Pillar

1 Executive Summary

This report presents the results of our engagement with Pillar Project to review Pillar accounts, wallets, and payment network.

The review was conducted over two weeks, from November 23, 2020 to Dec 4, 2020 by Shayan Eskandari and Sergii Kravchenko.

2 Scope

Our review focused on the commit hash 55ba306582a007b6e0f9c35bdba92a94dc85829c. The list of files in scope can be found in the Appendix.

Even though the files in the scope were clear and the solidity code is well written, the lack of documentation and work flow specification (off-chain with on-chain components) resulted in less in depth review of the overall system.

Update January 2021: Pillar team has worked on the issues reported in this review and their comments has been added to each section. Note that the fixes were not reviewed by ConsenSys Diligence.

3 Recommendations

    require(
      to != address(0),
      "cannot send to address 0x0"
    );

    require(
      to != address(this),
    "cannot send to the contract address"
    );

4 Trust Model

In any system, it’s important to identify what trust is expected/required between various actors. For this audit, we established the following trust model:

• The system is semi-trusted. The main point of centralization is the guardians’ mechanism. The guardians are signing messages that are needed to commit a payment channel to the smart contract. When doing so, they are checking that the sender account has enough funds to make the payment. If the guardians go offline, users are still able to withdraw funds using a complex mechanism. The main risk is that if a guardian goes malicious, it can approve double-spending, resulting in stealing some funds.

5 Findings

Each issue has an assigned severity:

• Minor issues are subjective in nature. They are typically suggestions around best practices or readability. Code maintainers should use their own judgment as to whether to address such issues.
• Medium issues are objective in nature but are not security vulnerabilities. These should be addressed unless there is a clear reason not to.
• Major issues are security vulnerabilities that may not be directly exploitable or may require certain conditions in order to be exploited. All major issues should be addressed.
• Critical issues are directly exploitable security vulnerabilities that need to be fixed.

address sender = _hashPrimaryTypedData(
  _hashTypedData(
    nonce,
    to,
    data
  )
).recoverAddress(senderSignature);

accounts[account].owners[owner].removedAtBlockNumber = block.number;

emit AccountOwnerRemoved(
  account,
  owner
);

function _verifySender(
  address account
)
  private
  returns (address)
{
  address sender = _getContextSender();

  if (!accounts[account].owners[sender].added) {
    require(
      accounts[account].salt == 0
    );

    bytes32 salt = keccak256(
      abi.encodePacked(sender)
    );

    require(
      account == _computeAccountAddress(salt)
    );

    accounts[account].salt = salt;
    accounts[account].owners[sender].added = true;

    emit AccountOwnerAdded(
      account,
      sender
    );
  }

  return sender;
}

function withdrawDeposit(
  address token
)
  external
{
  address owner = _getContextAccount();
  uint256 lockedUntil = deposits[owner].withdrawalLockedUntil[token];

  /* solhint-disable not-rely-on-time */

  if (lockedUntil != 0 && lockedUntil <= now) {
    deposits[owner].withdrawalLockedUntil[token] = 0;

    address depositAccount = deposits[owner].account;
    uint256 depositValue;

    if (token == address(0)) {
      depositValue = depositAccount.balance;
    } else {
      depositValue = ERC20Token(token).balanceOf(depositAccount);
    }

    _transferFromDeposit(
      depositAccount,
      owner,
      token,
      depositValue
    );

    emit DepositWithdrawn(
      depositAccount,
      owner,
      token,
      depositValue
    );
  } else {
    _deployDepositAccount(owner);

    lockedUntil = now.add(depositWithdrawalLockPeriod);

    deposits[owner].withdrawalLockedUntil[token] = lockedUntil;

    emit DepositWithdrawalRequested(
      deposits[owner].account,
      owner,
      token,
      lockedUntil
    );
  }
  /* solhint-enable not-rely-on-time */
}

if (deposits[sender].withdrawalLockedUntil[token] > 0) {
  deposits[sender].withdrawalLockedUntil[token] = 0;

if (lockedUntil != 0 && lockedUntil <= now) {
  deposits[owner].withdrawalLockedUntil[token] = 0;

  address depositAccount = deposits[owner].account;
  uint256 depositValue;

  if (token == address(0)) {
    depositValue = depositAccount.balance;
  } else {
    depositValue = ERC20Token(token).balanceOf(depositAccount);
  }

  _transferFromDeposit(
    depositAccount,
    owner,
    token,
    depositValue
  );

  emit DepositWithdrawn(
    depositAccount,
    owner,
    token,
    depositValue
  );
} else {
  _deployDepositAccount(owner);

  lockedUntil = now.add(depositWithdrawalLockPeriod);

  for (uint256 i = 0; i < data.length; i++) {
    require(
      to[i] != address(0)
    );

    // solhint-disable-next-line avoid-low-level-calls
    (succeeded,) = to[i].call(abi.encodePacked(data[i], account, sender));

    require(
      succeeded
    );
  }
}

  return _deployAccount(
    salt,
    0
  );
}

function _deployAccount(
  bytes32 salt,
  uint256 value
)
  internal
  returns (address)
{
  return address(new Account{salt: salt, value: value}());
}

sbeta> ens listSubdomains name="pillar.eth"
> Subdomains for 'pillar.eth'
> NameHash: '0x5bb02333b1f96385ba28fd63408843cfeee095b32196b718786a56e491e33387'

Appendix 1 - Files in Scope

This audit covered the following files:

• ./src/account/AccountOwnerRegistry.sol
• ./src/account/AccountProofRegistry.sol
• ./src/common/access/Controlled.sol
• ./src/common/access/Guarded.sol
• ./src/common/account/Account.sol
• ./src/common/account/AccountController.sol
• ./src/common/libs/BlockLib.sol
• ./src/common/libs/BytesLib.sol
• ./src/common/libs/SafeMathLib.sol
• ./src/common/libs/SignatureLib.sol
• ./src/common/lifecycle/Initializable.sol
• ./src/common/token/ERC20Token.sol
• ./src/common/typedData/TypedDataContainer.sol
• ./src/ens/ENSController.sol
• ./src/ens/ENSRegistry.sol
• ./src/gateway/Gateway.sol
• ./src/gateway/GatewayRecipient.sol
• ./src/gateway/GatewayRecipientMock.sol
• ./src/payment/PaymentRegistry.sol
• ./src/personal/PersonalAccountRegistry.sol
• ./src/utils/BalanceChecker.sol

Appendix 2 - Disclosure

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