Increasing relayer fee could break minting of deposits

Summary

If the relayer fee is increased, the function to mint deposits could be broken due to underflow.

Vulnerability Detail

The function mintDepositInQueue calculates the amount of shares to mint as difference of assets and relayerFee:

_mintShares(
    queue[i].receiver,
    _epochId,
    queue[i].assets - relayerFee
);

When the queue item is inserted it is asserted through the minRequiredDeposit modifier that queue[i].assets is at least equal to the relayer fee. However, if the relayer fee is increased, this invariant can be broken. An attacker would be able to frontrun the relayer fee increase with the insert of an item that only covers the old fee. This would cause the mintDepositInQueue to revert and all unprocessed items that are still in queue before the malicious item to not be processable.

Impact

Harm to users, break of functionality.

Code Snippet

https://github.com/sherlock-audit/2023-03-Y2K/blob/ae7f210d8fbf21b9abf09ef30edfa548f7ae1aef/Earthquake/src/v2/Carousel/Carousel.sol#L334-L338

Tool used

Manual Review

Recommendation

Check that queue[i].assets >= relayerFee and pop if not

Duplicate of #1

sherlock-audit / 2023-03-Y2K-judging

minhtrng - Increasing relayer fee could break minting of deposits #485