Inverse Finance contest - robee's results

Loss Of Precision

This issue is about arithmetic computation that could have been done more percise. The following are places in the codebase in which you multiplied after the divisions. Doing the multiplications at start lead to more accurate calculations. This is a list of places in the code that this appears (Solidity file, line number, actual line):

Code instances:

    Market.sol, 605, uint liquidationFee = repaidDebt * 1 ether / price * liquidationFeeBps / 10000;
    Market.sol, 376, uint minimumCollateral = debt * 1 ether / oracle.viewPrice(address(collateral), collateralFactorBps) * 10000 / collateralFactorBps;
    Market.sol, 359, uint minimumCollateral = debt * 1 ether / oracle.getPrice(address(collateral), collateralFactorBps) * 10000 / collateralFactorBps;

Mult instead div in compares

To improve algorithm precision instead using division in comparison use multiplication in the following scenario:

    Instead a < b / c use a * c < b. 

In all of the big and trusted contracts this rule is maintained.

Code instance:

    Market.sol, 595, require(repaidDebt <= debt * liquidationFactorBps / 10000, "Exceeded liquidation factor");

Missing fee parameter validation

Some fee parameters of functions are not checked for invalid values. Validate the parameters:

Code instances:

    Market.setLiquidationFeeBps (_liquidationFeeBps)
    Oracle.setFeed (feed)

safeApprove of openZeppelin is deprecated

You use safeApprove of openZeppelin although it's deprecated. (see https://github.com/OpenZeppelin/openzeppelin-contracts/blob/566a774222707e424896c0c390a84dc3c13bdcb2/contracts/token/ERC20/utils/SafeERC20.sol#L38) You should change it to increase/decrease Allowance as OpenZeppilin says.

Code instance:

    Deprecated safeApprove in INVEscrow.sol line 49: _token.approve(address(xINV), type(uint).max);

Require with empty message

The following requires are with empty messages. This is very important to add a message for any require. So the user has enough information to know the reason of failure.

Code instances:

    Solidity file: Fed.sol, In line 93 with Empty Require message.
    Solidity file: GovTokenEscrow.sol, In line 67 with Empty Require message.
    Solidity file: INVEscrow.sol, In line 91 with Empty Require message.

Require with not comprehensive message

The following requires has a non comprehensive messages. This is very important to add a comprehensive message for any require. Such that the user has enough information to know the reason of failure:

Code instances:

    Solidity file: DBR.sol, In line 328 with Require message: No deficit
    Solidity file: Fed.sol, In line 104 with Require message: ONLY CHAIR
    Solidity file: Fed.sol, In line 49 with Require message: ONLY GOV
    Solidity file: Fed.sol, In line 58 with Require message: ONLY GOV
    Solidity file: Fed.sol, In line 76 with Require message: ONLY CHAIR
    Solidity file: Fed.sol, In line 67 with Require message: ONLY GOV
    Solidity file: Fed.sol, In line 87 with Require message: ONLY CHAIR

Not verified input

external / public functions parameters should be validated to make sure the address is not 0. Otherwise if not given the right input it can mistakenly lead to loss of user funds.

Code instances:

    Market.sol.forceReplenish user
    GovTokenEscrow.sol.delegate delegatee
    Market.sol.liquidate user
    Oracle.sol.getPrice token
    DBR.sol.approve spender
    DBR.sol.setPendingOperator newOperator_
    Oracle.sol.setPendingOperator newOperator_
    Market.sol.setLender _lender
    BorrowController.sol.allow allowedContract
    Oracle.sol.setFixedPrice token
    Market.sol.setGov _gov
    DBR.sol.transferFrom to
    DBR.sol.accrueDueTokens user
    GovTokenEscrow.sol.initialize _beneficiary
    DBR.sol.onRepay user
    Fed.sol.changeGov _gov
    DBR.sol.transferFrom from
    Market.sol.withdrawOnBehalf from
    DBR.sol.removeMinter minter_
    DBR.sol.onForceReplenish user
    DBR.sol.addMinter minter_
    BorrowController.sol.deny deniedContract
    INVEscrow.sol.initialize _beneficiary
    Fed.sol.changeChair _chair
    INVEscrow.sol.delegate delegatee
    Market.sol.repay user
    GovTokenEscrow.sol.pay recipient
    DBR.sol.permit spender
    Market.sol.setPauseGuardian _pauseGuardian
    Oracle.sol.setFeed token
    Market.sol.deposit user
    DBR.sol.onBorrow user
    BorrowController.sol.setOperator _operator
    INVEscrow.sol.pay recipient
    DBR.sol.addMarket market_
    DBR.sol.mint to
    SimpleERC20Escrow.sol.pay recipient
    Market.sol.borrowOnBehalf from
    DBR.sol.transfer to

Solidity compiler versions mismatch

The project is compiled with different versions of solidity, which is not recommended because it can lead to undefined behaviors.

Code instance:

Use safe math for solidity version <8

You should use safe math for solidity version <8 since there is no default over/under flow check it suchversions of solidity.

Code instances:

    The contract Test.sol doesn't use safe math and is of solidity version < 8
    The contract console.sol doesn't use safe math and is of solidity version < 8
    The contract console2.sol doesn't use safe math and is of solidity version < 8
    The contract Script.sol doesn't use safe math and is of solidity version < 8
    The contract Vm.sol doesn't use safe math and is of solidity version < 8

Not verified owner

    owner param should be validated to make sure the owner address is not address(0).
    Otherwise if not given the right input all only owner accessible functions will be unaccessible.
    
    

Code instance:

    DBR.sol.permit owner

Two Steps Verification before Transferring Ownership

The following contracts have a function that allows them an admin to change it to a different address. If the admin accidentally uses an invalid address for which they do not have the private key, then the system gets locked. It is important to have two steps admin change where the first is announcing a pending new admin and the new address should then claim its ownership. A similar issue was reported in a previous contest and was assigned a severity of medium: code-423n4/2021-06-realitycards-findings#105

Code instance:

    Market.sol

Never used parameters

Those are functions and parameters pairs that the function doesn't use the parameter. In case those functions are external/public this is even worst since the user is required to put value that never used and can misslead him and waste its time.

Code instances:

    Market.sol: function setGov parameter _gov isn't used. (setGov is public)
    Oracle.sol: function setFeed parameter tokenDecimals isn't used. (setFeed is public)
    Market.sol: function setOracle parameter _oracle isn't used. (setOracle is public)
    Oracle.sol: function setPendingOperator parameter newOperator_ isn't used. (setPendingOperator is public)
    Market.sol: function setBorrowController parameter _borrowController isn't used. (setBorrowController is public)
    BorrowController.sol: function allow parameter allowedContract isn't used. (allow is public)
    Market.sol: function setPauseGuardian parameter _pauseGuardian isn't used. (setPauseGuardian is public)
    Oracle.sol: function setFeed parameter token isn't used. (setFeed is public)
    Market.sol: function setLender parameter _lender isn't used. (setLender is public)
    BorrowController.sol: function deny parameter deniedContract isn't used. (deny is public)
    Oracle.sol: function setFixedPrice parameter price isn't used. (setFixedPrice is public)
    BorrowController.sol: function setOperator parameter _operator isn't used. (setOperator is public)
    Oracle.sol: function setFixedPrice parameter token isn't used. (setFixedPrice is public)
    Oracle.sol: function setFeed parameter feed isn't used. (setFeed is public)

Dangerous usage of tx.origin

Use of tx.origin for authorization may be abused by a MITM malicious contract forwarding calls from the legitimate user who interacts with it. Use msg.sender instead.

Code instance:

    BorrowController.sol, 47: if(msgSender == tx.origin) return true;

Open TODOs

Open TODOs can hint at programming or architectural errors that still need to be fixed. These files has open TODOs:

Code instance:

Open TODO in INVEscrow.sol line 34 : xINV = _xINV; // TODO: Test whether an immutable variable will persist across proxies

Check transfer receiver is not 0 to avoid burned money

Transferring tokens to the zero address is usually prohibited to accidentally avoid "burning" tokens by sending them to an unrecoverable zero address.

Code instances:

    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L399
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/DBR.sol#L176
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/DBR.sol#L291
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L537
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/DBR.sol#L378
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/DBR.sol#L200
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/DBR.sol#L364
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/escrows/GovTokenEscrow.sol#L45
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/escrows/INVEscrow.sol#L63
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/escrows/SimpleERC20Escrow.sol#L38
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L205
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L570
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L602
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Fed.sol#L135
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L280

Add a timelock

To give more trust to users: functions that set key/critical variables should be put behind a timelock.

Code instances:

    https://github.com/code-423n4/2022-10-inverse/tree/main/src/DBR.sol#L53
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L183
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L124
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L136

Must approve 0 first

Some tokens (like USDT) do not work when changing the allowance from an existing non-zero allowance value. They must first be approved by zero and then the actual allowance must be approved.

Code instance:

approve without approving 0 first INVEscrow.sol, 49, _token.approve(address(xINV), type(uint).max);

Unsafe Cast

use openzeppilin's safeCast in:

Code instances:

    https://github.com/code-423n4/2022-10-inverse/tree/main/lib/forge-std/src/Script.sol#L17 : unsafe cast uint8(nonce)
    https://github.com/code-423n4/2022-10-inverse/tree/main/lib/forge-std/src/Script.sol#L17 : unsafe cast uint16(nonce)
    https://github.com/code-423n4/2022-10-inverse/tree/main/lib/forge-std/src/Script.sol#L17 : unsafe cast uint32(nonce)
    https://github.com/code-423n4/2022-10-inverse/tree/main/lib/forge-std/src/Script.sol#L17 : unsafe cast uint24(nonce)
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/DBR.sol#L146 : unsafe cast int(accrued)

Div by 0

Division by 0 can lead to accidentally revert, (An example of a similar issue - https://github.com/code-423n4/2021-10-defiprotocol-findings/issues/84)

Code instances:

    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Oracle.sol#L137 collateralFactorBps might be 0
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L597 price might be 0
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Market.sol#L606 price might be 0
    https://github.com/code-423n4/2022-10-inverse/tree/main/lib/forge-std/src/Test.sol#L765 a, b, absB might be 0
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/Oracle.sol#L98 collateralFactorBps might be 0

approve return value is ignored

Some tokens don't correctly implement the EIP20 standard and their approve function returns void instead of a success boolean. Calling these functions with the correct EIP20 function signatures will always revert. Tokens that don't correctly implement the latest EIP20 spec, like USDT, will be unusable in the mentioned contracts as they revert the transaction because of the missing return value. We recommend using OpenZeppelin’s SafeERC20 versions with the safeApprove function that handle the return value check as well as non-standard-compliant tokens. The list of occurrences in format (solidity file, line number, actual line)

Code instance:

INVEscrow.sol, 49, _token.approve(address(xINV), type(uint).max);

transfer return value of a general ERC20 is ignored

Need to use safeTransfer instead of transfer. As there are popular tokens, such as USDT that transfer/trasnferFrom method doesn’t return anything. The transfer return value has to be checked (as there are some other tokens that returns false instead revert), that means you must

1. Check the transfer return value Another popular possibility is to add a whiteList. Those are the appearances (solidity file, line number, actual line):

Code instances:

    Fed.sol, 135 (takeProfit), dola.transfer(gov, profit);
    GovTokenEscrow.sol, 45 (pay), token.transfer(recipient, amount);
    SimpleERC20Escrow.sol, 38 (pay), token.transfer(recipient, amount);
    Market.sol, 280 (deposit), collateral.transferFrom(msg.sender, address(escrow), amount);
    INVEscrow.sol, 63 (pay), token.transfer(recipient, amount);

More efficient Struct packing of StdStorage in the contract Test.sol

    The following structs could change the order of their stored elements to decrease memory uses.
    and number of occupied slots. Therefore will save gas at every store and load from memory.
    

In Test.sol, StdStorage is optimized to: 6 slots from: 7 slots. The new order of types (you choose the actual variables): 1. mapping 2. mapping 3. bytes32[] 4. uint256 5. bytes32 6. address 7. bytes4

Unnecessary equals boolean

Boolean variables can be checked within conditionals directly without the use of equality operators to true/false.

Code instances:

    BorrowController.sol, 47: if(msgSender == tx.origin) return true;
    DBR.sol, 350: require(minters[msg.sender] == true || msg.sender == operator, "ONLY MINTERS OR OPERATOR");

Unused state variables

Unused state variables are gas consuming at deployment (since they are located in storage) and are a bad code practice. Removing those variables will decrease deployment gas cost and improve code quality. This is a full list of all the unused storage variables we found in your code base.

Code instances:

    Script.sol, IS_SCRIPT
    DBR.sol, decimals

Storage double reading. Could save SLOAD

Reading a storage variable is gas costly (SLOAD). In cases of multiple read of a storage variable in the same scope, caching the first read (i.e saving as a local variable) can save gas and decrease the overall gas uses. The following is a list of functions and the storage variables that you read twice:

Code instances:

    Market.sol: gov is read twice in pauseBorrows
    Market.sol: lender is read twice in recall

Rearrange state variables

You can change the order of the storage variables to decrease memory uses.

Code instances:

In DBR.sol,rearranging the storage fields can optimize to: 9 slots from: 10 slots. The new order of types (you choose the actual variables): 1. string 2. string 3. uint256 4. uint 5. uint 6. uint256 7. bytes32 8. address 9. uint8 10. address

In Market.sol,rearranging the storage fields can optimize to: 17 slots from: 18 slots. The new order of types (you choose the actual variables): 1. IDolaBorrowingRights 2. IBorrowController 3. IERC20 4. IERC20 5. IOracle 6. uint 7. uint 8. uint 9. uint 10. uint 11. uint 12. uint256 13. bytes32 14. address 15. bool 16. bool 17. address 18. address 19. address

Short the following require messages

The following require messages are of length more than 32 and we think are short enough to short them into exactly 32 characters such that it will be placed in one slot of memory and the require function will cost less gas. The list:

Code instances:

    Solidity file: DBR.sol, In line 63, Require message length to shorten: 34, The message: replenishment price must be over 0
    Solidity file: DBR.sol, In line 326, Require message length to shorten: 38, The message: Only markets can call onForceReplenish

Use != 0 instead of > 0

Using != 0 is slightly cheaper than > 0. (see https://github.com/code-423n4/2021-12-maple-findings/issues/75 for similar issue)

Code instances:

    Market.sol, 605: change 'liquidationFeeBps > 0' to 'liquidationFeeBps != 0'
    Market.sol, 184: change '_liquidationIncentiveBps > 0' to '_liquidationIncentiveBps != 0'
    Market.sol, 195: change '_liquidationFeeBps > 0' to '_liquidationFeeBps != 0'
    Market.sol, 162: change '_liquidationFactorBps > 0' to '_liquidationFactorBps != 0'
    DBR.sol, 373: change 'balance > 0' to 'balance != 0'
    Market.sol, 162: change 'liquidationFactorBps > 0' to 'liquidationFactorBps != 0'
    Market.sol, 184: change 'liquidationIncentiveBps > 0' to 'liquidationIncentiveBps != 0'
    DBR.sol, 63: change 'newReplenishmentPriceBps_ > 0' to 'newReplenishmentPriceBps_ != 0'
    Market.sol, 173: change '_replenishmentIncentiveBps > 0' to '_replenishmentIncentiveBps != 0'
    Market.sol, 195: change 'liquidationFeeBps > 0' to 'liquidationFeeBps != 0'
    Market.sol, 75: change '_liquidationIncentiveBps > 0' to '_liquidationIncentiveBps != 0'
    DBR.sol, 123: change 'balance > 0' to 'balance != 0'
    Market.sol, 75: change 'liquidationIncentiveBps > 0' to 'liquidationIncentiveBps != 0'
    DBR.sol, 195: change 'balance > 0' to 'balance != 0'
    Market.sol, 592: change 'repaidDebt > 0' to 'repaidDebt != 0'
    DBR.sol, 171: change 'balance > 0' to 'balance != 0'
    Market.sol, 607: change 'balance > 0' to 'balance != 0'
    Market.sol, 173: change 'replenishmentIncentiveBps > 0' to 'replenishmentIncentiveBps != 0'
    Test.sol, 735: change 'a > 0' to 'a != 0'

Use unchecked to save gas for certain additive calculations that cannot overflow

You can use unchecked in the following calculations since there is no risk to overflow:

Code instance:

    Test.sol (L#33) - vm.warp(block.timestamp + time);

Consider inline the following functions to save gas

You can inline the following functions instead of writing a specific function to save gas.
(see https://github.com/code-423n4/2021-11-nested-findings/issues/167 for a similar issue.)


    Script.sol, addressFromLast20Bytes, { return address(uint160(uint256(bytesValue))); }

Inline one time use functions

The following functions are used exactly once. Therefore you can inline them and save gas and improve code clearness.

Code instances:

    Market.sol, getWithdrawalLimitInternal
    Market.sol, createEscrow

Upgrade pragma to at least 0.8.4

Using newer compiler versions and the optimizer gives gas optimizations and additional safety checks are available for free.

The advantages of versions 0.8.* over <0.8.0 are:

    1. Safemath by default from 0.8.0 (can be more gas efficient than library based safemath.)
    2. Low level inliner : from 0.8.2, leads to cheaper runtime gas. Especially relevant when the contract has small functions. For example, OpenZeppelin libraries typically have a lot of small helper functions and if they are not inlined, they cost an additional 20 to 40 gas because of 2 extra jump instructions and additional stack operations needed for function calls.
    3. Optimizer improvements in packed structs: Before 0.8.3, storing packed structs, in some cases used an additional storage read operation. After EIP-2929, if the slot was already cold, this means unnecessary stack operations and extra deploy time costs. However, if the slot was already warm, this means additional cost of 100 gas alongside the same unnecessary stack operations and extra deploy time costs.
    4. Custom errors from 0.8.4, leads to cheaper deploy time cost and run time cost. Note: the run time cost is only relevant when the revert condition is met. In short, replace revert strings by custom errors.

Code instances:

    Test.sol
    Script.sol
    console2.sol
    console.sol
    Vm.sol

Do not cache msg.sender

We recommend not to cache msg.sender since calling it is 2 gas while reading a variable is more.

Code instances:

    https://github.com/code-423n4/2022-10-inverse/tree/main/src/escrows/GovTokenEscrow.sol#L32
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/escrows/INVEscrow.sol#L46
    https://github.com/code-423n4/2022-10-inverse/tree/main/src/escrows/SimpleERC20Escrow.sol#L27