`advanceEpoch()` sets timestamp to a too large value

[code423n4]

Lines of code

https://github.com/code-423n4/2022-06-infinity/blob/main/contracts/token/InfinityToken.sol#L60-L82

Vulnerability details

Impact

Epochs may effectively start later than they are planned.

Proof of Concept

If advanceEpoch() was invoked at a different time than the epoch start, following code will renew the current epoch counter:

previousEpochTimestamp = block.timestamp;

While this should be:

previousEpochTimestamp += epochsPassedSinceLastAdvance * getEpochDuration();

It is also recommended to use cached values in the above code, against what's shown for clarity.

Tools Used

Manual analysis

[HardlyDifficult]

That may be a nice improvement, so that epochs are more predictable. Lowering risk and merging with the warden's QA report https://github.com/code-423n4/2022-06-infinity-findings/issues/285