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eth/fetcher: handle and test block announce DOS attacks

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This commit is contained in:
Péter Szilágyi 2015-06-22 14:07:08 +03:00
parent 9cf7913c61
commit d36c25bcbc
2 changed files with 82 additions and 7 deletions
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46
eth/fetcher/fetcher.go
View File

@ -20,6 +20,7 @@ const (
fetchTimeout = 5 * time.Second // Maximum alloted time to return an explicitly requested block
maxUncleDist = 7 // Maximum allowed backward distance from the chain head
maxQueueDist = 32 // Maximum allowed distance from the chain head to queue
announceLimit = 256 // Maximum number of unique blocks a peer may have announced
)
var (
@ -74,6 +75,7 @@ type Fetcher struct {
quit chan struct{}
// Announce states
announces map[string]int // Per peer announce counts to prevent memory exhaustion
announced map[common.Hash][]*announce // Announced blocks, scheduled for fetching
fetching map[common.Hash]*announce // Announced blocks, currently fetching
@ -98,6 +100,7 @@ func New(getBlock blockRetrievalFn, validateBlock blockValidatorFn, broadcastBlo
filter: make(chan chan []*types.Block),
done: make(chan common.Hash),
quit: make(chan struct{}),
announces: make(map[string]int),
announced: make(map[common.Hash][]*announce),
fetching: make(map[common.Hash]*announce),
queue: prque.New(),
@ -189,8 +192,7 @@ func (f *Fetcher) loop() {
// Clean up any expired block fetches
for hash, announce := range f.fetching {
if time.Since(announce.time) > fetchTimeout {
delete(f.announced, hash)
delete(f.fetching, hash)
f.forgetBlock(hash)
}
}
// Import any queued blocks that could potentially fit
@ -217,10 +219,17 @@ func (f *Fetcher) loop() {
return
case notification := <-f.notify:
// A block was announced, schedule if it's not yet downloading
// A block was announced, make sure the peer isn't DOSing us
count := f.announces[notification.origin] + 1
if count > announceLimit {
glog.V(logger.Debug).Infof("Peer %s: exceeded outstanding announces (%d)", notification.origin, announceLimit)
break
}
// All is well, schedule the announce if block's not yet downloading
if _, ok := f.fetching[notification.hash]; ok {
break
}
f.announces[notification.origin] = count
f.announced[notification.hash] = append(f.announced[notification.hash], notification)
if len(f.announced) == 1 {
f.reschedule(fetch)
@ -232,8 +241,7 @@ func (f *Fetcher) loop() {
case hash := <-f.done:
// A pending import finished, remove all traces of the notification
delete(f.announced, hash)
delete(f.fetching, hash)
f.forgetBlock(hash)
delete(f.queued, hash)
case <-fetch.C:
@ -242,12 +250,15 @@ func (f *Fetcher) loop() {
for hash, announces := range f.announced {
if time.Since(announces[0].time) > arriveTimeout-gatherSlack {
// Pick a random peer to retrieve from, reset all others
announce := announces[rand.Intn(len(announces))]
f.forgetBlock(hash)
// If the block still didn't arrive, queue for fetching
if f.getBlock(hash) == nil {
request[announce.origin] = append(request[announce.origin], hash)
f.fetching[hash] = announce
}
delete(f.announced, hash)
}
}
// Send out all block requests
@ -285,7 +296,7 @@ func (f *Fetcher) loop() {
if f.getBlock(hash) == nil {
explicit = append(explicit, block)
} else {
delete(f.fetching, hash)
f.forgetBlock(hash)
}
} else {
download = append(download, block)
@ -377,3 +388,24 @@ func (f *Fetcher) insert(peer string, block *types.Block) {
go f.broadcastBlock(block, false)
}()
}
// forgetBlock removes all traces of a block from the fetcher's internal state.
func (f *Fetcher) forgetBlock(hash common.Hash) {
// Remove all pending announces and decrement DOS counters
for _, announce := range f.announced[hash] {
f.announces[announce.origin]--
if f.announces[announce.origin] == 0 {
delete(f.announces, announce.origin)
}
}
delete(f.announced, hash)
// Remove any pending fetches and decrement the DOS counters
if announce := f.fetching[hash]; announce != nil {
f.announces[announce.origin]--
if f.announces[announce.origin] == 0 {
delete(f.announces, announce.origin)
}
delete(f.fetching, hash)
}
}

43
eth/fetcher/fetcher_test.go
View File

@ -395,3 +395,46 @@ func TestDistantDiscarding(t *testing.T) {
t.Fatalf("fetcher queued future block")
}
}
// Tests that a peer is unable to use unbounded memory with sending infinite
// block announcements to a node, but that even in the face of such an attack,
// the fetcher remains operational.
func TestAnnounceMemoryExhaustionAttack(t *testing.T) {
tester := newTester()
// Create a valid chain and an infinite junk chain
hashes := createHashes(announceLimit+2*maxQueueDist, knownHash)
blocks := createBlocksFromHashes(hashes)
valid := tester.makeFetcher(blocks)
attack := createHashes(announceLimit+2*maxQueueDist, unknownHash)
attacker := tester.makeFetcher(nil)
// Feed the tester a huge hashset from the attacker, and a limited from the valid peer
for i := 0; i < len(attack); i++ {
if i < maxQueueDist {
tester.fetcher.Notify("valid", hashes[len(hashes)-1-i], time.Now().Add(arriveTimeout/2), valid)
}
tester.fetcher.Notify("attacker", attack[i], time.Now().Add(arriveTimeout/2), attacker)
}
if len(tester.fetcher.announced) != announceLimit+maxQueueDist {
t.Fatalf("queued announce count mismatch: have %d, want %d", len(tester.fetcher.announced), announceLimit+maxQueueDist)
}
// Wait for synchronisation to complete and check success for the valid peer
time.Sleep(2 * arriveTimeout)
if imported := len(tester.blocks); imported != maxQueueDist {
t.Fatalf("partial synchronised block mismatch: have %v, want %v", imported, maxQueueDist)
}
// Feed the remaining valid hashes to ensure DOS protection state remains clean
for i := len(hashes) - maxQueueDist; i >= 0; {
for j := 0; j < maxQueueDist && i >= 0; j++ {
tester.fetcher.Notify("valid", hashes[i], time.Now().Add(time.Millisecond), valid)
i--
}
time.Sleep(256 * time.Millisecond)
}
time.Sleep(256 * time.Millisecond)
if imported := len(tester.blocks); imported != len(hashes) {
t.Fatalf("fully synchronised block mismatch: have %v, want %v", imported, len(hashes))
}
}