Create fixed solidity

fixed solidity

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+/**
+ * @title FixedContract
+ * @dev 修复了 Ethernaut 原关卡中的漏洞，防止重入攻击
+ */
+contract FixedContract {
+    mapping(address => uint256) public balances;
+    bool private locked;
+
+    modifier noReentrant() {
+        require(!locked, "Reentrant call");
+        locked = true;
+        _;
+        locked = false;
+    }
+
+    function deposit() public payable {
+        balances[msg.sender] += msg.value;
+    }
+
+    function withdraw(uint256 _amount) public noReentrant {
+        require(balances[msg.sender] >= _amount, "Insufficient balance");
+        balances[msg.sender] -= _amount;
+        (bool success, ) = msg.sender.call{value: _amount}("");
+        require(success, "Withdraw failed");
+    }
+}