Solidity Compatibility Configuration

Question

I am a cyber security analyst who is new to ethereum and working on a project to study crypto security. It's a series of 22 vulnerable smart contracts that you're supposed to exploit. For anyone who is interested, here's the challenge:

https://ethernaut.zeppelin.solutions/

I'm trying to configure a truffle project for the challenge using this guide: https://www.notonlyowner.com/ethereum/solving-zeppelin-ethernaut-ctf-fallback/ and after I run the installation command:

npm i truffle@4 ganache-cli@6 openzeppelin-solidity@2.0.0

I'll try to deploy the contract and I get a bunch of errors. I started trying to fix them and knocked out a few, but I feel like there's gotta be a better solution. If an experienced blockchain dev would help me get this deployed I'd really appreciate it, been bashing my head against my desk at work all day. I've posted the source code and my errors below:

pragma solidity ^0.4.18;

import 'zeppelin-solidity/contracts/ownership/Ownable.sol';

contract Fallback is Ownable {

  mapping(address => uint) public contributions;

  function Fallback() public {
    contributions[msg.sender] = 1000 * (1 ether);
  }

  function contribute() public payable {
    require(msg.value < 0.001 ether);
    contributions[msg.sender] += msg.value;
    if(contributions[msg.sender] > contributions[owner]) {
      owner = msg.sender;
    }
  }

  function getContribution() public view returns (uint) {
    return contributions[msg.sender];
  }

  function withdraw() public onlyOwner {
    owner.transfer(this.balance);
  }

  function() payable public {
    require(msg.value > 0 && contributions[msg.sender] > 0);
    owner = msg.sender;
  }
}

The errors:

Compiling ./contracts/Fallback.sol...
Compiling ./contracts/Migrations.sol...
Compiling openzeppelin-solidity/contracts/ownership/Ownable.sol...

/home/awile/smart_contracts/ethernaut/contracts/Fallback.sol:16:48: TypeError: Type function () view returns (address) is not implicitly convertible to expected type address.
        if(contributions[msg.sender] > contributions[owner]) {
                                                     ^---^
,/home/awile/smart_contracts/ethernaut/contracts/Fallback.sol:17:4: TypeError: Expression has to be an lvalue.
            owner = msg.sender;
            ^---^
,/home/awile/smart_contracts/ethernaut/contracts/Fallback.sol:17:12: TypeError: Type address is not implicitly convertible to expected type function () view returns (address).
            owner = msg.sender;
                    ^--------^
,/home/awile/smart_contracts/ethernaut/contracts/Fallback.sol:31:3: TypeError: Expression has to be an lvalue.
        owner = msg.sender;
        ^---^
,/home/awile/smart_contracts/ethernaut/contracts/Fallback.sol:31:11: TypeError: Type address is not implicitly convertible to expected type function () view returns (address).
        owner = msg.sender;
                ^--------^
Compilation failed. See above.

Edit: fixed by downgrading openzeppelin-solidity to 1.11.0

npm uninstall openzeppelin-solidity
npm i openzeppelin-solidity@1.11.0

Answer 1

Great to hear that you are using Ethernaut to learn more about smart contract security.

I would suggest that for the Fallback level you just use the console. I can then help with getting an environment setup.

Some hints on the Fallback level.

• How to send ether when interacting with an ABI e.g. await contract.someFunction(parameter1, {value: toWei(0.1)})
• Converting to and from wei/ether units -see help() command-
• Fallback methods https://solidity.readthedocs.io/en/latest/contracts.html#fallback-function
• How to send ether outside of the ABI e.g. await sendTransaction({from: player, to: instance, value:toWei(0.1), gas: 100000}) You can also adjust the gas limit using MetaMask. https://metamask.zendesk.com/hc/en-us/articles/360015488771-How-to-Adjust-Gas-Price-and-Gas-Limit-
• Check your progress:
  • Owner of the contract: await contract.owner()
  • Balance of the contract: await getBalance(instance)

There are a number of community solutions to Ethernaut levels and you could even add your own as you work through them. https://forum.zeppelin.solutions/t/ethernaut-community-solutions/561

If you have any feedback on Ethernaut please post in the community forum: https://forum.zeppelin.solutions

The community are currently working on updating Ethernaut, you would be welcome to join.

Answer 2

Maybe it will be easier for you to start with http://remix.ethereum.org and move to ganache after you gather some experience (or just stay in remix).

The main problem here is that you will need openzeppelin-solidity@1.5.0 not openzeppelin-solidity@2.0.0

Then in Remix make sure to select v0.4.18 as your compiler

Answer 3

In OpenZeppelin v1.x, variable owner is public, hence a getter function owner() is implicitly added by the compiler.

In OpenZeppelin v2.x, they realized that since contract Ownable is designated to be inherited from, any contract which inherits from it may choose to change the owner variable.

This capability is undesired for this variable, so in order to protect it, they changed it from address public owner to address private _owner, and then added a getter function explicitly.

The bottom line is that you need to change contributions[owner] to contributions[owner()], but note that you would need to fix this whether you chose to work with OZ v1.x or OZ v2.x.

Subsequently, since you chose to work with OZ v2.x, in order to set this variable to a different value, you will need to use function renounceOwnership and function transferOwnership.

On a personal level, if contract Ownable is all you need from OZ, then I strongly recommend to work with OZ v1.12.0 and use contract Claimable (which inherits from contract Ownable).