eth/downloader: cap the hash ban set, add test for it

4 files changed, 61 insertions, 9 deletions

diff --git a/eth/downloader/downloader.go b/eth/downloader/downloader.go
index cd2fd81f1..7eda49186 100644
--- a/eth/downloader/downloader.go
+++ b/eth/downloader/downloader.go
@@ -17,18 +17,17 @@ import (
 	"gopkg.in/fatih/set.v0"
 )
 
-const (
+var (
 	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
 
-	hashTTL = 5 * time.Second // Time it takes for a hash request to time out
-)
-
-var (
+	hashTTL         = 5 * time.Second  // Time it takes for a hash request to time out
 	blockSoftTTL    = 3 * time.Second  // Request completion threshold for increasing or decreasing a peer's bandwidth
 	blockHardTTL    = 3 * blockSoftTTL // Maximum time allowance before a block request is considered expired
 	crossCheckCycle = time.Second      // Period after which to check for expired cross checks
+
+	maxBannedHashes = 4096 // Number of bannable hashes before phasing old ones out
 )
 
 var (
@@ -602,9 +601,19 @@ func (d *Downloader) banBlocks(peerId string, head common.Hash) error {
 				}
 				index++
 			}
+			// Ban the head hash and phase out any excess
 			d.banned.Add(blocks[index].Hash())
-
-			glog.V(logger.Debug).Infof("Banned %d blocks from: %s\n", index+1, peerId)
+			for d.banned.Size() > maxBannedHashes {
+				d.banned.Each(func(item interface{}) bool {
+					// Skip any hard coded bans
+					if core.BadHashes[item.(common.Hash)] {
+						return true
+					}
+					d.banned.Remove(item)
+					return false
+				})
+			}
+			glog.V(logger.Debug).Infof("Banned %d blocks from: %s", index+1, peerId)
 			return nil
 		}
 	}
diff --git a/eth/downloader/downloader_test.go b/eth/downloader/downloader_test.go
index 4219c2788..c9e84371c 100644
--- a/eth/downloader/downloader_test.go
+++ b/eth/downloader/downloader_test.go
@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/event"
 )
@@ -559,3 +560,45 @@ func TestBannedChainStarvationAttack(t *testing.T) {
 		banned = bans
 	}
 }
+
+// Tests that if a peer sends excessively many/large invalid chains that are
+// gradually banned, it will have an upper limit on the consumed memory and also
+// the origin bad hashes will not be evacuated.
+func TestBannedChainMemoryExhaustionAttack(t *testing.T) {
+	// Reduce the test size a bit
+	MaxBlockFetch = 4
+	maxBannedHashes = 256
+
+	// Construct a banned chain with more chunks than the ban limit
+	hashes := createHashes(0, maxBannedHashes*MaxBlockFetch)
+	hashes[len(hashes)-1] = bannedHash // weird index to have non multiple of ban chunk size
+
+	blocks := createBlocksFromHashes(hashes)
+
+	// Create the tester and ban the selected hash
+	tester := newTester(t, hashes, blocks)
+	tester.downloader.banned.Add(bannedHash)
+
+	// Iteratively try to sync, and verify that the banned hash list grows until
+	// the head of the invalid chain is blocked too.
+	tester.newPeer("attack", big.NewInt(10000), hashes[0])
+	for {
+		// Try to sync with the attacker, check hash chain failure
+		if _, err := tester.syncTake("attack", hashes[0]); err != ErrInvalidChain {
+			t.Fatalf("synchronisation error mismatch: have %v, want %v", err, ErrInvalidChain)
+		}
+		// Short circuit if the entire chain was banned
+		if tester.downloader.banned.Has(hashes[0]) {
+			break
+		}
+		// Otherwise ensure we never exceed the memory allowance and the hard coded bans are untouched
+		if bans := tester.downloader.banned.Size(); bans > maxBannedHashes {
+			t.Fatalf("ban cap exceeded: have %v, want max %v", bans, maxBannedHashes)
+		}
+		for hash, _ := range core.BadHashes {
+			if !tester.downloader.banned.Has(hash) {
+				t.Fatalf("hard coded ban evacuated: %x", hash)
+			}
+		}
+	}
+}
diff --git a/eth/downloader/peer.go b/eth/downloader/peer.go
index 5fbc64648..9614a6951 100644
--- a/eth/downloader/peer.go
+++ b/eth/downloader/peer.go
@@ -94,7 +94,7 @@ func (p *peer) SetIdle() {
 	for {
 		// Calculate the new download bandwidth allowance
 		prev := atomic.LoadInt32(&p.capacity)
-		next := int32(math.Max(1, math.Min(MaxBlockFetch, float64(prev)*scale)))
+		next := int32(math.Max(1, math.Min(float64(MaxBlockFetch), float64(prev)*scale)))
 
 		// Try to update the old value
 		if atomic.CompareAndSwapInt32(&p.capacity, prev, next) {
diff --git a/eth/downloader/queue.go b/eth/downloader/queue.go
index 3c99efb81..7abbd42fd 100644
--- a/eth/downloader/queue.go
+++ b/eth/downloader/queue.go
@@ -16,7 +16,7 @@ import (
 	"gopkg.in/karalabe/cookiejar.v2/collections/prque"
 )
 
-const (
+var (
 	blockCacheLimit = 8 * MaxBlockFetch // Maximum number of blocks to cache before throttling the download
 )