(uint256 borrowRateX96, uint256 supplyRateX96) = interestRateModel.getRatesPerSecondX96(available, debt);

supplyRateX96 = supplyRateX96.mulDiv(Q32 - reserveFactorX32, Q32);

// always growing or equal
uint256 lastRateUpdate = lastExchangeRateUpdate;

if (lastRateUpdate > 0) {
    newDebtExchangeRateX96 = oldDebtExchangeRateX96 + oldDebtExchangeRateX96 * (block.timestamp - lastRateUpdate) * borrowRateX96 / Q96;
    newLendExchangeRateX96 = oldLendExchangeRateX96 + oldLendExchangeRateX96 * (block.timestamp - lastRateUpdate) * supplyRateX96 / Q96;
} else {
    newDebtExchangeRateX96 = oldDebtExchangeRateX96;
    newLendExchangeRateX96 = oldLendExchangeRateX96;
}
RESULTS FROM FORGE TESTS 

with interest rate update occurring after reserve factor update:

- starting lendExchangeRateX96:  79243018781103204090820932736
- after reserve update lendExchangeRateX96:  79240047527736122590199028736

with interest rate update occurring before reserve factor update:

- starting lendExchangeRateX96:  79243018781103204090820932736
- after reserve update lendExchangeRateX96:  79243018781103204090820932736
function testLendingRateReserveFactorBugWithoutInterestUpdate() external {
    vault.setLimits(1000000, 1000e18, 1000e18, 1000e18, 1000e18);

    // set up basic vault settings
    _deposit(10000000, WHALE_ACCOUNT);
    _setupBasicLoan(true);
    vm.warp(block.timestamp + 7 days);

    (,,,,,,uint lendExchangeRateX96) = vault.vaultInfo();
    console.log("old lendExchangeRateX96: ", lendExchangeRateX96);

    vm.prank(vault.owner());

    vault.setReserveFactor(uint32(Q32 / 5)); // 20% reserve factor

    // AUDIT: Calling setLimits updates the exchange rate
    vault.setLimits(1000000, 1000e18, 1000e18, 1000e18, 1000e18);


    (,,,,,,lendExchangeRateX96) = vault.vaultInfo();
    console.log("new lendExchangeRateX96: ", lendExchangeRateX96);
}

function testLendingRateReserveFactorBugWithInterestUpdate() external {
    vault.setLimits(1000000, 1000e18, 1000e18, 1000e18, 1000e18);

    // set up basic vault settings
    _deposit(10000000, WHALE_ACCOUNT);
    _setupBasicLoan(true);
    vm.warp(block.timestamp + 7 days);

    (,,,,,,uint lendExchangeRateX96) = vault.vaultInfo();
    console.log("old lendExchangeRateX96: ", lendExchangeRateX96);

    vm.prank(vault.owner());

    // AUDIT: Calling setLimits updates the exchange rate
    vault.setLimits(1000000, 1000e18, 1000e18, 1000e18, 1000e18);
    vault.setReserveFactor(uint32(Q32 / 5)); // 20% reserve factor

    (,,,,,,lendExchangeRateX96) = vault.vaultInfo();
    console.log("new lendExchangeRateX96: ", lendExchangeRateX96);
}
function setReserveFactor(uint32 _reserveFactorX32) external onlyOwner {
    _updateGlobalInterest();
    reserveFactorX32 = _reserveFactorX32;
}
