From f6a5784f91d6782fcbb1c4a83d0312e4b50134c1 Mon Sep 17 00:00:00 2001
From: Clara van Staden <claravanstaden64@gmail.com>
Date: Fri, 17 May 2024 13:35:22 +0200
Subject: [PATCH] Snowbridge - Ethereum Client - Reject finalized updates
 without a sync committee in next store period (#4485)

This is a cherry-pick from master of
https://github.com/paritytech/polkadot-sdk/pull/4478

Expected patches for (1.10.0):
snowbridge-pallet-ethereum-client

Co-authored-by: Vincent Geddes <117534+vgeddes@users.noreply.github.com>
---
 .../snowbridge/pallets/ethereum-client/src/lib.rs  |  7 +++++++
 .../pallets/ethereum-client/src/tests.rs           | 14 +++++++++++++-
 prdoc/pr_4478.prdoc                                | 13 +++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 prdoc/pr_4478.prdoc

diff --git a/bridges/snowbridge/pallets/ethereum-client/src/lib.rs b/bridges/snowbridge/pallets/ethereum-client/src/lib.rs
index c1b9e19729bc..0ba1b8df4654 100644
--- a/bridges/snowbridge/pallets/ethereum-client/src/lib.rs
+++ b/bridges/snowbridge/pallets/ethereum-client/src/lib.rs
@@ -104,6 +104,7 @@ pub mod pallet {
 	#[pallet::error]
 	pub enum Error<T> {
 		SkippedSyncCommitteePeriod,
+		SyncCommitteeUpdateRequired,
 		/// Attested header is older than latest finalized header.
 		IrrelevantUpdate,
 		NotBootstrapped,
@@ -320,6 +321,7 @@ pub mod pallet {
 
 			// Verify update is relevant.
 			let update_attested_period = compute_period(update.attested_header.slot);
+			let update_finalized_period = compute_period(update.finalized_header.slot);
 			let update_has_next_sync_committee = !<NextSyncCommittee<T>>::exists() &&
 				(update.next_sync_committee_update.is_some() &&
 					update_attested_period == store_period);
@@ -395,6 +397,11 @@ pub mod pallet {
 					),
 					Error::<T>::InvalidSyncCommitteeMerkleProof
 				);
+			} else {
+				ensure!(
+					update_finalized_period == store_period,
+					Error::<T>::SyncCommitteeUpdateRequired
+				);
 			}
 
 			// Verify sync committee aggregate signature.
diff --git a/bridges/snowbridge/pallets/ethereum-client/src/tests.rs b/bridges/snowbridge/pallets/ethereum-client/src/tests.rs
index 765958c12821..da762dc2fd80 100644
--- a/bridges/snowbridge/pallets/ethereum-client/src/tests.rs
+++ b/bridges/snowbridge/pallets/ethereum-client/src/tests.rs
@@ -362,13 +362,14 @@ fn submit_update_with_sync_committee_in_current_period() {
 }
 
 #[test]
-fn submit_update_in_next_period() {
+fn reject_submit_update_in_next_period() {
 	let checkpoint = Box::new(load_checkpoint_update_fixture());
 	let sync_committee_update = Box::new(load_sync_committee_update_fixture());
 	let update = Box::new(load_next_finalized_header_update_fixture());
 	let sync_committee_period = compute_period(sync_committee_update.finalized_header.slot);
 	let next_sync_committee_period = compute_period(update.finalized_header.slot);
 	assert_eq!(sync_committee_period + 1, next_sync_committee_period);
+	let next_sync_committee_update = Box::new(load_next_sync_committee_update_fixture());
 
 	new_tester().execute_with(|| {
 		assert_ok!(EthereumBeaconClient::process_checkpoint_update(&checkpoint));
@@ -376,6 +377,17 @@ fn submit_update_in_next_period() {
 			RuntimeOrigin::signed(1),
 			sync_committee_update.clone()
 		));
+		// check an update in the next period is rejected
+		assert_err!(
+			EthereumBeaconClient::submit(RuntimeOrigin::signed(1), update.clone()),
+			Error::<Test>::SyncCommitteeUpdateRequired
+		);
+		// submit update with next sync committee
+		assert_ok!(EthereumBeaconClient::submit(
+			RuntimeOrigin::signed(1),
+			next_sync_committee_update
+		));
+		// check same header in the next period can now be submitted successfully
 		assert_ok!(EthereumBeaconClient::submit(RuntimeOrigin::signed(1), update.clone()));
 		let block_root: H256 = update.finalized_header.clone().hash_tree_root().unwrap();
 		assert!(<FinalizedBeaconState<Test>>::contains_key(block_root));
diff --git a/prdoc/pr_4478.prdoc b/prdoc/pr_4478.prdoc
new file mode 100644
index 000000000000..22e2e43db4ca
--- /dev/null
+++ b/prdoc/pr_4478.prdoc
@@ -0,0 +1,13 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Snowbridge - Ethereum Client - Reject finalized updates without a sync committee in next store period
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      Bug fix in the Ethereum light client that stalls the light client when an update in the next sync committee period is received without receiving the next sync committee update in the next period.
+
+crates:
+  - name: snowbridge-pallet-ethereum-client
+    bump: patch