C4: handle Chainlink oracle deprecation

contracts/plugins/assets/OracleLib.sol

@@ -6,6 +6,10 @@ import "../../libraries/Fixed.sol";
 
 error StalePrice();
 
+interface EACAggregatorProxy {
+    function aggregator() external view returns (address);
+}
+
 /// Used by asset plugins to price their collateral
 library OracleLib {
     /// @dev Use for on-the-fly calculations that should revert
@@ -16,6 +20,11 @@ library OracleLib {
         view
         returns (uint192)
     {
+        // If the aggregator is not set, the chainlink feed has been deprecated
+        if (EACAggregatorProxy(address(chainlinkFeed)).aggregator() == address(0)) {
+            revert StalePrice();
+        }
+
         (uint80 roundId, int256 p, , uint256 updateTime, uint80 answeredInRound) = chainlinkFeed
         .latestRoundData();
 

contracts/plugins/mocks/ChainlinkMock.sol

@@ -23,16 +23,22 @@ contract MockV3Aggregator is AggregatorV3Interface {
 
     // Additional variable to be able to test invalid behavior
     uint256 public latestAnsweredRound;
+    address public aggregator;
 
     mapping(uint256 => int256) public getAnswer;
     mapping(uint256 => uint256) public getTimestamp;
     mapping(uint256 => uint256) private getStartedAt;
 
     constructor(uint8 _decimals, int256 _initialAnswer) {
         decimals = _decimals;
+        aggregator = address(this);
         updateAnswer(_initialAnswer);
     }
 
+    function deprecate() external {
+        aggregator = address(0);
+    }
+
     function updateAnswer(int256 _answer) public {
         latestAnswer = _answer;
         latestTimestamp = block.timestamp;
@@ -80,6 +86,12 @@ contract MockV3Aggregator is AggregatorV3Interface {
             uint80 answeredInRound
         )
     {
+        if (aggregator == address(0)) {
+            // solhint-disable-next-line no-inline-assembly
+            assembly {
+                revert(0, 0)
+            }
+        }
         return (
             _roundId,
             getAnswer[_roundId],
@@ -102,6 +114,12 @@ contract MockV3Aggregator is AggregatorV3Interface {
             uint80 answeredInRound
         )
     {
+        if (aggregator == address(0)) {
+            // solhint-disable-next-line no-inline-assembly
+            assembly {
+                revert(0, 0)
+            }
+        }
         return (
             uint80(latestRound),
             getAnswer[latestRound],

test/fixtures.ts

@@ -1,4 +1,4 @@
-import { BigNumber, ContractFactory } from 'ethers'
+import { ContractFactory } from 'ethers'
 import { expect } from 'chai'
 import hre, { ethers } from 'hardhat'
 import { getChainId } from '../common/blockchain-utils'
@@ -149,19 +149,12 @@ async function gnosisFixture(): Promise<GnosisFixture> {
   }
 }
 
-interface CollateralFixture {
-  erc20s: ERC20Mock[] // all erc20 addresses
-  collateral: Collateral[] // all collateral
-  basket: Collateral[] // only the collateral actively backing the RToken
-  basketsNeededAmts: BigNumber[] // reference amounts
-}
-
 async function collateralFixture(
   compToken: ERC20Mock,
   comptroller: ComptrollerMock,
   aaveToken: ERC20Mock,
   config: IConfig
-): Promise<CollateralFixture> {
+) {
   const ERC20: ContractFactory = await ethers.getContractFactory('ERC20Mock')
   const USDC: ContractFactory = await ethers.getContractFactory('USDCMock')
   const ATokenMockFactory: ContractFactory = await ethers.getContractFactory('StaticATokenMock')
@@ -349,7 +342,7 @@ async function collateralFixture(
     ausdt[0],
     abusd[0],
     zcoin[0],
-  ]
+  ] as ERC20Mock[]
   const collateral = [
     dai[1],
     usdc[1],
@@ -374,9 +367,25 @@ async function collateralFixture(
     collateral,
     basket,
     basketsNeededAmts,
+    bySymbol: {
+      dai,
+      usdc,
+      usdt,
+      busd,
+      cdai,
+      cusdc,
+      cusdt,
+      adai,
+      ausdc,
+      ausdt,
+      abusd,
+      zcoin,
+    },
   }
 }
 
+type CollateralFixture = Awaited<ReturnType<typeof collateralFixture>>
+
 type RSRAndCompAaveAndCollateralAndModuleFixture = RSRFixture &
   COMPAAVEFixture &
   CollateralFixture &
@@ -663,7 +672,7 @@ const makeDefaultFixture = async (setBasket: boolean): Promise<DefaultFixture> =
   const stRSR: TestIStRSR = <TestIStRSR>await ethers.getContractAt('TestIStRSR', await main.stRSR())
 
   // Deploy collateral for Main
-  const { erc20s, collateral, basket, basketsNeededAmts } = await collateralFixture(
+  const { erc20s, collateral, basket, basketsNeededAmts, bySymbol } = await collateralFixture(
     compToken,
     compoundMock,
     aaveToken,
@@ -742,5 +751,6 @@ const makeDefaultFixture = async (setBasket: boolean): Promise<DefaultFixture> =
     facadeTest,
     rsrTrader,
     rTokenTrader,
+    bySymbol,
   }
 }

test/plugins/OracleDeprecation.test.ts

@@ -0,0 +1,64 @@
+import { Wallet } from 'ethers'
+import { ethers } from 'hardhat'
+import { loadFixture } from '@nomicfoundation/hardhat-network-helpers'
+import { fp } from '../../common/numbers'
+import { ERC20Mock, TestIRToken } from '../../typechain'
+import { Collateral, DefaultFixture, defaultFixture } from '../fixtures'
+import { expect } from 'chai'
+
+describe('Chainlink Oracle', () => {
+  // Tokens
+  let rsr: ERC20Mock
+  let compToken: ERC20Mock
+  let aaveToken: ERC20Mock
+  let rToken: TestIRToken
+
+  // Assets
+  let basket: Collateral[]
+
+  let wallet: Wallet
+
+  const amt = fp('1e4')
+  let fixture: DefaultFixture
+
+  before('create fixture loader', async () => {
+    ;[wallet] = (await ethers.getSigners()) as unknown as Wallet[]
+  })
+
+  beforeEach(async () => {
+    // Deploy fixture
+    fixture = await loadFixture(defaultFixture)
+    ;({ rsr, compToken, aaveToken, basket, rToken } = fixture)
+
+    // Get collateral tokens
+    await rsr.connect(wallet).mint(wallet.address, amt)
+    await compToken.connect(wallet).mint(wallet.address, amt)
+    await aaveToken.connect(wallet).mint(wallet.address, amt)
+
+    // Issue RToken to enable RToken.price
+    for (let i = 0; i < basket.length; i++) {
+      const tok = await ethers.getContractAt('ERC20Mock', await basket[i].erc20())
+      await tok.connect(wallet).mint(wallet.address, amt)
+      await tok.connect(wallet).approve(rToken.address, amt)
+    }
+    await rToken.connect(wallet).issue(amt)
+  })
+
+  describe('Chainlink deprecates an asset', () => {
+    it('Refresh should mark the asset as IFFY', async () => {
+      const MockV3AggregatorFactory = await ethers.getContractFactory('MockV3Aggregator')
+      const [, aUSDCCollateral] = fixture.bySymbol.ausdc
+      const chainLinkOracle = MockV3AggregatorFactory.attach(await aUSDCCollateral.chainlinkFeed())
+      await aUSDCCollateral.refresh()
+      await aUSDCCollateral.tryPrice()
+      expect(await aUSDCCollateral.status()).to.equal(0)
+      await chainLinkOracle.deprecate()
+      await aUSDCCollateral.refresh()
+      expect(await aUSDCCollateral.status()).to.equal(1)
+      await expect(aUSDCCollateral.tryPrice()).to.be.revertedWithCustomError(
+        aUSDCCollateral,
+        'StalePrice'
+      )
+    })
+  })
+})