From e482b5694faece927a29289f88d7a87b1ce1fbd1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= <peterke@gmail.com>
Date: Wed, 5 Oct 2016 16:31:48 +0300
Subject: [PATCH] eth: monitor malicious header retrieval requests

---
 eth/handler.go      | 21 ++++++++++++++++-----
 eth/handler_test.go | 15 +++++++++++++++
 2 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/eth/handler.go b/eth/handler.go
index e6c547c02..d72185dd3 100644
--- a/eth/handler.go
+++ b/eth/handler.go
@@ -17,6 +17,7 @@
 package eth
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"math"
@@ -371,14 +372,24 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 				}
 			case query.Origin.Hash != (common.Hash{}) && !query.Reverse:
 				// Hash based traversal towards the leaf block
-				if header := pm.blockchain.GetHeaderByNumber(origin.Number.Uint64() + query.Skip + 1); header != nil {
-					if pm.blockchain.GetBlockHashesFromHash(header.Hash(), query.Skip+1)[query.Skip] == query.Origin.Hash {
-						query.Origin.Hash = header.Hash()
+				var (
+					current = origin.Number.Uint64()
+					next    = current + query.Skip + 1
+				)
+				if next <= current {
+					infos, _ := json.MarshalIndent(p.Peer.Info(), "", "  ")
+					glog.V(logger.Warn).Infof("%v: GetBlockHeaders skip overflow attack (current %v, skip %v, next %v)\nMalicious peer infos: %s", p, current, query.Skip, next, infos)
+					unknown = true
+				} else {
+					if header := pm.blockchain.GetHeaderByNumber(next); header != nil {
+						if pm.blockchain.GetBlockHashesFromHash(header.Hash(), query.Skip+1)[query.Skip] == query.Origin.Hash {
+							query.Origin.Hash = header.Hash()
+						} else {
+							unknown = true
+						}
 					} else {
 						unknown = true
 					}
-				} else {
-					unknown = true
 				}
 			case query.Reverse:
 				// Number based traversal towards the genesis block
diff --git a/eth/handler_test.go b/eth/handler_test.go
index 91989cb8f..f0f18d0a6 100644
--- a/eth/handler_test.go
+++ b/eth/handler_test.go
@@ -17,6 +17,7 @@
 package eth
 
 import (
+	"math"
 	"math/big"
 	"math/rand"
 	"testing"
@@ -173,6 +174,20 @@ func testGetBlockHeaders(t *testing.T, protocol int) {
 				pm.blockchain.GetBlockByNumber(0).Hash(),
 			},
 		},
+		// Check a corner case where skipping overflow loops back into the chain start
+		{
+			&getBlockHeadersData{Origin: hashOrNumber{Hash: pm.blockchain.GetBlockByNumber(3).Hash()}, Amount: 2, Reverse: false, Skip: math.MaxUint64 - 1},
+			[]common.Hash{
+				pm.blockchain.GetBlockByNumber(3).Hash(),
+			},
+		},
+		// Check a corner case where skipping overflow loops back to the same header
+		{
+			&getBlockHeadersData{Origin: hashOrNumber{Hash: pm.blockchain.GetBlockByNumber(1).Hash()}, Amount: 2, Reverse: false, Skip: math.MaxUint64},
+			[]common.Hash{
+				pm.blockchain.GetBlockByNumber(1).Hash(),
+			},
+		},
 		// Check that non existing headers aren't returned
 		{
 			&getBlockHeadersData{Origin: hashOrNumber{Hash: unknown}, Amount: 1},