Issue M-1: Pairs with "MAX_FEE" can revert due to rounding inconsistencies

Source: https://github.com/sherlock-audit/2024-02-rubicon-finance-judging/issues/51

Found by

KingNFT, Kow, cawfree, mstpr-brainbot

Summary

If the pair has set the max fee by the fee controller admin which is "1_000" then depending on the amount to be swapped, the tx can revert due to rounding error.

Vulnerability Detail

When the fee amount is calculated inside the RubiconFeeController, the fee amount is rounded down.

uint256 feeAmount = fee.applyFee  
                ? order.outputs[i].amount.mulDivUp(fee.fee, DENOM)  
                : order.outputs[i].amount.mulDivUp(baseFee, DENOM);  

then, ProtocolFees abstract contract will do a double check on the fee taken as follows:

if (feeOutput.amount > tokenValue.mulDivDown(MAX_FEE, DENOM)) {  
                revert FeeTooLarge(  
                    feeOutput.token,  
                    feeOutput.amount,  
                    feeOutput.recipient  
                );  
            }  

As we can see, it uses mulDivDown, so if the calculation in the FeeController rounds up, the transaction will revert.

Textual PoC:
Suppose the fee pair is set to "1_000" for tokens A and B.
Alice sends an order to sell "111111111111111111111" (111.11 in 18 decimals) token A for token B.

Within the fee controller, the fee amount will be calculated as:
111111111111111111111 * 1000 / 100_000 (roundUp) = 1111111111111111112

Subsequently, during execution, within the ProtocolFees contract, the maximum fee amount will be computed as:
111111111111111111111 * 1000 / 100_000 (roundDown) = 1111111111111111111

Consequently, the transaction will revert because 1111111111111111111 > 1111111111111111112.

Coded PoC:

// forge test --match-contract GladiusReactorTest --match-test test_FeesRounding -vv  
    function test_FeesRounding(uint amount) external {  
        // @dev there will be plenty of values reverting this test.   
        vm.assume(amount <= type(uint128).max);  
        vm.assume(amount >= 1e6);  
  
        uint DENOM = 100_000;  
        uint FEE = 1_000;  
  
        uint resultDown = FixedPointMathLib.mulDivDown(amount, FEE, DENOM);  
        uint resultUp = FixedPointMathLib.mulDivUp(amount, FEE, DENOM);  
  
        assertEq(resultDown, resultUp);  
    }  

Impact

As stated in README:
Fee Controller Can DOS Trading Activity. Note, that, as said above, the resulting output shouldn't overflow MAX_FEE, but other possibilities of reverts are known/acceptable. Any fee setting in range 0<MAX_FEE should not revert and if it reverts then its acceptable. Hence, I'll label this as medium.

Code Snippet

https://github.com/sherlock-audit/2024-02-rubicon-finance/blob/11cac67919e8a1303b3a3177291b88c0c70bf03b/gladius-contracts-internal/src/fee-controllers/RubiconFeeController.sol#L63-L116

https://github.com/sherlock-audit/2024-02-rubicon-finance/blob/11cac67919e8a1303b3a3177291b88c0c70bf03b/gladius-contracts-internal/src/base/ProtocolFees.sol#L39-L105

Tool used

Manual Review

Recommendation

Discussion

sherlock-admin

1 comment(s) were left on this issue during the judging contest.

0xAadi commented:

sherlock-admin2

Escalate

Invalid this already a known issue reported in the open zeppelin audit of uniswapx
https://github.com/Uniswap/UniswapX/blob/main/audit/v1.1/OpenZeppelin.pdf
Look for L-02

from contest readme

Please list any known issues/acceptable risks that should not result in a valid finding.
From OZ audit - https://github.com/Uniswap/UniswapX/blob/main/audit/v1.1/OpenZeppelin.pdf

The uniswapX decided to keep this issue as wont fix.

also from rubicon readme

GladiusReactor is based on UniswapX’s ExclusiveDutchOrderReactor and intended to support ExclusiveDutchOrders.

Changes in fee calculation may result in support for ExclusiveDutchOrders not working. Therefore this should be set as wont fix and also invalid.

You've deleted an escalation for this issue.

daoio

the issue is valid, because the audit doc specifically states that while a DoS possibility from a fee-controller is a known and acceptable issue, the possibility of the MAX_FEE overflow isn't acceptable.
Moreover, it not only notes a likelihood of a rounding error, but the root of its occurency - an incosistency between calculations in RubiconFeeController and ProtocolFees, where validation of the fee calculation is performed with a different function call (mulDivDown instead of mulDivUp)

ArnieGod

@daoio you are right, oversight on my part will remove escalation.

sherlock-admin

The protocol team fixed this issue in PR/commit https://github.com/RubiconDeFi/gladius-contracts-internal/pull/16.

sherlock-admin

The Lead Senior Watson signed-off on the fix.