eth/downloader: prevent a peer from dripping bad hashes

1 files changed, 12 insertions, 8 deletions

diff --git a/eth/downloader/downloader.go b/eth/downloader/downloader.go
index d817b223c..f3a866441 100644
--- a/eth/downloader/downloader.go
+++ b/eth/downloader/downloader.go
@@ -28,10 +28,11 @@ var (
 )
 
 var (
-	errLowTd            = errors.New("peer's TD is too low")
+	errLowTd            = errors.New("peers TD is too low")
 	ErrBusy             = errors.New("busy")
-	errUnknownPeer      = errors.New("peer's unknown or unhealthy")
+	errUnknownPeer      = errors.New("peer is unknown or unhealthy")
 	ErrBadPeer          = errors.New("action from bad peer ignored")
+	ErrStallingPeer     = errors.New("peer is stalling")
 	errNoPeers          = errors.New("no peers to keep download active")
 	ErrPendingQueue     = errors.New("pending items in queue")
 	ErrTimeout          = errors.New("timeout")
@@ -283,15 +284,18 @@ func (d *Downloader) fetchHashes(p *peer, h common.Hash) error {
 				return ErrBadPeer
 			}
 			if !done {
+				// Check that the peer is not stalling the sync
+				if len(inserts) < maxHashFetch {
+					return ErrStallingPeer
+				}
 				// Try and fetch a random block to verify the hash batch
 				// Skip the last hash as the cross check races with the next hash fetch
-				if len(inserts) > 1 {
-					cross := inserts[rand.Intn(len(inserts)-1)]
-					glog.V(logger.Detail).Infof("Cross checking (%s) with %x", active.id, cross)
+				cross := inserts[rand.Intn(len(inserts)-1)]
+				glog.V(logger.Detail).Infof("Cross checking (%s) with %x", active.id, cross)
+
+				d.checks[cross] = time.Now().Add(blockTTL)
+				active.getBlocks([]common.Hash{cross})
 
-					d.checks[cross] = time.Now().Add(blockTTL)
-					active.getBlocks([]common.Hash{cross})
-				}
 				// Also fetch a fresh
 				active.getHashes(head)
 				continue