From d7962747c4bfe90f9991d121fd22ac625ae2de30 Mon Sep 17 00:00:00 2001 From: Pieter Wuille Date: Fri, 17 Feb 2012 17:58:02 +0100 Subject: [PATCH] Do not allow overwriting unspent transactions (BIP 30) Introduce the following network rule: * a block is not valid if it contains a transaction whose hash already exists in the block chain, unless all that transaction's outputs were already spent before said block. Warning: this is effectively a network rule change, with potential risk for forking the block chain. Leaving this unfixed carries the same risk however, for attackers that can cause a reorganisation in part of the network. Thanks to Russell O'Connor and Ben Reeves. --- src/main.cpp | 26 ++++++++++++++++++++++++-- 1 files changed, 24 insertions(+), 2 deletions(-) diff --git a/src/main.cpp b/src/main.cpp index 6a3bacc..812a551 100644 --- a/src/main.cpp +++ b/src/main.cpp @@ -792,8 +792,10 @@ bool CTransaction::DisconnectInputs(CTxDB& txdb) } // Remove transaction from index - if (!txdb.EraseTxIndex(*this)) - return error("DisconnectInputs() : EraseTxPos failed"); + // This can fail if a duplicate of this transaction was in a chain that got + // reorganized away. This is only possible if this transaction was completely + // spent, so erasing it would be a no-op anway. + txdb.EraseTxIndex(*this); return true; } @@ -982,6 +984,26 @@ bool CBlock::ConnectBlock(CTxDB& txdb, CBlockIndex* pindex) if (!CheckBlock()) return false; + // Do not allow blocks that contain transactions which 'overwrite' older transactions, + // unless those are already completely spent. + // If such overwrites are allowed, coinbases and transactions depending upon those + // can be duplicated to remove the ability to spend the first instance -- even after + // being sent to another address. + // See BIP30 and http://r6.ca/blog/20120206T005236Z.html for more information. + // This logic is not necessary for memory pool transactions, as AcceptToMemoryPool + // already refuses previously-known transaction id's entirely. + // This rule applies to all blocks whose timestamp is after March 15, 2012, 0:00 UTC. + // On testnet it is enabled as of februari 20, 2012, 0:00 UTC. + if (pindex->nTime > 1331769600 || (fTestNet && pindex->nTime > 1329696000)) + BOOST_FOREACH(CTransaction& tx, vtx) + { + CTxIndex txindexOld; + if (txdb.ReadTxIndex(tx.GetHash(), txindexOld)) + BOOST_FOREACH(CDiskTxPos &pos, txindexOld.vSpent) + if (pos.IsNull()) + return false; + } + //// issue here: it doesn't know the version unsigned int nTxPos = pindex->nBlockPos + ::GetSerializeSize(CBlock(), SER_DISK) - 1 + GetSizeOfCompactSize(vtx.size()); -- 1.7.1