From abdfcda4dd223f2a2a932628da1e9388d2670856 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= <peterke@gmail.com>
Date: Fri, 29 May 2015 21:15:28 +0300
Subject: [PATCH] eth/downloader: short circuit sync if head hash is banned

---
 eth/downloader/downloader.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/eth/downloader/downloader.go b/eth/downloader/downloader.go
index b0d55bc44..af9b6b2b1 100644
--- a/eth/downloader/downloader.go
+++ b/eth/downloader/downloader.go
@@ -165,6 +165,10 @@ func (d *Downloader) Synchronise(id string, hash common.Hash) error {
 	}
 	defer atomic.StoreInt32(&d.synchronising, 0)
 
+	// If the head hash is banned, terminate immediately
+	if d.banned.Has(hash) {
+		return ErrInvalidChain
+	}
 	// Post a user notification of the sync (only once per session)
 	if atomic.CompareAndSwapInt32(&d.notified, 0, 1) {
 		glog.V(logger.Info).Infoln("Block synchronisation started")