Mimo DeFi contest - luduvigo's results

Lines of code

https://github.com/code-423n4/2022-04-mimo/blob/main/core/contracts/liquidityMining/v2/PARMinerV2.sol#L361

Vulnerability details

Impact

Misleading variable usage in function _refreshPAR in PARMinerV2 contract.

Proof of Concept

The _refreshPAR function is checking a global variable that is competing with the parameter passed by the caller, but that should refer to the same chunk of data.

There seems to be some sense of doing this in some ways of calling the function, but more confusing code leads to more bugs or lower protocol adoption.

function _refreshPAR(uint256 newTotalStake) internal {
  if (_totalStake == 0) {
    return;
  }
  uint256 currentParBalance = _par.balanceOf(address(this)).sub(newTotalStake);
  uint256 parReward = currentParBalance.sub(_parBalanceTracker);

  _parBalanceTracker = currentParBalance;
  _accParAmountPerShare = _accParAmountPerShare.add(parReward.rayDiv(_totalStakeWithBoost));
} 

Tools Used

Hardhat gas optimizer

Recommended Mitigation Steps

Rewrite the function and make sure it doesn't lead to confusing and possibly misleading code.