Merge pull request namecoin#163 from phelixnmc/limit_txSize

Limit tx size to 20kb

src/main.cpp

@@ -421,6 +421,13 @@ CTransaction::AcceptToMemoryPool (DatabaseSet& dbset, bool fCheckInputs,
     if (GetSigOpCount() > nSize / 34 || nSize < 100)
         return error("AcceptToMemoryPool() : nonstandard transaction");
 
+    // 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.
+    if (nSize >= MAX_STANDARD_TX_SIZE)
+        return error("AcceptToMemoryPool() : transaction too large");
+
     // Rather not work on nonstandard transactions (unless -testnet)
     if (!fTestNet && !IsStandard())
         return error("AcceptToMemoryPool() : nonstandard transaction type");

src/main.h

@@ -39,9 +39,15 @@ class CHooks;
 
 class CAuxPow;
 
+/** The maximum allowed size for a serialized block, in bytes (network rule) */
 static const unsigned int MAX_BLOCK_SIZE = 1000000;
+/** The maximum size for a serialized block that we mine, in bytes */
 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 = 20000;
+/** The maximum allowed number of signature check operations in a block (network rule) */
 static const int MAX_BLOCK_SIGOPS = MAX_BLOCK_SIZE/50;
+
 static const int64 COIN = 100000000;
 static const int64 CENT = 1000000;
 static const int64 MIN_TX_FEE = 500000;

src/wallet.cpp

@@ -1035,7 +1035,7 @@ bool CWallet::CreateTransaction(const vector<pair<CScript, int64> >& vecSend, CW
 
                 // Limit size
                 unsigned int nBytes = ::GetSerializeSize(*(CTransaction*)&wtxNew, SER_NETWORK);
-                if (nBytes >= MAX_BLOCK_SIZE_GEN/5)
+                if (nBytes >= MAX_STANDARD_TX_SIZE)
                     return false;
                 dPriority /= nBytes;