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Merge pull request #1064 from karalabe/downloader-attacks

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Fix two additional download vulnerabilities
This commit is contained in:
Jeffrey Wilcke 2015-05-21 09:00:12 -07:00
commit af28736bd0
6 changed files with 99 additions and 28 deletions
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51
eth/downloader/downloader.go
View File

@ -15,8 +15,10 @@ import (
)
const (
maxHashFetch = 512 // Amount of hashes to be fetched per chunk
maxBlockFetch = 128 // Amount of blocks to be fetched per chunk
MinHashFetch = 512 // Minimum amount of hashes to not consider a peer stalling
MaxHashFetch = 2048 // Amount of hashes to be fetched per retrieval request
MaxBlockFetch = 128 // Amount of blocks to be fetched per retrieval request
peerCountTimeout = 12 * time.Second // Amount of time it takes for the peer handler to ignore minDesiredPeerCount
hashTTL = 5 * time.Second // Time it takes for a hash request to time out
)
@ -28,10 +30,11 @@ 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")
@ -60,13 +63,18 @@ 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
@ -157,7 +165,7 @@ 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)
@ -283,15 +291,22 @@ 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) < MinHashFetch {
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 := 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)
continue
@ -310,8 +325,8 @@ 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())
@ -319,8 +334,8 @@ 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
}
@ -438,7 +453,7 @@ out:
}
// Get a possible chunk. If nil is returned no chunk
// could be returned due to no hashes available.
request := d.queue.Reserve(peer, maxBlockFetch)
request := d.queue.Reserve(peer, MaxBlockFetch)
if request == nil {
continue
}

61
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) {
@ -479,7 +502,7 @@ func TestMadeupBlockChainAttack(t *testing.T) {
crossCheckCycle = 25 * time.Millisecond
// Create a long chain of blocks and simulate an invalid chain by dropping every second
hashes := createHashes(0, 32*blockCacheLimit)
hashes := createHashes(0, 16*blockCacheLimit)
blocks := createBlocksFromHashes(hashes)
gapped := make([]common.Hash, len(hashes)/2)
@ -502,3 +525,37 @@ func TestMadeupBlockChainAttack(t *testing.T) {
t.Fatalf("failed to synchronise blocks: %v", err)
}
}
// Advanced form of the above forged blockchain attack, where not only does the
// attacker make up a valid hashes for random blocks, but also forges the block
// parents to point to existing hashes.
func TestMadeupParentBlockChainAttack(t *testing.T) {
defaultBlockTTL := blockTTL
defaultCrossCheckCycle := crossCheckCycle
blockTTL = 100 * time.Millisecond
crossCheckCycle = 25 * time.Millisecond
// Create a long chain of blocks and simulate an invalid chain by dropping every second
hashes := createHashes(0, 16*blockCacheLimit)
blocks := createBlocksFromHashes(hashes)
forges := createBlocksFromHashes(hashes)
for hash, block := range forges {
block.ParentHeaderHash = hash // Simulate pointing to already known hash
}
// Try and sync with the malicious node and check that it fails
tester := newTester(t, hashes, forges)
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)
}
// Ensure that a valid chain can still pass sync
blockTTL = defaultBlockTTL
crossCheckCycle = defaultCrossCheckCycle
tester.blocks = blocks
tester.newPeer("valid", big.NewInt(20000), hashes[0])
if _, err := tester.syncTake("valid", hashes[0]); err != nil {
t.Fatalf("failed to synchronise blocks: %v", err)
}
}

2
eth/downloader/queue.go
View File

@ -17,7 +17,7 @@ import (
)
const (
blockCacheLimit = 1024 // Maximum number of blocks to cache before throttling the download
blockCacheLimit = 8 * MaxBlockFetch // Maximum number of blocks to cache before throttling the download
)
// fetchRequest is a currently running block retrieval operation.

6
eth/handler.go
View File

@ -206,8 +206,8 @@ func (self *ProtocolManager) handleMsg(p *peer) error {
return errResp(ErrDecode, "->msg %v: %v", msg, err)
}
if request.Amount > maxHashes {
request.Amount = maxHashes
if request.Amount > downloader.MaxHashFetch {
request.Amount = downloader.MaxHashFetch
}
hashes := self.chainman.GetBlockHashesFromHash(request.Hash, request.Amount)
@ -254,7 +254,7 @@ func (self *ProtocolManager) handleMsg(p *peer) error {
if block != nil {
blocks = append(blocks, block)
}
if i == maxBlocks {
if i == downloader.MaxBlockFetch {
break
}
}

5
eth/peer.go
View File

@ -8,6 +8,7 @@ import (
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/core/types"
"github.com/ethereum/go-ethereum/eth/downloader"
"github.com/ethereum/go-ethereum/logger"
"github.com/ethereum/go-ethereum/logger/glog"
"github.com/ethereum/go-ethereum/p2p"
@ -100,8 +101,8 @@ func (p *peer) sendTransaction(tx *types.Transaction) error {
}
func (p *peer) requestHashes(from common.Hash) error {
glog.V(logger.Debug).Infof("[%s] fetching hashes (%d) %x...\n", p.id, maxHashes, from[:4])
return p2p.Send(p.rw, GetBlockHashesMsg, getBlockHashesMsgData{from, maxHashes})
glog.V(logger.Debug).Infof("[%s] fetching hashes (%d) %x...\n", p.id, downloader.MaxHashFetch, from[:4])
return p2p.Send(p.rw, GetBlockHashesMsg, getBlockHashesMsgData{from, downloader.MaxHashFetch})
}
func (p *peer) requestBlocks(hashes []common.Hash) error {

2
eth/protocol.go
View File

@ -12,8 +12,6 @@ const (
NetworkId = 0
ProtocolLength = uint64(8)
ProtocolMaxMsgSize = 10 * 1024 * 1024
maxHashes = 512
maxBlocks = 128
)
// eth protocol message codes