Issue 4804: Notify chain selection of concluded disputes directly (#6512)

* Setting up new ChainSelectionMessage

* Partial first pass

* Got dispute conclusion data to provisioner

* Finished first draft for 4804 code

* A bit of polish and code comments

* cargo fmt

* Implementers guide and code comments

* More formatting, and naming issues

* Wrote test for ChainSelection side of change

* Added dispute coordinator side test

* FMT

* Addressing Marcin's comments

* fmt

* Addressing further Marcin comment

* Removing unnecessary test line

* Rough draft addressing Robert changes

* Clean up and test modification

* Majorly refactored scraper change

* Minor fixes for ChainSelection

* Polish and fmt

* Condensing inclusions per candidate logic

* Addressing Tsveto's comments

* Addressing Robert's Comments

* Altered inclusions struct to use nested BTreeMaps

* Naming fix

* Fixing inclusions struct comments

* Update node/core/dispute-coordinator/src/scraping/mod.rs

Add comment to split_off() use

Co-authored-by: Marcin S. <marcin@bytedude.com>

* Optimizing removal at block height for inclusions

* fmt

* Using copy trait

Co-authored-by: Marcin S. <marcin@bytedude.com>

polkadot/node/core/chain-selection/src/lib.rs

@@ -466,6 +466,10 @@ where
 
 							let _ = tx.send(best_containing);
 						}
+						ChainSelectionMessage::RevertBlocks(blocks_to_revert) => {
+							let write_ops = handle_revert_blocks(backend, blocks_to_revert)?;
+							backend.write(write_ops)?;
+						}
 					}
 				}
 			}
@@ -678,6 +682,21 @@ fn handle_approved_block(backend: &mut impl Backend, approved_block: Hash) -> Re
 	backend.write(ops)
 }
 
+// Here we revert a provided group of blocks. The most common cause for this is that
+// the dispute coordinator has notified chain selection of a dispute which concluded
+// against a candidate.
+fn handle_revert_blocks(
+	backend: &impl Backend,
+	blocks_to_revert: Vec<(BlockNumber, Hash)>,
+) -> Result<Vec<BackendWriteOp>, Error> {
+	let mut overlay = OverlayedBackend::new(backend);
+	for (block_number, block_hash) in blocks_to_revert {
+		tree::apply_single_reversion(&mut overlay, block_hash, block_number)?;
+	}
+
+	Ok(overlay.into_write_ops().collect())
+}
+
 fn detect_stagnant(
 	backend: &mut impl Backend,
 	now: Timestamp,

polkadot/node/core/chain-selection/src/tests.rs

@@ -2014,3 +2014,106 @@ fn stagnant_makes_childless_parent_leaf() {
 		virtual_overseer
 	})
 }
+
+#[test]
+fn revert_blocks_message_triggers_proper_reversion() {
+	test_harness(|backend, _, mut virtual_overseer| async move {
+		// Building mini chain with 1 finalized block and 3 unfinalized blocks
+		let finalized_number = 0;
+		let finalized_hash = Hash::repeat_byte(0);
+
+		let (head_hash, built_chain) =
+			construct_chain_on_base(vec![1, 2, 3], finalized_number, finalized_hash, |_| {});
+
+		import_blocks_into(
+			&mut virtual_overseer,
+			&backend,
+			Some((finalized_number, finalized_hash)),
+			built_chain.clone(),
+		)
+		.await;
+
+		// Checking mini chain
+		assert_backend_contains(&backend, built_chain.iter().map(|&(ref h, _)| h));
+		assert_leaves(&backend, vec![head_hash]);
+		assert_leaves_query(&mut virtual_overseer, vec![head_hash]).await;
+
+		let block_1_hash = backend.load_blocks_by_number(1).unwrap().get(0).unwrap().clone();
+		let block_2_hash = backend.load_blocks_by_number(2).unwrap().get(0).unwrap().clone();
+
+		// Sending revert blocks message
+		let (_, write_rx) = backend.await_next_write();
+		virtual_overseer
+			.send(FromOrchestra::Communication {
+				msg: ChainSelectionMessage::RevertBlocks(Vec::from([(2, block_2_hash)])),
+			})
+			.await;
+
+		write_rx.await.unwrap();
+
+		// Checking results:
+		// Block 2 should be explicitly reverted
+		assert_eq!(
+			backend
+				.load_block_entry(&block_2_hash)
+				.unwrap()
+				.unwrap()
+				.viability
+				.explicitly_reverted,
+			true
+		);
+		// Block 3 should be non-viable, with 2 as its earliest unviable ancestor
+		assert_eq!(
+			backend
+				.load_block_entry(&head_hash)
+				.unwrap()
+				.unwrap()
+				.viability
+				.earliest_unviable_ancestor,
+			Some(block_2_hash)
+		);
+		// Block 1 should be left as the only leaf
+		assert_leaves(&backend, vec![block_1_hash]);
+
+		virtual_overseer
+	})
+}
+
+#[test]
+fn revert_blocks_against_finalized_is_ignored() {
+	test_harness(|backend, _, mut virtual_overseer| async move {
+		// Building mini chain with 1 finalized block and 3 unfinalized blocks
+		let finalized_number = 0;
+		let finalized_hash = Hash::repeat_byte(0);
+
+		let (head_hash, built_chain) =
+			construct_chain_on_base(vec![1], finalized_number, finalized_hash, |_| {});
+
+		import_blocks_into(
+			&mut virtual_overseer,
+			&backend,
+			Some((finalized_number, finalized_hash)),
+			built_chain.clone(),
+		)
+		.await;
+
+		// Checking mini chain
+		assert_backend_contains(&backend, built_chain.iter().map(|&(ref h, _)| h));
+
+		// Sending dispute concluded against message
+		virtual_overseer
+			.send(FromOrchestra::Communication {
+				msg: ChainSelectionMessage::RevertBlocks(Vec::from([(
+					finalized_number,
+					finalized_hash,
+				)])),
+			})
+			.await;
+
+		// Leaf should be head if reversion of finalized was properly ignored
+		assert_leaves(&backend, vec![head_hash]);
+		assert_leaves_query(&mut virtual_overseer, vec![head_hash]).await;
+
+		virtual_overseer
+	})
+}

polkadot/node/core/chain-selection/src/tree.rs

@@ -247,7 +247,7 @@ pub(crate) fn import_block(
 	stagnant_at: Timestamp,
 ) -> Result<(), Error> {
 	add_block(backend, block_hash, block_number, parent_hash, weight, stagnant_at)?;
-	apply_reversions(backend, block_hash, block_number, reversion_logs)?;
+	apply_ancestor_reversions(backend, block_hash, block_number, reversion_logs)?;
 
 	Ok(())
 }
@@ -347,9 +347,9 @@ fn add_block(
 	Ok(())
 }
 
-// Assuming that a block is already imported, accepts the number of the block
-// as well as a list of reversions triggered by the block in ascending order.
-fn apply_reversions(
+/// Assuming that a block is already imported, accepts the number of the block
+/// as well as a list of reversions triggered by the block in ascending order.
+fn apply_ancestor_reversions(
 	backend: &mut OverlayedBackend<impl Backend>,
 	block_hash: Hash,
 	block_number: BlockNumber,
@@ -358,42 +358,79 @@ fn apply_reversions(
 	// Note: since revert numbers are  in ascending order, the expensive propagation
 	// of unviability is only heavy on the first log.
 	for revert_number in reversions {
-		let mut ancestor_entry =
-			match load_ancestor(backend, block_hash, block_number, revert_number)? {
-				None => {
-					gum::warn!(
-						target: LOG_TARGET,
-						?block_hash,
-						block_number,
-						revert_target = revert_number,
-						"The hammer has dropped. \
-					A block has indicated that its finalized ancestor be reverted. \
-					Please inform an adult.",
-					);
-
-					continue
-				},
-				Some(ancestor_entry) => {
-					gum::info!(
-						target: LOG_TARGET,
-						?block_hash,
-						block_number,
-						revert_target = revert_number,
-						revert_hash = ?ancestor_entry.block_hash,
-						"A block has signaled that its ancestor be reverted due to a bad parachain block.",
-					);
-
-					ancestor_entry
-				},
-			};
-
-		ancestor_entry.viability.explicitly_reverted = true;
-		propagate_viability_update(backend, ancestor_entry)?;
+		let maybe_block_entry = load_ancestor(backend, block_hash, block_number, revert_number)?;
+		revert_single_block_entry_if_present(
+			backend,
+			maybe_block_entry,
+			None,
+			revert_number,
+			Some(block_hash),
+			Some(block_number),
+		)?;
 	}
 
 	Ok(())
 }
 
+/// Marks a single block as explicitly reverted, then propagates viability updates
+/// to all its children. This is triggered when the disputes subsystem signals that
+/// a dispute has concluded against a candidate.
+pub(crate) fn apply_single_reversion(
+	backend: &mut OverlayedBackend<impl Backend>,
+	revert_hash: Hash,
+	revert_number: BlockNumber,
+) -> Result<(), Error> {
+	let maybe_block_entry = backend.load_block_entry(&revert_hash)?;
+	revert_single_block_entry_if_present(
+		backend,
+		maybe_block_entry,
+		Some(revert_hash),
+		revert_number,
+		None,
+		None,
+	)?;
+	Ok(())
+}
+
+fn revert_single_block_entry_if_present(
+	backend: &mut OverlayedBackend<impl Backend>,
+	maybe_block_entry: Option<BlockEntry>,
+	maybe_revert_hash: Option<Hash>,
+	revert_number: BlockNumber,
+	maybe_reporting_hash: Option<Hash>,
+	maybe_reporting_number: Option<BlockNumber>,
+) -> Result<(), Error> {
+	match maybe_block_entry {
+		None => {
+			gum::warn!(
+				target: LOG_TARGET,
+				?maybe_revert_hash,
+				revert_target = revert_number,
+				?maybe_reporting_hash,
+				?maybe_reporting_number,
+				"The hammer has dropped. \
+				The protocol has indicated that a finalized block be reverted. \
+				Please inform an adult.",
+			);
+		},
+		Some(mut block_entry) => {
+			gum::info!(
+				target: LOG_TARGET,
+				?maybe_revert_hash,
+				revert_target = revert_number,
+				?maybe_reporting_hash,
+				?maybe_reporting_number,
+				"Unfinalized block reverted due to a bad parachain block.",
+			);
+
+			block_entry.viability.explicitly_reverted = true;
+			// Marks children of reverted block as non-viable
+			propagate_viability_update(backend, block_entry)?;
+		},
+	}
+	Ok(())
+}
+
 /// Finalize a block with the given number and hash.
 ///
 /// This will prune all sub-trees not descending from the given block,

polkadot/node/core/dispute-coordinator/src/initialized.rs

@@ -30,7 +30,7 @@ use polkadot_node_primitives::{
 };
 use polkadot_node_subsystem::{
 	messages::{
-		ApprovalVotingMessage, BlockDescription, DisputeCoordinatorMessage,
+		ApprovalVotingMessage, BlockDescription, ChainSelectionMessage, DisputeCoordinatorMessage,
 		DisputeDistributionMessage, ImportStatementsResult,
 	},
 	overseer, ActivatedLeaf, ActiveLeavesUpdate, FromOrchestra, OverseerSignal,
@@ -1023,6 +1023,22 @@ impl Initialized {
 			}
 		}
 
+		// Notify ChainSelection if a dispute has concluded against a candidate. ChainSelection
+		// will need to mark the candidate's relay parent as reverted.
+		if import_result.is_freshly_concluded_against() {
+			let blocks_including = self.scraper.get_blocks_including_candidate(&candidate_hash);
+			if blocks_including.len() > 0 {
+				ctx.send_message(ChainSelectionMessage::RevertBlocks(blocks_including)).await;
+			} else {
+				gum::debug!(
+					target: LOG_TARGET,
+					?candidate_hash,
+					?session,
+					"Could not find an including block for candidate against which a dispute has concluded."
+				);
+			}
+		}
+
 		// Update metrics:
 		if import_result.is_freshly_disputed() {
 			self.metrics.on_open();

polkadot/node/core/dispute-coordinator/src/scraping/candidates.rs

@@ -102,15 +102,18 @@ impl ScrapedCandidates {
 	}
 
 	// Removes all candidates up to a given height. The candidates at the block height are NOT removed.
-	pub fn remove_up_to_height(&mut self, height: &BlockNumber) {
+	pub fn remove_up_to_height(&mut self, height: &BlockNumber) -> HashSet<CandidateHash> {
+		let mut candidates_modified: HashSet<CandidateHash> = HashSet::new();
 		let not_stale = self.candidates_by_block_number.split_off(&height);
 		let stale = std::mem::take(&mut self.candidates_by_block_number);
 		self.candidates_by_block_number = not_stale;
 		for candidates in stale.values() {
 			for c in candidates {
 				self.candidates.remove(c);
+				candidates_modified.insert(*c);
 			}
 		}
+		candidates_modified
 	}
 
 	pub fn insert(&mut self, block_number: BlockNumber, candidate_hash: CandidateHash) {

polkadot/node/core/dispute-coordinator/src/scraping/mod.rs

@@ -14,7 +14,10 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
-use std::num::NonZeroUsize;
+use std::{
+	collections::{BTreeMap, HashSet},
+	num::NonZeroUsize,
+};
 
 use futures::channel::oneshot;
 use lru::LruCache;
@@ -69,9 +72,73 @@ impl ScrapedUpdates {
 	}
 }
 
+/// A structure meant to facilitate chain reversions in the event of a dispute
+/// concluding against a candidate. Each candidate hash maps to a number of
+/// block heights, which in turn map to vectors of blocks at those heights.
+pub struct Inclusions {
+	inclusions_inner: BTreeMap<CandidateHash, BTreeMap<BlockNumber, Vec<Hash>>>,
+}
+
+impl Inclusions {
+	pub fn new() -> Self {
+		Self { inclusions_inner: BTreeMap::new() }
+	}
+
+	// Add parent block to the vector which has CandidateHash as an outer key and
+	// BlockNumber as an inner key
+	pub fn insert(
+		&mut self,
+		candidate_hash: CandidateHash,
+		block_number: BlockNumber,
+		block_hash: Hash,
+	) {
+		if let Some(blocks_including) = self.inclusions_inner.get_mut(&candidate_hash) {
+			if let Some(blocks_at_height) = blocks_including.get_mut(&block_number) {
+				blocks_at_height.push(block_hash);
+			} else {
+				blocks_including.insert(block_number, Vec::from([block_hash]));
+			}
+		} else {
+			let mut blocks_including: BTreeMap<BlockNumber, Vec<Hash>> = BTreeMap::new();
+			blocks_including.insert(block_number, Vec::from([block_hash]));
+			self.inclusions_inner.insert(candidate_hash, blocks_including);
+		}
+	}
+
+	pub fn remove_up_to_height(
+		&mut self,
+		height: &BlockNumber,
+		candidates_modified: HashSet<CandidateHash>,
+	) {
+		for candidate in candidates_modified {
+			if let Some(blocks_including) = self.inclusions_inner.get_mut(&candidate) {
+				// Returns everything after the given key, including the key. This works because the blocks are sorted in ascending order.
+				*blocks_including = blocks_including.split_off(height);
+			}
+		}
+		self.inclusions_inner
+			.retain(|_, blocks_including| blocks_including.keys().len() > 0);
+	}
+
+	pub fn get(&mut self, candidate: &CandidateHash) -> Vec<(BlockNumber, Hash)> {
+		let mut inclusions_as_vec: Vec<(BlockNumber, Hash)> = Vec::new();
+		if let Some(blocks_including) = self.inclusions_inner.get(candidate) {
+			for (height, blocks_at_height) in blocks_including.iter() {
+				for block in blocks_at_height {
+					inclusions_as_vec.push((*height, *block));
+				}
+			}
+		}
+		inclusions_as_vec
+	}
+}
+
 /// Chain scraper
 ///
-/// Scrapes unfinalized chain in order to collect information from blocks.
+/// Scrapes unfinalized chain in order to collect information from blocks. Chain scraping
+/// during disputes enables critical spam prevention. It does so by updating two important
+/// criteria determining whether a vote sent during dispute distribution is potential
+/// spam. Namely, whether the candidate being voted on is backed or included.
 ///
 /// Concretely:
 ///
@@ -95,6 +162,11 @@ pub struct ChainScraper {
 	/// We assume that ancestors of cached blocks are already processed, i.e. we have saved
 	/// corresponding included candidates.
 	last_observed_blocks: LruCache<Hash, ()>,
+	/// Maps included candidate hashes to one or more relay block heights and hashes.
+	/// These correspond to all the relay blocks which marked a candidate as included,
+	/// and are needed to apply reversions in case a dispute is concluded against the
+	/// candidate.
+	inclusions: Inclusions,
 }
 
 impl ChainScraper {
@@ -119,6 +191,7 @@ impl ChainScraper {
 			included_candidates: candidates::ScrapedCandidates::new(),
 			backed_candidates: candidates::ScrapedCandidates::new(),
 			last_observed_blocks: LruCache::new(LRU_OBSERVED_BLOCKS_CAPACITY),
+			inclusions: Inclusions::new(),
 		};
 		let update =
 			ActiveLeavesUpdate { activated: Some(initial_head), deactivated: Default::default() };
@@ -195,7 +268,9 @@ impl ChainScraper {
 		{
 			Some(key_to_prune) => {
 				self.backed_candidates.remove_up_to_height(&key_to_prune);
-				self.included_candidates.remove_up_to_height(&key_to_prune);
+				let candidates_modified =
+					self.included_candidates.remove_up_to_height(&key_to_prune);
+				self.inclusions.remove_up_to_height(&key_to_prune, candidates_modified);
 			},
 			None => {
 				// Nothing to prune. We are still in the beginning of the chain and there are not
@@ -233,6 +308,7 @@ impl ChainScraper {
 						"Processing included event"
 					);
 					self.included_candidates.insert(block_number, candidate_hash);
+					self.inclusions.insert(candidate_hash, block_number, block_hash);
 					included_receipts.push(receipt);
 				},
 				CandidateEvent::CandidateBacked(receipt, _, _, _) => {
@@ -318,6 +394,13 @@ impl ChainScraper {
 		}
 		return Ok(ancestors)
 	}
+
+	pub fn get_blocks_including_candidate(
+		&mut self,
+		candidate: &CandidateHash,
+	) -> Vec<(BlockNumber, Hash)> {
+		self.inclusions.get(candidate)
+	}
 }
 
 async fn get_finalized_block_number<Sender>(sender: &mut Sender) -> FatalResult<BlockNumber>

polkadot/node/core/dispute-coordinator/src/scraping/tests.rs

@@ -578,3 +578,73 @@ fn scraper_handles_the_same_candidate_incuded_in_two_different_block_heights() {
 		assert!(!scraper.is_candidate_included(&magic_candidate.hash()));
 	});
 }
+
+#[test]
+fn inclusions_per_candidate_properly_adds_and_prunes() {
+	const TEST_TARGET_BLOCK_NUMBER: BlockNumber = 2;
+	const TEST_TARGET_BLOCK_NUMBER_2: BlockNumber = 3;
+
+	// How many blocks should we skip before sending a leaf update.
+	const BLOCKS_TO_SKIP: usize = 4;
+
+	futures::executor::block_on(async {
+		let (state, mut virtual_overseer) = TestState::new().await;
+
+		let TestState { mut chain, mut scraper, mut ctx } = state;
+
+		// 1 because `TestState` starts at leaf 1.
+		let next_update = (1..BLOCKS_TO_SKIP).map(|_| next_leaf(&mut chain)).last().unwrap();
+
+		let mut finalized_block_number = 1;
+		let expected_ancestry_len = BLOCKS_TO_SKIP - finalized_block_number as usize;
+		let overseer_fut = overseer_process_active_leaves_update(
+			&mut virtual_overseer,
+			&chain,
+			finalized_block_number,
+			expected_ancestry_len,
+			|block_num| {
+				if block_num == TEST_TARGET_BLOCK_NUMBER || block_num == TEST_TARGET_BLOCK_NUMBER_2
+				{
+					get_backed_and_included_candidate_events(TEST_TARGET_BLOCK_NUMBER)
+				} else {
+					vec![]
+				}
+			},
+		);
+		join(process_active_leaves_update(ctx.sender(), &mut scraper, next_update), overseer_fut)
+			.await;
+
+		let candidate = make_candidate_receipt(get_block_number_hash(TEST_TARGET_BLOCK_NUMBER));
+
+		// We included the same candidate at two different block heights. So both blocks in which
+		// the candidate is included are recorded
+		assert_eq!(
+			scraper.get_blocks_including_candidate(&candidate.hash()),
+			Vec::from([
+				(TEST_TARGET_BLOCK_NUMBER, get_block_number_hash(TEST_TARGET_BLOCK_NUMBER)),
+				(TEST_TARGET_BLOCK_NUMBER_2, get_block_number_hash(TEST_TARGET_BLOCK_NUMBER_2))
+			])
+		);
+
+		// After `DISPUTE_CANDIDATE_LIFETIME_AFTER_FINALIZATION` blocks the earlier inclusion should be removed
+		finalized_block_number =
+			TEST_TARGET_BLOCK_NUMBER + DISPUTE_CANDIDATE_LIFETIME_AFTER_FINALIZATION;
+		process_finalized_block(&mut scraper, &finalized_block_number);
+
+		// The later inclusion should still be present, as we haven't exceeded its lifetime
+		assert_eq!(
+			scraper.get_blocks_including_candidate(&candidate.hash()),
+			Vec::from([(
+				TEST_TARGET_BLOCK_NUMBER_2,
+				get_block_number_hash(TEST_TARGET_BLOCK_NUMBER_2)
+			)])
+		);
+
+		finalized_block_number =
+			TEST_TARGET_BLOCK_NUMBER_2 + DISPUTE_CANDIDATE_LIFETIME_AFTER_FINALIZATION;
+		process_finalized_block(&mut scraper, &finalized_block_number);
+
+		// Now both inclusions have exceeded their lifetimes after finalization and should be purged
+		assert!(scraper.get_blocks_including_candidate(&candidate.hash()).len() == 0);
+	});
+}

polkadot/node/core/dispute-coordinator/src/tests.rs

@@ -36,7 +36,7 @@ use polkadot_node_primitives::{
 };
 use polkadot_node_subsystem::{
 	messages::{
-		ApprovalVotingMessage, ChainApiMessage, DisputeCoordinatorMessage,
+		ApprovalVotingMessage, ChainApiMessage, ChainSelectionMessage, DisputeCoordinatorMessage,
 		DisputeDistributionMessage, ImportStatementsResult,
 	},
 	overseer::FromOrchestra,
@@ -3281,3 +3281,152 @@ fn participation_requests_reprioritized_for_newly_included() {
 		})
 	});
 }
+
+// When a dispute has concluded against a parachain block candidate we want to notify
+// the chain selection subsystem. Then chain selection can revert the relay parents of
+// the disputed candidate and mark all descendants as non-viable. This direct
+// notification saves time compared to letting chain selection learn about a dispute
+// conclusion from an on chain revert log.
+#[test]
+fn informs_chain_selection_when_dispute_concluded_against() {
+	test_harness(|mut test_state, mut virtual_overseer| {
+		Box::pin(async move {
+			let session = 1;
+
+			test_state.handle_resume_sync(&mut virtual_overseer, session).await;
+
+			let candidate_receipt = make_invalid_candidate_receipt();
+			let parent_1_number = 1;
+			let parent_2_number = 2;
+
+			let candidate_hash = candidate_receipt.hash();
+
+			// Including test candidate in 2 different parent blocks
+			let block_1_header = Header {
+				parent_hash: test_state.last_block,
+				number: parent_1_number,
+				digest: dummy_digest(),
+				state_root: dummy_hash(),
+				extrinsics_root: dummy_hash(),
+			};
+			let parent_1_hash = block_1_header.hash();
+
+			test_state
+				.activate_leaf_at_session(
+					&mut virtual_overseer,
+					session,
+					parent_1_number,
+					vec![make_candidate_included_event(candidate_receipt.clone())],
+				)
+				.await;
+
+			let block_2_header = Header {
+				parent_hash: test_state.last_block,
+				number: parent_2_number,
+				digest: dummy_digest(),
+				state_root: dummy_hash(),
+				extrinsics_root: dummy_hash(),
+			};
+			let parent_2_hash = block_2_header.hash();
+
+			test_state
+				.activate_leaf_at_session(
+					&mut virtual_overseer,
+					session,
+					parent_2_number,
+					vec![make_candidate_included_event(candidate_receipt.clone())],
+				)
+				.await;
+
+			let supermajority_threshold =
+				polkadot_primitives::v2::supermajority_threshold(test_state.validators.len());
+
+			let (valid_vote, invalid_vote) = generate_opposing_votes_pair(
+				&test_state,
+				ValidatorIndex(2),
+				ValidatorIndex(1),
+				candidate_hash,
+				session,
+				VoteType::Explicit,
+			)
+			.await;
+
+			let (pending_confirmation, confirmation_rx) = oneshot::channel();
+			virtual_overseer
+				.send(FromOrchestra::Communication {
+					msg: DisputeCoordinatorMessage::ImportStatements {
+						candidate_receipt: candidate_receipt.clone(),
+						session,
+						statements: vec![
+							(valid_vote, ValidatorIndex(2)),
+							(invalid_vote, ValidatorIndex(1)),
+						],
+						pending_confirmation: Some(pending_confirmation),
+					},
+				})
+				.await;
+			handle_approval_vote_request(&mut virtual_overseer, &candidate_hash, HashMap::new())
+				.await;
+			assert_matches!(confirmation_rx.await.unwrap(),
+				ImportStatementsResult::ValidImport => {}
+			);
+
+			// Use a different expected commitments hash to ensure the candidate validation returns invalid.
+			participation_with_distribution(
+				&mut virtual_overseer,
+				&candidate_hash,
+				CandidateCommitments::default().hash(),
+			)
+			.await;
+
+			let mut statements = Vec::new();
+			// minus 2, because of local vote and one previously imported invalid vote.
+			for i in (0_u32..supermajority_threshold as u32 - 2).map(|i| i + 3) {
+				let vote = test_state
+					.issue_explicit_statement_with_index(
+						ValidatorIndex(i),
+						candidate_hash,
+						session,
+						false,
+					)
+					.await;
+
+				statements.push((vote, ValidatorIndex(i as _)));
+			}
+
+			virtual_overseer
+				.send(FromOrchestra::Communication {
+					msg: DisputeCoordinatorMessage::ImportStatements {
+						candidate_receipt: candidate_receipt.clone(),
+						session,
+						statements,
+						pending_confirmation: None,
+					},
+				})
+				.await;
+			handle_approval_vote_request(&mut virtual_overseer, &candidate_hash, HashMap::new())
+				.await;
+
+			// Checking that concluded dispute has signaled the reversion of all parent blocks.
+			assert_matches!(
+				virtual_overseer.recv().await,
+				AllMessages::ChainSelection(
+					ChainSelectionMessage::RevertBlocks(revert_set)
+				) => {
+					assert!(revert_set.contains(&(parent_1_number, parent_1_hash)));
+					assert!(revert_set.contains(&(parent_2_number, parent_2_hash)));
+				},
+				"Overseer did not receive `ChainSelectionMessage::RevertBlocks` message"
+			);
+
+			// Wrap up
+			virtual_overseer.send(FromOrchestra::Signal(OverseerSignal::Conclude)).await;
+			assert_matches!(
+				virtual_overseer.try_recv().await,
+				None => {}
+			);
+
+			test_state
+		})
+	});
+}

polkadot/node/overseer/src/lib.rs

@@ -593,6 +593,7 @@ pub struct Overseer<SupportsParachains> {
 		ApprovalVotingMessage,
 		AvailabilityStoreMessage,
 		AvailabilityRecoveryMessage,
+		ChainSelectionMessage,
 	])]
 	dispute_coordinator: DisputeCoordinator,
 

polkadot/node/subsystem-types/src/messages.rs

@@ -518,6 +518,9 @@ pub enum ChainSelectionMessage {
 	/// Request the best leaf containing the given block in its ancestry. Return `None` if
 	/// there is no such leaf.
 	BestLeafContaining(Hash, oneshot::Sender<Option<Hash>>),
+	/// The passed blocks must be marked as reverted, and their children must be marked
+	/// as non-viable.
+	RevertBlocks(Vec<(BlockNumber, Hash)>),
 }
 
 /// A sender for the result of a runtime API request.