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eth/downloader: prevent a peer from dripping bad hashes

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This commit is contained in:
Péter Szilágyi 2015-05-21 08:07:58 +03:00
parent 79042223dc
commit e8b22b9253
2 changed files with 36 additions and 9 deletions
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20
eth/downloader/downloader.go
View File

@ -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

25
eth/downloader/downloader_test.go
View File

@ -53,6 +53,8 @@ type downloadTester struct {
blocks map[common.Hash]*types.Block // Blocks associated with the hashes
chain []common.Hash // Block-chain being constructed
maxHashFetch int // Overrides the maximum number of retrieved hashes
t *testing.T
pcount int
done chan bool
@ -133,8 +135,12 @@ func (dl *downloadTester) getBlock(hash common.Hash) *types.Block {
// getHashes retrieves a batch of hashes for reconstructing the chain.
func (dl *downloadTester) getHashes(head common.Hash) error {
limit := maxHashFetch
if dl.maxHashFetch > 0 {
limit = dl.maxHashFetch
}
// Gather the next batch of hashes
hashes := make([]common.Hash, 0, maxHashFetch)
hashes := make([]common.Hash, 0, limit)
for i, hash := range dl.hashes {
if hash == head {
i++
@ -469,6 +475,23 @@ func TestMadeupHashChainAttack(t *testing.T) {
}
}
// Tests that if a malicious peer makes up a random hash chain, and tries to push
// indefinitely, one hash at a time, it actually gets caught with it. The reason
// this is separate from the classical made up chain attack is that sending hashes
// one by one prevents reliable block/parent verification.
func TestMadeupHashChainDrippingAttack(t *testing.T) {
// Create a random chain of hashes to drip
hashes := createHashes(0, 16*blockCacheLimit)
tester := newTester(t, hashes, nil)
// Try and sync with the attacker, one hash at a time
tester.maxHashFetch = 1
tester.newPeer("attack", big.NewInt(10000), hashes[0])
if _, err := tester.syncTake("attack", hashes[0]); err != ErrStallingPeer {
t.Fatalf("synchronisation error mismatch: have %v, want %v", err, ErrStallingPeer)
}
}
// Tests that if a malicious peer makes up a random block chain, and tried to
// push indefinitely, it actually gets caught with it.
func TestMadeupBlockChainAttack(t *testing.T) {