blackhole - stETH.transferFrom will transfer 1~2 wei less than the amount specified, leading to reverted transactions

[sherlock-admin3]

blackhole

High

stETH.transferFrom will transfer 1~2 wei less than the amount specified, leading to reverted transactions

Summary

When the DepositWrapper.deposit function is called, the stETH token is transferred to the contract using the transferFrom function.
The transferred amount of stETH tokens from the sender may be 1-2 wei less than the amount due to rounding error.
However, the _stethToWsteth function uses the originally specified amount instead of the actual transferred amount.
This discrepancy can lead to reverted transactions because of not enough amount.

Vulnerability Detail

The issue of the account's stETH balance getting lower was reported here: lidofinance/lido-dao#442
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 calling the wrap function, the revert will happen because the stETH balance is lower than the amount passed.

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

Impact

the deposit function may revert if the deposit token is not wstETH.

Code Snippet

https://github.com/sherlock-audit/2024-06-mellow/blob/main/mellow-lrt/src/utils/DepositWrapper.sol#L56
https://github.com/sherlock-audit/2024-06-mellow/blob/main/mellow-lrt/src/modules/obol/StakingModule.sol#L81

Tool used

Manual Review

Recommendation

Use Lido's recommendation to utilize the transferShares function so the _amount is accurate, or implement FoT approach, which compares the balance before and after the transfer to determine the actual transferred amount.

Duplicate of #299