BEEFY: add support for slashing validators signing forking commitments

client/consensus/beefy/src/communication/fisherman.rs

@@ -0,0 +1,215 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+use crate::{
+	error::Error, justification::BeefyVersionedFinalityProof, keystore::{BeefyKeystore, BeefySignatureHasher},
+	LOG_TARGET,
+};
+use log::debug;
+use sc_client_api::Backend;
+use sp_api::ProvideRuntimeApi;
+use sp_blockchain::HeaderBackend;
+use sp_consensus_beefy::{
+	check_fork_equivocation_proof,
+	ecdsa_crypto::{AuthorityId, Signature},
+	BeefyApi, ForkEquivocationProof, Payload, PayloadProvider, ValidatorSet, VoteMessage, Commitment, OpaqueKeyOwnershipProof, SignedCommitment,
+};
+use sp_runtime::{
+	generic::BlockId,
+	traits::{Block, Header, NumberFor},
+};
+use std::{marker::PhantomData, sync::Arc};
+
+pub(crate) trait BeefyFisherman<B: Block>: Send + Sync {
+	/// Check `vote` for contained block against expected payload.
+	fn check_vote(
+		&self,
+		vote: VoteMessage<NumberFor<B>, AuthorityId, Signature>,
+	) -> Result<(), Error>;
+
+	/// Check `signed_commitment` for contained block against expected payload.
+	fn check_signed_commitment(
+		&self,
+		signed_commitment: SignedCommitment<NumberFor<B>, Signature>,
+	) -> Result<(), Error>;
+
+	/// Check `proof` for contained block against expected payload.
+	fn check_proof(&self, proof: BeefyVersionedFinalityProof<B>) -> Result<(), Error>;
+}
+
+/// Helper wrapper used to check gossiped votes for (historical) equivocations,
+/// and report any such protocol infringements.
+pub(crate) struct Fisherman<B: Block, BE, R, P> {
+	pub backend: Arc<BE>,
+	pub runtime: Arc<R>,
+	pub key_store: Arc<BeefyKeystore>,
+	pub payload_provider: P,
+	pub _phantom: PhantomData<B>,
+}
+
+impl<B, BE, R, P> Fisherman<B, BE, R, P>
+where
+	B: Block,
+	BE: Backend<B>,
+	P: PayloadProvider<B>,
+	R: ProvideRuntimeApi<B> + Send + Sync,
+	R::Api: BeefyApi<B, AuthorityId>,
+{
+	fn expected_header_and_payload(&self, number: NumberFor<B>) -> Result<(B::Header, Payload), Error> {
+		// This should be un-ambiguous since `number` is finalized.
+		let hash = self
+			.backend
+			.blockchain()
+			.expect_block_hash_from_id(&BlockId::Number(number))
+			.map_err(|e| Error::Backend(e.to_string()))?;
+		let header = self
+			.backend
+			.blockchain()
+			.expect_header(hash)
+			.map_err(|e| Error::Backend(e.to_string()))?;
+		self.payload_provider
+			.payload(&header)
+			.map(|payload| (header, payload))
+			.ok_or_else(|| Error::Backend("BEEFY Payload not found".into()))
+	}
+
+	fn active_validator_set_at(
+		&self,
+		header: &B::Header,
+	) -> Result<ValidatorSet<AuthorityId>, Error> {
+		self.runtime
+			.runtime_api()
+			.validator_set(header.hash())
+			.map_err(Error::RuntimeApi)?
+			.ok_or_else(|| Error::Backend("could not get BEEFY validator set".into()))
+	}
+
+	pub(crate) fn report_fork_equivocation(
+		&self,
+		proof: ForkEquivocationProof<NumberFor<B>, AuthorityId, Signature, B::Header>,
+	) -> Result<(), Error> {
+		let validator_set = self.active_validator_set_at(&proof.correct_header)?;
+		let set_id = validator_set.id();
+
+		let expected_header_hash = self
+			.backend
+			.blockchain()
+			.expect_block_hash_from_id(&BlockId::Number(proof.commitment.block_number))
+			.map_err(|e| Error::Backend(e.to_string()))?;
+
+		if proof.commitment.validator_set_id != set_id ||
+			!check_fork_equivocation_proof::<NumberFor<B>, AuthorityId, BeefySignatureHasher, B::Header>(&proof, &expected_header_hash)
+		{
+			debug!(target: LOG_TARGET, "🥩 Skip report for bad invalid fork proof {:?}", proof);
+			return Ok(())
+		}
+
+		let offender_ids = proof.signatories.iter().cloned().map(|(id, _sig)| id).collect::<Vec<_>>();
+		if let Some(local_id) = self.key_store.authority_id(validator_set.validators()) {
+			if offender_ids.contains(&local_id) {
+				debug!(target: LOG_TARGET, "🥩 Skip equivocation report for own equivocation");
+				// TODO: maybe error here instead?
+				return Ok(())
+			}
+		}
+
+		let hash = proof.correct_header.hash();
+		let runtime_api = self.runtime.runtime_api();
+
+		// generate key ownership proof at that block
+		let key_owner_proofs = offender_ids.iter()
+										   .filter_map(|id| {
+											   match runtime_api.generate_key_ownership_proof(hash, set_id, id.clone()) {
+												   Ok(Some(proof)) => Some(Ok(proof)),
+												   Ok(None) => {
+													   debug!(
+														   target: LOG_TARGET,
+														   "🥩 Invalid fork vote offender not part of the authority set."
+													   );
+													   None
+												   },
+												   Err(e) => Some(Err(Error::RuntimeApi(e))),
+											   }
+										   })
+										   .collect::<Result<_, _>>()?;
+
+		// submit invalid fork vote report at **best** block
+		let best_block_hash = self.backend.blockchain().info().best_hash;
+		runtime_api
+			.submit_report_fork_equivocation_unsigned_extrinsic(best_block_hash, proof, key_owner_proofs)
+			.map_err(Error::RuntimeApi)?;
+
+		Ok(())
+	}
+}
+
+impl<B, BE, R, P> BeefyFisherman<B> for Fisherman<B, BE, R, P>
+where
+	B: Block,
+	BE: Backend<B>,
+	P: PayloadProvider<B>,
+	R: ProvideRuntimeApi<B> + Send + Sync,
+	R::Api: BeefyApi<B, AuthorityId>,
+{
+	/// Check `vote` for contained block against expected payload.
+	fn check_vote(
+		&self,
+		vote: VoteMessage<NumberFor<B>, AuthorityId, Signature>,
+	) -> Result<(), Error> {
+		let number = vote.commitment.block_number;
+		let (correct_header, expected_payload) = self.expected_header_and_payload(number)?;
+		if vote.commitment.payload != expected_payload {
+			let proof = ForkEquivocationProof { commitment: vote.commitment, signatories: vec![(vote.id, vote.signature)], correct_header: correct_header.clone() };
+			self.report_fork_equivocation(proof)?;
+		}
+		Ok(())
+	}
+
+	/// Check `signed_commitment` for contained block against expected payload.
+	fn check_signed_commitment(
+		&self,
+		signed_commitment: SignedCommitment<NumberFor<B>, Signature>,
+	) -> Result<(), Error> {
+		let SignedCommitment {commitment, signatures} = signed_commitment;
+		let number = commitment.block_number;
+		let (correct_header, expected_payload) = self.expected_header_and_payload(number)?;
+		if commitment.payload != expected_payload {
+			let validator_set = self.active_validator_set_at(&correct_header)?;
+			if signatures.len() != validator_set.validators().len() {
+				// invalid proof
+				return Ok(())
+			}
+			// report every signer of the bad justification
+			let signatories = validator_set.validators().iter().cloned().zip(signatures.into_iter())
+																		.filter_map(|(id, signature)| signature.map(|sig| (id, sig))).collect();
+
+			let proof = ForkEquivocationProof { commitment, signatories, correct_header: correct_header.clone() };
+			self.report_fork_equivocation(proof)?;
+		}
+		Ok(())
+	}
+
+	/// Check `proof` for contained block against expected payload.
+	fn check_proof(&self, proof: BeefyVersionedFinalityProof<B>) -> Result<(), Error> {
+		match proof {
+			BeefyVersionedFinalityProof::<B>::V1(signed_commitment) => {
+				self.check_signed_commitment(signed_commitment)
+			}
+		}
+	}
+}

client/consensus/beefy/src/communication/gossip.rs

@@ -32,6 +32,7 @@ use wasm_timer::Instant;
 use crate::{
 	communication::{
 		benefit, cost,
+		fisherman::BeefyFisherman,
 		peers::{KnownPeers, PeerReport},
 	},
 	justification::{
@@ -225,26 +226,29 @@ impl<B: Block> Filter<B> {
 /// Allows messages for 'rounds >= last concluded' to flow, everything else gets
 /// rejected/expired.
 ///
+/// Messages for active and expired rounds are validated for expected payloads and attempts
+/// to create forks before head of GRANDPA are reported.
+///
 ///All messaging is handled in a single BEEFY global topic.
-pub(crate) struct GossipValidator<B>
-where
-	B: Block,
-{
+pub(crate) struct GossipValidator<B: Block, F> {
 	votes_topic: B::Hash,
 	justifs_topic: B::Hash,
 	gossip_filter: RwLock<Filter<B>>,
 	next_rebroadcast: Mutex<Instant>,
 	known_peers: Arc<Mutex<KnownPeers<B>>>,
 	report_sender: TracingUnboundedSender<PeerReport>,
+	pub(crate) fisherman: F,
 }
 
-impl<B> GossipValidator<B>
+impl<B, F> GossipValidator<B, F>
 where
 	B: Block,
+	F: BeefyFisherman<B>,
 {
 	pub(crate) fn new(
 		known_peers: Arc<Mutex<KnownPeers<B>>>,
-	) -> (GossipValidator<B>, TracingUnboundedReceiver<PeerReport>) {
+		fisherman: F,
+	) -> (GossipValidator<B, F>, TracingUnboundedReceiver<PeerReport>) {
 		let (tx, rx) = tracing_unbounded("mpsc_beefy_gossip_validator", 10_000);
 		let val = GossipValidator {
 			votes_topic: votes_topic::<B>(),
@@ -253,6 +257,7 @@ where
 			next_rebroadcast: Mutex::new(Instant::now() + REBROADCAST_AFTER),
 			known_peers,
 			report_sender: tx,
+			fisherman,
 		};
 		(val, rx)
 	}
@@ -287,9 +292,18 @@ where
 			let filter = self.gossip_filter.read();
 
 			match filter.consider_vote(round, set_id) {
-				Consider::RejectPast => return Action::Discard(cost::OUTDATED_MESSAGE),
 				Consider::RejectFuture => return Action::Discard(cost::FUTURE_MESSAGE),
 				Consider::RejectOutOfScope => return Action::Discard(cost::OUT_OF_SCOPE_MESSAGE),
+				Consider::RejectPast => {
+					// We know `vote` is for some past (finalized) block. Have fisherman check
+					// for equivocations. Best-effort, ignore errors such as state pruned.
+					let _ = self.fisherman.check_vote(vote);
+					// TODO: maybe raise cost reputation when seeing votes that are intentional
+					// spam: votes that trigger fisherman reports, but don't go through either
+					// because signer is/was not authority or similar reasons.
+					// The idea is to more quickly disconnect neighbors which are attempting DoS.
+					return Action::Discard(cost::OUTDATED_MESSAGE)
+				},
 				Consider::Accept => {},
 			}
 
@@ -331,9 +345,18 @@ where
 		let guard = self.gossip_filter.read();
 		// Verify general usefulness of the justification.
 		match guard.consider_finality_proof(round, set_id) {
-			Consider::RejectPast => return Action::Discard(cost::OUTDATED_MESSAGE),
 			Consider::RejectFuture => return Action::Discard(cost::FUTURE_MESSAGE),
 			Consider::RejectOutOfScope => return Action::Discard(cost::OUT_OF_SCOPE_MESSAGE),
+			Consider::RejectPast => {
+				// We know `proof` is for some past (finalized) block. Have fisherman check
+				// for equivocations. Best-effort, ignore errors such as state pruned.
+				let _ = self.fisherman.check_proof(proof);
+				// TODO: maybe raise cost reputation when seeing votes that are intentional
+				// spam: votes that trigger fisherman reports, but don't go through either because
+				// signer is/was not authority or similar reasons.
+				// The idea is to more quickly disconnect neighbors which are attempting DoS.
+				return Action::Discard(cost::OUTDATED_MESSAGE)
+			},
 			Consider::Accept => {},
 		}
 		// Verify justification signatures.
@@ -359,9 +382,10 @@ where
 	}
 }
 
-impl<B> Validator<B> for GossipValidator<B>
+impl<B, F> Validator<B> for GossipValidator<B, F>
 where
 	B: Block,
+	F: BeefyFisherman<B>,
 {
 	fn peer_disconnected(&self, _context: &mut dyn ValidatorContext<B>, who: &PeerId) {
 		self.known_peers.lock().remove(who);
@@ -474,14 +498,15 @@ where
 #[cfg(test)]
 pub(crate) mod tests {
 	use super::*;
-	use crate::keystore::BeefyKeystore;
+	use crate::{keystore::BeefyKeystore, tests::DummyFisherman};
 	use sc_network_test::Block;
 	use sp_application_crypto::key_types::BEEFY as BEEFY_KEY_TYPE;
 	use sp_consensus_beefy::{
 		ecdsa_crypto::Signature, known_payloads, Commitment, Keyring, MmrRootHash, Payload,
 		SignedCommitment, VoteMessage,
 	};
 	use sp_keystore::{testing::MemoryKeystore, Keystore};
+	use std::marker::PhantomData;
 
 	#[test]
 	fn known_votes_insert_remove() {
@@ -577,8 +602,9 @@ pub(crate) mod tests {
 	fn should_validate_messages() {
 		let keys = vec![Keyring::Alice.public()];
 		let validator_set = ValidatorSet::<AuthorityId>::new(keys.clone(), 0).unwrap();
+		let fisherman = DummyFisherman { _phantom: PhantomData::<Block> };
 		let (gv, mut report_stream) =
-			GossipValidator::<Block>::new(Arc::new(Mutex::new(KnownPeers::new())));
+			GossipValidator::new(Arc::new(Mutex::new(KnownPeers::new())), fisherman);
 		let sender = PeerId::random();
 		let mut context = TestContext;
 
@@ -705,7 +731,8 @@ pub(crate) mod tests {
 	fn messages_allowed_and_expired() {
 		let keys = vec![Keyring::Alice.public()];
 		let validator_set = ValidatorSet::<AuthorityId>::new(keys.clone(), 0).unwrap();
-		let (gv, _) = GossipValidator::<Block>::new(Arc::new(Mutex::new(KnownPeers::new())));
+		let fisherman = DummyFisherman { _phantom: PhantomData::<Block> };
+		let (gv, _) = GossipValidator::new(Arc::new(Mutex::new(KnownPeers::new())), fisherman);
 		gv.update_filter(GossipFilterCfg { start: 0, end: 10, validator_set: &validator_set });
 		let sender = sc_network::PeerId::random();
 		let topic = Default::default();
@@ -782,7 +809,8 @@ pub(crate) mod tests {
 	fn messages_rebroadcast() {
 		let keys = vec![Keyring::Alice.public()];
 		let validator_set = ValidatorSet::<AuthorityId>::new(keys.clone(), 0).unwrap();
-		let (gv, _) = GossipValidator::<Block>::new(Arc::new(Mutex::new(KnownPeers::new())));
+		let fisherman = DummyFisherman { _phantom: PhantomData::<Block> };
+		let (gv, _) = GossipValidator::new(Arc::new(Mutex::new(KnownPeers::new())), fisherman);
 		gv.update_filter(GossipFilterCfg { start: 0, end: 10, validator_set: &validator_set });
 		let sender = sc_network::PeerId::random();
 		let topic = Default::default();

client/consensus/beefy/src/communication/mod.rs

@@ -21,6 +21,7 @@
 pub mod notification;
 pub mod request_response;
 
+pub(crate) mod fisherman;
 pub(crate) mod gossip;
 pub(crate) mod peers;