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eth, eth/downloader: detect and handle madeup hash attacks

This commit is contained in:
Péter Szilágyi 2015-05-15 13:14:46 +03:00
parent 9ad515d2dc
commit 83226762c2
4 changed files with 111 additions and 44 deletions
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98
eth/downloader/downloader.go
View File

@ -2,6 +2,7 @@ package downloader
import (
"errors"
"math/rand"
"sync"
"sync/atomic"
"time"
@ -14,15 +15,19 @@ import (
)
const (
maxBlockFetch = 128 // Amount of max blocks to be fetched per chunk
maxHashFetch = 512 // Amount of hashes to be fetched per chunk
maxBlockFetch = 128 // Amount of blocks to be fetched per chunk
peerCountTimeout = 12 * time.Second // Amount of time it takes for the peer handler to ignore minDesiredPeerCount
hashTtl = 20 * time.Second // The amount of time it takes for a hash request to time out
hashTTL = 5 * time.Second // Time it takes for a hash request to time out
)
var (
minDesiredPeerCount = 5 // Amount of peers desired to start syncing
blockTtl = 20 * time.Second // The amount of time it takes for a block request to time out
blockTTL = 5 * time.Second // Time it takes for a block request to time out
crossCheckCycle = time.Second // Period after which to check for expired cross checks
minDesiredPeerCount = 5 // Amount of peers desired to start syncing
)
var (
errLowTd = errors.New("peer's TD is too low")
ErrBusy = errors.New("busy")
errUnknownPeer = errors.New("peer's unknown or unhealthy")
@ -34,6 +39,7 @@ var (
errPeersUnavailable = errors.New("no peers available or all peers tried for block download process")
errAlreadyInPool = errors.New("hash already in pool")
ErrInvalidChain = errors.New("retrieved hash chain is invalid")
ErrCrossCheckFailed = errors.New("block cross-check failed")
errCancelHashFetch = errors.New("hash fetching cancelled (requested)")
errCancelBlockFetch = errors.New("block downloading cancelled (requested)")
errNoSyncActive = errors.New("no sync active")
@ -220,46 +226,47 @@ func (d *Downloader) fetchHashes(p *peer, h common.Hash) error {
start := time.Now()
// Add the hash to the queue first
// Add the hash to the queue first, and start hash retrieval
d.queue.Insert([]common.Hash{h})
// Get the first batch of hashes
p.getHashes(h)
var (
failureResponseTimer = time.NewTimer(hashTtl)
attemptedPeers = make(map[string]bool) // attempted peers will help with retries
activePeer = p // active peer will help determine the current active peer
hash common.Hash // common and last hash
)
attemptedPeers[p.id] = true
active = p // active peer will help determine the current active peer
head = common.Hash{} // common and last hash
out:
for {
timeout = time.NewTimer(hashTTL) // timer to dump a non-responsive active peer
attempted = make(map[string]bool) // attempted peers will help with retries
crossChecks = make(map[common.Hash]time.Time) // running cross checks and their deadline
crossTicker = time.NewTicker(crossCheckCycle) // ticker to periodically check expired cross checks
)
defer crossTicker.Stop()
attempted[p.id] = true
for finished := false; !finished; {
select {
case <-d.cancelCh:
return errCancelHashFetch
case hashPack := <-d.hashCh:
// Make sure the active peer is giving us the hashes
if hashPack.peerId != activePeer.id {
if hashPack.peerId != active.id {
glog.V(logger.Debug).Infof("Received hashes from incorrect peer(%s)\n", hashPack.peerId)
break
}
failureResponseTimer.Reset(hashTtl)
timeout.Reset(hashTTL)
// Make sure the peer actually gave something valid
if len(hashPack.hashes) == 0 {
glog.V(logger.Debug).Infof("Peer (%s) responded with empty hash set\n", activePeer.id)
glog.V(logger.Debug).Infof("Peer (%s) responded with empty hash set\n", active.id)
d.queue.Reset()
return errEmptyHashSet
}
// Determine if we're done fetching hashes (queue up all pending), and continue if not done
done, index := false, 0
for index, hash = range hashPack.hashes {
if d.hasBlock(hash) || d.queue.GetBlock(hash) != nil {
glog.V(logger.Debug).Infof("Found common hash %x\n", hash[:4])
for index, head = range hashPack.hashes {
if d.hasBlock(head) || d.queue.GetBlock(head) != nil {
glog.V(logger.Debug).Infof("Found common hash %x\n", head[:4])
hashPack.hashes = hashPack.hashes[:index]
done = true
break
@ -267,25 +274,50 @@ out:
}
// Insert all the new hashes, but only continue if got something useful
inserts := d.queue.Insert(hashPack.hashes)
if inserts == 0 && !done {
glog.V(logger.Debug).Infof("Peer (%s) responded with stale hashes\n", activePeer.id)
if len(inserts) == 0 && !done {
glog.V(logger.Debug).Infof("Peer (%s) responded with stale hashes\n", active.id)
d.queue.Reset()
return ErrBadPeer
}
if !done {
activePeer.getHashes(hash)
// Try and fetch a random block to verify the hash batch
cross := inserts[rand.Intn(len(inserts))]
glog.V(logger.Detail).Infof("Cross checking (%s) with %x", active.id, cross)
crossChecks[cross] = time.Now().Add(blockTTL)
active.getBlocks([]common.Hash{cross})
// Also fetch a fresh
active.getHashes(head)
continue
}
// We're done, allocate the download cache and proceed pulling the blocks
offset := 0
if block := d.getBlock(hash); block != nil {
if block := d.getBlock(head); block != nil {
offset = int(block.NumberU64() + 1)
}
d.queue.Alloc(offset)
break out
finished = true
case <-failureResponseTimer.C:
case blockPack := <-d.blockCh:
// Cross check the block with the random verifications
if blockPack.peerId != active.id || len(blockPack.blocks) != 1 {
continue
}
hash := blockPack.blocks[0].Hash()
delete(crossChecks, hash)
case <-crossTicker.C:
// Iterate over all the cross checks and fail the hash chain if they're not verified
for hash, deadline := range crossChecks {
if time.Now().After(deadline) {
glog.V(logger.Debug).Infof("Cross check timeout for %x", hash)
return ErrCrossCheckFailed
}
}
case <-timeout.C:
glog.V(logger.Debug).Infof("Peer (%s) didn't respond in time for hash request\n", p.id)
var p *peer // p will be set if a peer can be found
@ -293,21 +325,21 @@ out:
// already fetched hash list. This can't guarantee 100% correctness but does
// a fair job. This is always either correct or false incorrect.
for _, peer := range d.peers.AllPeers() {
if d.queue.Has(peer.head) && !attemptedPeers[peer.id] {
if d.queue.Has(peer.head) && !attempted[peer.id] {
p = peer
break
}
}
// if all peers have been tried, abort the process entirely or if the hash is
// the zero hash.
if p == nil || (hash == common.Hash{}) {
if p == nil || (head == common.Hash{}) {
d.queue.Reset()
return ErrTimeout
}
// set p to the active peer. this will invalidate any hashes that may be returned
// by our previous (delayed) peer.
activePeer = p
p.getHashes(hash)
active = p
p.getHashes(head)
glog.V(logger.Debug).Infof("Hash fetching switched to new peer(%s)\n", p.id)
}
}
@ -359,7 +391,7 @@ out:
// that badly or poorly behave are removed from the peer set (not banned).
// Bad peers are excluded from the available peer set and therefor won't be
// reused. XXX We could re-introduce peers after X time.
badPeers := d.queue.Expire(blockTtl)
badPeers := d.queue.Expire(blockTTL)
for _, pid := range badPeers {
// XXX We could make use of a reputation system here ranking peers
// in their performance

45
eth/downloader/downloader_test.go
View File

@ -130,8 +130,23 @@ func (dl *downloadTester) getBlock(hash common.Hash) *types.Block {
return dl.blocks[knownHash]
}
func (dl *downloadTester) getHashes(hash common.Hash) error {
dl.downloader.DeliverHashes(dl.activePeerId, dl.hashes)
// getHashes retrieves a batch of hashes for reconstructing the chain.
func (dl *downloadTester) getHashes(head common.Hash) error {
// Gather the next batch of hashes
hashes := make([]common.Hash, 0, maxHashFetch)
for i, hash := range dl.hashes {
if hash == head {
for len(hashes) < cap(hashes) && i < len(dl.hashes) {
hashes = append(hashes, dl.hashes[i])
i++
}
break
}
}
// Delay delivery a bit to allow attacks to unfold
time.Sleep(time.Millisecond)
dl.downloader.DeliverHashes(dl.activePeerId, hashes)
return nil
}
@ -166,7 +181,7 @@ func (dl *downloadTester) badBlocksPeer(id string, td *big.Int, hash common.Hash
func TestDownload(t *testing.T) {
minDesiredPeerCount = 4
blockTtl = 1 * time.Second
blockTTL = 1 * time.Second
targetBlocks := 1000
hashes := createHashes(0, targetBlocks)
@ -215,7 +230,7 @@ func TestMissing(t *testing.T) {
func TestTaking(t *testing.T) {
minDesiredPeerCount = 4
blockTtl = 1 * time.Second
blockTTL = 1 * time.Second
targetBlocks := 1000
hashes := createHashes(0, targetBlocks)
@ -256,7 +271,7 @@ func TestInactiveDownloader(t *testing.T) {
func TestCancel(t *testing.T) {
minDesiredPeerCount = 4
blockTtl = 1 * time.Second
blockTTL = 1 * time.Second
targetBlocks := 1000
hashes := createHashes(0, targetBlocks)
@ -282,7 +297,7 @@ func TestCancel(t *testing.T) {
func TestThrottling(t *testing.T) {
minDesiredPeerCount = 4
blockTtl = 1 * time.Second
blockTTL = 1 * time.Second
targetBlocks := 16 * blockCacheLimit
hashes := createHashes(0, targetBlocks)
@ -429,3 +444,21 @@ func TestInvalidHashOrderAttack(t *testing.T) {
t.Fatalf("failed to synchronise blocks: %v", err)
}
}
// Tests that if a malicious peer makes up a random hash chain and tries to push
// indefinitely, it actually gets caught with it.
func TestMadeupHashChainAttack(t *testing.T) {
blockTTL = 100 * time.Millisecond
crossCheckCycle = 25 * time.Millisecond
// Create a long chain of hashes without backing blocks
hashes := createHashes(0, 1024*blockCacheLimit)
hashes = hashes[:len(hashes)-1]
// Try and sync with the malicious node and check that it fails
tester := newTester(t, hashes, nil)
tester.newPeer("attack", big.NewInt(10000), hashes[0])
if _, err := tester.syncTake("attack", hashes[0]); err != ErrCrossCheckFailed {
t.Fatalf("synchronisation error mismatch: have %v, want %v", err, ErrCrossCheckFailed)
}
}

10
eth/downloader/queue.go
View File

@ -123,13 +123,13 @@ func (q *queue) Has(hash common.Hash) bool {
}
// Insert adds a set of hashes for the download queue for scheduling, returning
// the number of new hashes encountered.
func (q *queue) Insert(hashes []common.Hash) int {
// the new hashes encountered.
func (q *queue) Insert(hashes []common.Hash) []common.Hash {
q.lock.Lock()
defer q.lock.Unlock()
// Insert all the hashes prioritized in the arrival order
inserts := 0
inserts := make([]common.Hash, 0, len(hashes))
for _, hash := range hashes {
// Skip anything we already have
if old, ok := q.hashPool[hash]; ok {
@ -137,7 +137,9 @@ func (q *queue) Insert(hashes []common.Hash) int {
continue
}
// Update the counters and insert the hash
q.hashCounter, inserts = q.hashCounter+1, inserts+1
q.hashCounter = q.hashCounter + 1
inserts = append(inserts, hash)
q.hashPool[hash] = q.hashCounter
q.hashQueue.Push(hash, float32(q.hashCounter)) // Highest gets schedules first
}

2
eth/sync.go
View File

@ -101,7 +101,7 @@ func (pm *ProtocolManager) synchronise(peer *peer) {
case downloader.ErrBusy:
glog.V(logger.Debug).Infof("Synchronisation already in progress")
case downloader.ErrTimeout, downloader.ErrBadPeer, downloader.ErrInvalidChain:
case downloader.ErrTimeout, downloader.ErrBadPeer, downloader.ErrInvalidChain, downloader.ErrCrossCheckFailed:
glog.V(logger.Debug).Infof("Removing peer %v: %v", peer.id, err)
pm.removePeer(peer)