Pull upstream PR#4365 from bitcoin, to allow much more broad P2SH tra…

…nsactions to be relayed as standard.

src/main.cpp

@@ -494,16 +494,14 @@ bool IsFinalTx(const CTransaction &tx, int nBlockHeight, int64_t nBlockTime)
     return true;
 }
 
+
+// Check transaction inputs to mitigate two
+// potential denial-of-service attacks:
 //
-// Check transaction inputs, and make sure any
-// pay-to-script-hash transactions are evaluating IsStandard scripts
-//
-// Why bother? To avoid denial-of-service attacks; an attacker
-// can submit a standard HASH... OP_EQUAL transaction,
-// which will get accepted into blocks. The redemption
-// script can be anything; an attacker could use a very
-// expensive-to-check-upon-redemption script like:
-//   DUP CHECKSIG DROP ... repeated 100 times... OP_1
+// 1. scriptSigs with extra data stuffed into them,
+//    not consumed by scriptPubKey (or P2SH script)
+// 2. P2SH scripts with a crazy number of expensive
+//    CHECKSIG/CHECKMULTISIG operations
 //
 bool AreInputsStandard(const CTransaction& tx, CCoinsViewCache& mapInputs)
 {
@@ -527,8 +525,9 @@ bool AreInputsStandard(const CTransaction& tx, CCoinsViewCache& mapInputs)
         // Transactions with extra stuff in their scriptSigs are
         // non-standard. Note that this EvalScript() call will
         // be quick, because if there are any operations
-        // beside "push data" in the scriptSig the
-        // IsStandard() call returns false
+        // beside "push data" in the scriptSig
+        // IsStandard() will have already returned false
+        // and this method isn't called.
         vector<vector<unsigned char> > stack;
         if (!EvalScript(stack, tx.vin[i].scriptSig, tx, i, false, 0))
             return false;
@@ -540,16 +539,20 @@ bool AreInputsStandard(const CTransaction& tx, CCoinsViewCache& mapInputs)
             CScript subscript(stack.back().begin(), stack.back().end());
             vector<vector<unsigned char> > vSolutions2;
             txnouttype whichType2;
-            if (!Solver(subscript, whichType2, vSolutions2))
-                return false;
-            if (whichType2 == TX_SCRIPTHASH)
-                return false;
-
-            int tmpExpected;
-            tmpExpected = ScriptSigArgsExpected(whichType2, vSolutions2);
-            if (tmpExpected < 0)
-                return false;
-            nArgsExpected += tmpExpected;
+            if (Solver(subscript, whichType2, vSolutions2))
+            {
+                int tmpExpected = ScriptSigArgsExpected(whichType2, vSolutions2);
+                if (tmpExpected < 0)
+                    return false;
+                nArgsExpected += tmpExpected;
+            }
+            else
+            {
+                // Any other Script with less than 15 sigops OK:
+                unsigned int sigops = subscript.GetSigOpCount(true);
+                // ... extra data left on the stack after execution is OK, too:
+                return (sigops <= MAX_P2SH_SIGOPS);
+            }
         }
 
         if (stack.size() != (unsigned int)nArgsExpected)

src/main.h

@@ -47,6 +47,8 @@ static const unsigned int DEFAULT_BLOCK_PRIORITY_SIZE = 17000;
 static const unsigned int MAX_STANDARD_TX_SIZE = 400000;
 /** The maximum allowed number of signature check operations in a block (network rule) */
 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 orphan transactions kept in memory */
 static const unsigned int MAX_ORPHAN_TRANSACTIONS = MAX_BLOCK_SIZE/100;
 /** The maximum number of orphan blocks kept in memory */