From 9f3bb7d7a54ca24e42d358a9f0f78cf8944d3f98 Mon Sep 17 00:00:00 2001
From: Wilmer Paulino <wilmer@wilmerpaulino.com>
Date: Thu, 28 Sep 2023 12:12:19 -0700
Subject: [PATCH] Fix incorrect anchors `counterparty_payment_script` upon
 deserialization

---
 lightning/src/chain/channelmonitor.rs | 23 ++++++-
 lightning/src/ln/monitor_tests.rs     | 87 +++++++++++++++++++++++++++
 lightning/src/util/test_utils.rs      | 11 +++-
 3 files changed, 119 insertions(+), 2 deletions(-)

diff --git a/lightning/src/chain/channelmonitor.rs b/lightning/src/chain/channelmonitor.rs
index 95f68ba22..53ac85c29 100644
--- a/lightning/src/chain/channelmonitor.rs
+++ b/lightning/src/chain/channelmonitor.rs
@@ -1696,6 +1696,16 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitor<Signer> {
 			Vec::new()
 		}
 	}
+
+	#[cfg(test)]
+	pub fn get_counterparty_payment_script(&self) -> Script{
+		self.inner.lock().unwrap().counterparty_payment_script.clone()
+	}
+
+	#[cfg(test)]
+	pub fn set_counterparty_payment_script(&self, script: Script) {
+		self.inner.lock().unwrap().counterparty_payment_script = script;
+	}
 }
 
 impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitorImpl<Signer> {
@@ -4146,7 +4156,7 @@ impl<'a, 'b, ES: EntropySource, SP: SignerProvider> ReadableArgs<(&'a ES, &'b SP
 			1 => { None },
 			_ => return Err(DecodeError::InvalidValue),
 		};
-		let counterparty_payment_script = Readable::read(reader)?;
+		let mut counterparty_payment_script: Script = Readable::read(reader)?;
 		let shutdown_script = {
 			let script = <Script as Readable>::read(reader)?;
 			if script.is_empty() { None } else { Some(script) }
@@ -4347,6 +4357,17 @@ impl<'a, 'b, ES: EntropySource, SP: SignerProvider> ReadableArgs<(&'a ES, &'b SP
 			(17, initial_counterparty_commitment_info, option),
 		});
 
+		// Monitors for anchor outputs channels opened in v0.0.116 suffered from a bug in which the
+		// wrong `counterparty_payment_script` was being tracked. Fix it now on deserialization to
+		// give them a chance to recognize the spendable output.
+		if onchain_tx_handler.channel_type_features().supports_anchors_zero_fee_htlc_tx() &&
+			counterparty_payment_script.is_v0_p2wpkh()
+		{
+			let payment_point = onchain_tx_handler.channel_transaction_parameters.holder_pubkeys.payment_point;
+			counterparty_payment_script =
+				chan_utils::get_to_countersignatory_with_anchors_redeemscript(&payment_point).to_v0_p2wsh();
+		}
+
 		Ok((best_block.block_hash(), ChannelMonitor::from_impl(ChannelMonitorImpl {
 			latest_update_id,
 			commitment_transaction_number_obscure_factor,
diff --git a/lightning/src/ln/monitor_tests.rs b/lightning/src/ln/monitor_tests.rs
index 3a300bf07..00f8613cb 100644
--- a/lightning/src/ln/monitor_tests.rs
+++ b/lightning/src/ln/monitor_tests.rs
@@ -2318,3 +2318,90 @@ fn test_anchors_aggregated_revoked_htlc_tx() {
 	// revoked commitment which Bob has the preimage for.
 	assert_eq!(nodes[1].chain_monitor.chain_monitor.get_claimable_balances(&[]).len(), 6);
 }
+
+fn do_test_anchors_monitor_fixes_counterparty_payment_script_on_reload(confirm_commitment_before_reload: bool) {
+	// Tests that we'll fix a ChannelMonitor's `counterparty_payment_script` for an anchor outputs
+	// channel upon deserialization.
+	let chanmon_cfgs = create_chanmon_cfgs(2);
+	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
+	let persister;
+	let chain_monitor;
+	let mut user_config = test_default_channel_config();
+	user_config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx = true;
+	user_config.manually_accept_inbound_channels = true;
+	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[Some(user_config), Some(user_config)]);
+	let node_deserialized;
+	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+	let (_, _, chan_id, funding_tx) = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100_000, 50_000_000);
+
+	// Set the monitor's `counterparty_payment_script` to a dummy P2WPKH script.
+	let secp = Secp256k1::new();
+	let privkey = bitcoin::PrivateKey::from_slice(&[1; 32], bitcoin::Network::Testnet).unwrap();
+	let pubkey = bitcoin::PublicKey::from_private_key(&secp, &privkey);
+	let p2wpkh_script = Script::new_v0_p2wpkh(&pubkey.wpubkey_hash().unwrap());
+	get_monitor!(nodes[1], chan_id).set_counterparty_payment_script(p2wpkh_script.clone());
+	assert_eq!(get_monitor!(nodes[1], chan_id).get_counterparty_payment_script(), p2wpkh_script);
+
+	// Confirm the counterparty's commitment and reload the monitor (either before or after) such
+	// that we arrive at the correct `counterparty_payment_script` after the reload.
+	nodes[0].node.force_close_broadcasting_latest_txn(&chan_id, &nodes[1].node.get_our_node_id()).unwrap();
+	check_added_monitors(&nodes[0], 1);
+	check_closed_broadcast(&nodes[0], 1, true);
+	check_closed_event!(&nodes[0], 1, ClosureReason::HolderForceClosed, false,
+		 [nodes[1].node.get_our_node_id()], 100000);
+
+	let commitment_tx = {
+		let mut txn = nodes[0].tx_broadcaster.unique_txn_broadcast();
+		assert_eq!(txn.len(), 1);
+		assert_eq!(txn[0].output.len(), 4);
+		check_spends!(txn[0], funding_tx);
+		txn.pop().unwrap()
+	};
+
+	mine_transaction(&nodes[0], &commitment_tx);
+	let commitment_tx_conf_height = if confirm_commitment_before_reload {
+		// We should expect our round trip serialization check to fail as we're writing the monitor
+		// with the incorrect P2WPKH script but reading it with the correct P2WSH script.
+		*nodes[1].chain_monitor.expect_monitor_round_trip_fail.lock().unwrap() = Some(chan_id);
+		let commitment_tx_conf_height = block_from_scid(&mine_transaction(&nodes[1], &commitment_tx));
+		let serialized_monitor = get_monitor!(nodes[1], chan_id).encode();
+		reload_node!(nodes[1], user_config, &nodes[1].node.encode(), &[&serialized_monitor], persister, chain_monitor, node_deserialized);
+		commitment_tx_conf_height
+	} else {
+		let serialized_monitor = get_monitor!(nodes[1], chan_id).encode();
+		reload_node!(nodes[1], user_config, &nodes[1].node.encode(), &[&serialized_monitor], persister, chain_monitor, node_deserialized);
+		let commitment_tx_conf_height = block_from_scid(&mine_transaction(&nodes[1], &commitment_tx));
+		check_added_monitors(&nodes[1], 1);
+		check_closed_broadcast(&nodes[1], 1, true);
+		commitment_tx_conf_height
+	};
+	check_closed_event!(&nodes[1], 1, ClosureReason::CommitmentTxConfirmed, false,
+		 [nodes[0].node.get_our_node_id()], 100000);
+	assert!(get_monitor!(nodes[1], chan_id).get_counterparty_payment_script().is_v0_p2wsh());
+
+	connect_blocks(&nodes[0], ANTI_REORG_DELAY - 1);
+	connect_blocks(&nodes[1], ANTI_REORG_DELAY - 1);
+
+	if confirm_commitment_before_reload {
+		// If we saw the commitment before our `counterparty_payment_script` was fixed, we'll never
+		// get the spendable output event for the `to_remote` output, so we'll need to get it
+		// manually via `get_spendable_outputs`.
+		check_added_monitors(&nodes[1], 1);
+		let outputs = get_monitor!(nodes[1], chan_id).get_spendable_outputs(&commitment_tx, commitment_tx_conf_height);
+		assert_eq!(outputs.len(), 1);
+		let spend_tx = nodes[1].keys_manager.backing.spend_spendable_outputs(
+			&[&outputs[0]], Vec::new(), Builder::new().push_opcode(opcodes::all::OP_RETURN).into_script(),
+			253, None, &secp
+		).unwrap();
+		check_spends!(spend_tx, &commitment_tx);
+	} else {
+		test_spendable_output(&nodes[1], &commitment_tx);
+	}
+}
+
+#[test]
+fn test_anchors_monitor_fixes_counterparty_payment_script_on_reload() {
+	do_test_anchors_monitor_fixes_counterparty_payment_script_on_reload(false);
+	do_test_anchors_monitor_fixes_counterparty_payment_script_on_reload(true);
+}
diff --git a/lightning/src/util/test_utils.rs b/lightning/src/util/test_utils.rs
index 18c3db76f..b912221fa 100644
--- a/lightning/src/util/test_utils.rs
+++ b/lightning/src/util/test_utils.rs
@@ -207,6 +207,9 @@ pub struct TestChainMonitor<'a> {
 	/// ChannelForceClosed event for the given channel_id with should_broadcast set to the given
 	/// boolean.
 	pub expect_channel_force_closed: Mutex<Option<(ChannelId, bool)>>,
+	/// If this is set to Some(), the next round trip serialization check will not hold after an
+	/// update_channel call (not watch_channel) for the given channel_id.
+	pub expect_monitor_round_trip_fail: Mutex<Option<ChannelId>>,
 }
 impl<'a> TestChainMonitor<'a> {
 	pub fn new(chain_source: Option<&'a TestChainSource>, broadcaster: &'a chaininterface::BroadcasterInterface, logger: &'a TestLogger, fee_estimator: &'a TestFeeEstimator, persister: &'a chainmonitor::Persist<TestChannelSigner>, keys_manager: &'a TestKeysInterface) -> Self {
@@ -217,6 +220,7 @@ impl<'a> TestChainMonitor<'a> {
 			chain_monitor: chainmonitor::ChainMonitor::new(chain_source, broadcaster, logger, fee_estimator, persister),
 			keys_manager,
 			expect_channel_force_closed: Mutex::new(None),
+			expect_monitor_round_trip_fail: Mutex::new(None),
 		}
 	}
 
@@ -267,7 +271,12 @@ impl<'a> chain::Watch<TestChannelSigner> for TestChainMonitor<'a> {
 		monitor.write(&mut w).unwrap();
 		let new_monitor = <(BlockHash, channelmonitor::ChannelMonitor<TestChannelSigner>)>::read(
 			&mut io::Cursor::new(&w.0), (self.keys_manager, self.keys_manager)).unwrap().1;
-		assert!(new_monitor == *monitor);
+		if let Some(chan_id) = self.expect_monitor_round_trip_fail.lock().unwrap().take() {
+			assert_eq!(chan_id, funding_txo.to_channel_id());
+			assert!(new_monitor != *monitor);
+		} else {
+			assert!(new_monitor == *monitor);
+		}
 		self.added_monitors.lock().unwrap().push((funding_txo, new_monitor));
 		update_res
 	}
-- 
2.39.5