Wire Finality Verifier Pallet Into Runtimes (#696)

* Add Finality Verifier pallet to runtimes

* Implement simple ancestry checker

* Use the new checker in runtimes

* Remove unused import warning

* Bump max allowed ancestry proof size

* Add a few optimization suggestions when verifying ancestry

* Use session length as upper bound for ancestry proof size

* Remove unused time units

bridges/bin/millau/runtime/Cargo.toml

@@ -14,12 +14,14 @@ serde = { version = "1.0.121", optional = true, features = ["derive"] }
 
 # Bridge dependencies
 
+bp-header-chain = { path = "../../../primitives/header-chain", default-features = false }
 bp-message-lane = { path = "../../../primitives/message-lane", default-features = false }
 bp-millau = { path = "../../../primitives/millau", default-features = false }
 bp-rialto = { path = "../../../primitives/rialto", default-features = false }
 bp-runtime = { path = "../../../primitives/runtime", default-features = false }
 bridge-runtime-common = { path = "../../runtime-common", default-features = false }
 pallet-bridge-call-dispatch = { path = "../../../modules/call-dispatch", default-features = false }
+pallet-finality-verifier = { path = "../../../modules/finality-verifier", default-features = false }
 pallet-message-lane = { path = "../../../modules/message-lane", default-features = false }
 pallet-shift-session-manager = { path = "../../../modules/shift-session-manager", default-features = false }
 pallet-substrate-bridge = { path = "../../../modules/substrate", default-features = false }
@@ -58,6 +60,7 @@ wasm-builder-runner = { package = "substrate-wasm-builder-runner", version = "2.
 [features]
 default = ["std"]
 std = [
+	"bp-header-chain/std",
 	"bp-message-lane/std",
 	"bp-millau/std",
 	"bp-rialto/std",
@@ -71,6 +74,7 @@ std = [
 	"pallet-aura/std",
 	"pallet-balances/std",
 	"pallet-bridge-call-dispatch/std",
+	"pallet-finality-verifier/std",
 	"pallet-grandpa/std",
 	"pallet-message-lane/std",
 	"pallet-randomness-collective-flip/std",

bridges/bin/millau/runtime/src/lib.rs

@@ -132,15 +132,6 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	transaction_version: 1,
 };
 
-pub const MILLISECS_PER_BLOCK: u64 = 6000;
-
-pub const SLOT_DURATION: u64 = MILLISECS_PER_BLOCK;
-
-// These time units are defined in number of blocks.
-pub const MINUTES: BlockNumber = 60_000 / (MILLISECS_PER_BLOCK as BlockNumber);
-pub const HOURS: BlockNumber = MINUTES * 60;
-pub const DAYS: BlockNumber = HOURS * 24;
-
 /// The version information used to identify this runtime when compiled natively.
 #[cfg(feature = "std")]
 pub fn native_version() -> NativeVersion {
@@ -236,7 +227,7 @@ impl pallet_grandpa::Config for Runtime {
 }
 
 parameter_types! {
-	pub const MinimumPeriod: u64 = SLOT_DURATION / 2;
+	pub const MinimumPeriod: u64 = bp_millau::SLOT_DURATION / 2;
 }
 
 impl pallet_timestamp::Config for Runtime {
@@ -287,7 +278,7 @@ impl pallet_sudo::Config for Runtime {
 
 parameter_types! {
 	/// Authorities are changing every 5 minutes.
-	pub const Period: BlockNumber = 5 * MINUTES;
+	pub const Period: BlockNumber = bp_millau::SESSION_LENGTH;
 	pub const Offset: BlockNumber = 0;
 }
 
@@ -309,6 +300,19 @@ impl pallet_substrate_bridge::Config for Runtime {
 	type BridgedChain = bp_rialto::Rialto;
 }
 
+parameter_types! {
+	// We'll use the length of a session on the bridged chain as our bound since GRANDPA is
+	// guaranteed to produce a justification every session.
+	pub const MaxHeadersInSingleProof: bp_rialto::BlockNumber = bp_rialto::SESSION_LENGTH;
+}
+
+impl pallet_finality_verifier::Config for Runtime {
+	type BridgedChain = bp_rialto::Rialto;
+	type HeaderChain = pallet_substrate_bridge::Module<Runtime>;
+	type AncestryChecker = bp_header_chain::LinearAncestryChecker;
+	type MaxHeadersInSingleProof = MaxHeadersInSingleProof;
+}
+
 impl pallet_shift_session_manager::Config for Runtime {}
 
 parameter_types! {
@@ -362,6 +366,7 @@ construct_runtime!(
 		BridgeRialto: pallet_substrate_bridge::{Module, Call, Storage, Config<T>},
 		BridgeRialtoMessageLane: pallet_message_lane::{Module, Call, Storage, Event<T>},
 		BridgeCallDispatch: pallet_bridge_call_dispatch::{Module, Event<T>},
+		BridgeFinalityVerifier: pallet_finality_verifier::{Module, Call},
 		System: frame_system::{Module, Call, Config, Storage, Event<T>},
 		RandomnessCollectiveFlip: pallet_randomness_collective_flip::{Module, Call, Storage},
 		Timestamp: pallet_timestamp::{Module, Call, Storage, Inherent},

bridges/bin/rialto/runtime/Cargo.toml

@@ -27,6 +27,7 @@ bridge-runtime-common = { path = "../../runtime-common", default-features = fals
 pallet-bridge-eth-poa = { path = "../../../modules/ethereum", default-features = false }
 pallet-bridge-call-dispatch = { path = "../../../modules/call-dispatch", default-features = false }
 pallet-bridge-currency-exchange = { path = "../../../modules/currency-exchange", default-features = false }
+pallet-finality-verifier = { path = "../../../modules/finality-verifier", default-features = false }
 pallet-substrate-bridge = { path = "../../../modules/substrate", default-features = false }
 pallet-message-lane = { path = "../../../modules/message-lane", default-features = false }
 pallet-shift-session-manager = { path = "../../../modules/shift-session-manager", default-features = false }
@@ -90,6 +91,7 @@ std = [
 	"pallet-bridge-eth-poa/std",
 	"pallet-bridge-call-dispatch/std",
 	"pallet-bridge-currency-exchange/std",
+	"pallet-finality-verifier/std",
 	"pallet-grandpa/std",
 	"pallet-message-lane/std",
 	"pallet-randomness-collective-flip/std",

bridges/bin/rialto/runtime/src/lib.rs

@@ -140,15 +140,6 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	transaction_version: 1,
 };
 
-pub const MILLISECS_PER_BLOCK: u64 = 6000;
-
-pub const SLOT_DURATION: u64 = MILLISECS_PER_BLOCK;
-
-// These time units are defined in number of blocks.
-pub const MINUTES: BlockNumber = 60_000 / (MILLISECS_PER_BLOCK as BlockNumber);
-pub const HOURS: BlockNumber = MINUTES * 60;
-pub const DAYS: BlockNumber = HOURS * 24;
-
 /// The version information used to identify this runtime when compiled natively.
 #[cfg(feature = "std")]
 pub fn native_version() -> NativeVersion {
@@ -344,7 +335,7 @@ impl pallet_grandpa::Config for Runtime {
 }
 
 parameter_types! {
-	pub const MinimumPeriod: u64 = SLOT_DURATION / 2;
+	pub const MinimumPeriod: u64 = bp_rialto::SLOT_DURATION / 2;
 }
 
 impl pallet_timestamp::Config for Runtime {
@@ -394,7 +385,7 @@ impl pallet_sudo::Config for Runtime {
 }
 
 parameter_types! {
-	pub const Period: BlockNumber = 4;
+	pub const Period: BlockNumber = bp_rialto::SESSION_LENGTH;
 	pub const Offset: BlockNumber = 0;
 }
 
@@ -416,6 +407,19 @@ impl pallet_substrate_bridge::Config for Runtime {
 	type BridgedChain = bp_millau::Millau;
 }
 
+parameter_types! {
+	// We'll use the length of a session on the bridged chain as our bound since GRANDPA is
+	// guaranteed to produce a justification every session.
+	pub const MaxHeadersInSingleProof: bp_millau::BlockNumber = bp_millau::SESSION_LENGTH;
+}
+
+impl pallet_finality_verifier::Config for Runtime {
+	type BridgedChain = bp_millau::Millau;
+	type HeaderChain = pallet_substrate_bridge::Module<Runtime>;
+	type AncestryChecker = bp_header_chain::LinearAncestryChecker;
+	type MaxHeadersInSingleProof = MaxHeadersInSingleProof;
+}
+
 impl pallet_shift_session_manager::Config for Runtime {}
 
 parameter_types! {
@@ -471,6 +475,7 @@ construct_runtime!(
 		BridgeRialtoCurrencyExchange: pallet_bridge_currency_exchange::<Instance1>::{Module, Call},
 		BridgeKovanCurrencyExchange: pallet_bridge_currency_exchange::<Instance2>::{Module, Call},
 		BridgeMillau: pallet_substrate_bridge::{Module, Call, Storage, Config<T>},
+		BridgeFinalityVerifier: pallet_finality_verifier::{Module, Call},
 		BridgeCallDispatch: pallet_bridge_call_dispatch::{Module, Event<T>},
 		BridgeMillauMessageLane: pallet_message_lane::{Module, Call, Storage, Event<T>},
 		System: frame_system::{Module, Call, Config, Storage, Event<T>},

bridges/modules/finality-verifier/Cargo.toml

@@ -11,6 +11,7 @@ license = "GPL-3.0-or-later WITH Classpath-exception-2.0"
 codec = { package = "parity-scale-codec", version = "1.3.1", default-features = false }
 finality-grandpa = { version = "0.12.3", default-features = false }
 serde = { version = "1.0", optional = true }
+num-traits = { version = "0.2", default-features = false }
 
 # Bridge Dependencies
 
@@ -39,6 +40,7 @@ std = [
 	"finality-grandpa/std",
 	"frame-support/std",
 	"frame-system/std",
+	"num-traits/std",
 	"serde",
 	"sp-runtime/std",
 	"sp-std/std",

bridges/modules/finality-verifier/src/lib.rs

@@ -37,11 +37,16 @@ use bp_runtime::{Chain, HeaderOf};
 use finality_grandpa::voter_set::VoterSet;
 use frame_support::{dispatch::DispatchError, ensure, traits::Get};
 use frame_system::ensure_signed;
+use num_traits::AsPrimitive;
 use sp_runtime::traits::Header as HeaderT;
+use sp_std::vec::Vec;
 
 #[cfg(test)]
 mod mock;
 
+// Re-export in crate namespace for `construct_runtime!`
+pub use pallet::*;
+
 #[frame_support::pallet]
 pub mod pallet {
 	use super::*;
@@ -69,7 +74,7 @@ pub mod pallet {
 		/// The maximum length of headers we can have in a single ancestry proof. This prevents
 		/// unbounded iteration when verifying proofs.
 		#[pallet::constant]
-		type MaxHeadersInSingleProof: Get<u8>;
+		type MaxHeadersInSingleProof: Get<<Self::BridgedChain as Chain>::BlockNumber>;
 	}
 
 	#[pallet::pallet]
@@ -100,7 +105,7 @@ pub mod pallet {
 			let _ = ensure_signed(origin)?;
 
 			ensure!(
-				ancestry_proof.len() <= T::MaxHeadersInSingleProof::get() as usize,
+				ancestry_proof.len() <= T::MaxHeadersInSingleProof::get().as_(),
 				<Error<T>>::OversizedAncestryProof
 			);
 
@@ -149,7 +154,6 @@ pub mod pallet {
 
 #[cfg(test)]
 mod tests {
-	use super::pallet::*;
 	use super::*;
 	use crate::mock::{run_test, test_header, Origin, TestRuntime};
 	use bp_test_utils::{authority_list, make_justification_for_header};

bridges/primitives/header-chain/src/lib.rs

@@ -27,7 +27,9 @@ use core::fmt::Debug;
 #[cfg(feature = "std")]
 use serde::{Deserialize, Serialize};
 use sp_finality_grandpa::{AuthorityList, SetId};
+use sp_runtime::traits::Header as HeaderT;
 use sp_runtime::RuntimeDebug;
+use sp_std::vec::Vec;
 
 pub mod justification;
 
@@ -110,3 +112,101 @@ impl<H, P> AncestryChecker<H, P> for () {
 		true
 	}
 }
+
+/// A simple ancestry checker which verifies ancestry by walking every header between `child` and
+/// `ancestor`.
+pub struct LinearAncestryChecker;
+
+impl<H: HeaderT> AncestryChecker<H, Vec<H>> for LinearAncestryChecker {
+	fn are_ancestors(ancestor: &H, child: &H, proof: &Vec<H>) -> bool {
+		// You can't be your own parent
+		if proof.len() < 2 {
+			return false;
+		}
+
+		// Let's make sure that the given headers are actually in the proof
+		match proof.first() {
+			Some(first) if first == ancestor => {}
+			_ => return false,
+		}
+
+		match proof.last() {
+			Some(last) if last == child => {}
+			_ => return false,
+		}
+
+		// Now we actually check the proof
+		for i in 1..proof.len() {
+			if &proof[i - 1].hash() != proof[i].parent_hash() {
+				return false;
+			}
+		}
+
+		true
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use bp_test_utils::test_header;
+	use sp_runtime::testing::Header;
+
+	#[test]
+	fn can_verify_ancestry_correctly() {
+		let ancestor: Header = test_header(1);
+		let header2: Header = test_header(2);
+		let header3: Header = test_header(3);
+		let child: Header = test_header(4);
+
+		let ancestry_proof = vec![ancestor.clone(), header2, header3, child.clone()];
+
+		assert!(LinearAncestryChecker::are_ancestors(&ancestor, &child, &ancestry_proof));
+	}
+
+	#[test]
+	fn does_not_verify_invalid_proof() {
+		let ancestor: Header = test_header(1);
+		let header2: Header = test_header(2);
+		let header3: Header = test_header(3);
+		let child: Header = test_header(4);
+
+		let ancestry_proof = vec![ancestor.clone(), header3, header2, child.clone()];
+
+		let invalid = !LinearAncestryChecker::are_ancestors(&ancestor, &child, &ancestry_proof);
+		assert!(invalid);
+	}
+
+	#[test]
+	fn header_is_not_allowed_to_be_its_own_ancestor() {
+		let ancestor: Header = test_header(1);
+		let child: Header = ancestor.clone();
+		let ancestry_proof = vec![ancestor.clone()];
+
+		let invalid = !LinearAncestryChecker::are_ancestors(&ancestor, &child, &ancestry_proof);
+		assert!(invalid);
+	}
+
+	#[test]
+	fn proof_is_considered_invalid_if_child_and_ancestor_do_not_match() {
+		let ancestor: Header = test_header(1);
+		let header2: Header = test_header(2);
+		let header3: Header = test_header(3);
+		let child: Header = test_header(4);
+
+		let ancestry_proof = vec![ancestor, header3.clone(), header2.clone(), child];
+
+		let invalid = !LinearAncestryChecker::are_ancestors(&header2, &header3, &ancestry_proof);
+		assert!(invalid);
+	}
+
+	#[test]
+	fn empty_proof_is_invalid() {
+		let ancestor: Header = test_header(1);
+		let child: Header = ancestor.clone();
+		let ancestry_proof = vec![];
+
+		let invalid = !LinearAncestryChecker::are_ancestors(&ancestor, &child, &ancestry_proof);
+		assert!(invalid);
+	}
+}

bridges/primitives/millau/src/lib.rs

@@ -83,6 +83,24 @@ pub const MAX_SINGLE_MESSAGE_DELIVERY_TX_WEIGHT: Weight = 1_500_000_000;
 /// runtime upgrades.
 pub const MAX_SINGLE_MESSAGE_DELIVERY_CONFIRMATION_TX_WEIGHT: Weight = 2_000_000_000;
 
+/// The length of a session (how often authorities change) on Millau measured in of number of blocks.
+pub const SESSION_LENGTH: BlockNumber = 5 * time_units::MINUTES;
+
+/// Re-export `time_units` to make usage easier.
+pub use time_units::*;
+
+/// Human readable time units defined in terms of number of blocks.
+pub mod time_units {
+	use super::BlockNumber;
+
+	pub const MILLISECS_PER_BLOCK: u64 = 6000;
+	pub const SLOT_DURATION: u64 = MILLISECS_PER_BLOCK;
+
+	pub const MINUTES: BlockNumber = 60_000 / (MILLISECS_PER_BLOCK as BlockNumber);
+	pub const HOURS: BlockNumber = MINUTES * 60;
+	pub const DAYS: BlockNumber = HOURS * 24;
+}
+
 /// Block number type used in Millau.
 pub type BlockNumber = u64;
 

bridges/primitives/rialto/src/lib.rs

@@ -74,6 +74,24 @@ pub const MAX_SINGLE_MESSAGE_DELIVERY_TX_WEIGHT: Weight = 1_500_000_000;
 /// runtime upgrades.
 pub const MAX_SINGLE_MESSAGE_DELIVERY_CONFIRMATION_TX_WEIGHT: Weight = 2_000_000_000;
 
+/// The length of a session (how often authorities change) on Rialto measured in of number of blocks.
+pub const SESSION_LENGTH: BlockNumber = 4;
+
+/// Re-export `time_units` to make usage easier.
+pub use time_units::*;
+
+/// Human readable time units defined in terms of number of blocks.
+pub mod time_units {
+	use super::BlockNumber;
+
+	pub const MILLISECS_PER_BLOCK: u64 = 6000;
+	pub const SLOT_DURATION: u64 = MILLISECS_PER_BLOCK;
+
+	pub const MINUTES: BlockNumber = 60_000 / (MILLISECS_PER_BLOCK as BlockNumber);
+	pub const HOURS: BlockNumber = MINUTES * 60;
+	pub const DAYS: BlockNumber = HOURS * 24;
+}
+
 /// Block number type used in Rialto.
 pub type BlockNumber = u32;