LP Rewards can be increased infinitely by a malicious liquidity provider

[code423n4]

Lines of code

https://github.com/code-423n4/2022-12-tigris/blob/588c84b7bb354d20cbca6034544c4faa46e6a80e/contracts/BondNFT.sol#L178
https://github.com/code-423n4/2022-12-tigris/blob/588c84b7bb354d20cbca6034544c4faa46e6a80e/contracts/Lock.sol#L38

Vulnerability details

Impact

LP Rewards can be increased infinitely by a malicious liquidity provider

Proof of Concept

A Bond NFT holder can claim pending rewards from a bond using the function Lock.claim().

function claim(
    uint256 _id
) public returns (address) {
    claimGovFees();
    (uint _amount, address _tigAsset) = bondNFT.claim(_id, msg.sender);
    IERC20(_tigAsset).transfer(msg.sender, _amount);
    return _tigAsset;
}

This claim() function calls the BondNFT.claim() and if the bond is an expired one there is an additional process to reimburse the rewards for that expired bond.

So the protocol calculates how much rewards were allocated to that expired bond from the bond.expireEpoch to epoch[bond.asset] and reimburse that to the current accRewardsPerShare.

The problem is it calculates the _pendingDelta using the bond.expireEpoch and epoch[bond.asset] while this can be called multiple times.

    function claim(
        uint _id,
        address _claimer
    ) public onlyManager() returns(uint amount, address tigAsset) {
        Bond memory bond = idToBond(_id);
        require(_claimer == bond.owner, "!owner");
        amount = bond.pending;
        tigAsset = bond.asset;
        unchecked {
            if (bond.expired) {
                uint _pendingDelta = (bond.shares * accRewardsPerShare[bond.asset][epoch[bond.asset]] / 1e18 - bondPaid[_id][bond.asset]) - (bond.shares * accRewardsPerShare[bond.asset][bond.expireEpoch-1] / 1e18 - bondPaid[_id][bond.asset]);
                if (totalShares[bond.asset] > 0) {
                    accRewardsPerShare[bond.asset][epoch[bond.asset]] += _pendingDelta*1e18/totalShares[bond.asset];
                }
            }
            bondPaid[_id][bond.asset] += amount;
        }
        IERC20(tigAsset).transfer(manager, amount);
        emit ClaimFees(tigAsset, amount, _claimer, _id);
    }

As we can see, the claim() function does not do anything to release the expired bond or remember the time that this reimbursement happens.
So an expired bond holder can trigger this function by calling Lock.claim() repeatedly to increase the accRewardsPerShare.
This means the rewards for liquidity providers can be increased to infinite.

Tools Used

Manual Review

Recommended Mitigation Steps

Release the bond if expired in the function BondNFT.claim() or remember the last time that the _pendingDelta was calculated to make sure the reimbursement does not happen more than once.

[c4-judge]

GalloDaSballo marked the issue as duplicate of #68

[c4-judge]

GalloDaSballo marked the issue as duplicate of #170

[c4-judge]

GalloDaSballo marked the issue as satisfactory