The function _checkApprovals is designed to only set approvals if the current allowance is zero. This is a one-time setup meant to minimize gas costs associated with setting allowances for token transfers.
While setting the allowance to type(uint256).max reduces the need for repeated approvals (and thus saves gas), it neglects the scenario where the allowance might be fully utilized. In typical use cases, reaching type(uint256).max would require an unrealistic volume of transactions. However, it does not account for potential bugs, exploits, or changes in contract logic that could deplete this allowance unexpectedly.
The current implementation of the _checkApprovals function sets the token allowance to type(uint256).max for the nonfungiblePositionManager contract, intending to save on gas costs for future transactions. However, this approach introduces a vulnerability where, once the type(uint256).max allowance is exhausted, there would be no mechanism in place to renew the approval. This could lead to a situation where the smart contract is unable to perform operations requiring token transfers on behalf of users, effectively freezing any functionality dependent on these approvals.
Instead of only checking for an allowance of zero, implement a mechanism to check if the allowance is below a certain threshold and, if so, replenish it.
