The update of interest rates does not account for the real unbacked amount (can be bypassed if cap is 0)

[miguelmtzinf]

If there is unbacked liquidity in the system and governance decides to "switch off" portals (setting a zero unbackedMintCap), the calculation of the interest rates would be wrong since this function would pass 0 as unbacked because of 0 unbackedMintCap (when we could have non-zero unbacked).

aave-v3-core/contracts/protocol/libraries/logic/ReserveLogic.sol

Lines 167 to 198 in f3e037b

	function updateInterestRates(
	DataTypes.ReserveData storage reserve,
	DataTypes.ReserveCache memory reserveCache,
	address reserveAddress,
	uint256 liquidityAdded,
	uint256 liquidityTaken
	) internal {
	UpdateInterestRatesLocalVars memory vars;
	vars.totalVariableDebt = reserveCache.nextScaledVariableDebt.rayMul(
	reserveCache.nextVariableBorrowIndex
	);
	(
	vars.nextLiquidityRate,
	vars.nextStableRate,
	vars.nextVariableRate
	) = IReserveInterestRateStrategy(reserve.interestRateStrategyAddress).calculateInterestRates(
	DataTypes.CalculateInterestRatesParams({
	unbacked: reserveCache.reserveConfiguration.getUnbackedMintCap() != 0
	? reserve.unbacked
	: 0,
	liquidityAdded: liquidityAdded,
	liquidityTaken: liquidityTaken,
	totalStableDebt: reserveCache.nextTotalStableDebt,
	totalVariableDebt: vars.totalVariableDebt,
	averageStableBorrowRate: reserveCache.nextAvgStableBorrowRate,
	reserveFactor: reserveCache.reserveFactor,
	reserve: reserveAddress,
	aToken: reserveCache.aTokenAddress
	})
	);

Additionally, there is no check of the current unbacked amount in IPoolConfigurator.setUnbackedMintCap.

aave-v3-core/contracts/protocol/pool/PoolConfigurator.sol

Lines 416 to 426 in 32f0e72

	function setUnbackedMintCap(address asset, uint256 newUnbackedMintCap)
	external
	override
	onlyRiskOrPoolAdmins
	{
	DataTypes.ReserveConfigurationMap memory currentConfig = _pool.getConfiguration(asset);
	uint256 oldUnbackedMintCap = currentConfig.getUnbackedMintCap();
	currentConfig.setUnbackedMintCap(newUnbackedMintCap);
	_pool.setConfiguration(asset, currentConfig);
	emit UnbackedMintCapChanged(asset, oldUnbackedMintCap, newUnbackedMintCap);
	}

[eboadom]

Agree with fixing the first, but for now would leave the validation of the setter for a following iteration, because I think we should do a broader review of this type of cases (fairly sure there is more)

[miguelmtzinf]

I didn't mean we should fix the setter, because it is working as intended. I will create a PR for the other.