From 4ece5fd0f6433f0b834041edfbb327bd59affc48 Mon Sep 17 00:00:00 2001 From: Valentine Wallace Date: Fri, 23 Oct 2020 11:55:58 -0400 Subject: [PATCH] Update monitor with preimage after channel close If the channel is hitting the chain right as we receive a preimage, previous to this commit the relevant ChannelMonitor would never learn of this preimage. --- lightning/src/chain/channelmonitor.rs | 29 +++++++++++++++++++++++++-- lightning/src/ln/channelmanager.rs | 19 ++++++++++++++---- 2 files changed, 42 insertions(+), 6 deletions(-) diff --git a/lightning/src/chain/channelmonitor.rs b/lightning/src/chain/channelmonitor.rs index 889dfa211..1e0e7fef1 100644 --- a/lightning/src/chain/channelmonitor.rs +++ b/lightning/src/chain/channelmonitor.rs @@ -64,14 +64,29 @@ pub struct ChannelMonitorUpdate { pub(crate) updates: Vec, /// The sequence number of this update. Updates *must* be replayed in-order according to this /// sequence number (and updates may panic if they are not). The update_id values are strictly - /// increasing and increase by one for each new update. + /// increasing and increase by one for each new update, with one exception specified below. /// /// This sequence number is also used to track up to which points updates which returned /// ChannelMonitorUpdateErr::TemporaryFailure have been applied to all copies of a given /// ChannelMonitor when ChannelManager::channel_monitor_updated is called. + /// + /// The only instance where update_id values are not strictly increasing is the case where we + /// allow post-force-close updates with a special update ID of [`CLOSED_CHANNEL_UPDATE_ID`]. See + /// its docs for more details. + /// + /// [`CLOSED_CHANNEL_UPDATE_ID`]: constant.CLOSED_CHANNEL_UPDATE_ID.html pub update_id: u64, } +/// If: +/// (1) a channel has been force closed and +/// (2) we receive a preimage from a forward link that allows us to spend an HTLC output on +/// this channel's (the backward link's) broadcasted commitment transaction +/// then we allow the `ChannelManager` to send a `ChannelMonitorUpdate` with this update ID, +/// with the update providing said payment preimage. No other update types are allowed after +/// force-close. +pub const CLOSED_CHANNEL_UPDATE_ID: u64 = std::u64::MAX; + impl Writeable for ChannelMonitorUpdate { fn write(&self, w: &mut W) -> Result<(), ::std::io::Error> { self.update_id.write(w)?; @@ -1166,7 +1181,17 @@ impl ChannelMonitor { where B::Target: BroadcasterInterface, L::Target: Logger, { - if self.latest_update_id + 1 != updates.update_id { + // ChannelMonitor updates may be applied after force close if we receive a + // preimage for a broadcasted commitment transaction HTLC output that we'd + // like to claim on-chain. If this is the case, we no longer have guaranteed + // access to the monitor's update ID, so we use a sentinel value instead. + if updates.update_id == CLOSED_CHANNEL_UPDATE_ID { + match updates.updates[0] { + ChannelMonitorUpdateStep::PaymentPreimage { .. } => {}, + _ => panic!("Attempted to apply post-force-close ChannelMonitorUpdate that wasn't providing a payment preimage"), + } + assert_eq!(updates.updates.len(), 1); + } else if self.latest_update_id + 1 != updates.update_id { panic!("Attempted to apply ChannelMonitorUpdates out of order, check the update_id before passing an update to update_monitor!"); } for update in updates.updates.iter() { diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs index f3f13d3fb..a884b5f72 100644 --- a/lightning/src/ln/channelmanager.rs +++ b/lightning/src/ln/channelmanager.rs @@ -37,7 +37,7 @@ use bitcoin::secp256k1; use chain; use chain::Watch; use chain::chaininterface::{BroadcasterInterface, FeeEstimator}; -use chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, ChannelMonitorUpdateErr, HTLC_FAIL_BACK_BUFFER, CLTV_CLAIM_BUFFER, LATENCY_GRACE_PERIOD_BLOCKS, ANTI_REORG_DELAY, MonitorEvent}; +use chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, ChannelMonitorUpdateStep, ChannelMonitorUpdateErr, HTLC_FAIL_BACK_BUFFER, CLTV_CLAIM_BUFFER, LATENCY_GRACE_PERIOD_BLOCKS, ANTI_REORG_DELAY, MonitorEvent, CLOSED_CHANNEL_UPDATE_ID}; use chain::transaction::{OutPoint, TransactionData}; use ln::channel::{Channel, ChannelError}; use ln::features::{InitFeatures, NodeFeatures}; @@ -2152,12 +2152,23 @@ impl }); }, HTLCSource::PreviousHopData(hop_data) => { + let prev_outpoint = hop_data.outpoint; if let Err((counterparty_node_id, err)) = match self.claim_funds_from_hop(&mut channel_state_lock, hop_data, payment_preimage) { Ok(()) => Ok(()), Err(None) => { - // TODO: There is probably a channel monitor somewhere that needs to - // learn the preimage as the channel already hit the chain and that's - // why it's missing. + let preimage_update = ChannelMonitorUpdate { + update_id: CLOSED_CHANNEL_UPDATE_ID, + updates: vec![ChannelMonitorUpdateStep::PaymentPreimage { + payment_preimage: payment_preimage.clone(), + }], + }; + // We update the ChannelMonitor on the backward link, after + // receiving an offchain preimage event from the forward link (the + // event being update_fulfill_htlc). + if let Err(e) = self.chain_monitor.update_channel(prev_outpoint, preimage_update) { + log_error!(self.logger, "Critical error: failed to update channel monitor with preimage {:?}: {:?}", + payment_preimage, e); + } Ok(()) }, Err(Some(res)) => Err(res), -- 2.39.5