Overview
Currently in the repay function the user is able to call the function to repay there debt or repay for another user.
function repay(uint256 amount) external nonReentrant whenNotPaused onlyValidAmount(amount) {
_repay(amount, msg.sender);
}
function repayOnBehalf(uint256 amount, address onBehalfOf) external nonReentrant whenNotPaused onlyValidAmount(amount) {
if (!canPaybackDebt) revert PaybackDebtDisabled();
if (onBehalfOf == address(0)) revert AddressCannotBeZero();
_repay(amount, onBehalfOf);
}
function _repay(uint256 amount, address onBehalfOf) internal {
if (amount == 0) revert InvalidAmount();
if (onBehalfOf == address(0)) revert AddressCannotBeZero();
UserData storage user = userData[onBehalfOf];
ReserveLibrary.updateReserveState(reserve, rateData);
uint256 userDebt = IDebtToken(reserve.reserveDebtTokenAddress).balanceOf(onBehalfOf);
uint256 userScaledDebt = userDebt.rayDiv(reserve.usageIndex);
uint256 actualRepayAmount = amount > userScaledDebt ? userScaledDebt : amount;
uint256 scaledAmount = actualRepayAmount.rayDiv(reserve.usageIndex);
(uint256 amountScaled, uint256 newTotalSupply, uint256 amountBurned, uint256 balanceIncrease) =
IDebtToken(reserve.reserveDebtTokenAddress).burn(onBehalfOf, amount, reserve.usageIndex);
IERC20(reserve.reserveAssetAddress).safeTransferFrom(msg.sender, reserve.reserveRTokenAddress, amountScaled);
reserve.totalUsage = newTotalSupply;
user.scaledDebtBalance -= amountBurned;
ReserveLibrary.updateInterestRatesAndLiquidity(reserve, rateData, amountScaled, 0);
emit Repay(msg.sender, onBehalfOf, actualRepayAmount);
}
The issue here is that while calling this functions there are no checks to prevent the user from repaying when it is already too late. Like a user could be calling this function when the liquidation is just waiting to be finalized
POC
User notices they are about to be liquidated so they repay by calling this function
Since they realised abit late the grace period is over right after they call repay user tries to close liquidation by calling the function below
function closeLiquidation() external nonReentrant whenNotPaused {
address userAddress = msg.sender;
if (!isUnderLiquidation[userAddress]) revert NotUnderLiquidation();
ReserveLibrary.updateReserveState(reserve, rateData);
if (block.timestamp > liquidationStartTime[userAddress] + liquidationGracePeriod) {
revert GracePeriodExpired();
}
UserData storage user = userData[userAddress];
uint256 userDebt = user.scaledDebtBalance.rayMul(reserve.usageIndex);
if (userDebt > DUST_THRESHOLD) revert DebtNotZero();
isUnderLiquidation[userAddress] = false;
liquidationStartTime[userAddress] = 0;
emit LiquidationClosed(userAddress);
}
Recommendation
Add checks in the repay function so that user does not end up being eligible for liquidation even if they have already paid. maybe revert if the grace period is already over
