[stable] Missing AuRa backports (#7499)

* Merge pull request #7368 from paritytech/td-future-blocks

Wait for future blocks in AuRa

* Advance AuRa step as far as we can and prevent invalid blocks. (#7451)

* Advance AuRa step as far as we can.

* Wait for future blocks.

* Problem: AuRa's unsafeties around step duration (#7282)

Firstly, `Step.duration_remaining` casts it to u32, unnecesarily
limiting it to 2^32. While theoretically this is "good enough" (at 3
seconds steps it provides room for a little over 400 years), it is
still a lossy way to calculate the remaining time until the next step.

Secondly, step duration might be zero, triggering division by zero
in `Step.calibrate`

Solution: rework the code around the fact that duration is
typically in single digits and never grows, hence, it can be represented
by a much narrower range (u16) and this highlights the fact that
multiplying u64 by u16 will only result in an overflow in even further
future, at which point we should panic informatively (if anybody's
still around)

Similarly, panic when it is detected that incrementing the step
counter wrapped around on the overflow of usize.

As for the division by zero, prevent it by making zero an invalid
value for step duration. This will make AuRa log the constraint
mismatch and panic (after all, what purpose would zero step duration
serve? it makes no sense within the definition of the protocol,
as finality can only be achieved as per the specification
if messages are received within the step duration, which would violate
the speed of light and other physical laws in this case).

* Fix tests.

* detect different node, same-key signing in aura (#7245)

* detect different node, same-key signing in aura

* reduce scope of warning

ethcore/src/engines/authority_round/mod.rs

@@ -49,12 +49,16 @@ mod finality;
 pub struct AuthorityRoundParams {
 	/// Gas limit divisor.
 	pub gas_limit_bound_divisor: U256,
-	/// Time to wait before next block or authority switching.
-	pub step_duration: Duration,
 	/// Block reward.
 	pub block_reward: U256,
 	/// Namereg contract address.
 	pub registrar: Address,
+	/// Time to wait before next block or authority switching,
+	/// in seconds.
+	///
+	/// Deliberately typed as u16 as too high of a value leads
+	/// to slow block issuance.
+	pub step_duration: u16,
 	/// Starting step,
 	pub start_step: Option<u64>,
 	/// Valid validators.
@@ -73,11 +77,18 @@ pub struct AuthorityRoundParams {
 	pub maximum_uncle_count: usize,
 }
 
+const U16_MAX: usize = ::std::u16::MAX as usize;
+
 impl From<ethjson::spec::AuthorityRoundParams> for AuthorityRoundParams {
 	fn from(p: ethjson::spec::AuthorityRoundParams) -> Self {
+		let mut step_duration_usize: usize = p.step_duration.into();
+		if step_duration_usize > U16_MAX {
+			step_duration_usize = U16_MAX;
+			warn!(target: "engine", "step_duration is too high ({}), setting it to {}", step_duration_usize, U16_MAX);
+		}
 		AuthorityRoundParams {
 			gas_limit_bound_divisor: p.gas_limit_bound_divisor.into(),
-			step_duration: Duration::from_secs(p.step_duration.into()),
+			step_duration: step_duration_usize as u16,
 			validators: new_validator_set(p.validators),
 			block_reward: p.block_reward.map_or_else(U256::zero, Into::into),
 			registrar: p.registrar.map_or_else(Address::new, Into::into),
@@ -97,36 +108,74 @@ impl From<ethjson::spec::AuthorityRoundParams> for AuthorityRoundParams {
 struct Step {
 	calibrate: bool, // whether calibration is enabled.
 	inner: AtomicUsize,
-	duration: Duration,
+	duration: u16,
 }
 
 impl Step {
 	fn load(&self) -> usize { self.inner.load(AtomicOrdering::SeqCst) }
 	fn duration_remaining(&self) -> Duration {
 		let now = unix_now();
-		let step_end = self.duration * (self.load() as u32 + 1);
-		if step_end > now {
-			step_end - now
-		} else {
-			Duration::from_secs(0)
+		let expected_seconds = (self.load() as u64)
+			.checked_add(1)
+			.and_then(|ctr| ctr.checked_mul(self.duration as u64))
+			.map(Duration::from_secs);
+
+		match expected_seconds {
+			Some(step_end) if step_end > now => step_end - now,
+			Some(_) => Duration::from_secs(0),
+			None => {
+				let ctr = self.load();
+				error!(target: "engine", "Step counter is too high: {}, aborting", ctr);
+				panic!("step counter is too high: {}", ctr)
+			},
 		}
+
 	}
+
 	fn increment(&self) {
-		self.inner.fetch_add(1, AtomicOrdering::SeqCst);
+		use std::usize;
+		// fetch_add won't panic on overflow but will rather wrap
+		// around, leading to zero as the step counter, which might
+		// lead to unexpected situations, so it's better to shut down.
+		if self.inner.fetch_add(1, AtomicOrdering::SeqCst) == usize::MAX {
+			error!(target: "engine", "Step counter is too high: {}, aborting", usize::MAX);
+			panic!("step counter is too high: {}", usize::MAX);
+		}
+
 	}
+
 	fn calibrate(&self) {
 		if self.calibrate {
-			let new_step = unix_now().as_secs() / self.duration.as_secs();
+			let new_step = unix_now().as_secs() / (self.duration as u64);
 			self.inner.store(new_step as usize, AtomicOrdering::SeqCst);
 		}
 	}
-	fn is_future(&self, given: usize) -> bool {
-		if given > self.load() + 1 {
-			// Make absolutely sure that the given step is correct.
-			self.calibrate();
-			given > self.load() + 1
+
+	fn check_future(&self, given: usize) -> Result<(), Option<OutOfBounds<u64>>> {
+		const REJECTED_STEP_DRIFT: usize = 4;
+
+		// Verify if the step is correct.
+		if given <= self.load() {
+			return Ok(());
+		}
+
+		// Make absolutely sure that the given step is incorrect.
+		self.calibrate();
+		let current = self.load();
+
+		// reject blocks too far in the future
+		if given > current + REJECTED_STEP_DRIFT {
+			Err(None)
+		// wait a bit for blocks in near future
+		} else if given > current {
+			let d = self.duration as u64;
+			Err(Some(OutOfBounds {
+				min: None,
+				max: Some(d * current as u64),
+				found: d * given as u64,
+			}))
 		} else {
-			false
+			Ok(())
 		}
 	}
 }
@@ -322,22 +371,28 @@ fn verify_external<F: Fn(Report)>(header: &Header, validators: &ValidatorSet, st
 {
 	let header_step = header_step(header)?;
 
-	// Give one step slack if step is lagging, double vote is still not possible.
-	if step.is_future(header_step) {
-		trace!(target: "engine", "verify_block_external: block from the future");
-		report(Report::Benign(*header.author(), header.number()));
-		Err(BlockError::InvalidSeal)?
-	} else {
-		let proposer_signature = header_signature(header)?;
-		let correct_proposer = validators.get(header.parent_hash(), header_step);
-		let is_invalid_proposer = *header.author() != correct_proposer ||
-			!verify_address(&correct_proposer, &proposer_signature, &header.bare_hash())?;
-
-		if is_invalid_proposer {
-			trace!(target: "engine", "verify_block_external: bad proposer for step: {}", header_step);
-			Err(EngineError::NotProposer(Mismatch { expected: correct_proposer, found: header.author().clone() }))?
-		} else {
-			Ok(())
+	match step.check_future(header_step) {
+		Err(None) => {
+			trace!(target: "engine", "verify_block_external: block from the future");
+			report(Report::Benign(*header.author(), header.number()));
+			return Err(BlockError::InvalidSeal.into())
+		},
+		Err(Some(oob)) => {
+			trace!(target: "engine", "verify_block_external: block too early");
+			return Err(BlockError::TemporarilyInvalid(oob).into())
+		},
+		Ok(_) => {
+			let proposer_signature = header_signature(header)?;
+			let correct_proposer = validators.get(header.parent_hash(), header_step);
+			let is_invalid_proposer = *header.author() != correct_proposer ||
+				!verify_address(&correct_proposer, &proposer_signature, &header.bare_hash())?;
+
+			if is_invalid_proposer {
+				trace!(target: "engine", "verify_block_external: bad proposer for step: {}", header_step);
+				Err(EngineError::NotProposer(Mismatch { expected: correct_proposer, found: header.author().clone() }))?
+			} else {
+				Ok(())
+			}
 		}
 	}
 }
@@ -370,8 +425,12 @@ impl AsMillis for Duration {
 impl AuthorityRound {
 	/// Create a new instance of AuthorityRound engine.
 	pub fn new(params: CommonParams, our_params: AuthorityRoundParams, builtins: BTreeMap<Address, Builtin>) -> Result<Arc<Self>, Error> {
+		if our_params.step_duration == 0 {
+			error!(target: "engine", "Authority Round step duration can't be zero, aborting");
+			panic!("authority_round: step duration can't be zero")
+		}
 		let should_timeout = our_params.start_step.is_none();
-		let initial_step = our_params.start_step.unwrap_or_else(|| (unix_now().as_secs() / our_params.step_duration.as_secs())) as usize;
+		let initial_step = our_params.start_step.unwrap_or_else(|| (unix_now().as_secs() / (our_params.step_duration as u64))) as usize;
 		let engine = Arc::new(
 			AuthorityRound {
 				params: params,
@@ -519,6 +578,7 @@ impl Engine for AuthorityRound {
 			.expect("Header has been verified; qed").into();
 
 		let step = self.step.load();
+
 		let expected_diff = calculate_score(parent_step, step.into());
 
 		if header.difficulty() != &expected_diff {
@@ -558,6 +618,13 @@ impl Engine for AuthorityRound {
 		};
 
 		if is_step_proposer(validators, header.parent_hash(), step, header.author()) {
+			// this is guarded against by `can_propose` unless the block was signed
+			// on the same step (implies same key) and on a different node.
+			if parent_step == step.into() {
+				warn!("Attempted to seal block on the same step as parent. Is this authority sealing with more than one node?");
+				return Seal::None;
+			}
+
 			if let Ok(signature) = self.sign(header.bare_hash()) {
 				trace!(target: "engine", "generate_seal: Issuing a block for step {}.", step);
 
@@ -1099,9 +1166,9 @@ mod tests {
 		let last_benign = Arc::new(AtomicUsize::new(0));
 		let params = AuthorityRoundParams {
 			gas_limit_bound_divisor: U256::from_str("400").unwrap(),
-			step_duration: Default::default(),
 			block_reward: Default::default(),
 			registrar: Default::default(),
+			step_duration: 1,
 			start_step: Some(1),
 			validators: Box::new(TestSet::new(Default::default(), last_benign.clone())),
 			validate_score_transition: 0,
@@ -1137,9 +1204,9 @@ mod tests {
 		let last_benign = Arc::new(AtomicUsize::new(0));
 		let params = AuthorityRoundParams {
 			gas_limit_bound_divisor: 5.into(),
-			step_duration: Default::default(),
 			block_reward: Default::default(),
 			registrar: Default::default(),
+			step_duration: 1,
 			start_step: Some(1),
 			validators: Box::new(TestSet::new(Default::default(), last_benign.clone())),
 			validate_score_transition: 0,
@@ -1156,4 +1223,50 @@ mod tests {
 		assert_eq!(aura.maximum_uncle_count(1), 0);
 		assert_eq!(aura.maximum_uncle_count(100), 0);
 	}
+
+    #[test]
+    #[should_panic(expected="counter is too high")]
+    fn test_counter_increment_too_high() {
+        use super::Step;
+        let step = Step {
+            calibrate: false,
+            inner: AtomicUsize::new(::std::usize::MAX),
+            duration: 1,
+        };
+        step.increment();
+	}
+
+	#[test]
+	#[should_panic(expected="counter is too high")]
+	fn test_counter_duration_remaining_too_high() {
+		use super::Step;
+		let step = Step {
+			calibrate: false,
+			inner: AtomicUsize::new(::std::usize::MAX),
+			duration: 1,
+		};
+		step.duration_remaining();
+	}
+
+	#[test]
+	#[should_panic(expected="authority_round: step duration can't be zero")]
+	fn test_step_duration_zero() {
+		let last_benign = Arc::new(AtomicUsize::new(0));
+		let params = AuthorityRoundParams {
+			step_duration: 0,
+			start_step: Some(1),
+			validators: Box::new(TestSet::new(Default::default(), last_benign.clone())),
+			validate_score_transition: 0,
+			validate_step_transition: 0,
+			immediate_transitions: true,
+			maximum_uncle_count_transition: 0,
+			maximum_uncle_count: 0,
+			block_reward: Default::default(),
+			eip155_transition: 0,
+			registrar: Default::default(),
+			gas_limit_bound_divisor: 5.into(),
+		};
+
+		AuthorityRound::new(Default::default(), params, Default::default()).unwrap();
+	}
 }

ethcore/src/engines/validator_set/contract.rs

@@ -159,22 +159,36 @@ mod tests {
 
 		// Make sure reporting can be done.
 		client.miner().set_gas_floor_target(1_000_000.into());
-
 		client.miner().set_engine_signer(v1, "".into()).unwrap();
+
+		// Check a block that is a bit in future, reject it but don't report the validator.
 		let mut header = Header::default();
 		let seal = vec![encode(&5u8).into_vec(), encode(&(&H520::default() as &[u8])).into_vec()];
 		header.set_seal(seal);
 		header.set_author(v1);
 		header.set_number(2);
 		header.set_parent_hash(client.chain_info().best_block_hash);
+		assert!(client.engine().verify_block_external(&header, None).is_err());
+		client.engine().step();
+		assert_eq!(client.chain_info().best_block_number, 0);
 
+		// Now create one that is more in future. That one should be rejected and validator should be reported.
+		let mut header = Header::default();
+		let seal = vec![encode(&8u8).into_vec(), encode(&(&H520::default() as &[u8])).into_vec()];
+		header.set_seal(seal);
+		header.set_author(v1);
+		header.set_number(2);
+		header.set_parent_hash(client.chain_info().best_block_hash);
 		// `reportBenign` when the designated proposer releases block from the future (bad clock).
 		assert!(client.engine().verify_block_external(&header, None).is_err());
 		// Seal a block.
 		client.engine().step();
 		assert_eq!(client.chain_info().best_block_number, 1);
 		// Check if the unresponsive validator is `disliked`.
-		assert_eq!(client.call_contract(BlockId::Latest, validator_contract, "d8f2e0bf".from_hex().unwrap()).unwrap().to_hex(), "0000000000000000000000007d577a597b2742b498cb5cf0c26cdcd726d39e6e");
+		assert_eq!(
+			client.call_contract(BlockId::Latest, validator_contract, "d8f2e0bf".from_hex().unwrap()).unwrap().to_hex(),
+			"0000000000000000000000007d577a597b2742b498cb5cf0c26cdcd726d39e6e"
+		);
 		// Simulate a misbehaving validator by handling a double proposal.
 		let header = client.best_block_header().decode();
 		assert!(client.engine().verify_block_family(&header, &header, None).is_err());

ethcore/src/error.rs

@@ -157,6 +157,8 @@ pub enum BlockError {
 	InvalidReceiptsRoot(Mismatch<H256>),
 	/// Timestamp header field is invalid.
 	InvalidTimestamp(OutOfBounds<u64>),
+	/// Timestamp header field is too far in future.
+	TemporarilyInvalid(OutOfBounds<u64>),
 	/// Log bloom header field is invalid.
 	InvalidLogBloom(Mismatch<LogBloom>),
 	/// Parent hash field of header is invalid; this is an invalid error indicating a logic flaw in the codebase.
@@ -202,6 +204,7 @@ impl fmt::Display for BlockError {
 			InvalidGasLimit(ref oob) => format!("Invalid gas limit: {}", oob),
 			InvalidReceiptsRoot(ref mis) => format!("Invalid receipts trie root in header: {}", mis),
 			InvalidTimestamp(ref oob) => format!("Invalid timestamp in header: {}", oob),
+			TemporarilyInvalid(ref oob) => format!("Future timestamp in header: {}", oob),
 			InvalidLogBloom(ref oob) => format!("Invalid log bloom in header: {}", oob),
 			InvalidParentHash(ref mis) => format!("Invalid parent hash: {}", mis),
 			InvalidNumber(ref mis) => format!("Invalid number in header: {}", mis),

ethcore/src/verification/queue/mod.rs

@@ -500,7 +500,7 @@ impl<K: Kind> VerificationQueue<K> {
 			Err(err) => {
 				match err {
 					// Don't mark future blocks as bad.
-					Error::Block(BlockError::InvalidTimestamp(ref e)) if e.max.is_some() => {},
+					Error::Block(BlockError::TemporarilyInvalid(_)) => {},
 					_ => {
 						self.verification.bad.lock().insert(h.clone());
 					}