Send bogus ChannelReestablish for unknown channels
authorWilmer Paulino <wilmer@wilmerpaulino.com>
Wed, 11 Oct 2023 16:42:05 +0000 (09:42 -0700)
committerWilmer Paulino <wilmer@wilmerpaulino.com>
Wed, 18 Oct 2023 18:25:25 +0000 (11:25 -0700)
Unfortunately, lnd doesn't force close on errors
(https://github.com/lightningnetwork/lnd/blob/abb1e3463f3a83bbb843d5c399869dbe930ad94f/htlcswitch/link.go#L2119).
One of the few ways to get an lnd counterparty to force close is by
replicating what they do when restoring static channel backups (SCBs).
They send an invalid `ChannelReestablish` with `0` commitment numbers
and an invalid `your_last_per_commitment_secret`.

Since we received a `ChannelReestablish` for a channel that doesn't
exist, we can assume it's likely the channel closed from our point of
view, but it remains open on the counterparty's side. By sending this
bogus `ChannelReestablish` message now as a response to theirs, we
trigger them to force close broadcasting their latest state. If the
closing transaction from our point of view remains unconfirmed, it'll
enter a race with the counterparty's to-be-broadcast latest commitment
transaction.

lightning/src/ln/channel.rs
lightning/src/ln/channelmanager.rs
lightning/src/ln/payment_tests.rs
lightning/src/ln/reload_tests.rs
lightning/src/ln/shutdown_tests.rs

index a61a8de82debecd5906c0ee95bdcdb420aae48f4..2359d1ef0e3723bdf1ea28c62a2720fd6fd47bf2 100644 (file)
@@ -3992,7 +3992,7 @@ impl<SP: Deref> Channel<SP> where
 
                if msg.next_local_commitment_number >= INITIAL_COMMITMENT_NUMBER || msg.next_remote_commitment_number >= INITIAL_COMMITMENT_NUMBER ||
                        msg.next_local_commitment_number == 0 {
-                       return Err(ChannelError::Close("Peer sent a garbage channel_reestablish (usually an lnd node with lost state asking us to force-close for them)".to_owned()));
+                       return Err(ChannelError::Close("Peer sent an invalid channel_reestablish to force close in a non-standard way".to_owned()));
                }
 
                if msg.next_remote_commitment_number > 0 {
index 24ca65af00805a4463c6cac1c155a39f1b30cdf9..35107f10bee9a47eeb4704b14651c6b24ca8037e 100644 (file)
@@ -6785,7 +6785,10 @@ where
                        let peer_state_mutex = per_peer_state.get(counterparty_node_id)
                                .ok_or_else(|| {
                                        debug_assert!(false);
-                                       MsgHandleErrInternal::send_err_msg_no_close(format!("Can't find a peer matching the passed counterparty node_id {}", counterparty_node_id), msg.channel_id)
+                                       MsgHandleErrInternal::send_err_msg_no_close(
+                                               format!("Can't find a peer matching the passed counterparty node_id {}", counterparty_node_id),
+                                               msg.channel_id
+                                       )
                                })?;
                        let mut peer_state_lock = peer_state_mutex.lock().unwrap();
                        let peer_state = &mut *peer_state_lock;
@@ -6829,7 +6832,39 @@ where
                                                        "Got a channel_reestablish message for an unfunded channel!".into())), chan_phase_entry);
                                        }
                                },
-                               hash_map::Entry::Vacant(_) => return Err(MsgHandleErrInternal::send_err_msg_no_close(format!("Got a message for a channel from the wrong node! No such channel for the passed counterparty_node_id {}", counterparty_node_id), msg.channel_id))
+                               hash_map::Entry::Vacant(_) => {
+                                       log_debug!(self.logger, "Sending bogus ChannelReestablish for unknown channel {} to force channel closure",
+                                               log_bytes!(msg.channel_id.0));
+                                       // Unfortunately, lnd doesn't force close on errors
+                                       // (https://github.com/lightningnetwork/lnd/blob/abb1e3463f3a83bbb843d5c399869dbe930ad94f/htlcswitch/link.go#L2119).
+                                       // One of the few ways to get an lnd counterparty to force close is by
+                                       // replicating what they do when restoring static channel backups (SCBs). They
+                                       // send an invalid `ChannelReestablish` with `0` commitment numbers and an
+                                       // invalid `your_last_per_commitment_secret`.
+                                       //
+                                       // Since we received a `ChannelReestablish` for a channel that doesn't exist, we
+                                       // can assume it's likely the channel closed from our point of view, but it
+                                       // remains open on the counterparty's side. By sending this bogus
+                                       // `ChannelReestablish` message now as a response to theirs, we trigger them to
+                                       // force close broadcasting their latest state. If the closing transaction from
+                                       // our point of view remains unconfirmed, it'll enter a race with the
+                                       // counterparty's to-be-broadcast latest commitment transaction.
+                                       peer_state.pending_msg_events.push(MessageSendEvent::SendChannelReestablish {
+                                               node_id: *counterparty_node_id,
+                                               msg: msgs::ChannelReestablish {
+                                                       channel_id: msg.channel_id,
+                                                       next_local_commitment_number: 0,
+                                                       next_remote_commitment_number: 0,
+                                                       your_last_per_commitment_secret: [1u8; 32],
+                                                       my_current_per_commitment_point: PublicKey::from_slice(&[2u8; 33]).unwrap(),
+                                                       next_funding_txid: None,
+                                               },
+                                       });
+                                       return Err(MsgHandleErrInternal::send_err_msg_no_close(
+                                               format!("Got a message for a channel from the wrong node! No such channel for the passed counterparty_node_id {}",
+                                                       counterparty_node_id), msg.channel_id)
+                                       )
+                               }
                        }
                };
 
@@ -11219,6 +11254,67 @@ mod tests {
                let payment_preimage = PaymentPreimage([42; 32]);
                assert_eq!(format!("{}", &payment_preimage), "2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a");
        }
+
+       #[test]
+       fn test_trigger_lnd_force_close() {
+               let chanmon_cfg = create_chanmon_cfgs(2);
+               let node_cfg = create_node_cfgs(2, &chanmon_cfg);
+               let user_config = test_default_channel_config();
+               let node_chanmgr = create_node_chanmgrs(2, &node_cfg, &[Some(user_config), Some(user_config)]);
+               let nodes = create_network(2, &node_cfg, &node_chanmgr);
+
+               // Open a channel, immediately disconnect each other, and broadcast Alice's latest state.
+               let (_, _, chan_id, funding_tx) = create_announced_chan_between_nodes(&nodes, 0, 1);
+               nodes[0].node.peer_disconnected(&nodes[1].node.get_our_node_id());
+               nodes[1].node.peer_disconnected(&nodes[0].node.get_our_node_id());
+               nodes[0].node.force_close_broadcasting_latest_txn(&chan_id, &nodes[1].node.get_our_node_id()).unwrap();
+               check_closed_broadcast(&nodes[0], 1, true);
+               check_added_monitors(&nodes[0], 1);
+               check_closed_event!(nodes[0], 1, ClosureReason::HolderForceClosed, [nodes[1].node.get_our_node_id()], 100000);
+               {
+                       let txn = nodes[0].tx_broadcaster.txn_broadcast();
+                       assert_eq!(txn.len(), 1);
+                       check_spends!(txn[0], funding_tx);
+               }
+
+               // Since they're disconnected, Bob won't receive Alice's `Error` message. Reconnect them
+               // such that Bob sends a `ChannelReestablish` to Alice since the channel is still open from
+               // their side.
+               nodes[0].node.peer_connected(&nodes[1].node.get_our_node_id(), &msgs::Init {
+                       features: nodes[1].node.init_features(), networks: None, remote_network_address: None
+               }, true).unwrap();
+               nodes[1].node.peer_connected(&nodes[0].node.get_our_node_id(), &msgs::Init {
+                       features: nodes[0].node.init_features(), networks: None, remote_network_address: None
+               }, false).unwrap();
+               assert!(nodes[0].node.get_and_clear_pending_msg_events().is_empty());
+               let channel_reestablish = get_event_msg!(
+                       nodes[1], MessageSendEvent::SendChannelReestablish, nodes[0].node.get_our_node_id()
+               );
+               nodes[0].node.handle_channel_reestablish(&nodes[1].node.get_our_node_id(), &channel_reestablish);
+
+               // Alice should respond with an error since the channel isn't known, but a bogus
+               // `ChannelReestablish` should be sent first, such that we actually trigger Bob to force
+               // close even if it was an lnd node.
+               let msg_events = nodes[0].node.get_and_clear_pending_msg_events();
+               assert_eq!(msg_events.len(), 2);
+               if let MessageSendEvent::SendChannelReestablish { node_id, msg } = &msg_events[0] {
+                       assert_eq!(*node_id, nodes[1].node.get_our_node_id());
+                       assert_eq!(msg.next_local_commitment_number, 0);
+                       assert_eq!(msg.next_remote_commitment_number, 0);
+                       nodes[1].node.handle_channel_reestablish(&nodes[0].node.get_our_node_id(), &msg);
+               } else { panic!() };
+               check_closed_broadcast(&nodes[1], 1, true);
+               check_added_monitors(&nodes[1], 1);
+               let expected_close_reason = ClosureReason::ProcessingError {
+                       err: "Peer sent an invalid channel_reestablish to force close in a non-standard way".to_string()
+               };
+               check_closed_event!(nodes[1], 1, expected_close_reason, [nodes[0].node.get_our_node_id()], 100000);
+               {
+                       let txn = nodes[1].tx_broadcaster.txn_broadcast();
+                       assert_eq!(txn.len(), 1);
+                       check_spends!(txn[0], funding_tx);
+               }
+       }
 }
 
 #[cfg(ldk_bench)]
index 26ecbb0bd249d116cf8e54f440145c60d1796bbd..f35b67e98f1c703813095c991deb3424ae775960 100644 (file)
@@ -706,8 +706,8 @@ fn do_retry_with_no_persist(confirm_before_reload: bool) {
        let bs_reestablish = get_chan_reestablish_msgs!(nodes[1], nodes[0]).pop().unwrap();
        nodes[0].node.handle_channel_reestablish(&nodes[1].node.get_our_node_id(), &bs_reestablish);
        let as_err = nodes[0].node.get_and_clear_pending_msg_events();
-       assert_eq!(as_err.len(), 1);
-       match as_err[0] {
+       assert_eq!(as_err.len(), 2);
+       match as_err[1] {
                MessageSendEvent::HandleError { node_id, action: msgs::ErrorAction::SendErrorMessage { ref msg } } => {
                        assert_eq!(node_id, nodes[1].node.get_our_node_id());
                        nodes[1].node.handle_error(&nodes[0].node.get_our_node_id(), msg);
@@ -881,9 +881,9 @@ fn do_test_completed_payment_not_retryable_on_reload(use_dust: bool) {
        let bs_reestablish = get_chan_reestablish_msgs!(nodes[1], nodes[0]).pop().unwrap();
        nodes[0].node.handle_channel_reestablish(&nodes[1].node.get_our_node_id(), &bs_reestablish);
        let as_err = nodes[0].node.get_and_clear_pending_msg_events();
-       assert_eq!(as_err.len(), 1);
+       assert_eq!(as_err.len(), 2);
        let bs_commitment_tx;
-       match as_err[0] {
+       match as_err[1] {
                MessageSendEvent::HandleError { node_id, action: msgs::ErrorAction::SendErrorMessage { ref msg } } => {
                        assert_eq!(node_id, nodes[1].node.get_our_node_id());
                        nodes[1].node.handle_error(&nodes[0].node.get_our_node_id(), msg);
index 5f4009d642949ca42d0b1bbe73401b9bb657b233..9ea13f13109635174565e650c8cde03b076543ba 100644 (file)
@@ -589,18 +589,16 @@ fn do_test_data_loss_protect(reconnect_panicing: bool) {
 
        nodes[0].node.handle_channel_reestablish(&nodes[1].node.get_our_node_id(), &retry_reestablish[0]);
        let mut err_msgs_0 = Vec::with_capacity(1);
-       for msg in nodes[0].node.get_and_clear_pending_msg_events() {
-               if let MessageSendEvent::HandleError { ref action, .. } = msg {
-                       match action {
-                               &ErrorAction::SendErrorMessage { ref msg } => {
-                                       assert_eq!(msg.data, format!("Got a message for a channel from the wrong node! No such channel for the passed counterparty_node_id {}", &nodes[1].node.get_our_node_id()));
-                                       err_msgs_0.push(msg.clone());
-                               },
-                               _ => panic!("Unexpected event!"),
-                       }
-               } else {
-                       panic!("Unexpected event!");
+       if let MessageSendEvent::HandleError { ref action, .. } = nodes[0].node.get_and_clear_pending_msg_events()[1] {
+               match action {
+                       &ErrorAction::SendErrorMessage { ref msg } => {
+                               assert_eq!(msg.data, format!("Got a message for a channel from the wrong node! No such channel for the passed counterparty_node_id {}", &nodes[1].node.get_our_node_id()));
+                               err_msgs_0.push(msg.clone());
+                       },
+                       _ => panic!("Unexpected event!"),
                }
+       } else {
+               panic!("Unexpected event!");
        }
        assert_eq!(err_msgs_0.len(), 1);
        nodes[1].node.handle_error(&nodes[0].node.get_our_node_id(), &err_msgs_0[0]);
index 47361693693db731a85dee326f85ca54eeecad5f..9bc133f45a9ba6a1199b9534db2e05219d993ea7 100644 (file)
@@ -623,8 +623,8 @@ fn do_test_shutdown_rebroadcast(recv_count: u8) {
 
                nodes[0].node.handle_channel_reestablish(&nodes[1].node.get_our_node_id(), &node_1_2nd_reestablish);
                let msg_events = nodes[0].node.get_and_clear_pending_msg_events();
-               assert_eq!(msg_events.len(), 1);
-               if let MessageSendEvent::HandleError { ref action, .. } = msg_events[0] {
+               assert_eq!(msg_events.len(), 2);
+               if let MessageSendEvent::HandleError { ref action, .. } = msg_events[1] {
                        match action {
                                &ErrorAction::SendErrorMessage { ref msg } => {
                                        nodes[1].node.handle_error(&nodes[0].node.get_our_node_id(), &msg);