Make Gnosis account compatible with ERC-1271 (#191)

contracts/samples/gnosis/EIP4337Fallback.sol

@@ -5,16 +5,22 @@ pragma solidity ^0.8.7;
 
 import "@gnosis.pm/safe-contracts/contracts/handler/DefaultCallbackHandler.sol";
 import "@gnosis.pm/safe-contracts/contracts/GnosisSafe.sol";
+import "@openzeppelin/contracts/interfaces/IERC1271.sol";
+import "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";
 import "../../interfaces/IAccount.sol";
 import "./EIP4337Manager.sol";
 
+using ECDSA for bytes32;
+
 /**
  * The GnosisSafe enables adding custom functions implementation to the Safe by setting a 'fallbackHandler'.
  * This 'fallbackHandler' adds an implementation of 'validateUserOp' to the GnosisSafe.
  * Note that the implementation of the 'validateUserOp' method is located in the EIP4337Manager.
  * Upon receiving the 'validateUserOp', a Safe with EIP4337Fallback enabled makes a 'delegatecall' to EIP4337Manager.
  */
-contract EIP4337Fallback is DefaultCallbackHandler, IAccount {
+contract EIP4337Fallback is DefaultCallbackHandler, IAccount, IERC1271 {
+    bytes4 internal constant ERC1271_MAGIC_VALUE = 0x1626ba7e;
+
     address immutable public eip4337manager;
     constructor(address _eip4337manager) {
         eip4337manager = _eip4337manager;
@@ -55,4 +61,21 @@ contract EIP4337Fallback is DefaultCallbackHandler, IAccount {
     ) external {
         delegateToManager();
     }
-}
+
+    function isValidSignature(
+        bytes32 _hash,
+        bytes memory _signature
+    ) external override view returns (bytes4) {
+        bytes32 hash = _hash.toEthSignedMessageHash();
+        address recovered = hash.recover(_signature);
+
+        GnosisSafe safe = GnosisSafe(payable(address(msg.sender)));
+
+        // Validate signatures
+        if (safe.isOwner(recovered)) {
+            return ERC1271_MAGIC_VALUE;
+        } else {
+            return 0xffffffff;
+        }
+    }
+}

test/gnosis.test.ts

@@ -2,6 +2,7 @@ import './aa.init'
 import { ethers } from 'hardhat'
 import { Signer } from 'ethers'
 import {
+  EIP4337Fallback__factory,
   EIP4337Manager,
   EIP4337Manager__factory,
   EntryPoint,
@@ -205,6 +206,21 @@ describe('Gnosis Proxy', function () {
     console.log('gasUsed=', rcpt.gasUsed, rcpt.transactionHash)
   })
 
+  it('should validate ERC1271 signatures', async function () {
+    const safe = EIP4337Fallback__factory.connect(proxySafe.address, ethersSigner)
+
+    const message = ethers.utils.hexlify(ethers.utils.toUtf8Bytes('hello erc1271'))
+    const dataHash = ethers.utils.arrayify(ethers.utils.keccak256(message))
+
+    const sig = await owner.signMessage(dataHash)
+    expect(await safe.isValidSignature(dataHash, sig)).to.be.eq('0x1626ba7e')
+
+    // make an sig invalid
+    const badWallet = ethers.Wallet.createRandom()
+    const badSig = await badWallet.signMessage(dataHash)
+    expect(await safe.isValidSignature(dataHash, badSig)).to.be.not.eq('0x1626ba7e')
+  })
+
   context('#replaceEIP4337', () => {
     let signature: string
     let newEntryPoint: EntryPoint