Liquidity Management

[L-1] getPositionFeeUsd doesn’t cover all fees (borrowing, funding), causing minor pre-calculation errors

Description:
The PerpetualVault.sol contract uses vaultReader.getPositionFeeUsd() in afterOrderExecution and _withdraw to calculate GMX position fees for increasing or decreasing positions. However, this function only accounts for the opening/closing position fee (e.g., 0.1% of position size) and does not include borrowing fees (accrued over time based on position duration) or funding rates (periodic payments between long/short positions). These additional fees are handled by GMX during execution but are not pre-adjusted in the contract’s calculations, leading to minor discrepancies between the calculated feeAmount and the actual fees deducted by GMX.

impact:

• Minor Over/Underestimation: When opening a position (afterOrderExecution), users may receive slightly fewer shares if borrowing fees accrue later and reduce the realized collateral. During withdrawals (_withdraw), users might withdraw less than expected due to unaccounted funding or borrowing fees deducted by GMX, or more if positive funding isn’t pre-included.

• No Fund Loss: GMX correctly deducts all fees during execution, ensuring no vault shortfall, but the pre-calculation mismatch slightly affects user share issuance or withdrawal amounts.

• User Experience: Small inaccuracies (e.g., a few USDC) may reduce trust, though the impact is minimal and doesn’t drain the vault.

Proof of Concept:

Recomended Mitigation: