RadCet - stEth::transferFrom will transfer 1-2 less way result in revert in deposit function

[sherlock-admin3]

RadCet

High

stEth::transferFrom will transfer 1-2 less way result in revert in deposit function

Summary

Many cases stEth::transferFrom will transfer 1-2 less way, which would result in revert in consequent functions, because of not enough balance

Vulnerability Detail

In DepositWrapper:deposit, user call this function to deposit weth, steth,.. However when user try to deposit stETH, contract using IERC20(steth).safeTransferFrom(sender, wrapper, amount); to send seETH from user to contract. stETH is using shares for tracking balances and it is a known issue that due to rounding error, transferred shares may be 1-2 wei less than _amount passed. So when call _DepositWrapper:stethToWsteth will be revert due to not enough balance.

Impact

Deposit function for stETH is DOS
Possibility: The probability of issue appearing is high and you can check in the following discussion. It has also been classified as a High severity on past contests: lidofinance/lido-dao#442

Code Snippet

DepositWrapper:deposit

    function deposit(
        address to,
        address token,
        uint256 amount,
        uint256 minLpAmount,
        uint256 deadline
    ) external payable returns (uint256 lpAmount) {
        address wrapper = address(this);
        address sender = msg.sender;
        address[] memory tokens = vault.underlyingTokens();
        if (tokens.length != 1 || tokens[0] != wsteth)
            revert InvalidTokenList();
        if (amount == 0) revert InvalidAmount();
        if (token == steth) {
            IERC20(steth).safeTransferFrom(sender, wrapper, amount);
            amount = _stethToWsteth(amount);
        } else if (token == weth) {

    function _stethToWsteth(uint256 amount) private returns (uint256) {
        IERC20(steth).safeIncreaseAllowance(wsteth, amount);
        IWSteth(wsteth).wrap(amount);
        return IERC20(wsteth).balanceOf(address(this));
    }

Tool used

Manual Review

Recommendation

Use lido recommendation to utilize transferShares function, so the _amount is realistic, or compares the balance before and after the transfer.

Duplicate of #299