Include parent head in CandidateReceipt (#826)

* runtime: candidate receipt must pass parent head

* construct parachain candidates using correct parent_head

* validate that the parent header is correct in candidate receipt

* fix test fallout

* bump runtime versions

polkadot/availability-store/src/store.rs

@@ -459,6 +459,7 @@ mod tests {
 			collator: Default::default(),
 			signature: Default::default(),
 			head_data: Default::default(),
+			parent_head: Default::default(),
 			egress_queue_roots: Vec::new(),
 			fees: 0,
 			block_data_hash: block_data_1.hash(),
@@ -471,6 +472,7 @@ mod tests {
 			collator: Default::default(),
 			signature: Default::default(),
 			head_data: Default::default(),
+			parent_head: Default::default(),
 			egress_queue_roots: Vec::new(),
 			fees: 0,
 			block_data_hash: block_data_2.hash(),
@@ -575,6 +577,7 @@ mod tests {
 			collator: Default::default(),
 			signature: Default::default(),
 			head_data: Default::default(),
+			parent_head: Default::default(),
 			egress_queue_roots: Vec::new(),
 			fees: 0,
 			block_data_hash: block_data.hash(),

polkadot/network/src/collator_pool.rs

@@ -285,6 +285,7 @@ mod tests {
 				collator: primary.clone().into(),
 				signature: Default::default(),
 				head_data: HeadData(vec![1, 2, 3]),
+				parent_head: HeadData(vec![]),
 				egress_queue_roots: vec![],
 				fees: 0,
 				block_data_hash: [3; 32].into(),
@@ -314,6 +315,7 @@ mod tests {
 				collator: primary,
 				signature: Default::default(),
 				head_data: HeadData(vec![1, 2, 3]),
+				parent_head: HeadData(vec![]),
 				egress_queue_roots: vec![],
 				fees: 0,
 				block_data_hash: [3; 32].into(),

polkadot/network/src/gossip.rs

@@ -906,6 +906,7 @@ mod tests {
 			parachain_index: 5.into(),
 			collator: [255; 32].unchecked_into(),
 			head_data: HeadData(vec![9, 9, 9]),
+			parent_head: HeadData(vec![]),
 			signature: Default::default(),
 			egress_queue_roots: Vec::new(),
 			fees: 1_000_000,

polkadot/network/src/tests/mod.rs

@@ -173,6 +173,7 @@ fn fetches_from_those_with_knowledge() {
 		parachain_index: 5.into(),
 		collator: [255; 32].unchecked_into(),
 		head_data: HeadData(vec![9, 9, 9]),
+		parent_head: HeadData(vec![]),
 		signature: Default::default(),
 		egress_queue_roots: Vec::new(),
 		fees: 1_000_000,

polkadot/primitives/src/parachain.rs

@@ -292,6 +292,8 @@ pub struct CandidateReceipt {
 	pub signature: CollatorSignature,
 	/// The head-data
 	pub head_data: HeadData,
+	/// The parent head-data.
+	pub parent_head: HeadData,
 	/// Egress queue roots. Must be sorted lexicographically (ascending)
 	/// by parachain ID.
 	pub egress_queue_roots: Vec<(Id, Hash)>,

polkadot/runtime/common/src/parachains.rs

@@ -231,6 +231,8 @@ decl_error! {
 		InvalidSignature,
 		/// Extra untagged validity votes along with candidate.
 		UntaggedVotes,
+		/// Wrong parent head for parachain receipt.
+		ParentMismatch,
 	}
 }
 
@@ -781,6 +783,14 @@ impl<T: Trait> Module<T> {
 			let validator_group = validator_groups.group_for(para_id)
 				.ok_or(Error::<T>::NoValidatorGroup)?;
 
+			let actual_head = Self::parachain_head(&para_id)
+				.map(primitives::parachain::HeadData);
+
+			ensure!(
+				actual_head.as_ref() == Some(&candidate.candidate.parent_head),
+				Error::<T>::ParentMismatch,
+			);
+
 			ensure!(
 				candidate.validity_votes.len() >= majority_of(validator_group.len()),
 				Error::<T>::NotEnoughValidityVotes,
@@ -1287,6 +1297,7 @@ mod tests {
 				collator: Default::default(),
 				signature: Default::default(),
 				head_data: HeadData(vec![1, 2, 3]),
+				parent_head: HeadData(vec![]),
 				egress_queue_roots,
 				fees: 0,
 				block_data_hash: Default::default(),
@@ -1308,6 +1319,7 @@ mod tests {
 				collator: Default::default(),
 				signature: Default::default(),
 				head_data: HeadData(vec![1, 2, 3]),
+				parent_head: HeadData(vec![]),
 				egress_queue_roots: vec![],
 				fees: 0,
 				block_data_hash: Default::default(),
@@ -1718,6 +1730,7 @@ mod tests {
 					collator: Default::default(),
 					signature: Default::default(),
 					head_data: HeadData(vec![1, 2, 3]),
+					parent_head: HeadData(vec![]),
 					egress_queue_roots: vec![],
 					fees: 0,
 					block_data_hash: Default::default(),
@@ -1750,6 +1763,7 @@ mod tests {
 					collator: Default::default(),
 					signature: Default::default(),
 					head_data: HeadData(vec![1, 2, 3]),
+					parent_head: HeadData(vec![]),
 					egress_queue_roots: vec![],
 					fees: 0,
 					block_data_hash: Default::default(),
@@ -1766,6 +1780,7 @@ mod tests {
 					collator: Default::default(),
 					signature: Default::default(),
 					head_data: HeadData(vec![2, 3, 4]),
+					parent_head: HeadData(vec![]),
 					egress_queue_roots: vec![],
 					fees: 0,
 					block_data_hash: Default::default(),
@@ -1806,6 +1821,7 @@ mod tests {
 					collator: Default::default(),
 					signature: Default::default(),
 					head_data: HeadData(vec![1, 2, 3]),
+					parent_head: HeadData(vec![]),
 					egress_queue_roots: vec![],
 					fees: 0,
 					block_data_hash: Default::default(),
@@ -1844,6 +1860,7 @@ mod tests {
 					collator: Default::default(),
 					signature: Default::default(),
 					head_data: HeadData(vec![1, 2, 3]),
+					parent_head: HeadData(vec![]),
 					egress_queue_roots: vec![],
 					fees: 0,
 					block_data_hash: Default::default(),
@@ -1878,10 +1895,18 @@ mod tests {
 			assert_eq!(Parachains::ingress(ParaId::from(99), None), Some(Vec::new()));
 
 			init_block();
+
 			for i in 1..10 {
 				run_to_block(i);
 
 				let from_a = vec![(1.into(), [i as u8; 32].into())];
+
+				let parent_head = HeadData(if i == 1 {
+					vec![]
+				} else {
+					vec![1, 2, 3]
+				});
+
 				let mut candidate_a = AttestedCandidate {
 					validity_votes: vec![],
 					validator_indices: BitVec::new(),
@@ -1890,6 +1915,7 @@ mod tests {
 						collator: Default::default(),
 						signature: Default::default(),
 						head_data: HeadData(vec![1, 2, 3]),
+						parent_head:	parent_head.clone(),
 						egress_queue_roots: from_a.clone(),
 						fees: 0,
 						block_data_hash: Default::default(),
@@ -1907,6 +1933,7 @@ mod tests {
 						collator: Default::default(),
 						signature: Default::default(),
 						head_data: HeadData(vec![1, 2, 3]),
+						parent_head,
 						egress_queue_roots: from_b.clone(),
 						fees: 0,
 						block_data_hash: Default::default(),
@@ -1969,6 +1996,7 @@ mod tests {
 					collator: Default::default(),
 					signature: Default::default(),
 					head_data: HeadData(vec![1, 2, 3]),
+					parent_head: HeadData(vec![4, 5, 6]),
 					egress_queue_roots: Vec::new(),
 					fees: 0,
 					block_data_hash: Default::default(),

polkadot/runtime/common/src/registrar.rs

@@ -836,13 +836,14 @@ mod tests {
 		LOWEST_USER_ID + i
 	}
 
-	fn attest(id: ParaId, collator: &CollatorPair, head_data: &[u8], block_data: &[u8]) -> AttestedCandidate {
+	fn attest(id: ParaId, collator: &CollatorPair, head_data: &[u8], parent_head: &[u8], block_data: &[u8]) -> AttestedCandidate {
 		let block_data_hash = BlakeTwo256::hash(block_data);
 		let candidate = CandidateReceipt {
 			parachain_index: id,
 			collator: collator.public(),
 			signature: block_data_hash.using_encoded(|d| collator.sign(d)),
 			head_data: HeadData(head_data.to_vec()),
+			parent_head: HeadData(parent_head.to_vec()),
 			egress_queue_roots: vec![],
 			fees: 0,
 			block_data_hash,
@@ -1117,7 +1118,7 @@ mod tests {
 				(user_id(0), Some((col.clone(), Retriable::WithRetries(0))))
 			]);
 			assert_ok!(Parachains::set_heads(Origin::NONE, vec![
-				attest(user_id(0), &Sr25519Keyring::One.pair().into(), &[3; 3], &[0; 0])
+				attest(user_id(0), &Sr25519Keyring::One.pair().into(), &[3; 3], &[3; 3], &[0; 0])
 			]));
 
 			run_to_block(6);

polkadot/runtime/polkadot/src/lib.rs

@@ -78,7 +78,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	spec_name: create_runtime_str!("polkadot"),
 	impl_name: create_runtime_str!("parity-polkadot"),
 	authoring_version: 2,
-	spec_version: 1001,
+	spec_version: 1002,
 	impl_version: 0,
 	apis: RUNTIME_API_VERSIONS,
 };

polkadot/validation/src/collation.rs

@@ -68,7 +68,7 @@ pub async fn collation_fetch<C: Collators, P>(
 	collators: C,
 	client: Arc<P>,
 	max_block_data_size: Option<u64>,
-) -> Result<(Collation, OutgoingMessages, Balance),C::Error>
+) -> Result<(Collation, OutgoingMessages, HeadData, Balance),C::Error>
 	where
 		P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 		C: Collators + Unpin,
@@ -89,8 +89,8 @@ pub async fn collation_fetch<C: Collators, P>(
 		);
 
 		match res {
-			Ok((messages, fees)) => {
+			Ok((messages, parent_head, fees)) => {
-				return Ok((collation, messages, fees))
+				return Ok((collation, messages, parent_head, fees))
 			}
 			Err(e) => {
 				debug!("Failed to validate parachain due to API error: {}", e);
@@ -148,6 +148,10 @@ pub enum Error {
 	/// Candidate block collation info doesn't match candidate receipt.
 	#[display(fmt = "Got receipt mismatch for candidate {:?}", candidate)]
 	CandidateReceiptMismatch { candidate: Hash },
+	/// The parent header given in the candidate did not match current relay-chain
+	/// state.
+	#[display(fmt = "Got unexpected parachain parent.")]
+	ParentMismatch { expected: HeadData, got: HeadData },
 }
 
 impl std::error::Error for Error {
@@ -406,7 +410,7 @@ pub fn validate_incoming(
 // A utility function that implements most of the collation validation logic.
 //
 // Reused by `validate_collation` and `validate_receipt`.
-// Returns outgoing messages and fees charged for later reuse.
+// Returns outgoing messages, parent nead data, and fees charged for later reuse.
 fn do_validation<P>(
 	client: &P,
 	relay_parent: &BlockId,
@@ -417,7 +421,7 @@ fn do_validation<P>(
 	head_data: &HeadData,
 	queue_roots: &Vec<(ParaId, Hash)>,
 	upward_messages: &Vec<UpwardMessage>,
-) -> Result<(OutgoingMessages, Balance), Error> where
+) -> Result<(OutgoingMessages, HeadData, Balance), Error> where
 	P: ProvideRuntimeApi<Block>,
 	P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 {
@@ -443,7 +447,7 @@ fn do_validation<P>(
 	validate_incoming(&roots, &pov_block.ingress)?;
 
 	let params = ValidationParams {
-		parent_head: chain_status.head_data.0,
+		parent_head: chain_status.head_data.0.clone(),
 		block_data: pov_block.block_data.0.clone(),
 		ingress: pov_block.ingress.0.iter()
 			.flat_map(|&(source, ref messages)| {
@@ -471,7 +475,7 @@ fn do_validation<P>(
 					fees_charged
 				)?;
 
-				Ok((messages, fees))
+				Ok((messages, chain_status.head_data, fees))
 			} else {
 				Err(Error::WrongHeadData {
 					expected: head_data.0.clone(),
@@ -491,6 +495,7 @@ fn do_validation<P>(
 /// encoding's root returning both for re-use.
 pub fn produce_receipt_and_chunks(
 	n_validators: usize,
+	parent_head: HeadData,
 	pov: &PoVBlock,
 	messages: &OutgoingMessages,
 	fees: Balance,
@@ -523,6 +528,7 @@ pub fn produce_receipt_and_chunks(
 		collator: info.collator.clone(),
 		signature: info.signature.clone(),
 		head_data: info.head_data.clone(),
+		parent_head,
 		egress_queue_roots: info.egress_queue_roots.clone(),
 		fees,
 		block_data_hash: info.block_data_hash.clone(),
@@ -547,7 +553,7 @@ pub fn validate_receipt<P>(
 	P: ProvideRuntimeApi<Block>,
 	P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 {
-	let (messages, _fees) = do_validation(
+	let (messages, parent_head, _fees) = do_validation(
 		client,
 		relay_parent,
 		pov_block,
@@ -559,12 +565,20 @@ pub fn validate_receipt<P>(
 		&receipt.upward_messages,
 	)?;
 
+	if parent_head != receipt.parent_head {
+		return Err(Error::ParentMismatch {
+			expected: receipt.parent_head.clone(),
+			got: parent_head,
+		});
+	}
+
 	let api = client.runtime_api();
 	let validators = api.validators(&relay_parent)?;
 	let n_validators = validators.len();
 
 	let (validated_receipt, chunks) = produce_receipt_and_chunks(
 		n_validators,
+		parent_head,
 		pov_block,
 		&messages,
 		receipt.fees,
@@ -582,6 +596,7 @@ pub fn validate_receipt<P>(
 }
 
 /// Check whether a given collation is valid. Returns `Ok` on success, error otherwise.
+/// Returns outgoing messages, parent head-data, and fees.
 ///
 /// This assumes that basic validity checks have been done:
 ///   - Block data hash is the same as linked in collation info.
@@ -590,7 +605,7 @@ pub fn validate_collation<P>(
 	relay_parent: &BlockId,
 	collation: &Collation,
 	max_block_data_size: Option<u64>,
-) -> Result<(OutgoingMessages, Balance), Error> where
+) -> Result<(OutgoingMessages, HeadData, Balance), Error> where
 	P: ProvideRuntimeApi<Block>,
 	P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 {
@@ -698,6 +713,7 @@ mod tests {
 			collator: Default::default(),
 			signature: Default::default(),
 			head_data: HeadData(Vec::new()),
+			parent_head: HeadData(Vec::new()),
 			egress_queue_roots: Vec::new(),
 			fees: 0,
 			block_data_hash: Default::default(),
@@ -717,6 +733,7 @@ mod tests {
 			collator: Default::default(),
 			signature: Default::default(),
 			head_data: HeadData(Vec::new()),
+			parent_head: HeadData(Vec::new()),
 			egress_queue_roots: Vec::new(),
 			fees: 0,
 			block_data_hash: Default::default(),
@@ -735,6 +752,7 @@ mod tests {
 			collator: Default::default(),
 			signature: Default::default(),
 			head_data: HeadData(Vec::new()),
+			parent_head: HeadData(Vec::new()),
 			egress_queue_roots: Vec::new(),
 			fees: 0,
 			block_data_hash: Default::default(),
@@ -753,6 +771,7 @@ mod tests {
 			collator: Default::default(),
 			signature: Default::default(),
 			head_data: HeadData(Vec::new()),
+			parent_head: HeadData(Vec::new()),
 			egress_queue_roots: Vec::new(),
 			fees: 0,
 			block_data_hash: Default::default(),

polkadot/validation/src/shared_table/mod.rs

@@ -576,7 +576,9 @@ mod tests {
 	use super::*;
 	use sp_keyring::Sr25519Keyring;
 	use primitives::crypto::UncheckedInto;
-	use polkadot_primitives::parachain::{AvailableMessages, BlockData, ConsolidatedIngress, Collation};
+	use polkadot_primitives::parachain::{
+		AvailableMessages, BlockData, ConsolidatedIngress, Collation, HeadData,
+	};
 	use polkadot_erasure_coding::{self as erasure};
 	use availability_store::ProvideGossipMessages;
 	use futures::future;
@@ -662,7 +664,8 @@ mod tests {
 			parachain_index: para_id,
 			collator: [1; 32].unchecked_into(),
 			signature: Default::default(),
-			head_data: ::polkadot_primitives::parachain::HeadData(vec![1, 2, 3, 4]),
+			head_data: HeadData(vec![1, 2, 3, 4]),
+			parent_head: HeadData(vec![]),
 			egress_queue_roots: Vec::new(),
 			fees: 1_000_000,
 			block_data_hash: [2; 32].into(),
@@ -718,7 +721,8 @@ mod tests {
 			parachain_index: para_id,
 			collator: [1; 32].unchecked_into(),
 			signature: Default::default(),
-			head_data: ::polkadot_primitives::parachain::HeadData(vec![1, 2, 3, 4]),
+			head_data: HeadData(vec![1, 2, 3, 4]),
+			parent_head: HeadData(vec![]),
 			egress_queue_roots: Vec::new(),
 			fees: 1_000_000,
 			block_data_hash: [2; 32].into(),
@@ -755,7 +759,8 @@ mod tests {
 			parachain_index: para_id,
 			collator: [1; 32].unchecked_into(),
 			signature: Default::default(),
-			head_data: ::polkadot_primitives::parachain::HeadData(vec![1, 2, 3, 4]),
+			head_data: HeadData(vec![1, 2, 3, 4]),
+			parent_head: HeadData(vec![]),
 			egress_queue_roots: Vec::new(),
 			fees: 1_000_000,
 			block_data_hash,
@@ -819,7 +824,8 @@ mod tests {
 			parachain_index: para_id,
 			collator: [1; 32].unchecked_into(),
 			signature: Default::default(),
-			head_data: ::polkadot_primitives::parachain::HeadData(vec![1, 2, 3, 4]),
+			head_data: HeadData(vec![1, 2, 3, 4]),
+			parent_head: HeadData(vec![]),
 			egress_queue_roots: Vec::new(),
 			fees: 1_000_000,
 			block_data_hash: [2; 32].into(),
@@ -902,7 +908,8 @@ mod tests {
 			parachain_index: para_id,
 			collator: [1; 32].unchecked_into(),
 			signature: Default::default(),
-			head_data: ::polkadot_primitives::parachain::HeadData(vec![1, 2, 3, 4]),
+			head_data: HeadData(vec![1, 2, 3, 4]),
+			parent_head: HeadData(vec![]),
 			egress_queue_roots: Vec::new(),
 			fees: 1_000_000,
 			block_data_hash: [2; 32].into(),
@@ -969,7 +976,8 @@ mod tests {
 			parachain_index: para_id,
 			collator: [1; 32].unchecked_into(),
 			signature: Default::default(),
-			head_data: ::polkadot_primitives::parachain::HeadData(vec![1, 2, 3, 4]),
+			head_data: HeadData(vec![1, 2, 3, 4]),
+			parent_head: HeadData(vec![]),
 			egress_queue_roots: Vec::new(),
 			fees: 1_000_000,
 			block_data_hash: [2; 32].into(),

polkadot/validation/src/validation_service/mod.rs

@@ -396,10 +396,11 @@ impl<C, N, P, SP> ParachainValidationInstances<C, N, P, SP> where
 				max_block_data_size,
 			).await {
 				Ok(collation_work) => {
-					let (collation, outgoing_targeted, fees_charged) = collation_work;
+					let (collation, outgoing_targeted, parent_head, fees_charged) = collation_work;
 
 					match crate::collation::produce_receipt_and_chunks(
 						authorities_num,
+						parent_head,
 						&collation.pov,
 						&outgoing_targeted,
 						fees_charged,