Discard messages +- 1 round from our state

Author: qdm12

lib/grandpa/vote_message.go

@@ -126,55 +126,67 @@ func (s *Service) validateVoteMessage(from peer.ID, m *VoteMessage) (*Vote, erro
 	// check for message signature
 	pk, err := ed25519.NewPublicKey(m.Message.AuthorityID[:])
 	if err != nil {
+		// TODO: affect peer reputation
 		return nil, err
 	}
 
 	err = validateMessageSignature(pk, m)
 	if err != nil {
+		// TODO: affect peer reputation
 		return nil, err
 	}
 
 	if m.SetID != s.state.setID {
 		return nil, ErrSetIDMismatch
 	}
 
-	// check that vote is for current round
-	if m.Round != s.state.round {
-		if m.Round < s.state.round {
-			// peer doesn't know round was finalised, send out another commit message
-			header, err := s.blockState.GetFinalisedHeader(m.Round, m.SetID)
-			if err != nil {
-				return nil, err
-			}
+	const maxRoundsLag = 1
+	minRoundAccepted := s.state.round - maxRoundsLag
+	if minRoundAccepted > s.state.round {
+		// we overflowed below 0 so set the minimum to 0.
+		minRoundAccepted = 0
+	}
 
-			cm, err := s.newCommitMessage(header, m.Round)
-			if err != nil {
-				return nil, err
-			}
+	const maxRoundsAhead = 1
+	maxRoundAccepted := s.state.round + maxRoundsAhead
 
-			// send finalised block from previous round to network
-			msg, err := cm.ToConsensusMessage()
-			if err != nil {
-				return nil, err
-			}
+	if m.Round < minRoundAccepted || m.Round > maxRoundAccepted {
+		// Discard message
+		// TODO: affect peer reputation, this is shameful impolite behaviour
+		return nil, nil //nolint:nilnil
+	}
 
-			if err = s.network.SendMessage(from, msg); err != nil {
-				logger.Warnf("failed to send CommitMessage: %s", err)
-			}
-		} else {
-			// Message round is higher than the round of our state,
-			// we may be lagging behind, so store the message in the tracker
-			// for processing later.
-			const maxFutureRoundsDiff = 5
-			if m.Round < s.state.round+maxFutureRoundsDiff {
-				// We ensure the message round is not too far away
-				// from our state round, to avoid abuses of the tracker storage.
-				s.tracker.addVote(from, m)
-			}
+	if m.Round < s.state.round {
+		// message round is lagging by 1
+		// peer doesn't know round was finalised, send out another commit message
+		header, err := s.blockState.GetFinalisedHeader(m.Round, m.SetID)
+		if err != nil {
+			return nil, err
+		}
+
+		cm, err := s.newCommitMessage(header, m.Round)
+		if err != nil {
+			return nil, err
+		}
+
+		// send finalised block from previous round to network
+		msg, err := cm.ToConsensusMessage()
+		if err != nil {
+			return nil, err
+		}
+
+		if err = s.network.SendMessage(from, msg); err != nil {
+			logger.Warnf("failed to send CommitMessage: %s", err)
 		}
 
 		// TODO: get justification if your round is lower, or just do catch-up? (#1815)
 		return nil, errRoundMismatch(m.Round, s.state.round)
+	} else if m.Round > s.state.round {
+		// Message round is higher by 1 than the round of our state,
+		// we may be lagging behind, so store the message in the tracker
+		// for processing later in the coming few milliseconds.
+		s.tracker.addVote(from, m)
+		return nil, errRoundMismatch(m.Round, s.state.round)
 	}
 
 	// check for equivocation ie. multiple votes within one subround