From 1ab3f810773e12a70ef904a6c9a8df4e5d8701ed Mon Sep 17 00:00:00 2001
From: vyzo <vyzo@hackzen.org>
Date: Sat, 4 May 2019 22:53:57 +0300
Subject: [PATCH] put a hard limit on the number of active hop streams

---
 .../internal/circuitv1-deprecated/relay.go    | 66 +++++++------------
 1 file changed, 23 insertions(+), 43 deletions(-)

diff --git a/p2p/protocol/internal/circuitv1-deprecated/relay.go b/p2p/protocol/internal/circuitv1-deprecated/relay.go
index 2a5f740210..3fe6e666ef 100644
--- a/p2p/protocol/internal/circuitv1-deprecated/relay.go
+++ b/p2p/protocol/internal/circuitv1-deprecated/relay.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	pb "github.com/libp2p/go-libp2p-circuit/pb"
@@ -29,6 +30,9 @@ var (
 	RelayAcceptTimeout   = 10 * time.Second
 	HopConnectTimeout    = 30 * time.Second
 	StopHandshakeTimeout = 1 * time.Minute
+
+	HopStreamBuffer = 4096
+	HopStreamLimit  = 1 << 19 // 512K hops for 1M goroutines
 )
 
 // Relay is the relay transport and service.
@@ -47,9 +51,9 @@ type Relay struct {
 	relays map[peer.ID]struct{}
 	mx     sync.Mutex
 
-	liveHops map[peer.ID]map[peer.ID]int
-	lhCount  uint64
-	lhLk     sync.Mutex
+	// atomic counters
+	sCount  int32
+	lhCount int32
 }
 
 // RelayOpts are options for configuring the relay transport.
@@ -88,7 +92,6 @@ func NewRelay(ctx context.Context, h host.Host, upgrader *tptu.Upgrader, opts ..
 		self:     h.ID(),
 		incoming: make(chan *Conn),
 		relays:   make(map[peer.ID]struct{}),
-		liveHops: make(map[peer.ID]map[peer.ID]int),
 	}
 
 	for _, opt := range opts {
@@ -114,48 +117,15 @@ func NewRelay(ctx context.Context, h host.Host, upgrader *tptu.Upgrader, opts ..
 }
 
 func (r *Relay) addLiveHop(from, to peer.ID) {
-	r.lhLk.Lock()
-	defer r.lhLk.Unlock()
-
-	trg, ok := r.liveHops[from]
-	if !ok {
-		trg = make(map[peer.ID]int)
-		r.liveHops[from] = trg
-	}
-	trg[to]++
-	r.lhCount++
+	atomic.AddInt32(&r.lhCount, 1)
 }
 
 func (r *Relay) rmLiveHop(from, to peer.ID) {
-	r.lhLk.Lock()
-	defer r.lhLk.Unlock()
-
-	trg, ok := r.liveHops[from]
-	if !ok {
-		return
-	}
-	var count int
-	if count, ok = trg[to]; !ok {
-		return
-	}
-	count--
-
-	r.lhCount--
-	if count <= 0 {
-		delete(trg, to)
-		if len(trg) == 0 {
-			delete(r.liveHops, from)
-		}
-	} else {
-		trg[to] = count
-	}
+	atomic.AddInt32(&r.lhCount, -1)
 }
 
-func (r *Relay) GetActiveHops() uint64 {
-	r.lhLk.Lock()
-	defer r.lhLk.Unlock()
-
-	return r.lhCount
+func (r *Relay) GetActiveHops() int32 {
+	return atomic.LoadInt32(&r.lhCount)
 }
 
 func (r *Relay) DialPeer(ctx context.Context, relay pstore.PeerInfo, dest pstore.PeerInfo) (*Conn, error) {
@@ -283,6 +253,16 @@ func (r *Relay) handleHopStream(s inet.Stream, msg *pb.CircuitRelay) {
 		return
 	}
 
+	sCount := atomic.AddInt32(&r.sCount, 1)
+	lhCount := atomic.LoadInt32(&r.lhCount)
+	defer atomic.AddInt32(&r.sCount, -1)
+
+	if (sCount + lhCount) > int32(HopStreamLimit) {
+		log.Warning("hop stream limit exceeded; resetting stream")
+		s.Reset()
+		return
+	}
+
 	src, err := peerToPeerInfo(msg.GetSrcPeer())
 	if err != nil {
 		r.handleError(s, pb.CircuitRelay_HOP_SRC_MULTIADDR_INVALID)
@@ -389,7 +369,7 @@ func (r *Relay) handleHopStream(s inet.Stream, msg *pb.CircuitRelay) {
 	go func() {
 		defer r.rmLiveHop(src.ID, dst.ID)
 
-		buf := pool.Get(4096)
+		buf := pool.Get(HopStreamBuffer)
 		defer pool.Put(buf)
 
 		count, err := io.CopyBuffer(s, bs, buf)
@@ -406,7 +386,7 @@ func (r *Relay) handleHopStream(s inet.Stream, msg *pb.CircuitRelay) {
 	}()
 
 	go func() {
-		buf := pool.Get(4096)
+		buf := pool.Get(HopStreamBuffer)
 		defer pool.Put(buf)
 
 		count, err := io.CopyBuffer(bs, s, buf)