eth/downloader: circumvent a fake blockchain attack

eth/downloader/downloader_test.go

@@ -23,25 +23,26 @@ func createHashes(start, amount int) (hashes []common.Hash) {
 	for i := range hashes[:len(hashes)-1] {
 		binary.BigEndian.PutUint64(hashes[i][:8], uint64(i+2))
 	}
-
 	return
 }
 
-func createBlock(i int, prevHash, hash common.Hash) *types.Block {
+func createBlock(i int, parent, hash common.Hash) *types.Block {
 	header := &types.Header{Number: big.NewInt(int64(i))}
 	block := types.NewBlockWithHeader(header)
 	block.HeaderHash = hash
-	block.ParentHeaderHash = prevHash
+	block.ParentHeaderHash = parent
 	return block
 }
 
 func createBlocksFromHashes(hashes []common.Hash) map[common.Hash]*types.Block {
 	blocks := make(map[common.Hash]*types.Block)
-
-	for i, hash := range hashes {
-		blocks[hash] = createBlock(len(hashes)-i, knownHash, hash)
+	for i := 0; i < len(hashes); i++ {
+		parent := knownHash
+		if i < len(hashes)-1 {
+			parent = hashes[i+1]
+		}
+		blocks[hashes[i]] = createBlock(len(hashes)-i, parent, hashes[i])
 	}
-
 	return blocks
 }
 
@@ -136,6 +137,7 @@ func (dl *downloadTester) getHashes(head common.Hash) error {
 	hashes := make([]common.Hash, 0, maxHashFetch)
 	for i, hash := range dl.hashes {
 		if hash == head {
+			i++
 			for len(hashes) < cap(hashes) && i < len(dl.hashes) {
 				hashes = append(hashes, dl.hashes[i])
 				i++
@@ -144,9 +146,11 @@ func (dl *downloadTester) getHashes(head common.Hash) error {
 		}
 	}
 	// Delay delivery a bit to allow attacks to unfold
-	time.Sleep(time.Millisecond)
-
-	dl.downloader.DeliverHashes(dl.activePeerId, hashes)
+	id := dl.activePeerId
+	go func() {
+		time.Sleep(time.Millisecond)
+		dl.downloader.DeliverHashes(id, hashes)
+	}()
 	return nil
 }
 
@@ -424,12 +428,15 @@ func TestInvalidHashOrderAttack(t *testing.T) {
 	hashes := createHashes(0, 4*blockCacheLimit)
 	blocks := createBlocksFromHashes(hashes)
 
+	chunk1 := make([]common.Hash, blockCacheLimit)
+	chunk2 := make([]common.Hash, blockCacheLimit)
+	copy(chunk1, hashes[blockCacheLimit:2*blockCacheLimit])
+	copy(chunk2, hashes[2*blockCacheLimit:3*blockCacheLimit])
+
 	reverse := make([]common.Hash, len(hashes))
 	copy(reverse, hashes)
-
-	for i := len(hashes) / 4; i < 2*len(hashes)/4; i++ {
-		reverse[i], reverse[len(hashes)-i-1] = reverse[len(hashes)-i-1], reverse[i]
-	}
+	copy(reverse[2*blockCacheLimit:], chunk1)
+	copy(reverse[blockCacheLimit:], chunk2)
 
 	// Try and sync with the malicious node and check that it fails
 	tester := newTester(t, reverse, blocks)
@@ -453,7 +460,6 @@ func TestMadeupHashChainAttack(t *testing.T) {
 
 	// 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)
@@ -462,3 +468,31 @@ func TestMadeupHashChainAttack(t *testing.T) {
 		t.Fatalf("synchronisation error mismatch: have %v, want %v", err, ErrCrossCheckFailed)
 	}
 }
+
+// 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) {
+	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, 32*blockCacheLimit)
+	blocks := createBlocksFromHashes(hashes)
+
+	gapped := make([]common.Hash, len(hashes)/2)
+	for i := 0; i < len(gapped); i++ {
+		gapped[i] = hashes[2*i]
+	}
+	// Try and sync with the malicious node and check that it fails
+	tester := newTester(t, gapped, blocks)
+	tester.newPeer("attack", big.NewInt(10000), gapped[0])
+	if _, err := tester.syncTake("attack", gapped[0]); err != ErrCrossCheckFailed {
+		t.Fatalf("synchronisation error mismatch: have %v, want %v", err, ErrCrossCheckFailed)
+	}
+	// Ensure that a valid chain can still pass sync
+	tester.hashes = hashes
+	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)
+	}
+}