Putty contest - defsec's results

ISSUE LIST - Putty

C4-001 : Low level calls with solidity version 0.8.13 can result in optimiser bug. - LOW

C4-002 : Critical changes should use two-step procedure - Non Critical

C4-003 : Use of Block.timestamp - Non-critical

C4-004 : Incompatibility With Rebasing/Deflationary/Inflationary tokens - LOW

C4-005 : DoS With Block Gas Limit - LOW

C4-006 : Missing Re-entrancy Guard - LOW

C4-007 : _safeMint() should be used rather than _mint() wherever possible

ISSUES

C4-001 : Low level calls with solidity version 0.8.13 can result in optimiser bug.

Impact

The protocol is using low level calls with solidity version 0.8.9 which can result in optimizer bug.

https://medium.com/certora/overly-optimistic-optimizer-certora-bug-disclosure-2101e3f7994d

Proof of Concept

https://github.com/code-423n4/2022-06-yieldy/blob/main/src/contracts/LiquidityReserve.sol#L2

Tools Used

Code Review

Recommended Mitigation Steps

Consider upgrading to solidity 0.8.15.

C4-002 : Critical changes should use two-step procedure

Impact - NON CRITICAL

The critical procedures should be two step process. The contracts inherit OpenZeppelin's Ownable contract which enables the onlyOwner role to transfer ownership to another address. It's possible that the onlyOwner role mistakenly transfers ownership to the wrong address, resulting in a loss of the onlyOwner role. The current ownership transfer process involves the current owner calling Unlock.transferOwnership(). This function checks the new owner is not the zero address and proceeds to write the new owner's address into the owner's state variable. If the nominated EOA account is not a valid account, it is entirely possible the owner may accidentally transfer ownership to an uncontrolled account, breaking all functions with the onlyOwner() modifier. Lack of two-step procedure for critical operations leaves them error-prone if the address is incorrect, the new address will take on the functionality of the new role immediately

for Ex : -Alice deploys a new version of the whitehack group address. When she invokes the whitehack group address setter to replace the address, she accidentally enters the wrong address. The new address now has access to the role immediately and is too late to revert

Proof of Concept

1. Navigate to the following contract.

https://github.com/code-423n4/2022-06-putty/blob/main/contracts/src/PuttyV2.sol#L53

Tools Used

Code Review

Recommended Mitigation Steps

Lack of two-step procedure for critical operations leaves them error-prone. Consider adding two step procedure on the critical functions.

C4-003 : Use of Block.timestamp

Impact - Non-Critical

Block timestamps have historically been used for a variety of applications, such as entropy for random numbers (see the Entropy Illusion for further details), locking funds for periods of time, and various state-changing conditional statements that are time-dependent. Miners have the ability to adjust timestamps slightly, which can prove to be dangerous if block timestamps are used incorrectly in smart contracts.

Proof of Concept

1. Navigate to the following contract.

https://github.com/code-423n4/2022-06-putty/blob/main/contracts/src/PuttyV2.sol#L290

Tools Used

Manual Code Review

Recommended Mitigation Steps

Block timestamps should not be used for entropy or generating random numbers—i.e., they should not be the deciding factor (either directly or through some derivation) for winning a game or changing an important state.

Time-sensitive logic is sometimes required; e.g., for unlocking contracts (time-locking), completing an ICO after a few weeks, or enforcing expiry dates. It is sometimes recommended to use block.number and an average block time to estimate times; with a 10 second block time, 1 week equates to approximately, 60480 blocks. Thus, specifying a block number at which to change a contract state can be more secure, as miners are unable to easily manipulate the block number.

C4-004 : Incompatibility With Rebasing/Deflationary/Inflationary tokens

Impact - LOW

Putty protocol do not appear to support rebasing/deflationary/inflationary tokens whose balance changes during transfers or over time. The necessary checks include at least verifying the amount of tokens transferred to contracts before and after the actual transfer to infer any fees/interest.

Example Test

During the NFT operations, If the inflationary/deflationary tokens are used excepted amount will be lower than deposit.

Proof of Concept

1. Navigate to the following contract.

https://github.com/code-423n4/2022-06-putty/blob/main/contracts/src/PuttyV2.sol#L324

Tools Used

Manual Code Review

Recommended Mitigation Steps

• Ensure that to check previous balance/after balance equals to amount for any rebasing/inflation/deflation
• Add support in contracts for such tokens before accepting user-supplied tokens
• Consider supporting deflationary / rebasing / etc tokens by extra checking the balances before/after or strictly inform your users not to use such tokens if they don't want to lose them.

C4-005 : # DoS With Block Gas Limit

Impact - Non-Critical

When smart contracts are deployed or functions inside them are called, the execution of these actions always requires a certain amount of gas, based of how much computation is needed to complete them. The Ethereum network specifies a block gas limit and the sum of all transactions included in a block can not exceed the threshold.

Programming patterns that are harmless in centralized applications can lead to Denial of Service conditions in smart contracts when the cost of executing a function exceeds the block gas limit. Modifying an array of unknown size, that increases in size over time, can lead to such a Denial of Service condition.

Proof of Concept

1. Follow the functions shown below.

  2022-06-putty-main/contracts/src/PuttyV2.sol::556 => for (uint256 i = 0; i < orders.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::594 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::598 => require(token.code.length > 0, "ERC20: Token is not contract");
  2022-06-putty-main/contracts/src/PuttyV2.sol::611 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::627 => for (uint256 i = 0; i < floorTokens.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::637 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::647 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::658 => for (uint256 i = 0; i < floorTokens.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::670 => for (uint256 i = 0; i < whitelist.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::728 => for (uint256 i = 0; i < arr.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::742 => for (uint256 i = 0; i < arr.length; i++) {

Tools Used

Code Review

Recommended Mitigation Steps

Caution is advised when you expect to have large arrays that grow over time. Actions that require looping across the entire data structure should be avoided.

If you absolutely must loop over an array of unknown size, then you should plan for it to potentially take multiple blocks, and therefore require multiple transactions.

C4-006 : # Missing Re-entrancy Guard

Impact - LOW

The re-entrancy guard is missing on the some of the functions. The external interactions can cause to the re-entrancy vulnerability.

Proof of Concept

1. Navigate to the following contract.

https://github.com/code-423n4/2022-06-putty/blob/main/contracts/src/PuttyV2.sol#L268

https://github.com/code-423n4/2022-06-putty/blob/main/contracts/src/PuttyV2.sol#L389

Tools Used

Code Review

Recommended Mitigation Steps

Follow the check effect interaction pattern or put re-entrancy guard.

C4-007 : # _safeMint() should be used rather than _mint() wherever possible

Impact - LOW

_mint() (https://github.com/OpenZeppelin/openzeppelin-contracts/blob/d4d8d2ed9798cc3383912a23b5e8d5cb602f7d4b/contracts/token/ERC721/ERC721.sol#L271) is discouraged in favor of _safeMint() (https://github.com/Rari-Capital/solmate/blob/4eaf6b68202e36f67cab379768ac6be304c8ebde/src/tokens/ERC721.sol#L180) which ensures that the recipient is either an EOA or implements IERC721Receiver. Both open OpenZeppelin and solmate have versions of this function so that NFTs aren’t lost if they’re minted to contracts that cannot transfer them back out.

Proof of Concept

1. Navigate to the following contract.

https://github.com/code-423n4/2022-06-putty/blob/main/contracts/src/PuttyV2.sol#L303

https://github.com/code-423n4/2022-06-putty/blob/main/contracts/src/PuttyV2.sol#L308

Tools Used

Code Review

Recommended Mitigation Steps

Use _safeMint() instead of _mint().

[S]: Suggested optimation, save a decent amount of gas without compromising readability;

[M]: Minor optimation, the amount of gas saved is minor, change when you see fit;

[N]: Non-preferred, the amount of gas saved is at cost of readability, only apply when gas saving is a top priority.

ISSUE LIST

C4-001: Revert String Size Optimization [S]

C4-002 : Adding unchecked directive can save gas [S]

C4-003 : Check if amount > 0 before token transfer can save gas [S]

C4-004 : Using operator && used more gas [S]

C4-005 : Non-strict inequalities are cheaper than strict ones [M]

C4-006 : Use Custom Errors instead of Revert Strings to save Gas [S]

C4-007 : Use Shift Right/Left instead of Division/Multiplication if possible [N]

C4-008 : Use calldata instead of memory for function parameters [M]

C4-009 : > 0 can be replaced with != 0 for gas optimization [S]

C4-010 : Free gas savings for using solidity 0.8.13+ - [S]

C4-011 : Keccak functions in constants waste gas [M]

C4-012 : ++i is more gas efficient than i++ in loops forwarding

C4-013 : Cache array length in for loops can save gas

C4-001: Revert String Size Optimization

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:

  2022-06-putty-main/contracts/src/PuttyV2.sol::284 => require(order.whitelist.length == 0 || isWhitelisted(order.whitelist, msg.sender), "Not whitelisted");
  2022-06-putty-main/contracts/src/PuttyV2.sol::293 => require(order.baseAsset.code.length > 0, "baseAsset is not contract");
  2022-06-putty-main/contracts/src/PuttyV2.sol::295 => // check floor asset token ids length is 0 unless the order type is call and side is long
  2022-06-putty-main/contracts/src/PuttyV2.sol::297 => ? require(floorAssetTokenIds.length == order.floorTokens.length, "Wrong amount of floor tokenIds")
  2022-06-putty-main/contracts/src/PuttyV2.sol::298 => : require(floorAssetTokenIds.length == 0, "Invalid floor tokens length");
  2022-06-putty-main/contracts/src/PuttyV2.sol::403 => // check floor asset token ids length is 0 unless the position type is put
  2022-06-putty-main/contracts/src/PuttyV2.sol::405 => ? require(floorAssetTokenIds.length == order.floorTokens.length, "Wrong amount of floor tokenIds")
  2022-06-putty-main/contracts/src/PuttyV2.sol::406 => : require(floorAssetTokenIds.length == 0, "Invalid floor tokenIds length");
  2022-06-putty-main/contracts/src/PuttyV2.sol::551 => require(orders.length == signatures.length, "Length mismatch in input");
  2022-06-putty-main/contracts/src/PuttyV2.sol::552 => require(signatures.length == floorAssetTokenIds.length, "Length mismatch in input");

Tools Used

Manual Review

Recommended Mitigation Steps

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

C4-002 : Adding unchecked directive can save gas

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

  2022-06-putty-main/contracts/src/PuttyV2.sol::556 => for (uint256 i = 0; i < orders.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::594 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::598 => require(token.code.length > 0, "ERC20: Token is not contract");
  2022-06-putty-main/contracts/src/PuttyV2.sol::611 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::627 => for (uint256 i = 0; i < floorTokens.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::637 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::647 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::658 => for (uint256 i = 0; i < floorTokens.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::670 => for (uint256 i = 0; i < whitelist.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::728 => for (uint256 i = 0; i < arr.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::742 => for (uint256 i = 0; i < arr.length; i++) {

Tools Used

None

Recommended Mitigation Steps

Consider applying unchecked arithmetic where overflow/underflow is not possible. Example can be seen from below.

Unchecked{i++};

C4-003 : Check if amount > 0 before token transfer can save gas

Impact

Since _amount can be 0. Checking if (_amount != 0) before the transfer can potentially save an external call and the unnecessary gas cost of a 0 token transfer.

Proof of Concept

https://github.com/code-423n4/2022-06-putty/blob/main/contracts/src/PuttyV2.sol#L503

All Contracts

Tools Used

None

Recommended Mitigation Steps

Consider checking amount != 0.

C4-004 : Using operator && used more gas

Impact

Using double require instead of operator && can save more gas.

Proof of Concept

1. Navigate to the following contracts.

2022-06-putty-main/contracts/src/PuttyV2.sol:296:        order.isCall && order.isLong
2022-06-putty-main/contracts/src/PuttyV2.sol:311:        if (order.isLong && order.isCall) {
2022-06-putty-main/contracts/src/PuttyV2.sol:327:            if (weth == order.baseAsset && msg.value > 0) {
2022-06-putty-main/contracts/src/PuttyV2.sol:343:        if (!order.isLong && !order.isCall) {
2022-06-putty-main/contracts/src/PuttyV2.sol:349:        if (order.isLong && !order.isCall) {
2022-06-putty-main/contracts/src/PuttyV2.sol:351:            if (weth == order.baseAsset && msg.value > 0) {
2022-06-putty-main/contracts/src/PuttyV2.sol:367:        if (!order.isLong && order.isCall) {
2022-06-putty-main/contracts/src/PuttyV2.sol:374:        if (order.isLong && order.isCall) {
2022-06-putty-main/contracts/src/PuttyV2.sol:427:            if (weth == order.baseAsset && msg.value > 0) {
2022-06-putty-main/contracts/src/PuttyV2.sol:495:        if ((order.isCall && isExercised) || (!order.isCall && !isExercised)) {
2022-06-putty-main/contracts/src/PuttyV2.sol:509:        if ((order.isCall && !isExercised) || (!order.isCall && isExercised)) {

Tools Used

Code Review

Recommended Mitigation Steps

Example

using &&:

function check(uint x)public view{
require(x == 0 && x < 1 );
}
// gas cost 21630

using double require:

require(x == 0 );
require( x < 1);
}
}
// gas cost 21622

C4-005 : Non-strict inequalities are cheaper than strict ones

Impact

Strict inequalities add a check of non equality which costs around 3 gas.

Proof of Concept

  2022-06-putty-main/contracts/src/PuttyV2.sol::556 => for (uint256 i = 0; i < orders.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::594 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::598 => require(token.code.length > 0, "ERC20: Token is not contract");
  2022-06-putty-main/contracts/src/PuttyV2.sol::611 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::627 => for (uint256 i = 0; i < floorTokens.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::637 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::647 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::658 => for (uint256 i = 0; i < floorTokens.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::670 => for (uint256 i = 0; i < whitelist.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::728 => for (uint256 i = 0; i < arr.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::742 => for (uint256 i = 0; i < arr.length; i++) {

Tools Used

Code Review

Recommended Mitigation Steps

Use >= or <= instead of > and < when possible.

C4-006 : Use Custom Errors instead of Revert Strings to save Gas

Custom errors from Solidity 0.8.4 are cheaper than revert strings (cheaper deployment cost and runtime cost when the revert condition is met)

Source Custom Errors in Solidity:

Starting from Solidity v0.8.4, there is a convenient and gas-efficient way to explain to users why an operation failed through the use of custom errors. Until now, you could already use strings to give more information about failures (e.g., revert("Insufficient funds.");), but they are rather expensive, especially when it comes to deploy cost, and it is difficult to use dynamic information in them.

Custom errors are defined using the error statement, which can be used inside and outside of contracts (including interfaces and libraries).

Instances include:

  2022-06-putty-main/contracts/src/PuttyV2.sol::284 => require(order.whitelist.length == 0 || isWhitelisted(order.whitelist, msg.sender), "Not whitelisted");
  2022-06-putty-main/contracts/src/PuttyV2.sol::293 => require(order.baseAsset.code.length > 0, "baseAsset is not contract");
  2022-06-putty-main/contracts/src/PuttyV2.sol::295 => // check floor asset token ids length is 0 unless the order type is call and side is long
  2022-06-putty-main/contracts/src/PuttyV2.sol::297 => ? require(floorAssetTokenIds.length == order.floorTokens.length, "Wrong amount of floor tokenIds")
  2022-06-putty-main/contracts/src/PuttyV2.sol::298 => : require(floorAssetTokenIds.length == 0, "Invalid floor tokens length");
  2022-06-putty-main/contracts/src/PuttyV2.sol::403 => // check floor asset token ids length is 0 unless the position type is put
  2022-06-putty-main/contracts/src/PuttyV2.sol::405 => ? require(floorAssetTokenIds.length == order.floorTokens.length, "Wrong amount of floor tokenIds")
  2022-06-putty-main/contracts/src/PuttyV2.sol::406 => : require(floorAssetTokenIds.length == 0, "Invalid floor tokenIds length");
  2022-06-putty-main/contracts/src/PuttyV2.sol::551 => require(orders.length == signatures.length, "Length mismatch in input");
  2022-06-putty-main/contracts/src/PuttyV2.sol::552 => require(signatures.length == floorAssetTokenIds.length, "Length mismatch in input");

Tools Used

Code Review

Recommended Mitigation Steps

Recommended to replace revert strings with custom errors.

C4-007 : Use Shift Right/Left instead of Division/Multiplication if possible

Impact

A division/multiplication by any number x being a power of 2 can be calculated by shifting log2(x) to the right/left.

While the DIV opcode uses 5 gas, the SHR opcode only uses 3 gas. Furthermore, Solidity's division operation also includes a division-by-0 prevention which is bypassed using shifting.

Proof of Concept

Contracts

Tools Used

None

Recommended Mitigation Steps

A division/multiplication by any number x being a power of 2 can be calculated by shifting log2(x) to the right/left.

C4-008 : Use calldata instead of memory for function parameters

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.

Proof of Concept

1. Navigate to the following smart contract line.

2022-06-putty-main/contracts/src/PuttyV2.sol:593:    function _transferERC20sIn(ERC20Asset[] memory assets, address from) internal {
2022-06-putty-main/contracts/src/PuttyV2.sol:610:    function _transferERC721sIn(ERC721Asset[] memory assets, address from) internal {

Tools Used

None

Recommended Mitigation Steps

Some parameters in examples given above are later hashed. It may be beneficial for those parameters to be in memory rather than calldata.

C4-009 : > 0 can be replaced with != 0 for gas optimization

Impact

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

Proof of Concept

1. Navigate to the following contract sections.

  2022-06-putty-main/contracts/src/PuttyV2.sol::293 => require(order.baseAsset.code.length > 0, "baseAsset is not contract");
  2022-06-putty-main/contracts/src/PuttyV2.sol::327 => if (weth == order.baseAsset && msg.value > 0) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::351 => if (weth == order.baseAsset && msg.value > 0) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::427 => if (weth == order.baseAsset && msg.value > 0) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::498 => if (fee > 0) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::598 => require(token.code.length > 0, "ERC20: Token is not contract");
  2022-06-putty-main/contracts/src/PuttyV2.sol::599 => require(tokenAmount > 0, "ERC20: Amount too small");

Tools Used

None

Recommended Mitigation Steps

Consider to replace > 0 with != 0 for gas optimization.

C4-010 : Free gas savings for using solidity 0.8.10+

Impact

Using newer compiler versions and the optimizer gives gas optimizations and additional safety checks are available for free.

Proof of Concept

All Contracts

Solidity 0.8.10 has a useful change which reduced gas costs of external calls which expect a return value: https://blog.soliditylang.org/2021/11/09/solidity-0.8.10-release-announcement/

Solidity 0.8.13 has some improvements too but not well tested.

Code Generator: Skip existence check for external contract if return data is expected. In this case, the ABI decoder will revert if the contract does not exist

All Contracts

Tools Used

None

Recommended Mitigation Steps

Consider to upgrade pragma to at least 0.8.13.

C4-011 : Keccak functions in constants waste gas [M]

Impact

The contracts assigns two constants to the result of a keccak operation, which results in gas waste since the expression is computed each time the constant is accessed.

See this issue for more context: ethereum/solidity#9232 (https://github.com/ethereum/solidity/issues/9232)

Proof of Concept

  2022-06-putty-main/contracts/src/PuttyV2.sol::90 => keccak256(abi.encodePacked("ERC721Asset(address token,uint256 tokenId)"));
  2022-06-putty-main/contracts/src/PuttyV2.sol::96 => keccak256(abi.encodePacked("ERC20Asset(address token,uint256 tokenAmount)"));
  2022-06-putty-main/contracts/src/PuttyV2.sol::102 => keccak256(
  2022-06-putty-main/contracts/src/PuttyV2.sol::700 => orderHash = keccak256(
  2022-06-putty-main/contracts/src/PuttyV2.sol::712 => keccak256(abi.encodePacked(order.whitelist)),
  2022-06-putty-main/contracts/src/PuttyV2.sol::713 => keccak256(abi.encodePacked(order.floorTokens)),
  2022-06-putty-main/contracts/src/PuttyV2.sol::714 => keccak256(encodeERC20Assets(order.erc20Assets)),
  2022-06-putty-main/contracts/src/PuttyV2.sol::715 => keccak256(encodeERC721Assets(order.erc721Assets))
  2022-06-putty-main/contracts/src/PuttyV2.sol::731 => keccak256(abi.encode(ERC20ASSET_TYPE_HASH, arr[i].token, arr[i].tokenAmount))
  2022-06-putty-main/contracts/src/PuttyV2.sol::745 => keccak256(abi.encode(ERC721ASSET_TYPE_HASH, arr[i].token, arr[i].tokenId))

Tools Used

None

Recommended Mitigation Steps

Replace the constant directive with immutable, or assign the already hashed value to the constants.

C4-012 : ++i is more gas efficient than i++ in loops forwarding

Impact

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

Proof of Concept

1. Navigate to the following contracts.

  2022-06-putty-main/contracts/src/PuttyV2.sol::556 => for (uint256 i = 0; i < orders.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::594 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::598 => require(token.code.length > 0, "ERC20: Token is not contract");
  2022-06-putty-main/contracts/src/PuttyV2.sol::611 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::627 => for (uint256 i = 0; i < floorTokens.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::637 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::647 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::658 => for (uint256 i = 0; i < floorTokens.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::670 => for (uint256 i = 0; i < whitelist.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::728 => for (uint256 i = 0; i < arr.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::742 => for (uint256 i = 0; i < arr.length; i++) {

Tools Used

Code Review

Recommended Mitigation Steps

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

C4-013 : Cache array length in for loops can save gas

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.

  2022-06-putty-main/contracts/src/PuttyV2.sol::611 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::627 => for (uint256 i = 0; i < floorTokens.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::637 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::647 => for (uint256 i = 0; i < assets.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::658 => for (uint256 i = 0; i < floorTokens.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::670 => for (uint256 i = 0; i < whitelist.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::728 => for (uint256 i = 0; i < arr.length; i++) {
  2022-06-putty-main/contracts/src/PuttyV2.sol::742 => for (uint256 i = 0; i < arr.length; i++) {

Tools Used

None

Recommended Mitigation Steps

Consider to cache array length.