Timeswap contest - defsec's results

Handle

defsec

Vulnerability details

Impact

Reading array length at each iteration of the loop takes 6 gas (3 for mload and 3 to place memory_offset) in the stack.

Caching the array length in the stack saves around 3 gas per iteration.

Proof of Concept

1. Navigate to the following smart contract line.

https://github.com/code-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Core/contracts/TimeswapPair.sol#L359

Tools Used

None

Recommended Mitigation Steps

Consider to cache array length.

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-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Core/contracts/TimeswapPair.sol#L359

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

Shortening revert strings to fit in 32 bytes will decrease deploy time gas and will decrease runtime gas when the revert condition has been met.

Revert strings that are longer than 32 bytes require at least one additional mstore, along with additional overhead for computing memory offset, etc.

Proof of Concept

Revert strings > 32 bytes are here:

https://github.com/code-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Convenience/contracts/base/ERC721.sol#L57

Tools Used

Manual Review

Recommended Mitigation Steps

Shorten the revert strings to fit in 32 bytes. That will affect gas optimization.

Handle

defsec

Vulnerability details

Impact

!= 0 is a cheaper operation compared to > 0, when dealing with uint.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Core/contracts/TimeswapPair.sol#L374

https://github.com/code-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Core/contracts/TimeswapPair.sol#L369

https://github.com/code-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Core/contracts/TimeswapPair.sol#L314

https://github.com/code-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Core/contracts/TimeswapPair.sol#L292

https://github.com/code-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Core/contracts/TimeswapPair.sol#L239

Tools Used

Code Review

Recommended Mitigation Steps

Use "!=0" instead of ">0" for the gas optimization.

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-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Core/contracts/TimeswapPair.sol#L341

Tools Used

None

Recommended Mitigation Steps

Change memory definition with calldata.

Handle

defsec

Vulnerability details

Impact

Lower than uint256 size storage instance variables are actually less gas efficient. E.g. using uint16 does not give any efficiency, actually, it is the opposite as EVM operates on default of 256-bit values so uint16 is more expensive in this case as it needs a conversion. It only gives improvements in cases where you can pack variables together, e.g. structs.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Core/contracts/TimeswapFactory.sol#L23

https://github.com/code-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Core/contracts/TimeswapFactory.sol#L21

Tools Used

None

Recommended Mitigation Steps

Consider to review all uint types. Change them with uint256 If the integer is not necessary to present with uint16.

Handle

defsec

Vulnerability details

Impact

Native fund transfers into the TimeswapConvenience contract is only expected from the wrapped token contract. Hence, it would be good to restrict incoming fund transfers to prevent accidental native fund transfers from other sources.

Proof of Concept

1. Navigate to the following contract code.

https://github.com/code-423n4/2022-01-timeswap/blob/main/Timeswap/Timeswap-V1-Convenience/contracts/TimeswapConvenience.sol#L69

Tools Used

None

Recommended Mitigation Steps

receive() external payable {
require(msg.sender == address(WETH) | msg.sender == address(WAVAX), 'only wrapped eth');
}