Fraxlend (Frax Finance) contest - 0xkatana's results

Fraxlend: A permissionless lending platform and the final piece of the Frax Finance Defi Trinity.

General Information

Platform: Code4rena

Start Date: 12/08/2022

Pot Size: $50,000 USDC

Total HM: 15

Participants: 120

Period: 5 days

Judge: Justin Goro

Total Solo HM: 6

Id: 153

League: ETH

Frax Finance

Findings Distribution

Researcher Performance

Rank: 92/120

Findings: 1

Award: $23.13

🌟 Selected for report: 0

🚀 Solo Findings: 0

External Links

Code4rena Contest Page Github Contest Repository Github Findings Repository Frax Finance

Findings Information

🌟 Selected for report: IllIllI

Also found by: 0x1f8b, 0xA5DF, 0xDjango, 0xNazgul, 0xSmartContract, 0xackermann, 0xbepresent, 0xc0ffEE, 0xkatana, 2997ms, Amithuddar, Aymen0909, Bnke0x0, Chinmay, Chom, CodingNameKiki, Deivitto, Diraco, Dravee, ElKu, EthLedger, Fitraldys, Funen, IgnacioB, JC, Junnon, Lambda, LeoS, Metatron, MiloTruck, Noah3o6, NoamYakov, PaludoX0, Randyyy, ReyAdmirado, Rohan16, Rolezn, Ruhum, SaharAP, Sm4rty, SooYa, TomJ, Tomio, Waze, Yiko, _Adam, __141345__, a12jmx, ajtra, ak1, asutorufos, ballx, brgltd, c3phas, cRat1st0s, carlitox477, chrisdior4, d3e4, delfin454000, dharma09, djxploit, durianSausage, erictee, fatherOfBlocks, find_a_bug, flyx, francoHacker, gerdusx, gogo, gzeon, hakerbaya, ignacio, jag, kyteg, ladboy233, ltyu, m_Rassska, medikko, mics, mrpathfindr, newfork01, nxrblsrpr, oyc_109, pfapostol, rbserver, reassor, ret2basic, robee, sach1r0, saian, simon135, sryysryy, zeesaw

Awards

23.127 USDC - $23.13

Labels

bug

G (Gas Optimization)

old-submission-method

External Links

Link to GitHub issue

[G-01] Redundant zero initialization

Solidity does not recognize null as a value, so uint variables are initialized to zero. Setting a uint variable to zero is redundant and can waste gas.

Recommended Mitigation Steps

Remove the redundant zero initialization uint256 i; instead of uint256 i = 0;

[G-02] Split up require statements instead of &&

Combining require statement conditions with && logic uses unnecessary gas. It is better to split up each part of the logical statement into a separate require statements

One example is

require(
            _minInterest < MAX_INT && _minInterest <= _vertexInterest && _minInterest >= MIN_INT,
            "LinearInterestRate: _minInterest < MAX_INT && _minInterest <= _vertexInterest && _minInterest >= MIN_INT"
        );

This can be improved to

require(_minInterest < MAX_INT);
require(_minInterest <= _vertexInterest);
require(_minInterest >= MIN_INT,
            "LinearInterestRate: _minInterest < MAX_INT && _minInterest <= _vertexInterest && _minInterest >= MIN_INT"
        );

One part of code had require statements with many logical "and"s. Instead, split into two to save gas https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/LinearInterestRate.sol#L58-L67

Recommended Mitigation Steps

Use separate require statements instead of concatenating with &&

[G-03] Use calldata instead of memory for function arguments

Using calldata instead of memory for function arguments saves gas sometimes. This can happen when a function is called externally and the memory array values are kept in calldata and copied to memory during ABI decoding (using the opcode calldataload and mstore). If the array is used in a for loop, arr[i] accesses the value in memory using a mload. If calldata is used instead, then 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.

Many cases of function arguments using memory instead of calldata can use this improvement to save gas https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairDeployer.sol#L362 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairDeployer.sol#L363 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairDeployer.sol#L398

Source https://gist.github.com/hrkrshnn/ee8fabd532058307229d65dcd5836ddc#use-calldata-instead-of-memory-for-function-parameters

Recommended Mitigation Steps

Change function arguments from memory to calldata

[G-04] Use != 0 instead of > 0

Using > 0 uses slightly more gas than using != 0. Use != 0 when comparing uint variables to zero, which cannot hold values below zero

Recommended Mitigation Steps

Replace > 0 with != 0 to save gas

[G-05] Short require strings save gas

Strings in solidity are handled in 32 byte chunks. A require string longer than 32 bytes uses more gas. Shortening these strings will save gas.

Recommended Mitigation Steps

Shorten all require strings to less than 32 characters

[G-06] Use prefix not postfix in loops

Using a prefix increment (++i) instead of a postfix increment (i++) saves gas for each loop cycle and so can have a big gas impact when the loop executes on a large number of elements.

Recommended Mitigation Steps

Use prefix not postfix to increment in a loop

[G-07] For loop incrementing can be unsafe

For loops that use i++ do not need to use safemath for this operation because the loop would run out of gas long before this point. Making this addition operation unsafe using unchecked saves gas.

Sample code to make the for loop increment unsafe

for (uint i = 0; i < length; i = unchecked_inc(i)) {
    // do something that doesn't change the value of i
}

function unchecked_inc(uint i) returns (uint) {
    unchecked {
        return i + 1;
    }
}

Idea borrowed from https://gist.github.com/hrkrshnn/ee8fabd532058307229d65dcd5836ddc#the-increment-in-for-loop-post-condition-can-be-made-unchecked

Recommended Mitigation Steps

Make the increment in for loops unsafe to save gas

[G-08] Use iszero assembly for zero checks

Comparing a value to zero can be done using the iszero EVM opcode. This can save gas

Source from t11s https://twitter.com/transmissions11/status/1474465495243898885

Recommended Mitigation Steps

Use the assembly iszero evm opcode to compare values to zero

[G-09] Save gas with unchecked

Use unchecked math when there is no overflow risk to save gas. Solidity 0.8.X adds Safemath by default, and there are cases where Safemath provides no benefit and uses extra gas.

Locations where this was found include https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairCore.sol#L441 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairCore.sol#L454

Recommended Mitigation Steps

Add unchecked around math that can't overflow for gas savings. In Solidity before 0.8.0, use the normal math operators instead of safe math functions.

[G-10] Add payable to functions that won't receive ETH

Identifying a function as payable saves gas. Functions that have a modifier like onlyOwner or auth cannot be called by normal users and will not mistakenly receive ETH. These functions can be payable to save gas.

There are many functions that have the auth modifier in the contracts/. Some examples are https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairDeployer.sol#L170 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendWhitelist.sol#L50 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendWhitelist.sol#L65 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendWhitelist.sol#L80 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPair.sol#L204 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPair.sol#L234 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPair.sol#L274

Recommended Mitigation Steps

Add payable to these functions for gas savings

[G-11] Add payable to constructors that won't receive ETH

Identifying a constructor as payable saves gas. Constructors should only be called by the admin or deployer and should not mistakenly receive ETH. Constructors can be payable to save gas.

Locations where this was found include https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairDeployer.sol#L98 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairCore.sol#L151 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendWhitelist.sol#L40 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPair.sol#L45

Recommended Mitigation Steps

Add payable to these functions for gas savings

[G-12] Use internal function in place of modifier

An internal function can save gas vs. a modifier. A modifier inlines the code of the original function but an internal function does not.

Source https://blog.polymath.network/solidity-tips-and-tricks-to-save-gas-and-reduce-bytecode-size-c44580b218e6#dde7

Locations where this was found include https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairCore.sol#L330 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairCore.sol#L342 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairCore.sol#L351 https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairCore.sol#L359

Recommended Mitigation Steps

Use internal functions in place of modifiers to save gas.

[G-13] Use uint not bool

Booleans are more expensive than uint256 or any type that takes up a full word because each write operation emits an extra SLOAD to first read the slot's contents, replace the bits taken up by the boolean, and then write back. This is the compiler's defense against contract upgrades and pointer aliasing, and it cannot be disabled.

Recommended Mitigation Steps

Replace bool variables with uints

[G-14] Use uint256 not smaller ints

From the solidity docs

When using elements that are smaller than 32 bytes, your contract’s gas usage may be higher. This is because the EVM operates on 32 bytes at a time. Therefore, if the element is smaller than that, the EVM must use more operations in order to reduce the size of the element from 32 bytes to the desired size.

Locations where this was found include https://github.com/code-423n4/2022-06-nibbl/tree/main/contracts/NibblVaultFactory.sol#L71 https://github.com/code-423n4/2022-06-nibbl/tree/main/contracts/NibblVaultFactory.sol#L73 https://github.com/code-423n4/2022-06-nibbl/tree/main/contracts/NibblVaultFactory.sol#L90 https://github.com/code-423n4/2022-06-nibbl/tree/main/contracts/NibblVaultFactory.sol#L92

Recommended Mitigation Steps

Replace smaller int or uint variables with uint256 variables

[G-15] Use Solidity errors instead of require

Solidity errors introduced in version 0.8.4 can save gas on revert conditions https://blog.soliditylang.org/2021/04/21/custom-errors/ https://twitter.com/PatrickAlphaC/status/1505197417884528640

Recommended Mitigation Steps

Replace require blocks with new solidity errors described in https://blog.soliditylang.org/2021/04/21/custom-errors/

[G-16] Use simple comparison in trinary logic

The comparison operators >= and <= use more gas than >, <, or ==. Replacing the >= and ≤ operators with a comparison operator that has an opcode in the EVM saves gas

The existing code is https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairHelper.sol#L365

_collateralForLiquidator = _leftoverCollateral <= 0
? _userCollateralBalance
: (_liquidationAmountInCollateralUnits * (_LIQ_PRECISION + _fraxlendPair.dirtyLiquidationFee())) /
    _LIQ_PRECISION;

A simple comparison can be used for gas savings by reversing the logic

_collateralForLiquidator = _leftoverCollateral > 0
? (_liquidationAmountInCollateralUnits * (_LIQ_PRECISION + _fraxlendPair.dirtyLiquidationFee())) /
    _LIQ_PRECISION : _userCollateralBalance;

Recommended Mitigation Steps

Replace the comparison operator and reverse the logic to save gas using the suggestions above

[G-17] Use simple comparison in if statement

The comparison operators >= and <= use more gas than >, <, or ==. Replacing the >= and ≤ operators with a comparison operator that has an opcode in the EVM saves gas

The existing code is https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/FraxlendPairCore.sol#L525

if (_answer <= 0) {
    revert OracleLTEZero(oracleMultiply);
}
_price = _price * uint256(_answer);

A simple comparison can be used for gas savings by reversing the logic

if (_answer > 0) {
    _price = _price * uint256(_answer);
} else {
    revert OracleLTEZero(oracleMultiply);
}

Recommended Mitigation Steps

Replace the comparison operator and reverse the logic to save gas using the suggestions above

[G-18] Non-public variables save gas

Many constant variables are public, but changing the visibility of these variables to private or internal can save gas.

Recommended Mitigation Steps

Declare some public variables as private or internal to save gas

[G-19] Write contracts in vyper

The contracts are all written entirely in solidity. Writing contracts with vyper instead of solidity can save gas.

Source https://twitter.com/eiber_david/status/1515737811881807876 doggo demonstrates https://twitter.com/fubuloubu/status/1528179581974417414?t=-hcq_26JFDaHdAQZ-wYxCA&s=19

Recommended Mitigation Steps

Write some or all of the contracts in vyper to save gas

[G-20] Use `abi.encodePacked()` not `abi.encode()`

Changing abi.encode to abi.encodePacked can save gas. abi.encode pads extra null bytes at the end of the call data which is normally unnecessary. In general, abi.encodePacked is more gas-efficient.

There was at least one place where this change can be made: https://github.com/code-423n4/2022-08-frax/tree/main/src/contracts/VariableInterestRate.sol#L53

Recommended Mitigation Steps

Change abi.encode to abi.encodePacked

#0 - gititGoro
2022-10-09T12:18:15Z

The vyper deployment savings was interesting.

Fraxlend (Frax Finance) contest - 0xkatana's results

Fraxlend: A permissionless lending platform and the final piece of the Frax Finance Defi Trinity.

General Information

Findings Distribution

Researcher Performance

External Links

[G-09] Gas Report - $23.13

Findings Information

Awards

Labels

External Links

[G-01] Redundant zero initialization

Recommended Mitigation Steps

[G-02] Split up require statements instead of &&

Recommended Mitigation Steps

[G-03] Use calldata instead of memory for function arguments

Recommended Mitigation Steps

[G-04] Use != 0 instead of > 0

Recommended Mitigation Steps

[G-05] Short require strings save gas

Recommended Mitigation Steps

[G-06] Use prefix not postfix in loops

Recommended Mitigation Steps

[G-07] For loop incrementing can be unsafe

Recommended Mitigation Steps

[G-08] Use iszero assembly for zero checks

Recommended Mitigation Steps

[G-09] Save gas with unchecked

Recommended Mitigation Steps

[G-10] Add payable to functions that won't receive ETH

Recommended Mitigation Steps

[G-11] Add payable to constructors that won't receive ETH

Recommended Mitigation Steps

[G-12] Use internal function in place of modifier

Recommended Mitigation Steps

[G-13] Use uint not bool

Recommended Mitigation Steps

[G-14] Use uint256 not smaller ints

Recommended Mitigation Steps

[G-15] Use Solidity errors instead of require

Recommended Mitigation Steps

[G-16] Use simple comparison in trinary logic

Recommended Mitigation Steps

[G-17] Use simple comparison in if statement

Recommended Mitigation Steps

[G-18] Non-public variables save gas

Recommended Mitigation Steps

[G-19] Write contracts in vyper

Recommended Mitigation Steps

[G-20] Use abi.encodePacked() not abi.encode()

Recommended Mitigation Steps

#0 - gititGoro2022-10-09T12:18:15Z

[G-20] Use `abi.encodePacked()` not `abi.encode()`

#0 - gititGoro
2022-10-09T12:18:15Z