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

Division truncation in closePot permanently locks dust funds in the contract

goat

Root + Impact

Division truncation in closePot permanently locks dust funds in the contract

Description

  • The claimantCut is calculated as (remainingRewards - managerCut) / i_players.length. Integer division truncates the result, and the remainder is never distributed or recovered — it stays locked in the contract forever.

// Root cause in the codebase with @> marks to highlight the relevant section
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); //audit-low we are not checking the transaction return false or true
​
@> uint256 claimantCut = (remainingRewards - managerCut) / i_players.length; // audit-high logic issue with division lead to stuck funds in contract forever
for (uint256 i = 0; i < claimants.length; i++) { //audit-gas better store calimants length in a variable and loop through it
_transferReward(claimants[i], claimantCut);
}
}
}

Risk

Likelihood:

  • This occurs on every closePot call where (remainingRewards - managerCut) is not perfectly divisible by i_players.length

  • With arbitrary reward amounts and player counts this is the common case, not the exception

Impact:

  • A portion of ERC20 funds becomes permanently inaccessible in the contract

  • The higher the player count and the more uneven the division, the larger the stuck amount

Proof of Concept

// remainingRewards = 100, managerCut = 10, i_players.length = 7
// claimantCut = 90 / 7 = 12 each
// distributed = 12 * 7 = 84
// stuck forever = 6 tokens

Recommended Mitigation

- remove this code
uint256 claimantCut = (remainingRewards - managerCut) / claimants.length;
+uint256 dust = (remainingRewards - managerCut) - (claimantCut * claimants.length);
for (uint256 i = 0; i < claimants.length; i++) {
_transferReward(claimants[i], claimantCut);
}
+if (dust > 0) i_token.safeTransfer(msg.sender, dust);
+ add this code
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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