MyCut
AI First Flight #8
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Submission Details
Severity: low
Valid

Rounding issues

hugoh

Root + Impact

Description

  • In the function Pot::closePotthere are rounding issues. If remainingRewards is bigger than zero this is distributed to the contest manager. The reward is divided by 10 but as in solidity there is no decimals if the remainingRewards for ex is 9 the manager does not get any money. And this remaining is locked in the contract.

  • Similar issue could happen when the reward is distributed between the players. For ex: if there are 10 players but the remainingRewards is 9. None of them get any money.

function closePot() external onlyOwner {
if (block.timestamp - i_deployedAt < 90 days) {
revert Pot__StillOpenForClaim();
}
if (remainingRewards > 0) {
@> uint256 managerCut = remainingRewards / managerCutPercent;
i_token.transfer(msg.sender, managerCut);
​
@> uint256 claimantCut = (remainingRewards - managerCut) / i_players.length;
for (uint256 i = 0; i < claimants.length; i++) {
_transferReward(claimants[i], claimantCut);
}
}
}

Risk

Likelihood:

  • This occurs when the Pot is closed and the remainingRewards is lesser than 10.

  • In the case of claimant it can occurs when the numerator is lesser than denominator. It means, when the (remainingRewards - managerCut) is lesser than players length.

Impact:

  • Manager could get any cut even in the cases when this corresponds.

  • The same applies for claimant.

Proof of Concept

Put below coding in TestMyCut.t.sol. The managerBalance should be greater than zero but it is zero because the rounding issues in Solidity.

function testRoundingIssue() public mintAndApproveTokens {
vm.startPrank(user);
rewards = [2, 1];
contest = ContestManager(conMan).createContest(players, rewards, IERC20(ERC20Mock(weth)), 4);
ContestManager(conMan).fundContest(0);
vm.stopPrank();
​
vm.startPrank(player1);
Pot(contest).claimCut();
vm.stopPrank();
vm.startPrank(player2);
Pot(contest).claimCut();
vm.stopPrank();
​
vm.warp(91 days);
​
vm.startPrank(user);
ContestManager(conMan).closeContest(contest);
uint256 managerBalance = ERC20Mock(weth).balanceOf(conMan);
vm.stopPrank();
assert(managerBalance == 0);
}

Recommended Mitigation

One solution could be get the remainder and transfer this to the manager or the last player.

function closePot() external onlyOwner {
if (block.timestamp - i_deployedAt < 90 days) {
revert Pot__StillOpenForClaim();
}
if (remainingRewards > 0) {
uint256 managerCut = remainingRewards / managerCutPercent;
+ uint256 remainder = remainingRewards % managerCutPercent;
​
+ managerCut = managerCut + remainder;
​
i_token.transfer(msg.sender, managerCut);
​
.
.
.
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 5 hours ago
Submission Judgement Published
Validated
Assigned finding tags:

[L-03] [H-03] Precision loss can lead to rewards getting stuck in the pot forever

### \[H-03] Precision loss can lead to rewards getting stuck in the pot forever **Description:** When contest manager closes the pot by calling `Pot::closePot`, 10 percent of the remaining rewards are transferred to the contest manager and the rest are distributed equally among the claimants. It does this by dividing the rewards by the manager's cut percentage which is 10. Then the remaining rewards are divided by the number of players to distribute equally among claimants. Since solidity allows only integer division this will lead to precision loss which will cause a portion of funds to be left in the pot forever. Each pot follows the same method, so as number of pots grow, the loss of funds is very significant. **Impact:** Reward tokens get stuck in the pot forever which causes loss of funds. **Proof of code:** Add the below test to `test/TestMyCut.t.sol` ```javascript function testPrecisionLoss() public mintAndApproveTokens { ContestManager cm = ContestManager(conMan); uint playersLength = 3; address[] memory p = new address[](playersLength); uint256[] memory r = new uint256[](playersLength); uint tr = 86; p[0] = makeAddr("_player1"); p[1] = makeAddr("_player2"); p[2] = makeAddr("_player3"); r[0] = 20; r[1] = 23; r[2] = 43; vm.startPrank(user); address pot = cm.createContest(p, r, weth, tr); cm.fundContest(0); vm.stopPrank(); console.log("\n\ntoken balance in pot before: ", weth.balanceOf(pot)); vm.prank(p[1]); // player 2 Pot(pot).claimCut(); vm.prank(p[0]); // player 1 Pot(pot).claimCut(); vm.prank(user); vm.warp(block.timestamp + 90 days + 1); cm.closeContest(pot); console.log( "\n\ntoken balance in pot after closing pot: ", weth.balanceOf(pot) ); assert(weth.balanceOf(pot) != 0); } ``` Run the below test command in terminal ```Solidity forge test --mt testPrecisionLoss -vv ``` Which results in the below output ```Solidity [⠒] Compiling... [⠆] Compiling 1 files with 0.8.20 [⠰] Solc 0.8.20 finished in 2.57s Compiler run successful! Ran 1 test for test/TestMyCut.t.sol:TestMyCut [PASS] testPrecisionLoss() (gas: 936926) Logs: token balance in pot before: 86 token balance in pot after closing pot: 1 Suite result: ok. 1 passed; 0 failed; 0 skipped; finished in 1.75ms (654.60µs CPU time) Ran 1 test suite in 261.16ms (1.75ms CPU time): 1 tests passed, 0 failed, 0 skipped (1 total tests) ``` If you observe the output you can see the pot still has rewards despite distributing them to claimants. **Recommended Mitigations:** Fixed-Point Arithmetic: Utilize a fixed-point arithmetic library or implement a custom solution to handle fee calculations with greater precision.

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