Merge pull request #963 from blockpanda/main

09.22

Writeup/blockpanda/readme.md/Ethernaut第26题.md

@@ -0,0 +1,153 @@
+### 第二十六题 DoubleEntryPoint
+### 题目
+找出 CryptoVault 中的错误位置，并保护它不被耗尽代币。
+### 提示
+- 代币合约的双入口是如何运行的？
+### 源码
+```solidity
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import "openzeppelin-contracts-08/access/Ownable.sol";
+import "openzeppelin-contracts-08/token/ERC20/ERC20.sol";
+
+interface DelegateERC20 {
+    function delegateTransfer(address to, uint256 value, address origSender) external returns (bool);
+}
+
+interface IDetectionBot {
+    function handleTransaction(address user, bytes calldata msgData) external;
+}
+
+interface IForta {
+    function setDetectionBot(address detectionBotAddress) external;
+    function notify(address user, bytes calldata msgData) external;
+    function raiseAlert(address user) external;
+}
+
+contract Forta is IForta {
+    mapping(address => IDetectionBot) public usersDetectionBots;
+    mapping(address => uint256) public botRaisedAlerts;
+
+    function setDetectionBot(address detectionBotAddress) external override {
+        usersDetectionBots[msg.sender] = IDetectionBot(detectionBotAddress);
+    }
+
+    function notify(address user, bytes calldata msgData) external override {
+        if (address(usersDetectionBots[user]) == address(0)) return;
+        try usersDetectionBots[user].handleTransaction(user, msgData) {
+            return;
+        } catch {}
+    }
+
+    function raiseAlert(address user) external override {
+        if (address(usersDetectionBots[user]) != msg.sender) return;
+        botRaisedAlerts[msg.sender] += 1;
+    }
+}
+
+contract CryptoVault {
+    address public sweptTokensRecipient;
+    IERC20 public underlying;
+
+    constructor(address recipient) {
+        sweptTokensRecipient = recipient;
+    }
+
+    function setUnderlying(address latestToken) public {
+        require(address(underlying) == address(0), "Already set");
+        underlying = IERC20(latestToken);
+    }
+
+    /*
+    ...
+    */
+
+    function sweepToken(IERC20 token) public {
+        require(token != underlying, "Can't transfer underlying token");
+        token.transfer(sweptTokensRecipient, token.balanceOf(address(this)));
+    }
+}
+
+contract LegacyToken is ERC20("LegacyToken", "LGT"), Ownable {
+    DelegateERC20 public delegate;
+
+    function mint(address to, uint256 amount) public onlyOwner {
+        _mint(to, amount);
+    }
+
+    function delegateToNewContract(DelegateERC20 newContract) public onlyOwner {
+        delegate = newContract;
+    }
+
+    function transfer(address to, uint256 value) public override returns (bool) {
+        if (address(delegate) == address(0)) {
+            return super.transfer(to, value);
+        } else {
+            return delegate.delegateTransfer(to, value, msg.sender);
+        }
+    }
+}
+
+contract DoubleEntryPoint is ERC20("DoubleEntryPointToken", "DET"), DelegateERC20, Ownable {
+    address public cryptoVault;
+    address public player;
+    address public delegatedFrom;
+    Forta public forta;
+
+    constructor(address legacyToken, address vaultAddress, address fortaAddress, address playerAddress) {
+        delegatedFrom = legacyToken;
+        forta = Forta(fortaAddress);
+        player = playerAddress;
+        cryptoVault = vaultAddress;
+        _mint(cryptoVault, 100 ether);
+    }
+
+    modifier onlyDelegateFrom() {
+        require(msg.sender == delegatedFrom, "Not legacy contract");
+        _;
+    }
+
+    modifier fortaNotify() {
+        address detectionBot = address(forta.usersDetectionBots(player));
+
+        // Cache old number of bot alerts
+        uint256 previousValue = forta.botRaisedAlerts(detectionBot);
+
+        // Notify Forta
+        forta.notify(player, msg.data);
+
+        // Continue execution
+        _;
+
+        // Check if alarms have been raised
+        if (forta.botRaisedAlerts(detectionBot) > previousValue) revert("Alert has been triggered, reverting");
+    }
+
+    function delegateTransfer(address to, uint256 value, address origSender)
+        publicoverrideonlyDelegateFromfortaNotifyreturns (bool)
+    {
+        _transfer(origSender, to, value);
+        return true;
+    }
+```
+### 解题思路&过程
+1. CryptoVault 的 sweepToken 可以将 vault 内除 underlying (DET) 以外的代币提走，LegacyToken (LGT) 代币的 transfer 被 delegate 给了 DoubleEntryPoint (DET) 代币，Forta 合约的 bot 可以实现对某些函数的 calldata 的检测, 当满足一定条件时会 alert (回滚交易)。
+2.  CryptoVault 的 sweepToken 被设计成不能够提出 DET, 但是如果将 token 的地址指定为 LGT, 那么就可以通过一系列的函数调用, 最终将 vault 内的所有 DET 代币提走, 我们需要编写一个 detection bot 以阻止这种攻击
+```solidity
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+// ...
+contract DetectionBot is IDetectionBot {    
+    IForta forta;    CryptoVault vault;
+    constructor(address _forta, address _vault) {        
+        forta = IForta(_forta);        
+        vault = CryptoVault(_vault);    }
+    function handleTransaction(address user, bytes calldata msgData) external {        
+        (, , address origSender) = abi.decode(msgData[4:], (address, uint256, address));        
+        if (origSender == address(vault)) {            
+            forta.raiseAlert(user);        
+            }   
+        } 
+}
+```

blockpanda.md

@@ -75,4 +75,7 @@ timezone: Asia/Shanghai
 
 ### 2024.09.21
 - 总复习
+
+### 2024.09.22
+- [Ethernaut 第25题](/Writeup/blockpanda/readme.md/Ethernaut第26题.md)
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