Reapply: Reject transactions with excessive numbers of sigops

Reverting was based on a misunderstanding, it appears.

Github-Pull: #4150

src/main.cpp

@@ -956,9 +956,18 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
         if (Params().RequireStandard() && !AreInputsStandard(tx, view))
             return error("AcceptToMemoryPool: : nonstandard transaction input");
 
-        // Note: if you modify this code to accept non-standard transactions, then
+        // Check that the transaction doesn't have an excessive number of
-        // you should add code here to check that the transaction does a
+        // sigops, making it impossible to mine. Since the coinbase transaction
-        // reasonable number of ECDSA signature verifications.
+        // itself can contain sigops MAX_TX_SIGOPS is less than
+        // MAX_BLOCK_SIGOPS; we still consider this an invalid rather than
+        // merely non-standard transaction.
+        unsigned int nSigOps = GetLegacySigOpCount(tx);
+        nSigOps += GetP2SHSigOpCount(tx, view);
+        if (nSigOps > MAX_TX_SIGOPS)
+            return state.DoS(0,
+                             error("AcceptToMemoryPool : too many sigops %s, %d > %d",
+                                   hash.ToString(), nSigOps, MAX_TX_SIGOPS),
+                             REJECT_NONSTANDARD, "bad-txns-too-many-sigops");
 
         int64_t nValueOut = tx.GetValueOut();
         int64_t nFees = nValueIn-nValueOut;

src/main.h

@@ -45,6 +45,8 @@ static const unsigned int MAX_STANDARD_TX_SIZE = 100000;
 static const unsigned int MAX_BLOCK_SIGOPS = MAX_BLOCK_SIZE/50;
 /** Maxiumum number of signature check operations in an IsStandard() P2SH script */
 static const unsigned int MAX_P2SH_SIGOPS = 15;
+/** The maximum number of sigops we're willing to relay/mine in a single tx */
+static const unsigned int MAX_TX_SIGOPS = MAX_BLOCK_SIGOPS/5;
 /** The maximum number of orphan transactions kept in memory */
 static const unsigned int MAX_ORPHAN_TRANSACTIONS = MAX_BLOCK_SIZE/100;
 /** Default for -maxorphanblocks, maximum number of orphan blocks kept in memory */