Fei Protocol contest - defsec's results

Handle

defsec

Vulnerability details

Impact

During the code review, It has been observed that, minProtocolEquity is not updated on the ngmi function. That can cause to out of date data for the minProtocolEquity variable.

Proof of Concept

1. Navigate to the following contract.

"https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L59"

2. On the requery function, minProtocolEquity is updated.

"https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L110"

Tools Used

None

Recommended Mitigation Steps

Consider to call requery function on the ngmi function.

    function ngmi(
        uint256 multiplier,
        uint256 key,
        bytes32[] memory merkleProof
    ) public {
requery();
....
}

Handle

defsec

Vulnerability details

Impact

In some cases, having function arguments in calldata instead of memory is more optimal.

Consider the following generic example:

contract C {
    function add(uint[] memory arr) external returns (uint sum) {
        uint length = arr.length;
        for (uint i = 0; i < arr.length; i++) {
            sum += arr[i];
        }
    }
}

In the above example, the dynamic array arr has the storage location memory. When the function gets called externally, the array values are kept in calldata and copied to memory during ABI decoding (using the opcode calldataload and mstore). And during the for loop, arr[i] accesses the value in memory using a mload. However, for the above example this is inefficient. Consider the following snippet instead:

contract C {
    function add(uint[] calldata arr) external returns (uint sum) {
        uint length = arr.length;
        for (uint i = 0; i < arr.length; i++) {
            sum += arr[i];
        }
    }
}

In the above snippet, instead of going via memory, the value is directly read from calldata using calldataload. That is, there are no intermediate memory operations that carries this value.

Gas savings: In the former example, the ABI decoding begins with copying value from calldata to memory in a for loop. Each iteration would cost at least 60 gas. In the latter example, this can be completely avoided. This will also reduce the number of instructions and therefore reduces the deploy time cost of the contract.

In short, use calldata instead of memory if the function argument is only read.

Note that in older Solidity versions, changing some function arguments from memory to calldata may cause "unimplemented feature error". This can be avoided by using a newer (0.8.*) Solidity compiler.

Examples Note: The following pattern is prevalent in the codebase:

function f(bytes memory data) external {
    (...) = abi.decode(data, (..., types, ...));
}

Here, changing to bytes calldata will decrease the gas. The total savings for this change across all such uses would be quite significant.

Proof Of Concept

Examples:

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L141

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L165

Tools Used

None

Recommended Mitigation Steps

Change memory definition with calldata.

Handle

defsec

Vulnerability details

Impact

For the arithmetic operations that will never over/underflow, using the unchecked directive (Solidity v0.8 has default overflow/underflow checks) can save some gas from the unnecessary internal over/underflow checks.

Proof of Concept

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L229

Tools Used

None

Recommended Mitigation Steps

Consider applying unchecked arithmetic where overflow/underflow is not possible.

Handle

defsec

Vulnerability details

Impact

During the code review, The require(msg.sender != address(this), "????"); check looks like redundant. The condition can be removed for the gas optimisation.

Proof of Concept

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/PegExchanger.sol#L39

Tools Used

None

Recommended Mitigation Steps

Consider to delete redundant check.

Handle

defsec

Vulnerability details

Impact

This does not directly impact the smart contract in anyway besides cost. This is a gas optimization to reduce cost of smart contract. Calling each function, we can see that the public function uses 496 gas, while the external function uses only 261.

Proof of Concept

According to Slither Analyzer documentation (https://github.com/crytic/slither/wiki/Detector-Documentation#public-function-that-could-be-declared-external), there are functions in the contract that are never called. These functions should be declared as external in order to save gas.

Slither Detector:

external-function:

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/PegExchanger.sol#L36

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/PegExchanger.sol#L80

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/PegExchanger.sol#L89

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/PegExchanger.sol#L101

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L59

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L87

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L110

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L204

https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L216

Tools Used

Slither

Recommended Mitigation Steps

1. Get Smart Contracts from the Repository.
2. Create a python virtual environment with a stable python version.
3. Install Slither Analyzer on the python VEM.
4. Run Slither against all contracts.
5. Define public functions as an external for the gas optimization.

Handle

defsec

Vulnerability details

Impact

++i is more gas efficient than i++ in loops forwarding.

Proof of Concept

1. Navigate to the following contracts.

"https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L165"

Tools Used

Code Review

Recommended Mitigation Steps

It is recommend to use unchecked{++i} and change i declaration to uint256.

Handle

defsec

Vulnerability details

Impact

On the following contract, msg.sender is set to internal variable. However, this code is redundant.

Proof of Concept

1. Navigate to the following contract.

"https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L67"

2. The simple demo is developed.

Execution Cost - ngmi function costs to 21508

pragma solidity >=0.7.0 <0.9.0;

/** 
 * @title Ballot
 * @dev Implements voting process along with vote delegation
 */
contract Ballot {
   
    function ngmi() public view  {
    require(msg.sender == address(this),"GG");
    }

}

Execution Cost - ngmi function costs to 21519

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

/** 
 * @title Ballot
 * @dev Implements voting process along with vote delegation
 */
contract Ballot {
   
    function ngmi() public view  {
    address thisSender = msg.sender;
    require(thisSender == address(this),"GG");
    }

}

Tools Used

None

Recommended Mitigation Steps

Consider to use msg.sender directly.

Handle

defsec

Vulnerability details

Impact

Various projects (e.g. Uniswap - https://github.com/Uniswap/interface/blob/main/src/hooks/useApproveCallback.ts#L88 , see here 1 using the constant MaxUint256 from ethers.js) set the default value of the user's allowance to 2^256 - 1. Now the value 2^256 - 1 can also be represented in hex as 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff. From Ethereum's yellow paper we know that zeros are cheaper than non-zero values in the hex representation. Considering this fact, an alternative choice could be now 0x8000000000000000000000000000000000000000000000000000000000000000 or 2^255 to represent "infinity". If you do the calculations with Remix, you will see that the former costs 47'872 gas, while the latter costs 45'888 gas. If you accept that infinity can also be represented via 2^255 (instead of 2^256-1) - and I think most projects can live with that - you can already save 1'984 gas (or 4.1%) leveraging this optimisation trick.

Proof of Concept

1. Navigate to the following contract.

"https://github.com/code-423n4/2021-11-fei/blob/main/contracts/TRIBERagequit.sol#L25"

Tools Used

Code Review

Recommended Mitigation Steps

Change 2^256-1 With 2^255.

Reference

https://ethereum.github.io/yellowpaper/paper.pdf

https://forum.openzeppelin.com/t/a-collection-of-gas-optimisation-tricks/19966