Fixes #35

contracts/lendingpool/LendingPool.sol

@@ -385,6 +385,8 @@ contract LendingPool is VersionedInitializable, ILendingPool {
     uint256 purchaseAmount,
     bool receiveAToken
   ) external override {
+    ValidationLogic.validateLiquidation(_reserves[collateral], _reserves[asset]);
+    
     address liquidationManager = _addressesProvider.getLendingPoolLiquidationManager();
 
     //solium-disable-next-line
@@ -444,6 +446,8 @@ contract LendingPool is VersionedInitializable, ILendingPool {
     require(!_flashLiquidationLocked, Errors.REENTRANCY_NOT_ALLOWED);
     _flashLiquidationLocked = true;
 
+    ValidationLogic.validateLiquidation(_reserves[collateral], _reserves[principal]);
+
     address liquidationManager = _addressesProvider.getLendingPoolLiquidationManager();
 
     //solium-disable-next-line

contracts/libraries/logic/ValidationLogic.sol

@@ -329,4 +329,20 @@ library ValidationLogic {
     require(premium > 0, Errors.REQUESTED_AMOUNT_TOO_SMALL);
     require(mode <= uint256(ReserveLogic.InterestRateMode.VARIABLE), Errors.INVALID_FLASHLOAN_MODE);
   }
+
+  /**
+   * @dev Validates configurations for liquidation actions, both liquidationCall() and repayWithCollateral()
+   * @param collateralReserve The reserve data of the collateral
+   * @param principalReserve The reserve data of the principal
+   **/
+  function validateLiquidation(
+    ReserveLogic.ReserveData storage collateralReserve,
+    ReserveLogic.ReserveData storage principalReserve
+  ) internal view {
+    require(
+        collateralReserve.configuration.getActive() && 
+        principalReserve.configuration.getActive(), 
+      Errors.NO_ACTIVE_RESERVE
+    );
+  }
 }

test/liquidation-underlying.spec.ts

@@ -7,6 +7,7 @@ import {makeSuite} from './helpers/make-suite';
 import {ProtocolErrors, RateMode} from '../helpers/types';
 import {calcExpectedStableDebtTokenBalance} from './helpers/utils/calculations';
 import {getUserData} from './helpers/utils/helpers';
+import {parseEther} from 'ethers/lib/utils';
 
 const chai = require('chai');
 
@@ -23,6 +24,26 @@ makeSuite('LendingPool liquidation - liquidator receiving the underlying asset',
     BigNumber.config({DECIMAL_PLACES: 20, ROUNDING_MODE: BigNumber.ROUND_HALF_UP});
   });
 
+  it("It's not possible to liquidate on a non-active collateral or a non active principal", async () => {
+    const {configurator, weth, pool, users, dai} = testEnv;
+    const user = users[1];
+    await configurator.deactivateReserve(weth.address);
+
+    await expect(
+      pool.liquidationCall(weth.address, dai.address, user.address, parseEther('1000'), false)
+    ).to.be.revertedWith('2');
+
+    await configurator.activateReserve(weth.address);
+
+    await configurator.deactivateReserve(dai.address);
+
+    await expect(
+      pool.liquidationCall(weth.address, dai.address, user.address, parseEther('1000'), false)
+    ).to.be.revertedWith('2');
+
+    await configurator.activateReserve(dai.address);
+  });
+
   it('LIQUIDATION - Deposits WETH, borrows DAI', async () => {
     const {dai, weth, users, pool, oracle} = testEnv;
     const depositor = users[0];

test/repay-with-collateral.spec.ts

@@ -39,6 +39,44 @@ export const expectRepayWithCollateralEvent = (
 };
 
 makeSuite('LendingPool. repayWithCollateral()', (testEnv: TestEnv) => {
+  it("It's not possible to repayWithCollateral() on a non-active collateral or a non active principal", async () => {
+    const {configurator, weth, pool, users, dai, mockSwapAdapter} = testEnv;
+    const user = users[1];
+    await configurator.deactivateReserve(weth.address);
+
+    await expect(
+      pool
+        .connect(user.signer)
+        .repayWithCollateral(
+          weth.address,
+          dai.address,
+          user.address,
+          parseEther('100'),
+          mockSwapAdapter.address,
+          '0x'
+        )
+    ).to.be.revertedWith('2');
+
+    await configurator.activateReserve(weth.address);
+
+    await configurator.deactivateReserve(dai.address);
+
+    await expect(
+      pool
+        .connect(user.signer)
+        .repayWithCollateral(
+          weth.address,
+          dai.address,
+          user.address,
+          parseEther('100'),
+          mockSwapAdapter.address,
+          '0x'
+        )
+    ).to.be.revertedWith('2');
+
+    await configurator.activateReserve(dai.address);
+  });
+
   it('User 1 provides some liquidity for others to borrow', async () => {
     const {pool, weth, dai, usdc, deployer} = testEnv;