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authorPéter Szilágyi <peterke@gmail.com>2015-06-22 19:07:08 +0800
committerPéter Szilágyi <peterke@gmail.com>2015-06-22 19:07:08 +0800
commitd36c25bcbcbc1986ab238465a187789c82818238 (patch)
tree5fc01efc6581c92e338fc57cf4d81b60708f8f62
parent9cf7913c61c6f9c1f36a44778a75e6a91a741be4 (diff)
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eth/fetcher: handle and test block announce DOS attacks
-rw-r--r--eth/fetcher/fetcher.go46
-rw-r--r--eth/fetcher/fetcher_test.go43
2 files changed, 82 insertions, 7 deletions
diff --git a/eth/fetcher/fetcher.go b/eth/fetcher/fetcher.go
index b80182a45..8d707da5c 100644
--- a/eth/fetcher/fetcher.go
+++ b/eth/fetcher/fetcher.go
@@ -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)
+ }
+}
diff --git a/eth/fetcher/fetcher_test.go b/eth/fetcher/fetcher_test.go
index 0d069ac65..d594d830c 100644
--- a/eth/fetcher/fetcher_test.go
+++ b/eth/fetcher/fetcher_test.go
@@ -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))
+ }
+}