audit(14): arbitrum block number (#280)

* Use IArbSys for Arbitrum block number fetching

* fmt

* style: forge fmt

* Add BlockNumberish and tests

* nit: comment

* add attribution

* Move MockArbSys to test/util/mock/

* forge fmt

---------

Co-authored-by: Alan Wu <alanwu100@gmail.com>
Co-authored-by: Cody Born <cody.born@uniswap.org>

.forge-snapshots/Base-V3DutchOrder-BaseExecuteSingleWithFee.snap

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.forge-snapshots/Base-V3DutchOrder-ExecuteBatch.snap

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.forge-snapshots/Base-V3DutchOrder-ExecuteBatchMultipleOutputs.snap

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.forge-snapshots/Base-V3DutchOrder-ExecuteBatchMultipleOutputsDifferentTokens.snap

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.forge-snapshots/Base-V3DutchOrder-ExecuteBatchNativeOutput.snap

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.forge-snapshots/Base-V3DutchOrder-ExecuteSingle.snap

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.forge-snapshots/Base-V3DutchOrder-ExecuteSingleNativeOutput.snap

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.forge-snapshots/Base-V3DutchOrder-ExecuteSingleValidation.snap

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.forge-snapshots/Base-V3DutchOrder-RevertInvalidNonce.snap

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.forge-snapshots/Base-V3DutchOrder-V3-ExclusiveFiller.snap

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.forge-snapshots/Base-V3DutchOrder-V3-InputOverride.snap

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.forge-snapshots/Base-V3DutchOrder-V3-OutputOverride.snap

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.forge-snapshots/V3-DutchDecay.snap

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.forge-snapshots/V3-DutchDecayBounded.snap

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.forge-snapshots/V3-DutchDecayFullyDecayed.snap

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.forge-snapshots/V3-DutchDecayFullyDecayedNegative.snap

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.forge-snapshots/V3-DutchDecayNegative.snap

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.forge-snapshots/V3-DutchDecayNoDecay.snap

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.forge-snapshots/V3-DutchDecayNoDecayYet.snap

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.forge-snapshots/V3-DutchDecayRange.snap

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.forge-snapshots/V3-ExtendedMultiPointDutchDecay.snap

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.forge-snapshots/V3-MultiPointDutchDecay.snap

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src/base/BlockNumberish.sol

@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import {IArbSys} from "../interfaces/IArbSys.sol";
+
+/// @title BlockNumberish
+/// A helper contract to get the current block number on different chains
+/// inspired by https://github.com/ProjectOpenSea/tstorish/blob/main/src/Tstorish.sol
+contract BlockNumberish {
+    // Declare an immutable function type variable for the _getBlockNumberish function
+    function() view returns (uint256) internal immutable _getBlockNumberish;
+
+    uint256 private constant ARB_CHAIN_ID = 42161;
+    address private constant ARB_SYS_ADDRESS = 0x0000000000000000000000000000000000000064;
+
+    constructor() {
+        // Set the function to use based on chainid
+        if (block.chainid == ARB_CHAIN_ID) {
+            _getBlockNumberish = _getBlockNumberSyscall;
+        } else {
+            _getBlockNumberish = _getBlockNumber;
+        }
+    }
+
+    /// @dev Private function to get the block number on arbitrum
+    function _getBlockNumberSyscall() private view returns (uint256) {
+        return IArbSys(ARB_SYS_ADDRESS).arbBlockNumber();
+    }
+
+    /// @dev Private function to get the block number using the opcode
+    function _getBlockNumber() private view returns (uint256) {
+        return block.number;
+    }
+}

src/interfaces/IArbSys.sol

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+pragma solidity ^0.8.0;
+
+/**
+ * @notice Minimal interface for interacting with Arbitrum system contracts
+ */
+interface IArbSys {
+    /**
+     * @notice Get Arbitrum block number (distinct from L1 block number; Arbitrum genesis block has block number 0)
+     * @return block number as int
+     */
+    function arbBlockNumber() external view returns (uint256);
+}

src/lib/ExclusivityLib.sol

@@ -3,6 +3,7 @@ pragma solidity ^0.8.0;
 
 import {FixedPointMathLib} from "solmate/src/utils/FixedPointMathLib.sol";
 import {ResolvedOrder, OutputToken} from "../base/ReactorStructs.sol";
+import {IArbSys} from "../interfaces/IArbSys.sol";
 
 /// @title ExclusiveOverride
 /// @dev This library handles order exclusivity
@@ -40,9 +41,10 @@ library ExclusivityLib {
         ResolvedOrder memory order,
         address exclusive,
         uint256 exclusivityEnd,
-        uint256 exclusivityOverrideBps
+        uint256 exclusivityOverrideBps,
+        uint256 blockNumberish
     ) internal view {
-        _handleExclusiveOverride(order, exclusive, exclusivityEnd, exclusivityOverrideBps, block.number);
+        _handleExclusiveOverride(order, exclusive, exclusivityEnd, exclusivityOverrideBps, blockNumberish);
     }
 
     /// @notice Applies exclusivity override to the resolved order if necessary

src/lib/NonlinearDutchDecayLib.sol

@@ -8,6 +8,7 @@ import {MathExt} from "./MathExt.sol";
 import {Math} from "openzeppelin-contracts/utils/math/Math.sol";
 import {Uint16ArrayLibrary, Uint16Array, fromUnderlying} from "../types/Uint16Array.sol";
 import {DutchDecayLib} from "./DutchDecayLib.sol";
+import {IArbSys} from "../interfaces/IArbSys.sol";
 
 /// @notice helpers for handling non-linear dutch order objects
 library NonlinearDutchDecayLib {
@@ -18,41 +19,47 @@ library NonlinearDutchDecayLib {
     /// @notice thrown when the decay curve is invalid
     error InvalidDecayCurve();
 
-    /// @notice Calculates the decayed amount based on the current block and the defined curve
+    /// @notice Struct to hold decay parameters
     /// @param curve The nonlinear decay curve definition
     /// @param startAmount The initial amount at the start of the decay
     /// @param decayStartBlock The absolute block number when the decay begins
+    /// @param blockNumberish The current block number
     /// @param minAmount The minimum amount to decay to
     /// @param maxAmount The maximum amount to decay to
     /// @param decayFunc The decay function to use
     /// @dev Expects the relativeBlocks in curve to be strictly increasing
+    struct DecayParams {
+        NonlinearDutchDecay curve;
+        uint256 startAmount;
+        uint256 decayStartBlock;
+        uint256 blockNumberish;
+        uint256 minAmount;
+        uint256 maxAmount;
+        function(uint256, uint256, uint256, int256, int256) internal pure returns (int256) decayFunc;
+    }
+
+    /// @notice Calculates the decayed amount based on the current block and the defined curve
+    /// @param params The decay parameters
     /// @return decayedAmount The decayed amount
-    function decay(
-        NonlinearDutchDecay memory curve,
-        uint256 startAmount,
-        uint256 decayStartBlock,
-        uint256 minAmount,
-        uint256 maxAmount,
-        function(uint256, uint256, uint256, int256, int256) internal pure returns (int256) decayFunc
-    ) internal view returns (uint256 decayedAmount) {
+    function decay(DecayParams memory params) internal pure returns (uint256 decayedAmount) {
         // mismatch of relativeAmounts and relativeBlocks
-        if (curve.relativeAmounts.length > 16) {
+        if (params.curve.relativeAmounts.length > 16) {
             revert InvalidDecayCurve();
         }
 
         // handle current block before decay or no decay
-        if (decayStartBlock >= block.number || curve.relativeAmounts.length == 0) {
-            return startAmount.bound(minAmount, maxAmount);
+        if (params.decayStartBlock >= params.blockNumberish || params.curve.relativeAmounts.length == 0) {
+            return params.startAmount.bound(params.minAmount, params.maxAmount);
         }
         // If the blockDelta is larger than type(uint16).max, a downcast overflow will occur
         // We prevent this by capping the blockDelta to type(uint16).max to express a full decay
-        uint16 blockDelta = uint16(Math.min(block.number - decayStartBlock, type(uint16).max));
+        uint16 blockDelta = uint16(Math.min(params.blockNumberish - params.decayStartBlock, type(uint16).max));
         (uint16 startPoint, uint16 endPoint, int256 relStartAmount, int256 relEndAmount) =
-            locateCurvePosition(curve, blockDelta);
+            locateCurvePosition(params.curve, blockDelta);
         // get decay of only the relative amounts
-        int256 curveDelta = decayFunc(startPoint, endPoint, blockDelta, relStartAmount, relEndAmount);
+        int256 curveDelta = params.decayFunc(startPoint, endPoint, blockDelta, relStartAmount, relEndAmount);
 
-        return startAmount.boundedSub(curveDelta, minAmount, maxAmount);
+        return params.startAmount.boundedSub(curveDelta, params.minAmount, params.maxAmount);
     }
 
     /// @notice Locates the current position on the decay curve based on the elapsed blocks
@@ -98,45 +105,63 @@ library NonlinearDutchDecayLib {
     /// @notice returns a decayed output using the given dutch spec and blocks
     /// @param output The output to decay
     /// @param decayStartBlock The block to start decaying
+    /// @param blockNumberish The block number to decay to
     /// @return result a decayed output
-    function decay(V3DutchOutput memory output, uint256 decayStartBlock)
+    function decay(V3DutchOutput memory output, uint256 decayStartBlock, uint256 blockNumberish)
         internal
-        view
+        pure
         returns (OutputToken memory result)
     {
-        uint256 decayedOutput = decay(
-            output.curve, output.startAmount, decayStartBlock, output.minAmount, type(uint256).max, v3LinearOutputDecay
-        );
+        DecayParams memory params = DecayParams({
+            curve: output.curve,
+            startAmount: output.startAmount,
+            decayStartBlock: decayStartBlock,
+            blockNumberish: blockNumberish,
+            minAmount: output.minAmount,
+            maxAmount: type(uint256).max,
+            decayFunc: v3LinearOutputDecay
+        });
+        uint256 decayedOutput = decay(params);
         result = OutputToken(output.token, decayedOutput, output.recipient);
     }
 
     /// @notice returns a decayed output array using the given dutch spec and blocks
     /// @param outputs The output array to decay
     /// @param decayStartBlock The block to start decaying
+    /// @param blockNumberish The block number to decay to
     /// @return result a decayed output array
-    function decay(V3DutchOutput[] memory outputs, uint256 decayStartBlock)
+    function decay(V3DutchOutput[] memory outputs, uint256 decayStartBlock, uint256 blockNumberish)
         internal
-        view
+        pure
         returns (OutputToken[] memory result)
     {
         uint256 outputLength = outputs.length;
         result = new OutputToken[](outputLength);
         for (uint256 i = 0; i < outputLength; i++) {
-            result[i] = decay(outputs[i], decayStartBlock);
+            result[i] = decay(outputs[i], decayStartBlock, blockNumberish);
         }
     }
 
     /// @notice returns a decayed input using the given dutch spec and times
     /// @param input The input to decay
     /// @param decayStartBlock The block to start decaying
+    /// @param blockNumberish The block number to decay to
     /// @return result a decayed input
-    function decay(V3DutchInput memory input, uint256 decayStartBlock)
+    function decay(V3DutchInput memory input, uint256 decayStartBlock, uint256 blockNumberish)
         internal
-        view
+        pure
         returns (InputToken memory result)
     {
-        uint256 decayedInput =
-            decay(input.curve, input.startAmount, decayStartBlock, 0, input.maxAmount, v3LinearInputDecay);
+        DecayParams memory params = DecayParams({
+            curve: input.curve,
+            startAmount: input.startAmount,
+            decayStartBlock: decayStartBlock,
+            blockNumberish: blockNumberish,
+            minAmount: 0,
+            maxAmount: input.maxAmount,
+            decayFunc: v3LinearInputDecay
+        });
+        uint256 decayedInput = decay(params);
         result = InputToken(input.token, decayedInput, input.maxAmount);
     }
 

src/reactors/V3DutchOrderReactor.sol

@@ -8,6 +8,7 @@ import {ExclusivityLib} from "../lib/ExclusivityLib.sol";
 import {NonlinearDutchDecayLib} from "../lib/NonlinearDutchDecayLib.sol";
 import {V3DutchOrderLib, V3DutchOrder, CosignerData, V3DutchOutput, V3DutchInput} from "../lib/V3DutchOrderLib.sol";
 import {SignedOrder, ResolvedOrder} from "../base/ReactorStructs.sol";
+import {BlockNumberish} from "../base/BlockNumberish.sol";
 import {FixedPointMathLib} from "solmate/src/utils/FixedPointMathLib.sol";
 import {MathExt} from "../lib/MathExt.sol";
 import {Math} from "openzeppelin-contracts/utils/math/Math.sol";
@@ -22,7 +23,7 @@ import {CosignerLib} from "../lib/CosignerLib.sol";
 /// - For each outputAmount:
 ///   - If amount is 0, then use baseOutput
 ///   - If amount is nonzero, then ensure it is greater than specified baseOutput and replace startAmount
-contract V3DutchOrderReactor is BaseReactor {
+contract V3DutchOrderReactor is BaseReactor, BlockNumberish {
     using Permit2Lib for ResolvedOrder;
     using V3DutchOrderLib for V3DutchOrder;
     using NonlinearDutchDecayLib for V3DutchOutput[];
@@ -40,7 +41,10 @@ contract V3DutchOrderReactor is BaseReactor {
     /// @notice thrown when an order's cosigner output is less than the specified
     error InvalidCosignerOutput();
 
-    constructor(IPermit2 _permit2, address _protocolFeeOwner) BaseReactor(_permit2, _protocolFeeOwner) {}
+    constructor(IPermit2 _permit2, address _protocolFeeOwner)
+        BaseReactor(_permit2, _protocolFeeOwner)
+        BlockNumberish()
+    {}
 
     /// @inheritdoc BaseReactor
     function _resolve(SignedOrder calldata signedOrder)
@@ -58,17 +62,20 @@ contract V3DutchOrderReactor is BaseReactor {
         _updateWithCosignerAmounts(order);
         _updateWithGasAdjustment(order);
 
+        uint256 blockNumberish = _getBlockNumberish();
+
         resolvedOrder = ResolvedOrder({
             info: order.info,
-            input: order.baseInput.decay(order.cosignerData.decayStartBlock),
-            outputs: order.baseOutputs.decay(order.cosignerData.decayStartBlock),
+            input: order.baseInput.decay(order.cosignerData.decayStartBlock, blockNumberish),
+            outputs: order.baseOutputs.decay(order.cosignerData.decayStartBlock, blockNumberish),
             sig: signedOrder.sig,
             hash: orderHash
         });
         resolvedOrder.handleExclusiveOverrideBlock(
             order.cosignerData.exclusiveFiller,
             order.cosignerData.decayStartBlock,
-            order.cosignerData.exclusivityOverrideBps
+            order.cosignerData.exclusivityOverrideBps,
+            blockNumberish
         );
     }