Merge pull request #3843

787ee0c Check redeemScript size does not exceed 520 byte limit (Peter Todd)
4d79098 Increase IsStandard() scriptSig length (Peter Todd)
f80cffa Do not trigger a DoS ban if SCRIPT_VERIFY_NULLDUMMY fails (Peter Todd)
6380180 Add rejection of non-null CHECKMULTISIG dummy values (Peter Todd)
29c1749 Let tx (in)valid tests use any SCRIPT_VERIFY flag (Peter Todd)
68f7d1d Create (MANDATORY|STANDARD)_SCRIPT_VERIFY_FLAGS constants (Peter Todd)

1 files changed, 16 insertions, 2 deletions

diff --git a/src/script.cpp b/src/script.cpp
index 81d2754453..4e2eeaf075 100644
--- a/src/script.cpp
+++ b/src/script.cpp
@@ -923,8 +923,22 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, co
                             fSuccess = false;
                     }
 
-                    while (i-- > 0)
+                    // Clean up stack of actual arguments
+                    while (i-- > 1)
                         popstack(stack);
+
+                    // A bug causes CHECKMULTISIG to consume one extra argument
+                    // whose contents were not checked in any way.
+                    //
+                    // Unfortunately this is a potential source of mutability,
+                    // so optionally verify it is exactly equal to zero prior
+                    // to removing it from the stack.
+                    if (stack.size() < 1)
+                        return false;
+                    if ((flags & SCRIPT_VERIFY_NULLDUMMY) && stacktop(-1).size())
+                        return error("CHECKMULTISIG dummy argument not null");
+                    popstack(stack);
+
                     stack.push_back(fSuccess ? vchTrue : vchFalse);
 
                     if (opcode == OP_CHECKMULTISIGVERIFY)
@@ -1659,7 +1673,7 @@ bool SignSignature(const CKeyStore &keystore, const CScript& fromPubKey, CTransa
     }
 
     // Test solution
-    return VerifyScript(txin.scriptSig, fromPubKey, txTo, nIn, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_STRICTENC, 0);
+    return VerifyScript(txin.scriptSig, fromPubKey, txTo, nIn, STANDARD_SCRIPT_VERIFY_FLAGS, 0);
 }
 
 bool SignSignature(const CKeyStore &keystore, const CTransaction& txFrom, CTransaction& txTo, unsigned int nIn, int nHashType)