From a3446507ec44d75d57dcfe0f9a971e2160c9709c Mon Sep 17 00:00:00 2001 From: Mikko Ohtamaa Date: Wed, 17 May 2017 01:33:13 +0300 Subject: [PATCH] Add fix for the approve() mitigation. --- contracts/token/StandardToken.sol | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/contracts/token/StandardToken.sol b/contracts/token/StandardToken.sol index ee499b964..1eb4e114a 100644 --- a/contracts/token/StandardToken.sol +++ b/contracts/token/StandardToken.sol @@ -29,6 +29,13 @@ contract StandardToken is BasicToken, ERC20 { } function approve(address _spender, uint _value) { + + // To change the approve amount you first have to reduce the addresses` + // allowance to zero by calling `approve(_spender,0)` if it is not + // already 0 to mitigate the race condition described here: + // https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729 + if ((_amount!=0) && (allowed[msg.sender][_spender] !=0)) throw; + allowed[msg.sender][_spender] = _value; Approval(msg.sender, _spender, _value); }