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Merge pull request #219 from TokenMarketNet/feat/approve-mitigation

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approve() race condition mitigation
This commit is contained in:
Manuel Aráoz
2017-05-17 13:26:19 -06:00
committed by GitHub
parent ff61c7d92d e1cf602487
commit 5c491987f3
1 changed files with 7 additions and 0 deletions
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7
contracts/token/StandardToken.sol
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@ -29,6 +29,13 @@ contract StandardToken is BasicToken, ERC20 {
} }
function approve(address _spender, uint _value) { 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 ((_value != 0) && (allowed[msg.sender][_spender] != 0)) throw;
allowed[msg.sender][_spender] = _value; allowed[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value); Approval(msg.sender, _spender, _value);
} }