fix: reject zero scale factor

.github/workflows/certora.yml

@@ -0,0 +1,44 @@
+name: Certora
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  verify:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+        with:
+          submodules: recursive
+
+      - uses: actions/setup-java@be666c2fcd27ec809703dec50e508c2fdc7f6654 # v5
+        with:
+          distribution: temurin
+          java-version: "21"
+
+      - uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6
+        with:
+          python-version: ">=3.11"
+
+      - name: Install certora
+        run: pip install certora-cli
+
+      - name: Install solc (0.8.21)
+        env:
+          EXPECTED_SOLC_SHA256: f2857a898be15c69e8de5598dcd3f3e169e94964a0ce9a0bbb1b111f145a81df
+        run: |
+          wget https://github.com/ethereum/solidity/releases/download/v0.8.21/solc-static-linux
+          actual="$(sha256sum solc-static-linux | awk '{print $1}')"
+          [ "$actual" = "$EXPECTED_SOLC_SHA256" ] || { echo "solc hash mismatch"; exit 1; }
+          chmod +x solc-static-linux
+          sudo mv solc-static-linux /usr/local/bin/solc-0.8.21
+
+      - name: Verify MorphoChainlinkOracleV2 specification
+        run: certoraRun certora/confs/MorphoChainlinkOracleV2.conf
+        env:
+          CERTORAKEY: ${{ secrets.CERTORAKEY }}

certora/README.md

@@ -0,0 +1,12 @@
+This folder contains the verification of MorphoChainlinkOracleV2 using CVL, Certora's Verification Language.
+
+# Getting started
+
+Install the `certora-cli` package with `pip install certora-cli`.
+The verification requires `solc-0.8.21` and the `CERTORAKEY` environment variable to be set to a valid Certora key.
+
+To prove that every successful deployment has a non-zero scale factor, run from the repository root:
+
+```bash
+certoraRun certora/confs/MorphoChainlinkOracleV2.conf --rule scaleFactorCannotBeZero
+```

certora/confs/MorphoChainlinkOracleV2.conf

@@ -0,0 +1,14 @@
+{
+  "files": [
+    "certora/helpers/MorphoChainlinkOracleV2Harness.sol"
+  ],
+  "solc": "solc-0.8.21",
+  "solc_evm_version": "paris",
+  "solc_optimize": "999999",
+  "solc_via_ir": true,
+  "verify": "MorphoChainlinkOracleV2Harness:certora/specs/MorphoChainlinkOracleV2.spec",
+  "optimistic_loop": true,
+  "rule_sanity": "basic",
+  "server": "production",
+  "msg": "MorphoChainlinkOracleV2 scale factor"
+}

certora/helpers/MorphoChainlinkOracleV2Harness.sol

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+pragma solidity 0.8.21;
+
+import {MorphoChainlinkOracleV2} from "../../src/morpho-chainlink/MorphoChainlinkOracleV2.sol";
+import {AggregatorV3Interface} from "../../src/morpho-chainlink/interfaces/AggregatorV3Interface.sol";
+import {IERC4626} from "../../src/morpho-chainlink/interfaces/IERC4626.sol";
+
+contract MorphoChainlinkOracleV2Harness is MorphoChainlinkOracleV2 {
+    constructor()
+        MorphoChainlinkOracleV2(
+            IERC4626(address(0)),
+            1,
+            AggregatorV3Interface(address(0)),
+            AggregatorV3Interface(address(0)),
+            0,
+            IERC4626(address(0)),
+            1,
+            AggregatorV3Interface(address(0)),
+            AggregatorV3Interface(address(0)),
+            0
+        )
+    {}
+
+    function computeScaleFactor(
+        uint256 quoteTokenDecimals,
+        uint256 quoteFeed1Decimals,
+        uint256 quoteFeed2Decimals,
+        uint256 baseTokenDecimals,
+        uint256 baseFeed1Decimals,
+        uint256 baseFeed2Decimals,
+        uint256 quoteVaultConversionSample,
+        uint256 baseVaultConversionSample
+    ) external pure returns (uint256) {
+        return _scaleFactor(
+            quoteTokenDecimals,
+            quoteFeed1Decimals,
+            quoteFeed2Decimals,
+            baseTokenDecimals,
+            baseFeed1Decimals,
+            baseFeed2Decimals,
+            quoteVaultConversionSample,
+            baseVaultConversionSample
+        );
+    }
+}

certora/specs/MorphoChainlinkOracleV2.spec

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+methods {
+    function computeScaleFactor(uint256, uint256, uint256, uint256, uint256, uint256, uint256, uint256) external returns (uint256) envfree;
+}
+
+// Checks that every successful scale factor computation returns a non-zero value.
+rule scaleFactorCannotBeZero(uint256 quoteTokenDecimals, uint256 quoteFeed1Decimals, uint256 quoteFeed2Decimals, uint256 baseTokenDecimals, uint256 baseFeed1Decimals, uint256 baseFeed2Decimals, uint256 quoteVaultConversionSample, uint256 baseVaultConversionSample) {
+    uint256 scaleFactor = computeScaleFactor@withrevert(quoteTokenDecimals, quoteFeed1Decimals, quoteFeed2Decimals, baseTokenDecimals, baseFeed1Decimals, baseFeed2Decimals, quoteVaultConversionSample, baseVaultConversionSample);
+
+    require !lastReverted;
+
+    assert scaleFactor != 0, "scale factor is zero after a successful computation";
+}

src/morpho-chainlink/MorphoChainlinkOracleV2.sol

@@ -134,14 +134,37 @@ contract MorphoChainlinkOracleV2 is IMorphoChainlinkOracleV2 {
 
         // So SCALE_FACTOR = 1e36 * 1e(-dB1) * 1e(dQ1) * 1e(-fpB1) * 1e(-fpB2) * 1e(fpQ1) * 1e(fpQ2)
         //                 = 1e(36 + dQ1 + fpQ1 + fpQ2 - dB1 - fpB1 - fpB2)
-        SCALE_FACTOR = 10
+        SCALE_FACTOR = _scaleFactor(
+            quoteTokenDecimals,
+            quoteFeed1.getDecimals(),
+            quoteFeed2.getDecimals(),
+            baseTokenDecimals,
+            baseFeed1.getDecimals(),
+            baseFeed2.getDecimals(),
+            quoteVaultConversionSample,
+            baseVaultConversionSample
+        );
+    }
+
+    function _scaleFactor(
+        uint256 quoteTokenDecimals,
+        uint256 quoteFeed1Decimals,
+        uint256 quoteFeed2Decimals,
+        uint256 baseTokenDecimals,
+        uint256 baseFeed1Decimals,
+        uint256 baseFeed2Decimals,
+        uint256 quoteVaultConversionSample,
+        uint256 baseVaultConversionSample
+    ) internal pure returns (uint256 scaleFactor) {
+        scaleFactor = 10
             ** (36
                 + quoteTokenDecimals
-                + quoteFeed1.getDecimals()
-                + quoteFeed2.getDecimals()
+                + quoteFeed1Decimals
+                + quoteFeed2Decimals
                 - baseTokenDecimals
-                - baseFeed1.getDecimals()
-                - baseFeed2.getDecimals()) * quoteVaultConversionSample / baseVaultConversionSample;
+                - baseFeed1Decimals
+                - baseFeed2Decimals) * quoteVaultConversionSample / baseVaultConversionSample;
+        require(scaleFactor != 0, ErrorsLib.SCALE_FACTOR_IS_ZERO);
     }
 
     /* PRICE */

src/morpho-chainlink/libraries/ErrorsLib.sol

@@ -14,4 +14,7 @@ library ErrorsLib {
 
     /// @notice Thrown when the vault conversion sample is not 1 while vault = address(0).
     string constant VAULT_CONVERSION_SAMPLE_IS_NOT_ONE = "vault conversion sample is not one";
+
+    /// @notice Thrown when the scale factor is 0.
+    string constant SCALE_FACTOR_IS_ZERO = "scale factor is zero";
 }

test/MorphoChainlinkOracleV2ScaleFactorTest.sol

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+pragma solidity ^0.8.0;
+
+import "../lib/forge-std/src/Test.sol";
+import "../src/morpho-chainlink/MorphoChainlinkOracleV2.sol";
+import "../src/morpho-chainlink/interfaces/IERC4626.sol";
+import "./helpers/Constants.sol";
+
+contract MorphoChainlinkOracleV2ScaleFactorTest is Test {
+    function testConstructorScaleFactorZero() public {
+        vm.expectRevert(bytes(ErrorsLib.SCALE_FACTOR_IS_ZERO));
+        new MorphoChainlinkOracleV2(
+            IERC4626(address(1)), 2, feedZero, feedZero, 36, vaultZero, 1, feedZero, feedZero, 0
+        );
+    }
+}