Precision Loss in Share Calculation Leads to Incorrect Withdrawals
Summary
Precision loss in the share calculation logic when withdrawing funds from the vault. Due to Solidity's integer division behavior, users with small shares relative to totalShares will receive fewer funds than expected, leading to an unfair distribution of withdrawals.
Vulnerability Details
2025-02-gamma/contracts/PerpetualVault.sol at main · CodeHawks-Contests/2025-02-gamma
2025-02-gamma/contracts/PerpetualVault.sol at main · CodeHawks-Contests/2025-02-gamma
The issue occurs in the following calculation:
Since Solidity performs integer division, if shares is significantly smaller than totalShares, the result of balanceBeforeWithdrawal * shares / totalShares may round down to zero, causing some depositors to lose a portion of their rightful withdrawal amount.
Impact
Users with smaller shares will receive significantly less than their fair share of withdrawals.
In extreme cases, small withdrawals will result in receiving nothing, leading to a loss of funds.
Tools Used
Manual code review
Recommendations
Use OpenZeppelin’s SafeMath, Multiply first, then divide to avoid precision loss.
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