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

[miguelmtz]

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); 
 } 

[Ernesto Boado]

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)

[miguelmtz]

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