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

Precision loss in `closePot` integer division leaves dust permanently stuck in the `Pot`

0xki

Root + Impact

Description

  • `closePot` computes the manager cut and each claimant's share with integer division. Solidity truncates, so the sum of the manager cut plus all claimant payouts is generally slightly less than `remainingRewards`.

  • The truncated remainder (dust) is never transferred out and stays in the `Pot` forever. This is independent of H-02 — even after fixing the denominator to `claimants.length`, integer truncation still strands a small amount, and it accumulates across many contests.

/ src/Pot.sol :: closePot
@> uint256 managerCut = remainingRewards / managerCutPercent; // truncates
i_token.transfer(msg.sender, managerCut);
​
@> uint256 claimantCut = (remainingRewards - managerCut) / claimants.length; // truncates
for (uint256 i = 0; i < claimants.length; i++) {
_transferReward(claimants[i], claimantCut);
}
// managerCut + claimantCut * claimants.length <= remainingRewards ; the leftover dust is never distributed

Risk

Likelihood:

  • Occurs whenever `remainingRewards` is not perfectly divisible — i.e. most closes.

Impact:

  • Small amounts of tokens are permanently locked per contest; negligible individually but accumulates and is unrecoverable. No large or direct theft.


Proof of Concept

N/A

Recommended Mitigation

Track and forward the truncation remainder rather than leaving it stuck. For example, after distributing, send any leftover to the manager (or the last claimant):

uint256 managerCut = remainingRewards / managerCutPercent;
i_token.transfer(msg.sender, managerCut);
​
uint256 claimantCut = (remainingRewards - managerCut) / claimants.length;
+ uint256 distributed = claimantCut * claimants.length;
for (uint256 i = 0; i < claimants.length; i++) {
_transferReward(claimants[i], claimantCut);
}
+ uint256 dust = (remainingRewards - managerCut) - distributed;
+ if (dust > 0) {
+ i_token.transfer(msg.sender, dust); // forward leftover instead of locking it
+ }
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 2 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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