Reentrancy in solidity smart contract

[MukulKolpe]

Hello, I was reviewing the smart contract and noticed a common pattern where state variables are updated after external calls. This often creates a vulnerability for reentrancy attacks. To confirm this, I used Slither, a static analysis tool, to check for any potential reentrancy issues. The analysis revealed several instances where reentrancy attacks are possible. Here is a list of some of the functions where this vulnerability exists:

• LearningToken.batchMintAttendanceToken
• LearningToken.batchMintHelpingToken
• LearningToken.batchMintInstructorScoreToken
• LearningToken.batchMintScoreToken
• LearningToken.mintInstructorScoreToken
• LearningToken.mintAttendanceToken
• LearningToken.mintScoreToken
• LearningToken.transferInstructorScoringToken
• LearningToken.transferHelpingToken

To address these vulnerabilities, the following are some of the mitigation approaches:

• Follow the Checks-Effects-Interactions (CEI) pattern, ensuring that external calls are placed at the end of functions.
• Implement a mutex lock pattern to prevent reentrant calls.
• Utilize OpenZeppelin's ReentrancyGuard.

OpenZeppelin's ReentrancyGuard is gas-efficient and can be implemented without interfering with the existing business logic of the contract, making it a suitable solution for this case.

Please let me know if you would like me to proceed with a pull request to address this issue.