Add fuzz coverage of (potential) fee update messages

TheBlueMatt · TheBlueMatt · commit 02cb99ceef1f · 2021-07-13T18:01:29.000Z
diff --git a/fuzz/src/chanmon_consistency.rs b/fuzz/src/chanmon_consistency.rs
@@ -37,6 +37,7 @@ use lightning::chain::chaininterface::{BroadcasterInterface, ConfirmationTarget,
 use lightning::chain::keysinterface::{KeysInterface, InMemorySigner};
 use lightning::ln::{PaymentHash, PaymentPreimage, PaymentSecret};
 use lightning::ln::channelmanager::{ChainParameters, ChannelManager, PaymentSendFailure, ChannelManagerReadArgs};
+use lightning::ln::channel::CHAN_STUCK_FEE_INCREASE_MULTIPLE;
 use lightning::ln::features::{ChannelFeatures, InitFeatures, NodeFeatures};
 use lightning::ln::msgs::{CommitmentUpdate, ChannelMessageHandler, DecodeError, UpdateAddHTLC, Init};
 use lightning::util::enforcing_trait_impls::{EnforcingSigner, INITIAL_REVOKED_COMMITMENT_NUMBER};
@@ -57,16 +58,27 @@ use bitcoin::secp256k1::recovery::RecoverableSignature;
 use bitcoin::secp256k1::Secp256k1;
 
 use std::mem;
-use std::cmp::Ordering;
+use std::cmp::{self, Ordering};
 use std::collections::{HashSet, hash_map, HashMap};
 use std::sync::{Arc,Mutex};
 use std::sync::atomic;
 use std::io::Cursor;
 
-struct FuzzEstimator {}
+const MAX_FEE: u32 = 10_000;
+struct FuzzEstimator {
+	ret_val: atomic::AtomicU32,
+}
 impl FeeEstimator for FuzzEstimator {
-	fn get_est_sat_per_1000_weight(&self, _: ConfirmationTarget) -> u32 {
-		253
+	fn get_est_sat_per_1000_weight(&self, conf_target: ConfirmationTarget) -> u32 {
+		// We force-close channels if our counterparty sends us a feerate which is a small multiple
+		// of our HighPriority fee estimate or smaller than our Background fee estimate. Thus, we
+		// always return a HighPriority feerate here which is >= the maximum Normal feerate and a
+		// Background feerate which is <= the minimum Normal feerate.
+		match conf_target {
+			ConfirmationTarget::HighPriority => MAX_FEE,
+			ConfirmationTarget::Background => 253,
+			ConfirmationTarget::Normal => cmp::min(self.ret_val.load(atomic::Ordering::Acquire), MAX_FEE),
+		}
 	}
 }
 
@@ -131,7 +143,7 @@ impl chain::Watch<EnforcingSigner> for TestChainMonitor {
 		};
 		let deserialized_monitor = <(BlockHash, channelmonitor::ChannelMonitor<EnforcingSigner>)>::
 			read(&mut Cursor::new(&map_entry.get().1), &*self.keys).unwrap().1;
-		deserialized_monitor.update_monitor(&update, &&TestBroadcaster{}, &&FuzzEstimator{}, &self.logger).unwrap();
+		deserialized_monitor.update_monitor(&update, &&TestBroadcaster{}, &&FuzzEstimator { ret_val: atomic::AtomicU32::new(253) }, &self.logger).unwrap();
 		let mut ser = VecWriter(Vec::new());
 		deserialized_monitor.write(&mut ser).unwrap();
 		map_entry.insert((update.update_id, ser.0));
@@ -328,14 +340,13 @@ fn send_hop_payment(source: &ChanMan, middle: &ChanMan, middle_chan_id: u64, des
 
 #[inline]
 pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
-	let fee_est = Arc::new(FuzzEstimator{});
 	let broadcast = Arc::new(TestBroadcaster{});
 
 	macro_rules! make_node {
-		($node_id: expr) => { {
+		($node_id: expr, $fee_estimator: expr) => { {
 			let logger: Arc<dyn Logger> = Arc::new(test_logger::TestLogger::new($node_id.to_string(), out.clone()));
 			let keys_manager = Arc::new(KeyProvider { node_id: $node_id, rand_bytes_id: atomic::AtomicU32::new(0), revoked_commitments: Mutex::new(HashMap::new()) });
-			let monitor = Arc::new(TestChainMonitor::new(broadcast.clone(), logger.clone(), fee_est.clone(), Arc::new(TestPersister{}), Arc::clone(&keys_manager)));
+			let monitor = Arc::new(TestChainMonitor::new(broadcast.clone(), logger.clone(), $fee_estimator.clone(), Arc::new(TestPersister{}), Arc::clone(&keys_manager)));
 
 			let mut config = UserConfig::default();
 			config.channel_options.forwarding_fee_proportional_millionths = 0;
@@ -345,16 +356,16 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 				network,
 				best_block: BestBlock::from_genesis(network),
 			};
-			(ChannelManager::new(fee_est.clone(), monitor.clone(), broadcast.clone(), Arc::clone(&logger), keys_manager.clone(), config, params),
+			(ChannelManager::new($fee_estimator.clone(), monitor.clone(), broadcast.clone(), Arc::clone(&logger), keys_manager.clone(), config, params),
 			monitor, keys_manager)
 		} }
 	}
 
 	macro_rules! reload_node {
-		($ser: expr, $node_id: expr, $old_monitors: expr, $keys_manager: expr) => { {
+		($ser: expr, $node_id: expr, $old_monitors: expr, $keys_manager: expr, $fee_estimator: expr) => { {
 		    let keys_manager = Arc::clone(& $keys_manager);
 			let logger: Arc<dyn Logger> = Arc::new(test_logger::TestLogger::new($node_id.to_string(), out.clone()));
-			let chain_monitor = Arc::new(TestChainMonitor::new(broadcast.clone(), logger.clone(), fee_est.clone(), Arc::new(TestPersister{}), Arc::clone(& $keys_manager)));
+			let chain_monitor = Arc::new(TestChainMonitor::new(broadcast.clone(), logger.clone(), $fee_estimator.clone(), Arc::new(TestPersister{}), Arc::clone(& $keys_manager)));
 
 			let mut config = UserConfig::default();
 			config.channel_options.forwarding_fee_proportional_millionths = 0;
@@ -373,7 +384,7 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 
 			let read_args = ChannelManagerReadArgs {
 				keys_manager,
-				fee_estimator: fee_est.clone(),
+				fee_estimator: $fee_estimator.clone(),
 				chain_monitor: chain_monitor.clone(),
 				tx_broadcaster: broadcast.clone(),
 				logger,
@@ -488,11 +499,18 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 		} }
 	}
 
+	let fee_est_a = Arc::new(FuzzEstimator { ret_val: atomic::AtomicU32::new(253) });
+	let mut last_htlc_clear_fee_a =  253;
+	let fee_est_b = Arc::new(FuzzEstimator { ret_val: atomic::AtomicU32::new(253) });
+	let mut last_htlc_clear_fee_b =  253;
+	let fee_est_c = Arc::new(FuzzEstimator { ret_val: atomic::AtomicU32::new(253) });
+	let mut last_htlc_clear_fee_c =  253;
+
 	// 3 nodes is enough to hit all the possible cases, notably unknown-source-unknown-dest
 	// forwarding.
-	let (node_a, mut monitor_a, keys_manager_a) = make_node!(0);
-	let (node_b, mut monitor_b, keys_manager_b) = make_node!(1);
-	let (node_c, mut monitor_c, keys_manager_c) = make_node!(2);
+	let (node_a, mut monitor_a, keys_manager_a) = make_node!(0, fee_est_a);
+	let (node_b, mut monitor_b, keys_manager_b) = make_node!(1, fee_est_b);
+	let (node_c, mut monitor_c, keys_manager_c) = make_node!(2, fee_est_c);
 
 	let mut nodes = [node_a, node_b, node_c];
 
@@ -630,7 +648,6 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 						events::MessageSendEvent::UpdateHTLCs { node_id, updates: CommitmentUpdate { update_add_htlcs, update_fail_htlcs, update_fulfill_htlcs, update_fail_malformed_htlcs, update_fee, commitment_signed } } => {
 							for dest in nodes.iter() {
 								if dest.get_our_node_id() == node_id {
-									assert!(update_fee.is_none());
 									for update_add in update_add_htlcs.iter() {
 										if !$corrupt_forward {
 											dest.handle_update_add_htlc(&nodes[$node].get_our_node_id(), update_add);
@@ -654,6 +671,9 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 									for update_fail_malformed in update_fail_malformed_htlcs.iter() {
 										dest.handle_update_fail_malformed_htlc(&nodes[$node].get_our_node_id(), update_fail_malformed);
 									}
+									if let Some(msg) = update_fee {
+										dest.handle_update_fee(&nodes[$node].get_our_node_id(), &msg);
+									}
 									let processed_change = !update_add_htlcs.is_empty() || !update_fulfill_htlcs.is_empty() ||
 										!update_fail_htlcs.is_empty() || !update_fail_malformed_htlcs.is_empty();
 									if $limit_events != ProcessMessages::AllMessages && processed_change {
@@ -918,7 +938,7 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 					node_a_ser.0.clear();
 					nodes[0].write(&mut node_a_ser).unwrap();
 				}
-				let (new_node_a, new_monitor_a) = reload_node!(node_a_ser, 0, monitor_a, keys_manager_a);
+				let (new_node_a, new_monitor_a) = reload_node!(node_a_ser, 0, monitor_a, keys_manager_a, fee_est_a);
 				nodes[0] = new_node_a;
 				monitor_a = new_monitor_a;
 			},
@@ -937,7 +957,7 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 					bc_events.clear();
 					cb_events.clear();
 				}
-				let (new_node_b, new_monitor_b) = reload_node!(node_b_ser, 1, monitor_b, keys_manager_b);
+				let (new_node_b, new_monitor_b) = reload_node!(node_b_ser, 1, monitor_b, keys_manager_b, fee_est_b);
 				nodes[1] = new_node_b;
 				monitor_b = new_monitor_b;
 			},
@@ -951,7 +971,7 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 					node_c_ser.0.clear();
 					nodes[2].write(&mut node_c_ser).unwrap();
 				}
-				let (new_node_c, new_monitor_c) = reload_node!(node_c_ser, 2, monitor_c, keys_manager_c);
+				let (new_node_c, new_monitor_c) = reload_node!(node_c_ser, 2, monitor_c, keys_manager_c, fee_est_c);
 				nodes[2] = new_node_c;
 				monitor_c = new_monitor_c;
 			},
@@ -1013,6 +1033,33 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 			0x6c => { send_hop_payment(&nodes[0], &nodes[1], chan_a, &nodes[2], chan_b, 1, &mut payment_id); },
 			0x6d => { send_hop_payment(&nodes[2], &nodes[1], chan_b, &nodes[0], chan_a, 1, &mut payment_id); },
 
+			0x80 => {
+				let max_feerate = last_htlc_clear_fee_a * CHAN_STUCK_FEE_INCREASE_MULTIPLE as u32;
+				if fee_est_a.ret_val.fetch_add(250, atomic::Ordering::AcqRel) + 250 > max_feerate {
+					fee_est_a.ret_val.store(max_feerate, atomic::Ordering::Release);
+				}
+				nodes[0].maybe_update_chan_fees();
+			},
+			0x81 => { fee_est_a.ret_val.store(253, atomic::Ordering::Release); nodes[0].maybe_update_chan_fees(); },
+
+			0x84 => {
+				let max_feerate = last_htlc_clear_fee_b * CHAN_STUCK_FEE_INCREASE_MULTIPLE as u32;
+				if fee_est_b.ret_val.fetch_add(250, atomic::Ordering::AcqRel) + 250 > max_feerate {
+					fee_est_b.ret_val.store(max_feerate, atomic::Ordering::Release);
+				}
+				nodes[1].maybe_update_chan_fees();
+			},
+			0x85 => { fee_est_b.ret_val.store(253, atomic::Ordering::Release); nodes[1].maybe_update_chan_fees(); },
+
+			0x88 => {
+				let max_feerate = last_htlc_clear_fee_c * CHAN_STUCK_FEE_INCREASE_MULTIPLE as u32;
+				if fee_est_c.ret_val.fetch_add(250, atomic::Ordering::AcqRel) + 250 > max_feerate {
+					fee_est_c.ret_val.store(max_feerate, atomic::Ordering::Release);
+				}
+				nodes[2].maybe_update_chan_fees();
+			},
+			0x89 => { fee_est_c.ret_val.store(253, atomic::Ordering::Release); nodes[2].maybe_update_chan_fees(); },
+
 			0xff => {
 				// Test that no channel is in a stuck state where neither party can send funds even
 				// after we resolve all pending events.
@@ -1068,6 +1115,10 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], out: Out) {
 				assert!(
 					send_payment(&nodes[1], &nodes[2], chan_b, 10_000_000, &mut payment_id) ||
 					send_payment(&nodes[2], &nodes[1], chan_b, 10_000_000, &mut payment_id));
+
+				last_htlc_clear_fee_a = fee_est_a.ret_val.load(atomic::Ordering::Acquire);
+				last_htlc_clear_fee_b = fee_est_b.ret_val.load(atomic::Ordering::Acquire);
+				last_htlc_clear_fee_c = fee_est_c.ret_val.load(atomic::Ordering::Acquire);
 			},
 			_ => test_return!(),
 		}
diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
@@ -301,6 +301,21 @@ pub struct CounterpartyForwardingInfo {
 	pub cltv_expiry_delta: u16,
 }
 
+/// When a node increases the feerate on an outbound channel, it can cause the channel to get
+/// "stuck" if the other side holds most of the funds, and suddenly is unable to send an HTLC as it
+/// would effectively debit the channel initiator to pay for the new HTLC's fee. If the initiator's
+/// balance is right at or near the channel reserve, neither side will be able to send an HTLC.
+/// Thus, before sending an HTLC when we are the initiator, we check that the feerate can increase
+/// by this multiple without hitting this case, before sending.
+/// This multiple is effectively the maximum feerate "jump" we expect until more HTLCs flow over
+/// the channel. Sadly, there isn't really a good number for this - if we expect to have no new
+/// HTLCs for days we may need this to suffice for feerate increases across days, but that may
+/// leave the channel less usable as we hold a bigger reserve.
+#[cfg(fuzzing)]
+pub const CHAN_STUCK_FEE_INCREASE_MULTIPLE: u64 = 2;
+#[cfg(not(fuzzing))]
+const CHAN_STUCK_FEE_INCREASE_MULTIPLE: u64 = 2;
+
 // TODO: We should refactor this to be an Inbound/OutboundChannel until initial setup handshaking
 // has been completed, and then turn into a Channel to get compiler-time enforcement of things like
 // calling channel_id() before we're set up or things like get_outbound_funding_signed on an
@@ -4102,7 +4117,7 @@ impl<Signer: Sign> Channel<Signer> {
 		// `2 *` and extra HTLC are for the fee spike buffer.
 		let commit_tx_fee_msat = if self.is_outbound() {
 			let htlc_candidate = HTLCCandidate::new(amount_msat, HTLCInitiator::LocalOffered);
-			2 * self.next_local_commit_tx_fee_msat(htlc_candidate, Some(()))
+			CHAN_STUCK_FEE_INCREASE_MULTIPLE * self.next_local_commit_tx_fee_msat(htlc_candidate, Some(()))
 		} else { 0 };
 		if pending_value_to_self_msat - amount_msat < commit_tx_fee_msat {
 			return Err(ChannelError::Ignore(format!("Cannot send value that would not leave enough to pay for fees. Pending value to self: {}. local_commit_tx_fee {}", pending_value_to_self_msat, commit_tx_fee_msat)));
diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
@@ -2453,6 +2453,37 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 		(retain_channel, should_persist, ret_err)
 	}
 
+	#[cfg(fuzzing)]
+	/// In chanmon_consistency we want to sometimes do the channel fee updates done in
+	/// timer_tick_occurred, but we can't generate the disabled channel updates as it considers
+	/// these a fuzz failure (as they usually indicate a channel force-close, which is exactly what
+	/// it wants to detect). Thus, we have a variant exposed here for its benefit.
+	pub fn maybe_update_chan_fees(&self) {
+		PersistenceNotifierGuard::optionally_notify(&self.total_consistency_lock, &self.persistence_notifier, || {
+			let mut should_persist = NotifyOption::SkipPersist;
+
+			let new_feerate = self.fee_estimator.get_est_sat_per_1000_weight(ConfirmationTarget::Normal);
+
+			let mut handle_errors = Vec::new();
+			{
+				let mut channel_state_lock = self.channel_state.lock().unwrap();
+				let channel_state = &mut *channel_state_lock;
+				let pending_msg_events = &mut channel_state.pending_msg_events;
+				let short_to_id = &mut channel_state.short_to_id;
+				channel_state.by_id.retain(|chan_id, chan| {
+					let (retain_channel, chan_needs_persist, err) = self.update_channel_fee(short_to_id, pending_msg_events, chan_id, chan, new_feerate);
+					if chan_needs_persist == NotifyOption::DoPersist { should_persist = NotifyOption::DoPersist; }
+					if err.is_err() {
+						handle_errors.push(err);
+					}
+					retain_channel
+				});
+			}
+
+			should_persist
+		});
+	}
+
 	/// If a peer is disconnected we mark any channels with that peer as 'disabled'.
 	/// After some time, if channels are still disabled we need to broadcast a ChannelUpdate
 	/// to inform the network about the uselessness of these channels.
diff --git a/lightning/src/ln/mod.rs b/lightning/src/ln/mod.rs
@@ -33,7 +33,11 @@ pub mod peer_channel_encryptor;
 #[cfg(not(feature = "fuzztarget"))]
 pub(crate) mod peer_channel_encryptor;
 
+#[cfg(feature = "fuzztarget")]
+pub mod channel;
+#[cfg(not(feature = "fuzztarget"))]
 mod channel;
+
 mod onion_utils;
 mod wire;
 
