AaveYield.getTokensForShares(), AaveYield.getSharesForTokens() Implementation can be simpler and save some gas

[code423n4]

Handle

WatchPug

Vulnerability details

Based on the current implementation, shares are in aToken, which is 1:1 to the underlying token.

Therefore, getTokensForShares() and getSharesForTokens() can be much simplier.

https://github.com/code-423n4/2021-12-sublime/blob/9df1b7c4247f8631647c7627a8da9bdc16db8b11/contracts/yield/AaveYield.sol#L256-L265

    function getTokensForShares(uint256 shares, address asset) public view override returns (uint256 amount) {
        if (shares == 0) return 0;
        address aToken = liquidityToken(asset);

        (, , , , , , , uint256 liquidityIndex, , ) = IProtocolDataProvider(protocolDataProvider).getReserveData(asset);

        amount = IScaledBalanceToken(aToken).scaledBalanceOf(address(this)).mul(liquidityIndex).mul(shares).div(
            IERC20(aToken).balanceOf(address(this))
        );
    }

can be changed to:

    function getTokensForShares(uint256 shares, address asset) public view override returns (uint256) {
        return shares;
    }

https://github.com/code-423n4/2021-12-sublime/blob/9df1b7c4247f8631647c7627a8da9bdc16db8b11/contracts/yield/AaveYield.sol#L273-L275

    function getSharesForTokens(uint256 amount, address asset) external view override returns (uint256 shares) {
        shares = (amount.mul(1e18)).div(getTokensForShares(1e18, asset));
    }

can be changed to:

    function getSharesForTokens(uint256 amount, address asset) external view override returns (uint256) {
        return amount;
    }

[ritik99]

Instead of making the proposed changes, we plan to use Aave's wrappers for aTokens so that it conforms with the behaviour of other LP tokens