add L2Relayer check (#144)

packages/contracts/contracts/optimistic-ethereum/OVM/bridge/OVM_L1CrossDomainMessenger.sol

@@ -45,6 +45,25 @@ contract OVM_L1CrossDomainMessenger is iOVM_L1CrossDomainMessenger, OVM_BaseCros
     }
 
 
+    /**********************
+     * Function Modifiers *
+     **********************/
+
+    /**
+     * Modifier to enforce that, if configured, only the OVM_L2MessageRelayer contract may successfully call a method.
+     */
+    modifier onlyRelayer() {
+        address relayer = resolve("OVM_L2MessageRelayer");
+        if (relayer != address(0)) {
+            require(
+                msg.sender == relayer,
+                "Only OVM_L2MessageRelayer can relay L2-to-L1 messages."
+            );
+        }
+        _;
+    }
+
+
     /********************
      * Public Functions *
      ********************/
@@ -62,6 +81,7 @@ contract OVM_L1CrossDomainMessenger is iOVM_L1CrossDomainMessenger, OVM_BaseCros
     )
         override
         public
+        onlyRelayer()
     {
         bytes memory xDomainCalldata = _getXDomainCalldata(
             _target,

packages/contracts/test/contracts/OVM/bridge/OVM_L1CrossDomainMessenger.spec.ts

@@ -352,5 +352,23 @@ describe('OVM_L1CrossDomainMessenger', () => {
         )
       ).to.be.revertedWith('Provided message has already been received.')
     })
+
+    it('when the OVM_L2MessageRelayer address is set, should revert if called by a different account', async () => {
+      // set to a random NON-ZERO address
+      await AddressManager.setAddress(
+        'OVM_L2MessageRelayer',
+        '0x1234123412341234123412341234123412341234'
+      )
+
+      await expect(
+        OVM_L1CrossDomainMessenger.relayMessage(
+          target,
+          sender,
+          message,
+          0,
+          proof
+        )
+      ).to.be.revertedWith('Only OVM_L2MessageRelayer can relay L2-to-L1 messages.')
+    })
   })
 })