fix: updated implementation of the atokens/debt tokens to store additional data (user index/borrow rate) per user

contracts/interfaces/IScaledBalanceToken.sol

@@ -23,4 +23,11 @@ interface IScaledBalanceToken {
    * @return The scaled total supply
    **/
   function scaledTotalSupply() external view returns (uint256);
+
+  /**
+   * @dev Returns the index at the moment of the last action (mint/burn/transfer)
+   * @param user The address of the user
+   * @return The last user index
+   **/
+  function lastUserIndex(address user) external view returns (uint256);
 }

contracts/protocol/lendingpool/LendingPool.sol

@@ -781,8 +781,6 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
       vars.releaseUnderlying ? vars.amount : 0
     );
 
-    _usersLastBorrowTimestamp[vars.asset][vars.user] = block.timestamp;
-
     if (vars.releaseUnderlying) {
       IAToken(reserveCache.aTokenAddress).transferUnderlyingTo(vars.user, vars.amount);
     }
@@ -906,8 +904,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
       interestRateMode,
       onBehalfOf,
       stableDebt,
-      variableDebt,
+      variableDebt
-      _usersLastBorrowTimestamp
     );
 
     uint256 paybackAmount =

contracts/protocol/lendingpool/LendingPoolStorage.sol

@@ -35,7 +35,4 @@ contract LendingPoolStorage {
   mapping(address => bool) _authorizedFlashBorrowers;
 
   uint256 internal _flashLoanPremiumToProtocol;
-
-  mapping(address => mapping(address => uint256)) _usersLastBorrowTimestamp;
-
 }

contracts/protocol/libraries/logic/ValidationLogic.sol

@@ -255,7 +255,6 @@ library ValidationLogic {
    * @param onBehalfOf The address of the user msg.sender is repaying for
    * @param stableDebt The borrow balance of the user
    * @param variableDebt The borrow balance of the user
-   * @param lastUsersBorrowTimestamp The data structure that keeps track of all the latest borrowings from the users
    */
   function validateRepay(
     DataTypes.ReserveCache memory reserveCache,
@@ -264,8 +263,7 @@ library ValidationLogic {
     DataTypes.InterestRateMode rateMode,
     address onBehalfOf,
     uint256 stableDebt,
-    uint256 variableDebt,
+    uint256 variableDebt
-    mapping(address => mapping(address => uint256)) storage lastUsersBorrowTimestamp
   ) external view {
     (bool isActive, , , , bool isPaused) = reserveCache.reserveConfiguration.getFlagsMemory();
     require(isActive, Errors.VL_NO_ACTIVE_RESERVE);
@@ -273,18 +271,22 @@ library ValidationLogic {
 
     require(amountSent > 0, Errors.VL_INVALID_AMOUNT);
 
-    require(
+    if (DataTypes.InterestRateMode(rateMode) == DataTypes.InterestRateMode.STABLE) {
-      lastUsersBorrowTimestamp[asset][onBehalfOf] != uint40(block.timestamp),
+      require(
-      Errors.VL_SAME_BLOCK_BORROW_REPAY
+        reserveCache.stableDebtLastUpdateTimestamp != block.timestamp,
-    );
+        Errors.VL_SAME_BLOCK_BORROW_REPAY
-
+      );
-    require(
+      require(stableDebt > 0, Errors.VL_NO_DEBT_OF_SELECTED_TYPE);
-      (stableDebt > 0 &&
+    } else if (DataTypes.InterestRateMode(rateMode) == DataTypes.InterestRateMode.VARIABLE) {
-        DataTypes.InterestRateMode(rateMode) == DataTypes.InterestRateMode.STABLE) ||
+      require(
-        (variableDebt > 0 &&
+        IVariableDebtToken(reserveCache.variableDebtTokenAddress).lastUserIndex(onBehalfOf) !=
-          DataTypes.InterestRateMode(rateMode) == DataTypes.InterestRateMode.VARIABLE),
+          reserveCache.currVariableBorrowIndex,
-      Errors.VL_NO_DEBT_OF_SELECTED_TYPE
+        Errors.VL_SAME_BLOCK_BORROW_REPAY
-    );
+      );
+      require(variableDebt > 0, Errors.VL_NO_DEBT_OF_SELECTED_TYPE);
+    } else {
+      revert(Errors.VL_INVALID_INTEREST_RATE_MODE_SELECTED);
+    }
 
     require(
       amountSent != uint256(-1) || msg.sender == onBehalfOf,

contracts/protocol/tokenization/AToken.sol

@@ -125,7 +125,7 @@ contract AToken is
   ) external override onlyLendingPool {
     uint256 amountScaled = amount.rayDiv(index);
     require(amountScaled != 0, Errors.CT_INVALID_BURN_AMOUNT);
-    _burn(user, amountScaled);
+    _burn(user, amountScaled, index);
 
     IERC20(_underlyingAsset).safeTransfer(receiverOfUnderlying, amount);
 
@@ -150,7 +150,7 @@ contract AToken is
 
     uint256 amountScaled = amount.rayDiv(index);
     require(amountScaled != 0, Errors.CT_INVALID_MINT_AMOUNT);
-    _mint(user, amountScaled);
+    _mint(user, amountScaled, index);
 
     emit Transfer(address(0), user, amount);
     emit Mint(user, amount, index);
@@ -175,7 +175,7 @@ contract AToken is
     // The amount to mint can easily be very small since it is a fraction of the interest ccrued.
     // In that case, the treasury will experience a (very small) loss, but it
     // wont cause potentially valid transactions to fail.
-    _mint(treasury, amount.rayDiv(index));
+    _mint(treasury, amount.rayDiv(index), uint128(index));
 
     emit Transfer(address(0), treasury, amount);
     emit Mint(treasury, amount, index);
@@ -263,6 +263,15 @@ contract AToken is
     return super.totalSupply();
   }
 
+  /**
+   * @dev Returns the index at the moment of the last action (mint/burn/transfer)
+   * @param user The address of the user 
+   * @return The last user index
+   **/
+  function lastUserIndex(address user) external view virtual override returns (uint256) {
+    return _usersData[user].data;
+  }
+
   /**
    * @dev Returns the address of the Aave treasury, receiving the fees on this aToken
    **/
@@ -383,6 +392,9 @@ contract AToken is
 
     super._transfer(from, to, amount.rayDiv(index));
     
+    _usersData[from].data = uint128(index);
+    _usersData[to].data = uint128(index);
+
     if (validate) {
       pool.finalizeTransfer(underlyingAsset, from, to, amount, fromBalanceBefore, toBalanceBefore);
     }

contracts/protocol/tokenization/IncentivizedERC20.sol

@@ -15,7 +15,12 @@ import {IAaveIncentivesController} from '../../interfaces/IAaveIncentivesControl
 abstract contract IncentivizedERC20 is Context, IERC20, IERC20Detailed {
   using SafeMath for uint256;
 
-  mapping(address => uint256) internal _balances;
+  struct BalanceInfo {
+    uint128 balance;
+    uint128 data;
+  }
+
+  mapping(address => BalanceInfo) internal _usersData;
 
   mapping(address => mapping(address => uint256)) private _allowances;
   uint256 internal _totalSupply;
@@ -65,7 +70,7 @@ abstract contract IncentivizedERC20 is Context, IERC20, IERC20Detailed {
    * @return The balance of the token
    **/
   function balanceOf(address account) public view virtual override returns (uint256) {
-    return _balances[account];
+    return _usersData[account].balance;
   }
 
   /**
@@ -177,10 +182,11 @@ abstract contract IncentivizedERC20 is Context, IERC20, IERC20Detailed {
 
     _beforeTokenTransfer(sender, recipient, amount);
 
-    uint256 oldSenderBalance = _balances[sender];
+    uint256 oldSenderBalance = _usersData[sender].balance;
-    _balances[sender] = oldSenderBalance.sub(amount, 'ERC20: transfer amount exceeds balance');
+    _usersData[sender].balance = uint128(oldSenderBalance.sub(amount, 'ERC20: transfer amount exceeds balance'));
-    uint256 oldRecipientBalance = _balances[recipient];
+
-    _balances[recipient] = _balances[recipient].add(amount);
+    uint256 oldRecipientBalance = _usersData[recipient].balance;
+    require((_usersData[recipient].balance = uint128(oldRecipientBalance.add(amount))) >= oldRecipientBalance, 'ERC20: Balance overflow');
     
     if (address(_getIncentivesController()) != address(0)) {
       uint256 currentTotalSupply = _totalSupply;
@@ -191,7 +197,7 @@ abstract contract IncentivizedERC20 is Context, IERC20, IERC20Detailed {
     }
   }
 
-  function _mint(address account, uint256 amount) internal virtual {
+  function _mint(address account, uint256 amount, uint256 data) internal virtual {
     require(account != address(0), 'ERC20: mint to the zero address');
 
     _beforeTokenTransfer(address(0), account, amount);
@@ -199,15 +205,16 @@ abstract contract IncentivizedERC20 is Context, IERC20, IERC20Detailed {
     uint256 oldTotalSupply = _totalSupply;
     _totalSupply = oldTotalSupply.add(amount);
 
-    uint256 oldAccountBalance = _balances[account];
+    uint256 oldAccountBalance = _usersData[account].balance;
-    _balances[account] = oldAccountBalance.add(amount);
+    require((_usersData[account].balance = uint128(oldAccountBalance.add(amount))) >= oldAccountBalance, 'ERC20: Balance overflow');
+    require((_usersData[account].data = uint128(data)) == data, 'ERC20: Data field overflow');
 
     if (address(_getIncentivesController()) != address(0)) {
       _getIncentivesController().handleAction(account, oldTotalSupply, oldAccountBalance);
     }
   }
 
-  function _burn(address account, uint256 amount) internal virtual {
+  function _burn(address account, uint256 amount, uint256 data) internal virtual {
     require(account != address(0), 'ERC20: burn from the zero address');
 
     _beforeTokenTransfer(account, address(0), amount);
@@ -215,8 +222,9 @@ abstract contract IncentivizedERC20 is Context, IERC20, IERC20Detailed {
     uint256 oldTotalSupply = _totalSupply;
     _totalSupply = oldTotalSupply.sub(amount);
 
-    uint256 oldAccountBalance = _balances[account];
+    uint256 oldAccountBalance = _usersData[account].balance;
-    _balances[account] = oldAccountBalance.sub(amount, 'ERC20: burn amount exceeds balance');
+    _usersData[account].balance = uint128(oldAccountBalance.sub(amount, 'ERC20: burn amount exceeds balance'));
+    require((_usersData[account].data = uint128(data)) == data, 'ERC20: Data field overflow');
 
     if (address(_getIncentivesController()) != address(0)) {
       _getIncentivesController().handleAction(account, oldTotalSupply, oldAccountBalance);

contracts/protocol/tokenization/StableDebtToken.sol

@@ -22,7 +22,6 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
 
   uint256 internal _avgStableRate;
   mapping(address => uint40) internal _timestamps;
-  mapping(address => uint256) internal _usersStableRate;
   uint40 internal _totalSupplyTimestamp;
 
   ILendingPool internal _pool;
@@ -96,7 +95,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
    * @return The stable rate of user
    **/
   function getUserStableRate(address user) external view virtual override returns (uint256) {
-    return _usersStableRate[user];
+    return _usersData[user].data;
   }
 
   /**
@@ -105,7 +104,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
    **/
   function balanceOf(address account) public view virtual override returns (uint256) {
     uint256 accountBalance = super.balanceOf(account);
-    uint256 stableRate = _usersStableRate[account];
+    uint256 stableRate = _usersData[account].data;
     if (accountBalance == 0) {
       return 0;
     }
@@ -120,6 +119,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
     uint256 amountInRay;
     uint256 newStableRate;
     uint256 currentAvgStableRate;
+    uint256 currentStableRate;
   }
 
   /**
@@ -150,16 +150,18 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
     vars.previousSupply = totalSupply();
     vars.currentAvgStableRate = _avgStableRate;
     vars.nextSupply = _totalSupply = vars.previousSupply.add(amount);
-
     vars.amountInRay = amount.wadToRay();
+    vars.currentStableRate = _usersData[onBehalfOf].data;
 
-    vars.newStableRate = _usersStableRate[onBehalfOf]
+    
+    if(vars.currentStableRate == 0){
+      vars.newStableRate = rate;
+    }else {
+      vars.newStableRate = vars.currentStableRate
       .rayMul(currentBalance.wadToRay())
       .add(vars.amountInRay.rayMul(rate))
       .rayDiv(currentBalance.add(amount).wadToRay());
-
+    }
-    require(vars.newStableRate <= type(uint128).max, Errors.SDT_STABLE_DEBT_OVERFLOW);
-    _usersStableRate[onBehalfOf] = vars.newStableRate;
 
     //solium-disable-next-line
     _totalSupplyTimestamp = _timestamps[onBehalfOf] = uint40(block.timestamp);
@@ -171,7 +173,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
       .add(rate.rayMul(vars.amountInRay))
       .rayDiv(vars.nextSupply.wadToRay());
 
-    _mint(onBehalfOf, amount.add(balanceIncrease), vars.previousSupply);
+    _mint(onBehalfOf, amount.add(balanceIncrease), vars.previousSupply, vars.newStableRate);
 
     emit Transfer(address(0), onBehalfOf, amount);
 
@@ -200,7 +202,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
     uint256 previousSupply = totalSupply();
     uint256 newAvgStableRate = 0;
     uint256 nextSupply = 0;
-    uint256 userStableRate = _usersStableRate[user];
+    uint256 userStableRate = _usersData[user].data;
 
     // Since the total supply and each single user debt accrue separately,
     // there might be accumulation errors so that the last borrower repaying
@@ -225,7 +227,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
     }
 
     if (amount == currentBalance) {
-      _usersStableRate[user] = 0;
+      _usersData[user].data = 0;
       _timestamps[user] = 0;
     } else {
       //solium-disable-next-line
@@ -236,7 +238,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
 
     if (balanceIncrease > amount) {
       uint256 amountToMint = balanceIncrease.sub(amount);
-      _mint(user, amountToMint, previousSupply);
+      _mint(user, amountToMint, previousSupply, userStableRate);
       emit Mint(
         user,
         user,
@@ -249,7 +251,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
       );
     } else {
       uint256 amountToBurn = amount.sub(balanceIncrease);
-      _burn(user, amountToBurn, previousSupply);
+      _burn(user, amountToBurn, previousSupply, userStableRate);
       emit Burn(user, amountToBurn, currentBalance, balanceIncrease, newAvgStableRate, nextSupply);
     }
 
@@ -404,11 +406,15 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
   function _mint(
     address account,
     uint256 amount,
-    uint256 oldTotalSupply
+    uint256 oldTotalSupply,
+    uint256 data
   ) internal {
-    uint256 oldAccountBalance = _balances[account];
+    uint256 oldAccountBalance = _usersData[account].balance;
-    _balances[account] = oldAccountBalance.add(amount);
+    require(
-
+      (_usersData[account].balance = uint128(oldAccountBalance.add(amount))) >= oldAccountBalance,
+      'ERC20: Balance overflow'
+    );
+    _usersData[account].data = uint128(data);
     if (address(_incentivesController) != address(0)) {
       _incentivesController.handleAction(account, oldTotalSupply, oldAccountBalance);
     }
@@ -423,11 +429,14 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
   function _burn(
     address account,
     uint256 amount,
-    uint256 oldTotalSupply
+    uint256 oldTotalSupply,
+    uint256 data
   ) internal {
-    uint256 oldAccountBalance = _balances[account];
+    uint256 oldAccountBalance = _usersData[account].balance;
-    _balances[account] = oldAccountBalance.sub(amount, Errors.SDT_BURN_EXCEEDS_BALANCE);
+    _usersData[account].balance = uint128(
-
+      oldAccountBalance.sub(amount, Errors.SDT_BURN_EXCEEDS_BALANCE)
+    );
+    _usersData[account].data = uint128(data);
     if (address(_incentivesController) != address(0)) {
       _incentivesController.handleAction(account, oldTotalSupply, oldAccountBalance);
     }

contracts/protocol/tokenization/VariableDebtToken.sol

@@ -106,7 +106,7 @@ contract VariableDebtToken is DebtTokenBase, IVariableDebtToken {
     uint256 amountScaled = amount.rayDiv(index);
     require(amountScaled != 0, Errors.CT_INVALID_MINT_AMOUNT);
 
-    _mint(onBehalfOf, amountScaled);
+    _mint(onBehalfOf, amountScaled, index);
 
     emit Transfer(address(0), onBehalfOf, amount);
     emit Mint(user, onBehalfOf, amount, index);
@@ -129,7 +129,7 @@ contract VariableDebtToken is DebtTokenBase, IVariableDebtToken {
     uint256 amountScaled = amount.rayDiv(index);
     require(amountScaled != 0, Errors.CT_INVALID_BURN_AMOUNT);
 
-    _burn(user, amountScaled);
+    _burn(user, amountScaled, index);
 
     emit Transfer(user, address(0), amount);
     emit Burn(user, amount, index);
@@ -159,6 +159,15 @@ contract VariableDebtToken is DebtTokenBase, IVariableDebtToken {
     return super.totalSupply();
   }
 
+  /**
+   * @dev Returns the index at the moment of the last action (mint/burn/transfer)
+   * @param user The address of the user
+   * @return The last user index
+   **/
+  function lastUserIndex(address user) external view virtual override returns (uint256) {
+    return _usersData[user].data;
+  }
+
   /**
    * @dev Returns the principal balance of the user and principal total supply.
    * @param user The address of the user

test-suites/test-aave/ltv-validation.spec.ts

@@ -0,0 +1,98 @@
+import { TestEnv, makeSuite } from './helpers/make-suite';
+import {
+  APPROVAL_AMOUNT_LENDING_POOL,
+  MAX_UINT_AMOUNT,
+  RAY,
+  MAX_EXPOSURE_CAP,
+  MOCK_CHAINLINK_AGGREGATORS_PRICES,
+  oneEther,
+} from '../../helpers/constants';
+import { ProtocolErrors } from '../../helpers/types';
+import { MintableERC20, WETH9, WETH9Mocked } from '../../types';
+import { parseEther } from '@ethersproject/units';
+import { BigNumber } from '@ethersproject/bignumber';
+import { strategyDAI } from '../../markets/amm/reservesConfigs';
+import { strategyUSDC } from '../../markets/amm/reservesConfigs';
+import { ethers } from 'ethers';
+import { convertToCurrencyDecimals } from '../../helpers/contracts-helpers';
+
+const { expect } = require('chai');
+makeSuite('LTV validation tests', (testEnv: TestEnv) => {
+  const {
+    VL_LTV_VALIDATION_FAILED,
+    RC_INVALID_EXPOSURE_CAP,
+    VL_COLLATERAL_CANNOT_COVER_NEW_BORROW,
+  } = ProtocolErrors;
+  const daiPrice = Number(MOCK_CHAINLINK_AGGREGATORS_PRICES.DAI);
+  const usdcPrice = Number(MOCK_CHAINLINK_AGGREGATORS_PRICES.USDC);
+  const daiLTV = Number(strategyDAI.baseLTVAsCollateral);
+  const usdcLTV = Number(strategyUSDC.baseLTVAsCollateral);
+
+  it('User 1 deposits 10 Dai, 10 USDC, user 2 deposits 1 WETH', async () => {
+    const {
+      pool,
+      dai,
+      usdc,
+      weth,
+      users: [user1, user2],
+    } = testEnv;
+
+    const daiAmount = await convertToCurrencyDecimals(dai.address, '10');
+    const usdcAmount = await convertToCurrencyDecimals(usdc.address, '10');
+    const wethAmount = await convertToCurrencyDecimals(weth.address, '1');
+
+    await dai.connect(user1.signer).approve(pool.address, MAX_UINT_AMOUNT);
+    await usdc.connect(user1.signer).approve(pool.address, MAX_UINT_AMOUNT);
+    await weth.connect(user2.signer).approve(pool.address, MAX_UINT_AMOUNT);
+
+    await dai.connect(user1.signer).mint(daiAmount);
+    await usdc.connect(user1.signer).mint(usdcAmount);
+    await weth.connect(user2.signer).mint(wethAmount);
+
+    await pool.connect(user1.signer).deposit(dai.address, daiAmount, user1.address, 0);
+
+    await pool.connect(user1.signer).deposit(usdc.address, usdcAmount, user1.address, 0);
+
+    await pool.connect(user2.signer).deposit(weth.address, wethAmount, user2.address, 0);
+  });
+
+  it('Sets the ltv of DAI to 0', async () => {
+    const {
+      configurator,
+      dai,
+      helpersContract,
+      users: [],
+    } = testEnv;
+
+    await configurator.configureReserveAsCollateral(dai.address, 0, 8000, 10500);
+
+    const ltv = (await helpersContract.getReserveConfigurationData(dai.address)).ltv;
+
+    expect(ltv).to.be.equal(0);
+  });
+
+  it('Borrows 0.01 weth', async () => {
+    const {
+      pool,
+      weth,
+      users: [user1],
+    } = testEnv;
+    const borrowedAmount = await convertToCurrencyDecimals(weth.address, "0.01");
+
+    pool.connect(user1.signer).borrow(weth.address, borrowedAmount, 1, 0, user1.address);
+  });
+
+  it('Tries to withdraw USDC (revert expected)', async () => {
+    const {
+      pool,
+      usdc,
+      users: [user1],
+    } = testEnv;
+
+    const withdrawnAmount = await convertToCurrencyDecimals(usdc.address, "1");
+
+    await expect(
+      pool.connect(user1.signer).withdraw(usdc.address, withdrawnAmount, user1.address)
+    ).to.be.revertedWith(VL_LTV_VALIDATION_FAILED); 
+  });
+});