fix: maci 12 account can vote unlimited times in free for all policy

Author: JohnGuilding

packages/contracts/contracts/extensions/freeForAll/FreeForAllPolicy.sol

@@ -4,12 +4,28 @@ pragma solidity ^0.8.20;
 import {BasePolicy} from "../../policy/BasePolicy.sol";
 
 /// @title FreeForAllPolicy
-/// @notice A policy which allows anyone to sign up.
+/// @notice A policy which allows anyone to sign up, but only once per address.
 contract FreeForAllPolicy is BasePolicy {
+    /// @notice Store the addreses that have been enforced
+    mapping(address => bool) public enforcedUsers;
+
     /// @notice Create a new instance of FreeForAllPolicy
     // solhint-disable-next-line no-empty-blocks
     constructor() payable {}
 
+    /// @notice Enforce a user so they can only be enforced once
+    /// @param subject The user's Ethereum address.
+    /// @param evidence The ABI-encoded evidence data.
+    function _enforce(address subject, bytes calldata evidence) internal override {
+        if (enforcedUsers[subject]) {
+            revert AlreadyEnforced();
+        }
+
+        enforcedUsers[subject] = true;
+
+        super._enforce(subject, evidence);
+    }
+
     /// @notice Get the trait of the Policy
     /// @return The type of the Policy
     function trait() public pure override returns (string memory) {

packages/contracts/test/extensions/FreeForAll.test.ts

@@ -79,5 +79,11 @@ describe("FreeForAll", () => {
 
             expect(receipt?.status).to.eq(1)
         })
+
+        it("should prevent enforcing the same account twice", async () => {
+            await expect(
+                policy.connect(target).enforce(subject, AbiCoder.defaultAbiCoder().encode([], []))
+            ).to.be.revertedWithCustomError(policy, "AlreadyEnforced")
+        })
     })
 })