Import blocks with bad justification (#1977)

* init version

* chore: improve code

* fix test

* fix: log error resulting of bad justification

* fix: add test to check for disconnected peer

substrate/core/finality-grandpa/src/import.rs

@@ -460,7 +460,12 @@ impl<B, E, Block: BlockT<Hash=H256>, RA, PRA> BlockImport<Block>
 
 		match justification {
 			Some(justification) => {
-				self.import_justification(hash, number, justification, needs_justification)?;
+				self.import_justification(hash, number, justification, needs_justification).unwrap_or_else(|err| {
+					debug!(target: "finality", "Imported block #{} that enacts authority set change with \
+						invalid justification: {:?}, requesting justification from peers.", number, err);
+					imported_aux.bad_justification = true;
+					imported_aux.needs_justification = true;
+				});
 			},
 			None => {
 				if needs_justification {
@@ -476,7 +481,6 @@ impl<B, E, Block: BlockT<Hash=H256>, RA, PRA> BlockImport<Block>
 				if enacts_consensus_change {
 					self.consensus_changes.lock().note_change((number, hash));
 				}
-
 				imported_aux.needs_justification = true;
 			}
 		}

substrate/core/finality-grandpa/src/tests.rs

@@ -992,7 +992,50 @@ fn allows_reimporting_change_blocks() {
 
 	assert_eq!(
 		block_import.import_block(block(), None).unwrap(),
-		ImportResult::Imported(ImportedAux { needs_justification: true, clear_justification_requests: false }),
+		ImportResult::Imported(ImportedAux { needs_justification: true, clear_justification_requests: false, bad_justification: false }),
+	);
+
+	assert_eq!(
+		block_import.import_block(block(), None).unwrap(),
+		ImportResult::AlreadyInChain
+	);
+}
+
+#[test]
+fn test_bad_justification() {
+	let peers_a = &[Keyring::Alice, Keyring::Bob, Keyring::Charlie];
+	let peers_b = &[Keyring::Alice, Keyring::Bob];
+	let voters = make_ids(peers_a);
+	let api = TestApi::new(voters);
+	let net = GrandpaTestNet::new(api.clone(), 3);
+
+	let client = net.peer(0).client().clone();
+	let (block_import, ..) = net.make_block_import(client.clone());
+
+	let builder = client.new_block_at(&BlockId::Number(0)).unwrap();
+	let block = builder.bake().unwrap();
+	api.scheduled_changes.lock().insert(*block.header.parent_hash(), ScheduledChange {
+		next_authorities: make_ids(peers_b),
+		delay: 0,
+	});
+
+	let block = || {
+		let block = block.clone();
+		ImportBlock {
+			origin: BlockOrigin::File,
+			header: block.header,
+			justification: Some(Vec::new()),
+			post_digests: Vec::new(),
+			body: Some(block.extrinsics),
+			finalized: false,
+			auxiliary: Vec::new(),
+			fork_choice: ForkChoiceStrategy::LongestChain,
+		}
+	};
+
+	assert_eq!(
+		block_import.import_block(block(), None).unwrap(),
+		ImportResult::Imported(ImportedAux { needs_justification: true, clear_justification_requests: false, bad_justification: true }),
 	);
 
 	assert_eq!(