tornado-governance/contracts/v4-patch/GovernancePatchUpgrade.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.12;
pragma experimental ABIEncoderV2;

import "../v1/Governance.sol";
import "../v3-relayer-registry/GovernanceStakingUpgrade.sol";

contract GovernancePatchUpgrade is GovernanceStakingUpgrade {
  mapping(uint256 => bytes32) public proposalCodehashes;

  constructor(
    address stakingRewardsAddress,
    address gasCompLogic,
    address userVaultAddress
  ) public GovernanceStakingUpgrade(stakingRewardsAddress, gasCompLogic, userVaultAddress) {}

  /// @notice Return the version of the contract
  function version() external pure virtual override returns (string memory) {
    return "4.patch-exploit";
  }

  /**
   * @notice Execute a proposal
   * @dev This upgrade should protect against Metamorphic contracts by comparing the proposal's extcodehash with a stored one
   * @param proposalId The proposal's ID
   */
  function execute(uint256 proposalId) public payable virtual override(Governance) {
    require(msg.sender != address(this), "Governance::propose: pseudo-external function");

    Proposal storage proposal = proposals[proposalId];

    address target = proposal.target;

    bytes32 proposalCodehash;

    assembly {
      proposalCodehash := extcodehash(target)
    }

    require(proposalCodehash == proposalCodehashes[proposalId], "Governance::propose: metamorphic contracts not allowed");

    super.execute(proposalId);
  }

  /**
   * @notice Internal function called from propoese
   * @dev This should store the extcodehash of the proposal contract
   * @param proposer proposer address
   * @param target smart contact address that will be executed as result of voting
   * @param description description of the proposal
   * @return proposalId new proposal id
   */
  function _propose(
    address proposer,
    address target,
    string memory description
  ) internal virtual override(Governance) returns (uint256 proposalId) {
    // Implies all former predicates were valid
    proposalId = super._propose(proposer, target, description);

    bytes32 proposalCodehash;

    assembly {
      proposalCodehash := extcodehash(target)
    }

    proposalCodehashes[proposalId] = proposalCodehash;
  }
}