From ce1a071f6d6d1548974796c4327399659415b489 Mon Sep 17 00:00:00 2001 From: Gavin Andresen Date: Wed, 16 May 2012 11:26:56 -0400 Subject: Further DoS prevention: Verify signatures last Loop over all inputs doing inexpensive validity checks first, and then loop over them a second time doing expensive signature checks. This helps prevent possible CPU exhaustion attacks where an attacker tries to make a victim waste time checking signatures for invalid transactions. --- src/main.cpp | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-) (limited to 'src/main.cpp') diff --git a/src/main.cpp b/src/main.cpp index b7067b2092..00f0633431 100644 --- a/src/main.cpp +++ b/src/main.cpp @@ -1033,15 +1033,26 @@ bool CTransaction::ConnectInputs(MapPrevTx inputs, if (pindex->nBlockPos == txindex.pos.nBlockPos && pindex->nFile == txindex.pos.nFile) return error("ConnectInputs() : tried to spend coinbase at depth %d", pindexBlock->nHeight - pindex->nHeight); - // Check for conflicts (double-spend) - if (!txindex.vSpent[prevout.n].IsNull()) - return fMiner ? false : error("ConnectInputs() : %s prev tx already used at %s", GetHash().ToString().substr(0,10).c_str(), txindex.vSpent[prevout.n].ToString().c_str()); - // Check for negative or overflow input values nValueIn += txPrev.vout[prevout.n].nValue; if (!MoneyRange(txPrev.vout[prevout.n].nValue) || !MoneyRange(nValueIn)) return error("ConnectInputs() : txin values out of range"); + } + // The first loop above does all the inexpensive checks. + // Only if ALL inputs pass do we perform expensive ECDSA signature checks. + // Helps prevent CPU exhaustion attacks. + for (unsigned int i = 0; i < vin.size(); i++) + { + COutPoint prevout = vin[i].prevout; + assert(inputs.count(prevout.hash) > 0); + CTxIndex& txindex = inputs[prevout.hash].first; + CTransaction& txPrev = inputs[prevout.hash].second; + + // Check for conflicts (double-spend) + if (!txindex.vSpent[prevout.n].IsNull()) + return fMiner ? false : error("ConnectInputs() : %s prev tx already used at %s", GetHash().ToString().substr(0,10).c_str(), txindex.vSpent[prevout.n].ToString().c_str()); + // Verify signature if (!VerifySignature(txPrev, *this, i, fStrictPayToScriptHash, 0)) { -- cgit v1.2.3