From 38f6b8563828e089f1445bc703662e3ec4716fb9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= <peterke@gmail.com>
Date: Tue, 16 Apr 2019 13:20:38 +0300
Subject: eth, les, light: enforce CHT checkpoints on fast-sync too

---
 eth/downloader/downloader.go | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

(limited to 'eth/downloader/downloader.go')

diff --git a/eth/downloader/downloader.go b/eth/downloader/downloader.go
index d926d7aad..d94bfa27e 100644
--- a/eth/downloader/downloader.go
+++ b/eth/downloader/downloader.go
@@ -75,6 +75,7 @@ var (
 	errUnknownPeer             = errors.New("peer is unknown or unhealthy")
 	errBadPeer                 = errors.New("action from bad peer ignored")
 	errStallingPeer            = errors.New("peer is stalling")
+	errUnsyncedPeer            = errors.New("unsynced peer")
 	errNoPeers                 = errors.New("no peers to keep download active")
 	errTimeout                 = errors.New("timeout")
 	errEmptyHeaderSet          = errors.New("empty header set by peer")
@@ -99,10 +100,11 @@ type Downloader struct {
 	mode SyncMode       // Synchronisation mode defining the strategy used (per sync cycle)
 	mux  *event.TypeMux // Event multiplexer to announce sync operation events
 
-	genesis uint64   // Genesis block number to limit sync to (e.g. light client CHT)
-	queue   *queue   // Scheduler for selecting the hashes to download
-	peers   *peerSet // Set of active peers from which download can proceed
-	stateDB ethdb.Database
+	checkpoint uint64   // Checkpoint block number to enforce head against (e.g. fast sync)
+	genesis    uint64   // Genesis block number to limit sync to (e.g. light client CHT)
+	queue      *queue   // Scheduler for selecting the hashes to download
+	peers      *peerSet // Set of active peers from which download can proceed
+	stateDB    ethdb.Database
 
 	rttEstimate   uint64 // Round trip time to target for download requests
 	rttConfidence uint64 // Confidence in the estimated RTT (unit: millionths to allow atomic ops)
@@ -205,15 +207,15 @@ type BlockChain interface {
 }
 
 // New creates a new downloader to fetch hashes and blocks from remote peers.
-func New(mode SyncMode, stateDb ethdb.Database, mux *event.TypeMux, chain BlockChain, lightchain LightChain, dropPeer peerDropFn) *Downloader {
+func New(mode SyncMode, checkpoint uint64, stateDb ethdb.Database, mux *event.TypeMux, chain BlockChain, lightchain LightChain, dropPeer peerDropFn) *Downloader {
 	if lightchain == nil {
 		lightchain = chain
 	}
-
 	dl := &Downloader{
 		mode:           mode,
 		stateDB:        stateDb,
 		mux:            mux,
+		checkpoint:     checkpoint,
 		queue:          newQueue(),
 		peers:          newPeerSet(),
 		rttEstimate:    uint64(rttMaxEstimate),
@@ -326,7 +328,7 @@ func (d *Downloader) Synchronise(id string, head common.Hash, td *big.Int, mode
 	case nil:
 	case errBusy:
 
-	case errTimeout, errBadPeer, errStallingPeer,
+	case errTimeout, errBadPeer, errStallingPeer, errUnsyncedPeer,
 		errEmptyHeaderSet, errPeersUnavailable, errTooOld,
 		errInvalidAncestor, errInvalidChain:
 		log.Warn("Synchronisation failed, dropping peer", "peer", id, "err", err)
@@ -578,6 +580,10 @@ func (d *Downloader) fetchHeight(p *peerConnection) (*types.Header, error) {
 				return nil, errBadPeer
 			}
 			head := headers[0]
+			if d.mode == FastSync && head.Number.Uint64() < d.checkpoint {
+				p.log.Warn("Remote head below checkpoint", "number", head.Number, "hash", head.Hash())
+				return nil, errUnsyncedPeer
+			}
 			p.log.Debug("Remote head header identified", "number", head.Number, "hash", head.Hash())
 			return head, nil
 
-- 
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