Constant variables using keccak can be immutable

[code423n4]

Handle

ye0lde

Vulnerability details

Impact

Changing the variables from constant to immutable will reduce keccak operations and save gas.

A previous finding with additional explanation and a pointer to the ethereum/solidity issue is here:
code-423n4/2021-10-slingshot-findings#3

Proof of Concept

These variables can simply be changed from constant to immutable:
https://github.com/livepeer/arbitrum-lpt-bridge/blob/ebf68d11879c2798c5ec0735411b08d0bea4f287/contracts/L1/gateway/L1Migrator.sol#L114
https://github.com/livepeer/arbitrum-lpt-bridge/blob/ebf68d11879c2798c5ec0735411b08d0bea4f287/contracts/L1/gateway/L1Migrator.sol#L116
https://github.com/livepeer/arbitrum-lpt-bridge/blob/ebf68d11879c2798c5ec0735411b08d0bea4f287/contracts/L1/gateway/L1Migrator.sol#L121

Additional changes are needed for these variables since they are used in the constructor:
https://github.com/livepeer/arbitrum-lpt-bridge/blob/ebf68d11879c2798c5ec0735411b08d0bea4f287/contracts/L1/gateway/L1Migrator.sol#L111
https://github.com/livepeer/arbitrum-lpt-bridge/blob/ebf68d11879c2798c5ec0735411b08d0bea4f287/contracts/L2/gateway/L2Migrator.sol#L59
https://github.com/livepeer/arbitrum-lpt-bridge/blob/ebf68d11879c2798c5ec0735411b08d0bea4f287/contracts/L2/token/LivepeerToken.sol#L9-L10
https://github.com/livepeer/arbitrum-lpt-bridge/blob/ebf68d11879c2798c5ec0735411b08d0bea4f287/contracts/ControlledGateway.sol#L13

Here's an example of the changes needed in the constructor for:
https://github.com/livepeer/arbitrum-lpt-bridge/blob/ebf68d11879c2798c5ec0735411b08d0bea4f287/contracts/ControlledGateway.sol#L13

contract ControlledGateway is AccessControl, Pausable {
    bytes32 public immutable GOVERNOR_ROLE;  

    address public immutable l1Lpt;
    address public immutable l2Lpt;

    constructor(address _l1Lpt, address _l2Lpt) {
        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
        _setRoleAdmin(GOVERNOR_ROLE = keccak256("GOVERNOR_ROLE"), DEFAULT_ADMIN_ROLE);

        l1Lpt = _l1Lpt;
        l2Lpt = _l2Lpt;
    }

    function pause() external onlyRole(GOVERNOR_ROLE) {
        _pause();
    }

    function unpause() external onlyRole(GOVERNOR_ROLE) {
        _unpause();
    }
}

Tools Used

Visual Studio Code, Remix

Recommended Mitigation Steps

Change the constant variables to immutable as described in the POC.

[yondonfu]

Fixed in livepeer/arbitrum-lpt-bridge@46fa6b9 livepeer/arbitrum-lpt-bridge@a7fb964 livepeer/arbitrum-lpt-bridge@0eeec6b livepeer/arbitrum-lpt-bridge@2058a8a