Added ReentrancyGuard

contracts/receivers/aave-v2-receiver/main.sol

@@ -145,7 +145,7 @@ contract InstaFlash is AaveV2Migrator {
         uint256[] calldata _amounts,	
         uint /*_route */, // no use of route but just to follow current flashloan pattern
         bytes calldata data
-    ) external isDSA {	
+    ) external nonReentrant isDSA {	
         uint _length = _tokens.length;
         require(_length == _amounts.length, "not-equal-length");
         uint[] memory iniBal = new uint[](_length);

contracts/receivers/aave-v2-receiver/variables.sol

@@ -41,6 +41,12 @@ contract Variables {
      */
     address public constant maticReceiver = 0x0000000000000000000000000000000000001001;
 
+    /**
+    * @dev ReentrancyGuard
+    */
+    uint256 private constant _NOT_ENTERED = 1;
+    uint256 private constant _ENTERED = 2;
+
 
     // Storage variables //
 
@@ -66,4 +72,32 @@ contract Variables {
     * @dev last stateId from the onStateReceive
     */
     uint256 internal lastStateId;
+
+    /**
+    * @dev ReentrancyGuard status variable
+    */
+    uint256 private _reentrancyStatus;
+
+    // Modifer //
+
+    /**
+     * @dev Prevents a contract from calling itself, directly or indirectly.
+     * Calling a `nonReentrant` function from another `nonReentrant`
+     * function is not supported. It is possible to prevent this from happening
+     * by making the `nonReentrant` function external, and make it call a
+     * `private` function that does the actual work.
+     */
+    modifier nonReentrant() {
+        // On the first call to nonReentrant, _notEntered will be true
+        require(_reentrancyStatus != _ENTERED, "ReentrancyGuard: reentrant call");
+
+        // Any calls to nonReentrant after this point will fail
+        _reentrancyStatus = _ENTERED;
+
+        _;
+
+        // By storing the original value once again, a refund is triggered (see
+        // https://eips.ethereum.org/EIPS/eip-2200)
+        _reentrancyStatus = _NOT_ENTERED;
+    }
 }