From ad5a4c7c471912aa0bef52c33a1abfb01fe6d89d Mon Sep 17 00:00:00 2001
From: Gavin Andresen <gavinandresen@gmail.com>
Date: Sun, 29 Apr 2012 20:56:55 -0400
Subject: [PATCH 1/1] Check earlier for blocks with duplicate transactions. Fixes #1167

---
 src/main.cpp |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index e6f9421..e8cbc01 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1472,6 +1472,16 @@ bool CBlock::CheckBlock() const
         if (!tx.CheckTransaction())
             return error("CheckBlock() : CheckTransaction failed");
 
+    // Check for duplicate txids. This is caught by ConnectInputs(),
+    // but catching it earlier avoids a potential DoS attack:
+    set<uint256> uniqueTx;
+    BOOST_FOREACH(const CTransaction& tx, vtx)
+    {
+        uniqueTx.insert(tx.GetHash());
+    }
+    if (uniqueTx.size() != vtx.size())
+        return error("CheckBlock() : duplicate transaction");
+
     // Check that it's not full of nonstandard transactions
     if (GetSigOpCount() > MAX_BLOCK_SIGOPS)
         return error("CheckBlock() : out-of-bounds SigOpCount");
-- 
1.7.1