From 41e1a0d7663d479f437c779df90775fc2bbc4087 Mon Sep 17 00:00:00 2001 From: Gavin Andresen Date: Mon, 4 Feb 2013 16:56:26 -0500 Subject: [PATCH] Make transactions larger than 100K non-standard Extremely large transactions with lots of inputs can cost the network almost as much to process as they cost the sender in fees. We would never create transactions larger than 100K big; this change makes transactions larger than 100K non-standard, so they are not relayed/mined by default. This is most important for miners that might create blocks larger than 250K big, who could be vulnerable to a make-your-blocks-so-expensive-to-verify-they-get-orphaned attack. --- src/main.cpp | 8 ++++++++ src/main.h | 2 ++ src/wallet.cpp | 2 +- 3 files changed, 11 insertions(+), 1 deletion(-) diff --git a/src/main.cpp b/src/main.cpp index 847b1ea8..874769c4 100644 --- a/src/main.cpp +++ b/src/main.cpp @@ -362,6 +362,14 @@ bool CTransaction::IsStandard() const if (!IsFinal()) return false; + // Extremely large transactions with lots of inputs can cost the network + // almost as much to process as they cost the sender in fees, because + // computing signature hashes is O(ninputs*txsize). Limiting transactions + // to MAX_STANDARD_TX_SIZE mitigates CPU exhaustion attacks. + unsigned int sz = this->GetSerializeSize(SER_NETWORK, CTransaction::CURRENT_VERSION); + if (sz >= MAX_STANDARD_TX_SIZE) + return false; + BOOST_FOREACH(const CTxIn& txin, vin) { // Biggest 'standard' txin is a 3-signature 3-of-3 CHECKMULTISIG diff --git a/src/main.h b/src/main.h index 23a4d3ba..d8e6a1bd 100644 --- a/src/main.h +++ b/src/main.h @@ -28,6 +28,8 @@ struct CBlockIndexWorkComparator; static const unsigned int MAX_BLOCK_SIZE = 1000000; /** The maximum size for mined blocks */ static const unsigned int MAX_BLOCK_SIZE_GEN = MAX_BLOCK_SIZE/2; +/** The maximum size for transactions we're willing to relay/mine **/ +static const unsigned int MAX_STANDARD_TX_SIZE = MAX_BLOCK_SIZE_GEN/5; /** The maximum allowed number of signature check operations in a block (network rule) */ static const unsigned int MAX_BLOCK_SIGOPS = MAX_BLOCK_SIZE/50; /** The maximum number of orphan transactions kept in memory */ diff --git a/src/wallet.cpp b/src/wallet.cpp index b8ef2a20..2317ac31 100644 --- a/src/wallet.cpp +++ b/src/wallet.cpp @@ -1208,7 +1208,7 @@ bool CWallet::CreateTransaction(const vector >& vecSend, CW // Limit size unsigned int nBytes = ::GetSerializeSize(*(CTransaction*)&wtxNew, SER_NETWORK, PROTOCOL_VERSION); - if (nBytes >= MAX_BLOCK_SIZE_GEN/5) + if (nBytes >= MAX_STANDARD_TX_SIZE) return false; dPriority /= nBytes;