feat(ctb): Prevent duplicate `step` moves (#9653)

* Prevent duplicate steps

* Prevent duplicate step claims

packages/contracts-bedrock/semver-lock.json

@@ -100,8 +100,8 @@
     "sourceCodeHash": "0x1e5a6deded88804971fc1847c9eac65921771bff353437c0b29ed2f55513b984"
   },
   "src/dispute/FaultDisputeGame.sol": {
-    "initCodeHash": "0x44969c83852ed72e3152bcd98533fefa7b88116a939bf7ee4ad0f87dc9091ea2",
-    "sourceCodeHash": "0x47a93c22df3b8481be0a553ba0ecccfc63cccf1ce7a5d908f11c940f4924b09a"
+    "initCodeHash": "0xa06a5699121ff4b6f7bb89c43d56070fffee78c856363ead237e45ad6746db87",
+    "sourceCodeHash": "0x5f98e7357a45507c39366d3056a6c948d6be1a0b72a8758c66396041aa823fc9"
   },
   "src/legacy/DeployerWhitelist.sol": {
     "initCodeHash": "0x8de80fb23b26dd9d849f6328e56ea7c173cd9e9ce1f05c9beea559d1720deb3d",

packages/contracts-bedrock/snapshots/abi/FaultDisputeGame.json

@@ -623,6 +623,11 @@
     "name": "ClockTimeExceeded",
     "type": "error"
   },
+  {
+    "inputs": [],
+    "name": "DuplicateStep",
+    "type": "error"
+  },
   {
     "inputs": [],
     "name": "GameDepthExceeded",

packages/contracts-bedrock/snapshots/abi/PermissionedDisputeGame.json

@@ -638,6 +638,11 @@
     "name": "ClockTimeExceeded",
     "type": "error"
   },
+  {
+    "inputs": [],
+    "name": "DuplicateStep",
+    "type": "error"
+  },
   {
     "inputs": [],
     "name": "GameDepthExceeded",

packages/contracts-bedrock/src/dispute/FaultDisputeGame.sol

@@ -81,8 +81,8 @@ contract FaultDisputeGame is IFaultDisputeGame, Clone, ISemver {
     bool internal initialized;
 
     /// @notice Semantic version.
-    /// @custom:semver 0.5.0
-    string public constant version = "0.5.0";
+    /// @custom:semver 0.6.0
+    string public constant version = "0.6.0";
 
     /// @param _gameType The type ID of the game.
     /// @param _absolutePrestate The absolute prestate of the instruction trace.
@@ -193,6 +193,9 @@ contract FaultDisputeGame is IFaultDisputeGame, Clone, ISemver {
         bool parentPostAgree = (parentPos.depth() - postState.position.depth()) % 2 == 0;
         if (parentPostAgree == validStep) revert ValidStep();
 
+        // INVARIANT: A step cannot be made against a claim for a second time.
+        if (parent.counteredBy != address(0)) revert DuplicateStep();
+
         // Set the parent claim as countered. We do not need to append a new claim to the game;
         // instead, we can just set the existing parent as countered.
         parent.counteredBy = msg.sender;

packages/contracts-bedrock/src/libraries/DisputeErrors.sol

@@ -88,6 +88,10 @@ error ClaimAboveSplit();
 ///         depth of the game.
 error InvalidSplitDepth();
 
+/// @notice Thrown when trying to step against a claim for a second time, after it has already been countered with
+///         an instruction step.
+error DuplicateStep();
+
 ////////////////////////////////////////////////////////////////
 //              `PermissionedDisputeGame` Errors              //
 ////////////////////////////////////////////////////////////////

packages/contracts-bedrock/test/dispute/FaultDisputeGame.t.sol

@@ -442,6 +442,27 @@ contract FaultDisputeGame_Test is FaultDisputeGame_Init {
         gameProxy.attack{ value: 0 }(0, _dummyClaim());
     }
 
+    /// @dev Tests that a claim cannot be stepped against twice.
+    function test_step_duplicateStep_reverts() public {
+        // Give the test contract some ether
+        vm.deal(address(this), 100 ether);
+
+        // Make claims all the way down the tree.
+        gameProxy.attack{ value: 1 ether }(0, _dummyClaim());
+        gameProxy.attack{ value: 1 ether }(1, _dummyClaim());
+        gameProxy.attack{ value: 1 ether }(2, _dummyClaim());
+        gameProxy.attack{ value: 1 ether }(3, _dummyClaim());
+        gameProxy.attack{ value: 1 ether }(4, _changeClaimStatus(_dummyClaim(), VMStatuses.PANIC));
+        gameProxy.attack{ value: 1 ether }(5, _dummyClaim());
+        gameProxy.attack{ value: 1 ether }(6, _dummyClaim());
+        gameProxy.attack{ value: 1 ether }(7, _dummyClaim());
+        gameProxy.addLocalData(LocalPreimageKey.STARTING_L2_BLOCK_NUMBER, 8, 0);
+        gameProxy.step(8, true, absolutePrestateData, hex"");
+
+        vm.expectRevert(DuplicateStep.selector);
+        gameProxy.step(8, true, absolutePrestateData, hex"");
+    }
+
     /// @dev Static unit test for the correctness an uncontested root resolution.
     function test_resolve_rootUncontested_succeeds() public {
         vm.warp(block.timestamp + 3 days + 12 hours + 1 seconds);