On-chain Compound v3 USDT Arbitrum market (#864)

Co-authored-by: dmitriy-bergman-works <dmitriy@bergman.works>
Co-authored-by: GitHub Actions Bot <>
Co-authored-by: dmitriy-woof-software <dmitriy@woof.software>

.github/workflows/run-scenarios.yaml

@@ -7,7 +7,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        bases: [ development, mainnet, mainnet-weth, goerli, goerli-weth, sepolia-usdc, sepolia-weth, fuji, mumbai, polygon, arbitrum-usdc.e, arbitrum-usdc, arbitrum-weth, arbitrum-goerli-usdc, arbitrum-goerli-usdc.e, base-usdbc, base-weth, base-usdc, base-goerli, base-goerli-weth, linea-goerli, optimism-usdc, optimism-usdt, scroll-goerli, scroll-usdc]
+        bases: [ development, mainnet, mainnet-weth, goerli, goerli-weth, sepolia-usdc, sepolia-weth, fuji, mumbai, polygon, arbitrum-usdc.e, arbitrum-usdc, arbitrum-weth, arbitrum-usdt, arbitrum-goerli-usdc, arbitrum-goerli-usdc.e, base-usdbc, base-weth, base-usdc, base-goerli, base-goerli-weth, linea-goerli, optimism-usdc, optimism-usdt, scroll-goerli, scroll-usdc]
     name: Run scenarios
     env:
       ETHERSCAN_KEY: ${{ secrets.ETHERSCAN_KEY }}

contracts/Comet.sol

@@ -2,7 +2,7 @@
 pragma solidity 0.8.15;
 
 import "./CometMainInterface.sol";
-import "./ERC20.sol";
+import "./IERC20NonStandard.sol";
 import "./IPriceFeed.sol";
 
 /**
@@ -126,20 +126,14 @@ contract Comet is CometMainInterface {
     uint256 internal immutable asset10_b;
     uint256 internal immutable asset11_a;
     uint256 internal immutable asset11_b;
-    uint256 internal immutable asset12_a;
-    uint256 internal immutable asset12_b;
-    uint256 internal immutable asset13_a;
-    uint256 internal immutable asset13_b;
-    uint256 internal immutable asset14_a;
-    uint256 internal immutable asset14_b;
 
     /**
      * @notice Construct a new protocol instance
      * @param config The mapping of initial/constant parameters
      **/
     constructor(Configuration memory config) {
         // Sanity checks
-        uint8 decimals_ = ERC20(config.baseToken).decimals();
+        uint8 decimals_ = IERC20NonStandard(config.baseToken).decimals();
         if (decimals_ > MAX_BASE_DECIMALS) revert BadDecimals();
         if (config.storeFrontPriceFactor > FACTOR_SCALE) revert BadDiscount();
         if (config.assetConfigs.length > MAX_ASSETS) revert TooManyAssets();
@@ -196,9 +190,44 @@ contract Comet is CometMainInterface {
         (asset09_a, asset09_b) = getPackedAssetInternal(config.assetConfigs, 9);
         (asset10_a, asset10_b) = getPackedAssetInternal(config.assetConfigs, 10);
         (asset11_a, asset11_b) = getPackedAssetInternal(config.assetConfigs, 11);
-        (asset12_a, asset12_b) = getPackedAssetInternal(config.assetConfigs, 12);
-        (asset13_a, asset13_b) = getPackedAssetInternal(config.assetConfigs, 13);
-        (asset14_a, asset14_b) = getPackedAssetInternal(config.assetConfigs, 14);
+    }
+
+    /**
+     * @dev Prevents marked functions from being reentered 
+     * Note: this restrict contracts from calling comet functions in their hooks.
+     * Doing so will cause the transaction to revert.
+     */
+    modifier nonReentrant() {
+        nonReentrantBefore();
+        _;
+        nonReentrantAfter();
+    }
+
+    /**
+     * @dev Checks that the reentrancy flag is not set and then sets the flag
+     */
+    function nonReentrantBefore() internal {
+        bytes32 slot = REENTRANCY_GUARD_FLAG_SLOT;
+        uint256 status;
+        assembly ("memory-safe") {
+            status := sload(slot)
+        }
+
+        if (status == REENTRANCY_GUARD_ENTERED) revert ReentrantCallBlocked();
+        assembly ("memory-safe") {
+            sstore(slot, REENTRANCY_GUARD_ENTERED)
+        }
+    }
+
+    /**
+     * @dev Unsets the reentrancy flag
+     */
+    function nonReentrantAfter() internal {
+        bytes32 slot = REENTRANCY_GUARD_FLAG_SLOT;
+        uint256 status;
+        assembly ("memory-safe") {
+            sstore(slot, REENTRANCY_GUARD_NOT_ENTERED)
+        }
     }
 
     /**
@@ -241,7 +270,7 @@ contract Comet is CometMainInterface {
 
         // Sanity check price feed and asset decimals
         if (IPriceFeed(priceFeed).decimals() != PRICE_FEED_DECIMALS) revert BadDecimals();
-        if (ERC20(asset).decimals() != decimals_) revert BadDecimals();
+        if (IERC20NonStandard(asset).decimals() != decimals_) revert BadDecimals();
 
         // Ensure collateral factors are within range
         if (assetConfig.borrowCollateralFactor >= assetConfig.liquidateCollateralFactor) revert BorrowCFTooLarge();
@@ -319,15 +348,6 @@ contract Comet is CometMainInterface {
         } else if (i == 11) {
             word_a = asset11_a;
             word_b = asset11_b;
-        } else if (i == 12) {
-            word_a = asset12_a;
-            word_b = asset12_b;
-        } else if (i == 13) {
-            word_a = asset13_a;
-            word_b = asset13_b;
-        } else if (i == 14) {
-            word_a = asset14_a;
-            word_b = asset14_b;
         } else {
             revert Absurd();
         }
@@ -482,15 +502,15 @@ contract Comet is CometMainInterface {
      * @param asset The collateral asset
      */
     function getCollateralReserves(address asset) override public view returns (uint) {
-        return ERC20(asset).balanceOf(address(this)) - totalsCollateral[asset].totalSupplyAsset;
+        return IERC20NonStandard(asset).balanceOf(address(this)) - totalsCollateral[asset].totalSupplyAsset;
     }
 
     /**
      * @notice Gets the total amount of protocol reserves of the base asset
      */
     function getReserves() override public view returns (int) {
         (uint64 baseSupplyIndex_, uint64 baseBorrowIndex_) = accruedInterestIndices(getNowInternal() - lastAccrualTime);
-        uint balance = ERC20(baseToken).balanceOf(address(this));
+        uint balance = IERC20NonStandard(baseToken).balanceOf(address(this));
         uint totalSupply_ = presentValueSupply(baseSupplyIndex_, totalSupplyBase);
         uint totalBorrow_ = presentValueBorrow(baseBorrowIndex_, totalBorrowBase);
         return signed256(balance) - signed256(totalSupply_) + signed256(totalBorrow_);
@@ -760,18 +780,50 @@ contract Comet is CometMainInterface {
     }
 
     /**
-     * @dev Safe ERC20 transfer in, assumes no fee is charged and amount is transferred
+     * @dev Safe ERC20 transfer in and returns the final amount transferred (taking into account any fees)
+     * @dev Note: Safely handles non-standard ERC-20 tokens that do not return a value. See here: https://medium.com/coinmonks/missing-return-value-bug-at-least-130-tokens-affected-d67bf08521ca
      */
-    function doTransferIn(address asset, address from, uint amount) internal {
-        bool success = ERC20(asset).transferFrom(from, address(this), amount);
+    function doTransferIn(address asset, address from, uint amount) internal returns (uint) {
+        uint256 preTransferBalance = IERC20NonStandard(asset).balanceOf(address(this));
+        IERC20NonStandard(asset).transferFrom(from, address(this), amount);
+        bool success;
+        assembly ("memory-safe") {
+            switch returndatasize()
+                case 0 {                       // This is a non-standard ERC-20
+                    success := not(0)          // set success to true
+                }
+                case 32 {                      // This is a compliant ERC-20
+                    returndatacopy(0, 0, 32)
+                    success := mload(0)        // Set `success = returndata` of override external call
+                }
+                default {                      // This is an excessively non-compliant ERC-20, revert.
+                    revert(0, 0)
+                }
+        }
         if (!success) revert TransferInFailed();
+        return IERC20NonStandard(asset).balanceOf(address(this)) - preTransferBalance;
     }
 
     /**
      * @dev Safe ERC20 transfer out
+     * @dev Note: Safely handles non-standard ERC-20 tokens that do not return a value. See here: https://medium.com/coinmonks/missing-return-value-bug-at-least-130-tokens-affected-d67bf08521ca
      */
     function doTransferOut(address asset, address to, uint amount) internal {
-        bool success = ERC20(asset).transfer(to, amount);
+        IERC20NonStandard(asset).transfer(to, amount);
+        bool success;
+        assembly ("memory-safe") {
+            switch returndatasize()
+                case 0 {                       // This is a non-standard ERC-20
+                    success := not(0)          // set success to true
+                }
+                case 32 {                      // This is a compliant ERC-20
+                    returndatacopy(0, 0, 32)
+                    success := mload(0)        // Set `success = returndata` of override external call
+                }
+                default {                      // This is an excessively non-compliant ERC-20, revert.
+                    revert(0, 0)
+                }
+        }
         if (!success) revert TransferOutFailed();
     }
 
@@ -809,7 +861,7 @@ contract Comet is CometMainInterface {
      * @dev Supply either collateral or base asset, depending on the asset, if operator is allowed
      * @dev Note: Specifying an `amount` of uint256.max will repay all of `dst`'s accrued base borrow balance
      */
-    function supplyInternal(address operator, address from, address dst, address asset, uint amount) internal {
+    function supplyInternal(address operator, address from, address dst, address asset, uint amount) internal nonReentrant {
         if (isSupplyPaused()) revert Paused();
         if (!hasPermission(from, operator)) revert Unauthorized();
 
@@ -827,7 +879,7 @@ contract Comet is CometMainInterface {
      * @dev Supply an amount of base asset from `from` to dst
      */
     function supplyBase(address from, address dst, uint256 amount) internal {
-        doTransferIn(baseToken, from, amount);
+        amount = doTransferIn(baseToken, from, amount);
 
         accrueInternal();
 
@@ -854,7 +906,7 @@ contract Comet is CometMainInterface {
      * @dev Supply an amount of collateral asset from `from` to dst
      */
     function supplyCollateral(address from, address dst, address asset, uint128 amount) internal {
-        doTransferIn(asset, from, amount);
+        amount = safe128(doTransferIn(asset, from, amount));
 
         AssetInfo memory assetInfo = getAssetInfoByAddress(asset);
         TotalsCollateral memory totals = totalsCollateral[asset];
@@ -920,7 +972,7 @@ contract Comet is CometMainInterface {
      * @dev Transfer either collateral or base asset, depending on the asset, if operator is allowed
      * @dev Note: Specifying an `amount` of uint256.max will transfer all of `src`'s accrued base balance
      */
-    function transferInternal(address operator, address src, address dst, address asset, uint amount) internal {
+    function transferInternal(address operator, address src, address dst, address asset, uint amount) internal nonReentrant {
         if (isTransferPaused()) revert Paused();
         if (!hasPermission(src, operator)) revert Unauthorized();
         if (src == dst) revert NoSelfTransfer();
@@ -1031,7 +1083,7 @@ contract Comet is CometMainInterface {
      * @dev Withdraw either collateral or base asset, depending on the asset, if operator is allowed
      * @dev Note: Specifying an `amount` of uint256.max will withdraw all of `src`'s accrued base balance
      */
-    function withdrawInternal(address operator, address src, address to, address asset, uint amount) internal {
+    function withdrawInternal(address operator, address src, address to, address asset, uint amount) internal nonReentrant {
         if (isWithdrawPaused()) revert Paused();
         if (!hasPermission(src, operator)) revert Unauthorized();
 
@@ -1192,14 +1244,14 @@ contract Comet is CometMainInterface {
      * @param baseAmount The amount of base tokens used to buy the collateral
      * @param recipient The recipient address
      */
-    function buyCollateral(address asset, uint minAmount, uint baseAmount, address recipient) override external {
+    function buyCollateral(address asset, uint minAmount, uint baseAmount, address recipient) override external nonReentrant {
         if (isBuyPaused()) revert Paused();
 
         int reserves = getReserves();
         if (reserves >= 0 && uint(reserves) >= targetReserves) revert NotForSale();
 
         // Note: Re-entrancy can skip the reserves check above on a second buyCollateral call.
-        doTransferIn(baseToken, msg.sender, baseAmount);
+        baseAmount = doTransferIn(baseToken, msg.sender, baseAmount);
 
         uint collateralAmount = quoteCollateral(asset, baseAmount);
         if (collateralAmount < minAmount) revert TooMuchSlippage();
@@ -1254,14 +1306,15 @@ contract Comet is CometMainInterface {
      * @dev Only callable by governor
      * @dev Note: Setting the `asset` as Comet's address will allow the manager
      * to withdraw from Comet's Comet balance
+     * @dev Note: For USDT, if there is non-zero prior allowance, it must be reset to 0 first before setting a new value in proposal
      * @param asset The asset that the manager will gain approval of
      * @param manager The account which will be allowed or disallowed
      * @param amount The amount of an asset to approve
      */
     function approveThis(address manager, address asset, uint amount) override external {
         if (msg.sender != governor) revert Unauthorized();
 
-        ERC20(asset).approve(manager, amount);
+        IERC20NonStandard(asset).approve(manager, amount);
     }
 
     /**
@@ -1322,4 +1375,4 @@ contract Comet is CometMainInterface {
             default { return(0, returndatasize()) }
         }
     }
-}
+}

contracts/CometCore.sol

@@ -56,6 +56,13 @@ abstract contract CometCore is CometConfiguration, CometStorage, CometMath {
     /// @dev The scale for factors
     uint64 internal constant FACTOR_SCALE = 1e18;
 
+    /// @dev The storage slot for reentrancy guard flags
+    bytes32 internal constant REENTRANCY_GUARD_FLAG_SLOT = bytes32(keccak256("comet.reentrancy.guard"));
+
+    /// @dev The reentrancy guard statuses
+    uint256 internal constant REENTRANCY_GUARD_NOT_ENTERED = 0;
+    uint256 internal constant REENTRANCY_GUARD_ENTERED = 1;
+
     /**
      * @notice Determine if the manager has permission to act on behalf of the owner
      * @param owner The owner account

contracts/CometMainInterface.sol

@@ -25,6 +25,7 @@ abstract contract CometMainInterface is CometCore {
     error NotForSale();
     error NotLiquidatable();
     error Paused();
+    error ReentrantCallBlocked();
     error SupplyCapExceeded();
     error TimestampTooLarge();
     error TooManyAssets();

contracts/IERC20NonStandard.sol

@@ -7,8 +7,37 @@ pragma solidity 0.8.15;
  *  See https://medium.com/coinmonks/missing-return-value-bug-at-least-130-tokens-affected-d67bf08521ca
  */
 interface IERC20NonStandard {
+    function name() external view returns (string memory);
+    function symbol() external view returns (string memory);
+    function decimals() external view returns (uint8);
+
+    /**
+     * @notice Approve `spender` to transfer up to `amount` from `src`
+     * @dev This will overwrite the approval amount for `spender`
+     *  and is subject to issues noted [here](https://eips.ethereum.org/EIPS/eip-20#approve)
+     * @param spender The address of the account which may transfer tokens
+     * @param amount The number of tokens that are approved (-1 means infinite)
+     */
     function approve(address spender, uint256 amount) external;
+
+    /**
+     * @notice Transfer `value` tokens from `msg.sender` to `to`
+     * @param to The address of the destination account
+     * @param value The number of tokens to transfer
+     */
     function transfer(address to, uint256 value) external;
+
+    /**
+     * @notice Transfer `value` tokens from `from` to `to`
+     * @param from The address of the source account
+     * @param to The address of the destination account
+     * @param value The number of tokens to transfer
+     */
     function transferFrom(address from, address to, uint256 value) external;
+
+    /**
+     * @notice Gets the balance of the specified address
+     * @param account The address from which the balance will be retrieved
+     */
     function balanceOf(address account) external view returns (uint256);
-}
+}

contracts/test/EvilToken.sol

@@ -13,7 +13,8 @@ contract EvilToken is FaucetToken {
     enum AttackType {
         TRANSFER_FROM,
         WITHDRAW_FROM,
-        SUPPLY_FROM
+        SUPPLY_FROM,
+        BUY_COLLATERAL
     }
 
     struct ReentryAttack {
@@ -52,20 +53,27 @@ contract EvilToken is FaucetToken {
         attack = attack_;
     }
 
-    function transfer(address, uint256) external override returns (bool) {
-        return performAttack();
+    function transfer(address dst, uint256 amount) public override returns (bool) {
+        numberOfCalls++;
+        if (numberOfCalls > attack.maxCalls){
+            return super.transfer(dst, amount);
+        } else {
+            return performAttack(address(this), dst, amount);
+        }
     }
 
-    function transferFrom(address, address, uint256) external override returns (bool) {
-        return performAttack();
+    function transferFrom(address src, address dst, uint256 amount) public override returns (bool) {
+        numberOfCalls++;
+        if (numberOfCalls > attack.maxCalls) {
+            return super.transferFrom(src, dst, amount);
+        } else {
+            return performAttack(src, dst, amount);
+        }
     }
 
-    function performAttack() internal returns (bool) {
+    function performAttack(address src, address dst, uint256 amount) internal returns (bool) {
         ReentryAttack memory reentryAttack = attack;
-        numberOfCalls++;
-        if (numberOfCalls > reentryAttack.maxCalls) {
-            // do nothing
-        } else if (reentryAttack.attackType == AttackType.TRANSFER_FROM) {
+       if (reentryAttack.attackType == AttackType.TRANSFER_FROM) {
             Comet(payable(msg.sender)).transferFrom(
                 reentryAttack.source,
                 reentryAttack.destination,
@@ -85,6 +93,13 @@ contract EvilToken is FaucetToken {
                 reentryAttack.asset,
                 reentryAttack.amount
             );
+        }  else if (reentryAttack.attackType == AttackType.BUY_COLLATERAL) {
+            Comet(payable(msg.sender)).buyCollateral(
+                reentryAttack.asset,
+                0,
+                reentryAttack.amount,
+                reentryAttack.destination
+            );
         } else {
             revert("invalid reentry attack");
         }