Dapper Chartreuse Wolf - There is loss of funds in EthosBouch::calcFee

[sherlock-admin2]

Dapper Chartreuse Wolf

High

There is loss of funds in EthosBouch::calcFee

Impact

Calculating Fee as Floor makes huge funds loss for the protocol. EthosVouch::calcFee

Because if the calculation becomes 1.5 then it will be floor to 1
If we consider this for a lot of calls then it makes a huge impact on the protocol.

PoC

Here is the code
EthosVouch::calcFee

function calcFee(uint256 total, uint256 feeBasisPoints) internal pure returns (uint256 fee) {
    /*
     * Formula derivation:
     * 1. total = deposit + fee
     * 2. fee = deposit * (feeBasisPoints/10000)
     * 3. total = deposit + deposit * (feeBasisPoints/10000)
     * 4. total = deposit * (1 + feeBasisPoints/10000)
     * 5. deposit = total / (1 + feeBasisPoints/10000)
     * 6. fee = total - deposit
     * 7. fee = total - (total * 10000 / (10000 + feeBasisPoints))
     */
    return
      total -
      (total.mulDiv(BASIS_POINT_SCALE, (BASIS_POINT_SCALE + feeBasisPoints), Math.Rounding.Floor));  <@
  }

Mitigation

Make Floor to Ceil

function calcFee(uint256 total, uint256 feeBasisPoints) internal pure returns (uint256 fee) {
    /*
     * Formula derivation:
     * 1. total = deposit + fee
     * 2. fee = deposit * (feeBasisPoints/10000)
     * 3. total = deposit + deposit * (feeBasisPoints/10000)
     * 4. total = deposit * (1 + feeBasisPoints/10000)
     * 5. deposit = total / (1 + feeBasisPoints/10000)
     * 6. fee = total - deposit
     * 7. fee = total - (total * 10000 / (10000 + feeBasisPoints))
     */
-    return
-     total -
-    (total.mulDiv(BASIS_POINT_SCALE, (BASIS_POINT_SCALE + feeBasisPoints), Math.Rounding.Floor));

+      return
+      total -
+      (total.mulDiv(BASIS_POINT_SCALE, (BASIS_POINT_SCALE + feeBasisPoints), Math.Rounding.Ceil));
  }