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Add rejection of non-null CHECKMULTISIG dummy values

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This is a source of transaction mutability as the dummy value was
previously not checked and could be modified to something other than the
usual OP_0 value.
This commit is contained in:
Peter Todd
2014-03-10 17:36:35 -04:00
parent 29c17498a5
commit 6380180821
5 changed files with 63 additions and 5 deletions
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16
src/script.cpp
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@@ -934,8 +934,22 @@ 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)