Upgradeable contract is missing a __gap[50] storage variable to allow for new storage variables in later versions

[code423n4]

Lines of code

https://github.com/code-423n4/2022-11-stakehouse/blob/23c3cf65975cada7fd2255a141b359a6b31c2f9c/contracts/liquid-staking/LPToken.sol#L11

Vulnerability details

Upgradeable contract is missing a __gap[50] storage variable to allow for new storage variables in later versions

Impact

For upgradeable contracts, there must be storage gap to "allow developers to freely add new state variables in the future without compromising the storage compatibility with existing deployments" (quote OpenZeppelin). Otherwise it may be very difficult to write new implementation code. Without storage gap, the variable in child contract might be overwritten by the upgraded base contract if new variables are added to the base contract. This could have unintended and very serious consequences to the child contracts, potentially causing loss of user fund or cause the contract to malfunction completely.

See:
https://docs.openzeppelin.com/contracts/4.x/upgradeable#storage_gaps
For a description of this storage variable. While some contracts may not currently be sub-classed, adding the variable now protects against forgetting to add it in the future.

Proof of Concept

In the following context of the upgradeable contracts is expected to use gaps for avoiding collision in LPToken.sol
ERC20PermitUpgradeable
https://github.com/code-423n4/2022-11-stakehouse/blob/23c3cf65975cada7fd2255a141b359a6b31c2f9c/contracts/liquid-staking/LPToken.sol#L11

However, this contract doesn't contain storage gap. The storage gap is essential for upgradeable contract because "It allows us to freely add new state variables in the future without compromising the storage compatibility with existing deployments". Refer to the bottom part of this article:

https://docs.openzeppelin.com/contracts/4.x/upgradeable

If a contract inheriting from a base contract contains additional variable, then the base contract cannot be upgraded to include any additional variable, because it would overwrite the variable declared in its child contract. This greatly limits contract upgradeability.

Tools Used

Manual analysis

Recommended Mitigation Steps

Recommend adding appropriate storage gap at the end of upgradeable contracts such as the below.
Please reference OpenZeppelin upgradeable contract templates.
uint256[50] private __gap;

[c4-judge]

dmvt marked the issue as primary issue

[trust1995]

Contract unupgradeability has been standardized here: code-423n4/org#55

[c4-sponsor]

vince0656 marked the issue as sponsor acknowledged

[c4-judge]

Duplicate of #405

[c4-judge]

dmvt marked the issue as grade-b

[c4-judge]

dmvt marked the issue as grade-a