_onion_error = HTLCFailReason::reason(INVALID_ONION_BLINDING, vec![0; 32]);
+						blinded_onion_error.get_encrypted_failure_packet(
+							incoming_packet_shared_secret, phantom_shared_secret
+						)
+					},
+					None => {
+						onion_error.get_encrypted_failure_packet(incoming_packet_shared_secret, phantom_shared_secret)
+					}
+				};
 
 				let mut push_forward_ev = false;
 				let mut forward_htlcs = self.forward_htlcs.lock().unwrap();