Description

When calling redeemRequest(0), an integer underflow will occur due to fees rounding up:

function previewRedeem(uint256 shares) public view virtual override returns (uint256) {
    uint256 assets = super.previewRedeem(shares);
!    return assets - _feeOnTotal(assets, _getFeeBasisPoints());
}

// [...]
function _feeOnTotal(uint256 assets, uint256 _feeBasisPoints) private pure returns (uint256) {
    return assets.mulDiv(_feeBasisPoints, _feeBasisPoints + _BASIS_POINT_SCALE, Math.Rounding.Ceil);
}

Impact

There is no security impact of this. However, the error may be confusing.

If the underflow did not occur in previewRedeem, a bug would exist where users could grief the vault by redeeming no assets, which burns one base unit of asset every time.

Recommendations

Require that shares is greater than 0 in redeemRequest.

Remediation

This issue has been acknowledged by Solera Markets, and a fix was implemented in PR #10↗.