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code-423n4 / 2022-10-inverse-findings

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Gas Optimizations #559

Open code423n4 opened 2 years ago

code423n4 commented 2 years ago

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Gas Optimizations

[G-01]: Place subtractions where the operands can't underflow in unchecked {} block

Context:

  1. https://github.com/code-423n4/2022-10-inverse/blob/main/src/escrows/INVEscrow.sol#L62
  2. https://github.com/code-423n4/2022-10-inverse/blob/main/src/Fed.sol#L110
  3. https://github.com/code-423n4/2022-10-inverse/blob/main/src/Fed.sol#L124
  4. https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L111
  5. https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L124
  6. https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L137
  7. https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L172
  8. https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L196
  9. https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L374
  10. https://github.com/code-423n4/2022-10-inverse/blob/main/src/Market.sol#L362
  11. https://github.com/code-423n4/2022-10-inverse/blob/main/src/Market.sol#L379
  12. https://github.com/code-423n4/2022-10-inverse/blob/main/src/Market.sol#L534

Description:

Some gas can be saved by using an unchecked {} block if an underflow isn't possible because of a previous require() or if-statement.

[G-02]: If internal function called only once it can be inlined to save gas

Context:

  1. https://github.com/code-423n4/2022-10-inverse/blob/main/src/Market.sol#L226
  2. https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L372

[G-03]: Catch a value inside a mapping/array in local memory

Context:

        if(escrows[user] != IEscrow(address(0))) return escrows[user];

https://github.com/code-423n4/2022-10-inverse/blob/main/src/Market.sol#L246

        if(dueTokensAccrued[user] + accrued > balances[user]) return 0;
        return balances[user] - dueTokensAccrued[user] - accrued;

https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L123-L124

        if(dueTokensAccrued[user] + accrued < balances[user]) return 0;
        return dueTokensAccrued[user] + accrued - balances[user];

https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L136-L137

        if(lastUpdated[user] == block.timestamp) return;
        uint accrued = (block.timestamp - lastUpdated[user]) * debt / 365 days;

https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L286-L287

        if(feeds[token].feed != IChainlinkFeed(address(0))) {
            // get price from feed
            uint price = feeds[token].feed.latestAnswer();
            require(price > 0, "Invalid feed price");
            // normalize price
            uint8 feedDecimals = feeds[token].feed.decimals();
            uint8 tokenDecimals = feeds[token].tokenDecimals;

https://github.com/code-423n4/2022-10-inverse/blob/main/src/Oracle.sol#L80-L86

        if(feeds[token].feed != IChainlinkFeed(address(0))) {
            // get price from feed
            uint price = feeds[token].feed.latestAnswer();
            require(price > 0, "Invalid feed price");
            // normalize price
            uint8 feedDecimals = feeds[token].feed.decimals();
            uint8 tokenDecimals = feeds[token].tokenDecimals;

https://github.com/code-423n4/2022-10-inverse/blob/main/src/Oracle.sol#L114-L120

Recommendation:

Example how to fix. Change:

    function balanceOf(address user) public view returns (uint) {
        uint debt = debts[user];
        uint accrued = (block.timestamp - lastUpdated[user]) * debt / 365 days;
        if(dueTokensAccrued[user] + accrued > balances[user]) return 0;
        return balances[user] - dueTokensAccrued[user] - accrued;
    }

to:

    function balanceOf(address user) public view returns (uint) {
        uint debt = debts[user];
        uint accrued = (block.timestamp - lastUpdated[user]) * debt / 365 days;
        uint256 _dueTokensAccrue = dueTokensAccrued[user];
        uint256 _balance = balances[user];
        if(_dueTokensAccrue + accrued > _balance) return 0;
        return _balance - _dueTokensAccrue - accrued;
    }

[G-04]: Catch state variable in local memory and not re-read it from storage

Context:

        if(collateralFactorBps == 0) return 0;
        uint minimumCollateral = debt * 1 ether / oracle.getPrice(address(collateral), collateralFactorBps) * 10000 / collateralFactorBps;

https://github.com/code-423n4/2022-10-inverse/blob/main/src/Market.sol#L359-L360

        if(collateralFactorBps == 0) return 0;
        uint minimumCollateral = debt * 1 ether / oracle.viewPrice(address(collateral), collateralFactorBps) * 10000 / collateralFactorBps;

https://github.com/code-423n4/2022-10-inverse/blob/main/src/Market.sol#L376-L377

        if(liquidationFeeBps > 0) {
            uint liquidationFee = repaidDebt * 1 ether / price * liquidationFeeBps / 10000;

https://github.com/code-423n4/2022-10-inverse/blob/main/src/Market.sol#L605-L606

        require(msg.sender == pendingOperator, "ONLY PENDING OPERATOR");
        operator = pendingOperator;

https://github.com/code-423n4/2022-10-inverse/blob/main/src/Oracle.sol#L67-L68

Description:

Every reading from storage costs about 100 gas while every reading from memory costs only 3 gas. If state variable referred more than once within a function then it is cheaper to cached it in local memory (100 gas) and then read it from memory wnen it is neaded (3 gas) rather than read state variable from storage everytime (100 gas).

Recommendation:

Example how to fix. Change:

    function getWithdrawalLimitInternal(address user) internal returns (uint) {
        ...

        if(collateralFactorBps == 0) return 0;
        uint minimumCollateral = debt * 1 ether / oracle.getPrice(address(collateral), collateralFactorBps) * 10000 / collateralFactorBps;        
        if(collateralBalance <= minimumCollateral) return 0;
        return collateralBalance - minimumCollateral;
    }

to:

    function getWithdrawalLimitInternal(address user) internal returns (uint) {
        ...

        uint _collateralFactorBps = collateralFactorBps;

        if(_collateralFactorBps == 0) return 0;
        uint minimumCollateral = debt * 1 ether / oracle.getPrice(address(collateral), _collateralFactorBps) * 10000 / _collateralFactorBps;        

        ...
    }

[G-05]: No need to catch state variable in local memory if it only use once

Context:

  1. https://github.com/code-423n4/2022-10-inverse/blob/main/src/Market.sol#L532
  2. https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L121
  3. https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L134
  4. https://github.com/code-423n4/2022-10-inverse/blob/main/src/DBR.sol#L285
  5. https://github.com/code-423n4/2022-10-inverse/blob/main/src/Fed.sol#L106

Recommendation:

Read the state variable from storage.

c4-judge commented 2 years ago

0xean marked the issue as grade-b