fix: defend ddos voting attack with other mini fix according to audit

consensus/parlia/parlia.go

@@ -67,7 +67,7 @@ const (
 
 	systemRewardPercent = 4 // it means 1/2^4 = 1/16 percentage of gas fee incoming will be distributed to system
 
-	collectAdditionalVotesRewardRatio = float64(1) // ratio of additional reward for collecting more votes than needed
+	collectAdditionalVotesRewardRatio = 100 // ratio of additional reward for collecting more votes than needed, the denominator is 100
 )
 
 var (
@@ -1027,7 +1027,7 @@ func (p *Parlia) distributeFinalityReward(chain consensus.ChainHeaderReader, sta
 		}
 		quorum := cmath.CeilDiv(len(snap.Validators)*2, 3)
 		if validVoteCount > quorum {
-			accumulatedWeights[head.Coinbase] += uint64(float64(validVoteCount-quorum) * collectAdditionalVotesRewardRatio)
+			accumulatedWeights[head.Coinbase] += uint64((validVoteCount - quorum) * collectAdditionalVotesRewardRatio / 100)
 		}
 	}
 
@@ -1788,7 +1788,7 @@ func encodeSigHeader(w io.Writer, header *types.Header, chainId *big.Int) {
 		header.GasLimit,
 		header.GasUsed,
 		header.Time,
-		header.Extra[:len(header.Extra)-65], // this will panic if extra is too short, should check before calling encodeSigHeader
+		header.Extra[:len(header.Extra)-extraSeal], // this will panic if extra is too short, should check before calling encodeSigHeader
 		header.MixDigest,
 		header.Nonce,
 	})

eth/handler_bsc.go

@@ -61,6 +61,10 @@ func (h *bscHandler) Handle(peer *bsc.Peer, packet bsc.Packet) error {
 // handleVotesBroadcast is invoked from a peer's message handler when it transmits a
 // votes broadcast for the local node to process.
 func (h *bscHandler) handleVotesBroadcast(peer *bsc.Peer, votes []*types.VoteEnvelope) error {
+	if receiveLimit := peer.ReceiveLimit(); len(votes) > receiveLimit {
+		peer.Log().Warn("too many votes:%d, dropped:%d, may be a ddos attack", len(votes), len(votes)-receiveLimit)
+		votes = votes[:receiveLimit]
+	}
 	// Try to put votes into votepool
 	for _, vote := range votes {
 		h.votepool.PutVote(vote)

eth/protocols/bsc/peer.go

@@ -1,6 +1,9 @@
 package bsc
 
 import (
+	"math"
+	"time"
+
 	mapset "github.com/deckarep/golang-set"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -16,6 +19,12 @@ const (
 
 	// voteBufferSize is the maximum number of batch votes can be hold before sending
 	voteBufferSize = 21 * 2
+
+	// used to avoid of DDOS attack
+	// It's the max number of received votes per second from one peer
+	// 21 validators exist now, so 21 votes will be produced every one block interval
+	// so the limit is 7 = 21/3, here set it to 10 with a buffer.
+	receiveRateLimitPerSecond = 10
 )
 
 // max is a helper function which returns the larger of the two given integers.
@@ -28,9 +37,10 @@ func max(a, b int) int {
 
 // Peer is a collection of relevant information we have about a `bsc` peer.
 type Peer struct {
-	id            string                     // Unique ID for the peer, cached
-	knownVotes    *knownCache                // Set of vote hashes known to be known by this peer
-	voteBroadcast chan []*types.VoteEnvelope // Channel used to queue votes propagation requests
+	id              string                     // Unique ID for the peer, cached
+	knownVotes      *knownCache                // Set of vote hashes known to be known by this peer
+	voteBroadcast   chan []*types.VoteEnvelope // Channel used to queue votes propagation requests
+	lastArrivalTime time.Time                  // Arrival time of previous batch of votes
 
 	*p2p.Peer                   // The embedded P2P package peer
 	rw        p2p.MsgReadWriter // Input/output streams for bsc
@@ -44,14 +54,15 @@ type Peer struct {
 func NewPeer(version uint, p *p2p.Peer, rw p2p.MsgReadWriter) *Peer {
 	id := p.ID().String()
 	peer := &Peer{
-		id:            id,
-		knownVotes:    newKnownCache(maxKnownVotes),
-		voteBroadcast: make(chan []*types.VoteEnvelope, voteBufferSize),
-		Peer:          p,
-		rw:            rw,
-		version:       version,
-		logger:        log.New("peer", id[:8]),
-		term:          make(chan struct{}),
+		id:              id,
+		knownVotes:      newKnownCache(maxKnownVotes),
+		voteBroadcast:   make(chan []*types.VoteEnvelope, voteBufferSize),
+		lastArrivalTime: time.Now(),
+		Peer:            p,
+		rw:              rw,
+		version:         version,
+		logger:          log.New("peer", id[:8]),
+		term:            make(chan struct{}),
 	}
 	go peer.broadcastVotes()
 	return peer
@@ -114,6 +125,13 @@ func (p *Peer) AsyncSendVotes(votes []*types.VoteEnvelope) {
 	}
 }
 
+func (p *Peer) ReceiveLimit() int {
+	// the interval betweem two batch of votes is less than 9 seconds (3 block intervals) usually
+	timeInterval := int(math.Min(time.Since(p.lastArrivalTime).Seconds()+1, 9))
+	p.lastArrivalTime = time.Now()
+	return timeInterval * receiveRateLimitPerSecond
+}
+
 // broadcastVotes is a write loop that schedules votes broadcasts
 // to the remote peer. The goal is to have an async writer that does not lock up
 // node internals and at the same time rate limits queued data.