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eth/downloader: circumvent a forged block chain with known parent attack

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This commit is contained in:
Péter Szilágyi
2015-05-21 08:37:27 +03:00
parent e8b22b9253
commit 52db6d8be5
2 changed files with 56 additions and 13 deletions
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33
eth/downloader/downloader.go
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@ -61,13 +61,18 @@ type hashPack struct {
hashes []common.Hash
}
type crossCheck struct {
expire time.Time
parent common.Hash
}
type Downloader struct {
mux *event.TypeMux
mu sync.RWMutex
queue *queue // Scheduler for selecting the hashes to download
peers *peerSet // Set of active peers from which download can proceed
checks map[common.Hash]time.Time // Pending cross checks to verify a hash chain
queue *queue // Scheduler for selecting the hashes to download
peers *peerSet // Set of active peers from which download can proceed
checks map[common.Hash]*crossCheck // Pending cross checks to verify a hash chain
// Callbacks
hasBlock hashCheckFn
@ -158,7 +163,7 @@ func (d *Downloader) Synchronise(id string, hash common.Hash) error {
// Reset the queue and peer set to clean any internal leftover state
d.queue.Reset()
d.peers.Reset()
d.checks = make(map[common.Hash]time.Time)
d.checks = make(map[common.Hash]*crossCheck)
// Retrieve the origin peer and initiate the downloading process
p := d.peers.Peer(id)
@ -290,11 +295,15 @@ func (d *Downloader) fetchHashes(p *peer, h common.Hash) error {
}
// 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
cross := inserts[rand.Intn(len(inserts)-1)]
glog.V(logger.Detail).Infof("Cross checking (%s) with %x", active.id, cross)
cross := rand.Intn(len(inserts) - 1)
origin, parent := inserts[cross], inserts[cross+1]
glog.V(logger.Detail).Infof("Cross checking (%s) with %x/%x", active.id, origin, parent)
d.checks[cross] = time.Now().Add(blockTTL)
active.getBlocks([]common.Hash{cross})
d.checks[origin] = &crossCheck{
expire: time.Now().Add(blockTTL),
parent: parent,
}
active.getBlocks([]common.Hash{origin})
// Also fetch a fresh
active.getHashes(head)
@ -314,8 +323,8 @@ func (d *Downloader) fetchHashes(p *peer, h common.Hash) error {
continue
}
block := blockPack.blocks[0]
if _, ok := d.checks[block.Hash()]; ok {
if !d.queue.Has(block.ParentHash()) {
if check, ok := d.checks[block.Hash()]; ok {
if block.ParentHash() != check.parent {
return ErrCrossCheckFailed
}
delete(d.checks, block.Hash())
@ -323,8 +332,8 @@ func (d *Downloader) fetchHashes(p *peer, h common.Hash) error {
case <-crossTicker.C:
// Iterate over all the cross checks and fail the hash chain if they're not verified
for hash, deadline := range d.checks {
if time.Now().After(deadline) {
for hash, check := range d.checks {
if time.Now().After(check.expire) {
glog.V(logger.Debug).Infof("Cross check timeout for %x", hash)
return ErrCrossCheckFailed
}