Fjord Token Staking

Summary

In modifier _checkEpochRollover() pending rewards calculation has been calculated incorrectly

Vulnerability Details

Internal accounting:
New staked: per epoch, total fjord tokens staked also includes new vested-staked amount.
New vestedStaked: per epoch total vested-staked amount
Total staked: contains total fjord tokens staked excluding current epoch amount + total vestedStaked.
Total vestedStaked: contains the total vested-staked amount before the current epoch.
Total rewards: added reward amount by the reward admin

Now current balance would be the balance of the contract which would be:
Total staked+ new staked+ rewards.

Now _checkEpochRollover modifier main functionality is to update the epoch roll over and and also update the pending rewards amount
Here lies our main issue:

Pending rewards calculation would be: current balance of the contract- (total accounted tokens- rewards)
i.e pendingRewards = currentBalance - (totalStaked + newStaked - totalRewards);
which is different from what has been implemented this is due to the double counting of the amount that has been done in variables.

Impact

Incorrect calculation of rewards

Tools Used

Manual review

Recommendations

Implement the right calculations as mentioned in the vulnerability detail above.