Ensure relay chain block number strictly increases (#1280)

* Ensure relay chain block number strictly increases

This is a safeguard for when async backing is enabled on the relay chain and multiple parachain
blocks per relay chain block are legal. We will need to later change this to support then multiple
parachain blocks per relay chain block.

* Make the check configurable

* Fix compilation

* Update pallets/parachain-system/src/lib.rs

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

* Update pallets/parachain-system/src/lib.rs

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

* Fix test

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

cumulus/pallets/parachain-system/src/lib.rs

@@ -88,6 +88,51 @@ pub use relay_state_snapshot::{MessagingStateSnapshot, RelayChainStateProof};
 
 pub use pallet::*;
 
+/// Something that can check the associated relay block number.
+///
+/// Each Parachain block is built in the context of a relay chain block, this trait allows us
+/// to validate the given relay chain block number. With async backing it is legal to build
+/// multiple Parachain blocks per relay chain parent. With this trait it is possible for the
+/// Parachain to ensure that still only one Parachain block is build per relay chain parent.
+///
+/// By default [`RelayNumberStrictlyIncreases`] and [`AnyRelayNumber`] are provided.
+pub trait CheckAssociatedRelayNumber {
+	/// Check the current relay number versus the previous relay number.
+	///
+	/// The implementation should panic when there is something wrong.
+	fn check_associated_relay_number(
+		current: RelayChainBlockNumber,
+		previous: RelayChainBlockNumber,
+	);
+}
+
+/// Provides an implementation of [`CheckAssociatedRelayNumber`].
+///
+/// It will ensure that the associated relay block number strictly increases between Parachain
+/// blocks. This should be used by production Parachains when in doubt.
+pub struct RelayNumberStrictlyIncreases;
+
+impl CheckAssociatedRelayNumber for RelayNumberStrictlyIncreases {
+	fn check_associated_relay_number(
+		current: RelayChainBlockNumber,
+		previous: RelayChainBlockNumber,
+	) {
+		if current <= previous {
+			panic!("Relay chain block number needs to strictly increase between Parachain blocks!")
+		}
+	}
+}
+
+/// Provides an implementation of [`CheckAssociatedRelayNumber`].
+///
+/// This will accept any relay chain block number combination. This is mainly useful for
+/// test parachains.
+pub struct AnyRelayNumber;
+
+impl CheckAssociatedRelayNumber for AnyRelayNumber {
+	fn check_associated_relay_number(_: RelayChainBlockNumber, _: RelayChainBlockNumber) {}
+}
+
 #[frame_support::pallet]
 pub mod pallet {
 	use super::*;
@@ -128,6 +173,9 @@ pub mod pallet {
 
 		/// The weight we reserve at the beginning of the block for processing XCMP messages.
 		type ReservedXcmpWeight: Get<Weight>;
+
+		/// Something that can check the associated relay parent block number.
+		type CheckAssociatedRelayNumber: CheckAssociatedRelayNumber;
 	}
 
 	#[pallet::hooks]
@@ -232,7 +280,7 @@ pub mod pallet {
 			}
 
 			// Remove the validation from the old block.
-			<ValidationData<T>>::kill();
+			ValidationData::<T>::kill();
 			ProcessedDownwardMessages::<T>::kill();
 			HrmpWatermark::<T>::kill();
 			UpwardMessages::<T>::kill();
@@ -307,6 +355,13 @@ pub mod pallet {
 
 			Self::validate_validation_data(&vfp);
 
+			// Check that the associated relay chain block number is as expected.
+			T::CheckAssociatedRelayNumber::check_associated_relay_number(
+				vfp.relay_parent_number,
+				LastRelayChainBlockNumber::<T>::get(),
+			);
+			LastRelayChainBlockNumber::<T>::put(vfp.relay_parent_number);
+
 			let relay_state_proof = RelayChainStateProof::new(
 				T::SelfParaId::get(),
 				vfp.relay_parent_storage_root,
@@ -474,6 +529,11 @@ pub mod pallet {
 	#[pallet::storage]
 	pub(super) type DidSetValidationCode<T: Config> = StorageValue<_, bool, ValueQuery>;
 
+	/// The relay chain block number associated with the last parachain block.
+	#[pallet::storage]
+	pub(super) type LastRelayChainBlockNumber<T: Config> =
+		StorageValue<_, RelayChainBlockNumber, ValueQuery>;
+
 	/// An option which indicates if the relay-chain restricts signalling a validation code upgrade.
 	/// In other words, if this is `Some` and [`NewValidationCode`] is `Some` then the produced
 	/// candidate will be invalid.

cumulus/pallets/parachain-system/src/tests.rs

@@ -107,6 +107,7 @@ impl Config for Test {
 	type ReservedDmpWeight = ReservedDmpWeight;
 	type XcmpMessageHandler = SaveIntoThreadLocal;
 	type ReservedXcmpWeight = ReservedXcmpWeight;
+	type CheckAssociatedRelayNumber = RelayNumberStrictlyIncreases;
 }
 
 pub struct FromThreadLocal;
@@ -226,8 +227,7 @@ struct BlockTests {
 	ran: bool,
 	relay_sproof_builder_hook:
 		Option<Box<dyn Fn(&BlockTests, RelayChainBlockNumber, &mut RelayStateSproofBuilder)>>,
-	persisted_validation_data_hook:
-		Option<Box<dyn Fn(&BlockTests, RelayChainBlockNumber, &mut PersistedValidationData)>>,
+	persisted_validation_data_hook: Option<Box<dyn Fn(&BlockTests, &mut PersistedValidationData)>>,
 	inherent_data_hook:
 		Option<Box<dyn Fn(&BlockTests, RelayChainBlockNumber, &mut ParachainInherentData)>>,
 }
@@ -274,10 +274,9 @@ impl BlockTests {
 		self
 	}
 
-	#[allow(dead_code)] // might come in handy in future. If now is future and it still hasn't - feel free.
 	fn with_validation_data<F>(mut self, f: F) -> Self
 	where
-		F: 'static + Fn(&BlockTests, RelayChainBlockNumber, &mut PersistedValidationData),
+		F: 'static + Fn(&BlockTests, &mut PersistedValidationData),
 	{
 		self.persisted_validation_data_hook = Some(Box::new(f));
 		self
@@ -319,7 +318,7 @@ impl BlockTests {
 					..Default::default()
 				};
 				if let Some(ref hook) = self.persisted_validation_data_hook {
-					hook(self, *n as RelayChainBlockNumber, &mut vfp);
+					hook(self, &mut vfp);
 				}
 
 				<ValidationData<Test>>::put(&vfp);
@@ -964,3 +963,14 @@ fn receive_hrmp_after_pause() {
 			});
 		});
 }
+
+#[test]
+#[should_panic = "Relay chain block number needs to strictly increase between Parachain blocks!"]
+fn test() {
+	BlockTests::new()
+		.with_validation_data(|_, data| {
+			data.relay_parent_number = 1;
+		})
+		.add(1, || {})
+		.add(2, || {});
+}

cumulus/pallets/parachain-system/src/validate_block/implementation.rs

@@ -67,8 +67,8 @@ where
 	assert!(parent_head.hash() == *block.header().parent_hash(), "Invalid parent hash",);
 
 	// Create the db
-	let (db, root) = match storage_proof.to_memory_db(Some(parent_head.state_root())) {
-		Ok((db, root)) => (db, root),
+	let db = match storage_proof.to_memory_db(Some(parent_head.state_root())) {
+		Ok((db, _)) => db,
 		Err(_) => panic!("Compact proof decoding failure."),
 	};
 

cumulus/pallets/xcmp-queue/src/mock.rs

@@ -16,6 +16,7 @@
 use super::*;
 use crate as xcmp_queue;
 use core::marker::PhantomData;
+use cumulus_pallet_parachain_system::AnyRelayNumber;
 use cumulus_primitives_core::{IsSystem, ParaId};
 use frame_support::{parameter_types, traits::OriginTrait};
 use frame_system::EnsureRoot;
@@ -109,6 +110,7 @@ impl cumulus_pallet_parachain_system::Config for Test {
 	type ReservedDmpWeight = ();
 	type XcmpMessageHandler = XcmpQueue;
 	type ReservedXcmpWeight = ();
+	type CheckAssociatedRelayNumber = AnyRelayNumber;
 }
 
 parameter_types! {

cumulus/parachain-template/runtime/src/lib.rs

@@ -9,6 +9,7 @@ include!(concat!(env!("OUT_DIR"), "/wasm_binary.rs"));
 mod weights;
 pub mod xcm_config;
 
+use cumulus_pallet_parachain_system::RelayNumberStrictlyIncreases;
 use smallvec::smallvec;
 use sp_api::impl_runtime_apis;
 use sp_core::{crypto::KeyTypeId, OpaqueMetadata};
@@ -369,11 +370,12 @@ impl cumulus_pallet_parachain_system::Config for Runtime {
 	type Event = Event;
 	type OnSystemEvent = ();
 	type SelfParaId = parachain_info::Pallet<Runtime>;
+	type OutboundXcmpMessageSource = XcmpQueue;
 	type DmpMessageHandler = DmpQueue;
 	type ReservedDmpWeight = ReservedDmpWeight;
-	type OutboundXcmpMessageSource = XcmpQueue;
 	type XcmpMessageHandler = XcmpQueue;
 	type ReservedXcmpWeight = ReservedXcmpWeight;
+	type CheckAssociatedRelayNumber = RelayNumberStrictlyIncreases;
 }
 
 impl parachain_info::Config for Runtime {}

cumulus/parachains/runtimes/assets/statemine/src/lib.rs

@@ -28,6 +28,7 @@ pub mod constants;
 mod weights;
 pub mod xcm_config;
 
+use cumulus_pallet_parachain_system::RelayNumberStrictlyIncreases;
 use sp_api::impl_runtime_apis;
 use sp_core::{crypto::KeyTypeId, OpaqueMetadata};
 use sp_runtime::{
@@ -416,6 +417,7 @@ impl cumulus_pallet_parachain_system::Config for Runtime {
 	type OutboundXcmpMessageSource = XcmpQueue;
 	type XcmpMessageHandler = XcmpQueue;
 	type ReservedXcmpWeight = ReservedXcmpWeight;
+	type CheckAssociatedRelayNumber = RelayNumberStrictlyIncreases;
 }
 
 impl parachain_info::Config for Runtime {}

cumulus/parachains/runtimes/assets/statemint/src/lib.rs

@@ -57,6 +57,7 @@ pub mod constants;
 mod weights;
 pub mod xcm_config;
 
+use cumulus_pallet_parachain_system::RelayNumberStrictlyIncreases;
 use sp_api::impl_runtime_apis;
 use sp_core::{crypto::KeyTypeId, OpaqueMetadata};
 use sp_runtime::{
@@ -446,6 +447,7 @@ impl cumulus_pallet_parachain_system::Config for Runtime {
 	type OutboundXcmpMessageSource = XcmpQueue;
 	type XcmpMessageHandler = XcmpQueue;
 	type ReservedXcmpWeight = ReservedXcmpWeight;
+	type CheckAssociatedRelayNumber = RelayNumberStrictlyIncreases;
 }
 
 impl parachain_info::Config for Runtime {}

cumulus/parachains/runtimes/assets/westmint/src/lib.rs

@@ -28,6 +28,7 @@ pub mod constants;
 mod weights;
 pub mod xcm_config;
 
+use cumulus_pallet_parachain_system::RelayNumberStrictlyIncreases;
 use sp_api::impl_runtime_apis;
 use sp_core::{crypto::KeyTypeId, OpaqueMetadata};
 use sp_runtime::{
@@ -406,11 +407,12 @@ impl cumulus_pallet_parachain_system::Config for Runtime {
 	type Event = Event;
 	type OnSystemEvent = ();
 	type SelfParaId = parachain_info::Pallet<Runtime>;
+	type OutboundXcmpMessageSource = XcmpQueue;
 	type DmpMessageHandler = DmpQueue;
 	type ReservedDmpWeight = ReservedDmpWeight;
-	type OutboundXcmpMessageSource = XcmpQueue;
 	type XcmpMessageHandler = XcmpQueue;
 	type ReservedXcmpWeight = ReservedXcmpWeight;
+	type CheckAssociatedRelayNumber = RelayNumberStrictlyIncreases;
 }
 
 impl parachain_info::Config for Runtime {}

cumulus/parachains/runtimes/contracts/contracts-rococo/src/lib.rs

@@ -30,6 +30,7 @@ mod contracts;
 mod weights;
 mod xcm_config;
 
+use cumulus_pallet_parachain_system::RelayNumberStrictlyIncreases;
 use sp_api::impl_runtime_apis;
 use sp_core::{crypto::KeyTypeId, OpaqueMetadata};
 use sp_runtime::{
@@ -252,6 +253,7 @@ impl cumulus_pallet_parachain_system::Config for Runtime {
 	type OutboundXcmpMessageSource = XcmpQueue;
 	type XcmpMessageHandler = XcmpQueue;
 	type ReservedXcmpWeight = ConstU64<{ MAXIMUM_BLOCK_WEIGHT / 4 }>;
+	type CheckAssociatedRelayNumber = RelayNumberStrictlyIncreases;
 }
 
 impl pallet_randomness_collective_flip::Config for Runtime {}

cumulus/parachains/runtimes/starters/seedling/src/lib.rs

@@ -27,6 +27,7 @@
 #[cfg(feature = "std")]
 include!(concat!(env!("OUT_DIR"), "/wasm_binary.rs"));
 
+use cumulus_pallet_parachain_system::RelayNumberStrictlyIncreases;
 use sp_api::impl_runtime_apis;
 use sp_core::OpaqueMetadata;
 use sp_runtime::{
@@ -166,6 +167,7 @@ impl cumulus_pallet_parachain_system::Config for Runtime {
 	type ReservedDmpWeight = ();
 	type XcmpMessageHandler = ();
 	type ReservedXcmpWeight = ();
+	type CheckAssociatedRelayNumber = RelayNumberStrictlyIncreases;
 }
 
 impl parachain_info::Config for Runtime {}

cumulus/parachains/runtimes/starters/shell/src/lib.rs

@@ -32,6 +32,7 @@ include!(concat!(env!("OUT_DIR"), "/wasm_binary.rs"));
 pub mod xcm_config;
 
 use codec::{Decode, Encode};
+use cumulus_pallet_parachain_system::RelayNumberStrictlyIncreases;
 use frame_support::unsigned::TransactionValidityError;
 use scale_info::TypeInfo;
 use sp_api::impl_runtime_apis;
@@ -170,6 +171,7 @@ impl cumulus_pallet_parachain_system::Config for Runtime {
 	type ReservedDmpWeight = ReservedDmpWeight;
 	type XcmpMessageHandler = ();
 	type ReservedXcmpWeight = ();
+	type CheckAssociatedRelayNumber = RelayNumberStrictlyIncreases;
 }
 
 impl parachain_info::Config for Runtime {}

cumulus/parachains/runtimes/testing/rococo-parachain/src/lib.rs

@@ -22,6 +22,7 @@
 #[cfg(feature = "std")]
 include!(concat!(env!("OUT_DIR"), "/wasm_binary.rs"));
 
+use cumulus_pallet_parachain_system::RelayNumberStrictlyIncreases;
 use sp_api::impl_runtime_apis;
 use sp_core::OpaqueMetadata;
 use sp_runtime::{
@@ -265,6 +266,7 @@ impl cumulus_pallet_parachain_system::Config for Runtime {
 	type ReservedDmpWeight = ReservedDmpWeight;
 	type XcmpMessageHandler = XcmpQueue;
 	type ReservedXcmpWeight = ReservedXcmpWeight;
+	type CheckAssociatedRelayNumber = RelayNumberStrictlyIncreases;
 }
 
 impl parachain_info::Config for Runtime {}

cumulus/test/runtime/src/lib.rs

@@ -265,6 +265,7 @@ impl cumulus_pallet_parachain_system::Config for Runtime {
 	type ReservedDmpWeight = ();
 	type XcmpMessageHandler = ();
 	type ReservedXcmpWeight = ();
+	type CheckAssociatedRelayNumber = cumulus_pallet_parachain_system::AnyRelayNumber;
 }
 
 parameter_types! {