add _setCollateralPaused()

contracts/Comptroller.sol

@@ -12,7 +12,7 @@ import "./Governance/IINV.sol";
  * @title Compound's Comptroller Contract
  * @author Compound
  */
-contract Comptroller is ComptrollerV5Storage, ComptrollerInterface, ComptrollerErrorReporter, ExponentialNoError {
+contract Comptroller is ComptrollerV6Storage, ComptrollerInterface, ComptrollerErrorReporter, ExponentialNoError {
     /// @notice Emitted when an admin supports a market
     event MarketListed(CToken cToken);
 
@@ -721,6 +721,13 @@ contract Comptroller is ComptrollerV5Storage, ComptrollerInterface, ComptrollerE
             if (oErr != 0) { // semi-opaque error code, we assume NO_ERROR == 0 is invariant between upgrades
                 return (Error.SNAPSHOT_ERROR, 0, 0);
             }
+
+            // New code
+            // Check if the collateral is paused, only for borrowing
+            if (collateralGuardianPaused[address(asset)] == true && borrowAmount > 0 && vars.cTokenBalance > 0){
+                return (Error.COLLATERAL_PAUSED, 0, 0);
+            }
+
             vars.collateralFactor = Exp({mantissa: markets[address(asset)].collateralFactorMantissa});
             vars.exchangeRate = Exp({mantissa: vars.exchangeRateMantissa});
 
@@ -1037,6 +1044,17 @@ contract Comptroller is ComptrollerV5Storage, ComptrollerInterface, ComptrollerE
         return state;
     }
 
+    //New code
+    function _setCollateralPaused(CToken cToken, bool state) public returns (bool) {
+        require(markets[address(cToken)].isListed, "cannot pause a market that is not listed");
+        require(msg.sender == pauseGuardian || msg.sender == admin, "only pause guardian and admin can pause");
+        require(msg.sender == admin || state == true, "only admin can unpause");
+
+        collateralGuardianPaused[address(cToken)] = state;
+        emit ActionPaused(cToken, "Collateral", state);
+        return state;
+    }
+
     function _become(Unitroller unitroller) public {
         require(msg.sender == unitroller.admin(), "only unitroller admin can change brains");
         require(unitroller._acceptImplementation() == 0, "change not authorized");

contracts/ComptrollerStorage.sol

@@ -143,3 +143,17 @@ contract ComptrollerV5Storage is ComptrollerV4Storage {
     /// @notice Last block at which a contributor's COMP rewards have been allocated
     mapping(address => uint) public lastContributorBlock;
 }
+
+//New code
+contract ComptrollerV6Storage is ComptrollerV5Storage {
+
+    /** 
+     * @notice Addition to the Pause Guardian storage slots in V2. 
+     * Appended as V6 to avoid introducing storage slot conflicts.
+     */
+
+
+    /// @notice Whether a cToken is paused for borrowing or not
+    mapping(address => bool) public collateralGuardianPaused; 
+}
+

contracts/ErrorReporter.sol

@@ -19,7 +19,8 @@ contract ComptrollerErrorReporter {
         REJECTION,
         SNAPSHOT_ERROR,
         TOO_MANY_ASSETS,
-        TOO_MUCH_REPAY
+        TOO_MUCH_REPAY,
+        COLLATERAL_PAUSED
     }
 
     enum FailureInfo {
@@ -204,4 +205,4 @@ contract TokenErrorReporter {
 
         return uint(err);
     }
-}
+}