Incorrect Calculation of maxStakeDebt in Unstake Function

[hats-bug-reporter[bot]]

Github username: @0xmahdirostami Twitter username: 0xmahdirostami Submission hash (on-chain): 0xad0fb59acb53719666b679fc578e0f6c12114049a33c1b7b028ddb102800ec61 Severity: low

Description: Description\ As mentioned in issue #7, maxStakeDebt will be calculated in the following way:

accounts[_user].maxStakeDebt = (accounts[msg.sender].stakedBalance * maxLockDuration) / SECONDS_PER_YEAR

but in unstake function, it's calculated in the following way:

        uint256 maxStakeDebt = accounts[msg.sender].maxStakeDebt -= (_amount * maxLockDuration) / SECONDS_PER_YEAR;

Impact\ The incorrect calculation of maxStakeDebt in the unstake function may lead to inaccurate values for maxStakeDebt and availableToWithdraw.

Attachments\

1. Proof of Concept (PoC) File

   add the following helper functions:

   function unstakeA(uint256 _amount) external nonReentrant existingAccount returns(uint256){
   _updateAccount(msg.sender,0);
   
   uint256 stakedBalance = accounts[msg.sender].stakedBalance - _amount;
   uint256 maxStakeDebt = accounts[msg.sender].maxStakeDebt - (_amount * maxLockDuration) / SECONDS_PER_YEAR;
   return(maxStakeDebt);
   }
   function unstakeB(uint256 _amount) external nonReentrant existingAccount returns(uint256){
   _updateAccount(msg.sender,0);
   
   uint256 stakedBalance = accounts[msg.sender].stakedBalance =- _amount;
   uint256 maxStakeDebt = (accounts[msg.sender].stakedBalance * maxLockDuration) / SECONDS_PER_YEAR;
   return(maxStakeDebt);
   }

   test:

   function testFuzz_mahdi(uint256 x) public {
   help_fundAndActivate();
   help_stake(); // stake 1e22
   vm.startPrank(Alice);
   vm.assume(x>0&&x<1e22);
   assertEq(portal.unstakeA(x), portal.unstakeB(x));
   }

   output:

   Failing tests:
   Encountered 1 failing test in test/fuzz/PortalFuzz.t.sol:PortalTest
   [FAIL. Reason: assertion failed; counterexample: calldata=0xbd0e12b300000000000000000000000000000000000000000000000000000000000000de args=[222]] testFuzz_mahdi(uint256) (runs: 3, μ: 1028058, ~: 1028058)

2. Revised Code File (Optional)

   Replace the incorrect calculation with the correct formula:

   
   -           uint256 maxStakeDebt = accounts[msg.sender].maxStakeDebt -= (_amount * maxLockDuration) / SECONDS_PER_YEAR;

• uint256 maxStakeDebt = accounts[msg.sender].maxStakeDebt = (stakedBalance * maxLockDuration) / SECONDS_PER_YEAR;

[PossumLabsCrypto]

Thank you ✅

https://github.com/PossumLabsCrypto/Portals/commit/aaaba6e63759e3546119d0c5385c47edd6082f93