[L-03] Implicit double-voting prevention in DAO voting system

[softstackio]

Severity: Low
Likelihood: Medium

Description:

The DiamondDao contract implements a voting system for proposals using an EnumerableSet to track voters and a mapping to store vote records. While the current implementation implicitly prevents double-voting by overwriting previous votes, it lacks
explicit checks and clear feedback mechanisms to handle attempted double-voting scenarios.

Recommendation:

1. Implement an explicit check for existing votes:

function _submitVote(address voter, uint256 proposalId, Vote _vote, string memory reason) private {
    _requireState(proposalId, ProposalState.Active);
    require(!_proposalVoters[proposalId].contains(voter), "Already
voted");
    require(_proposalVoters[proposalId].add(voter), "Failed to record
voter");
    votes[proposalId][voter] = VoteRecord({
        timestamp: uint64(block.timestamp),
        vote: _vote,
        reason: reason
    });
}

2. Consider adding a separate function for vote changes if that's an intended feature:

function changeVote(uint256 proposalId, Vote newVote) external {
    require(_proposalVoters[proposalId].contains(msg.sender), "No
previous vote found");
    // Update vote logic here
}