Beedle - Oracle free perpetual lending

Summary

Callback functions that can reenter functions with events lead to Event Reentrancy

Vulnerability Details

1. event Borrowed emitted Lender.sol line 277 after external calls to transfer()... line 269 loanToken

2. event Repaid emitted Lender.sol line 333 after external calls to transfer collateral tokens to borrower lines 329

3. event Repaid emitted Lender.sol lines 405 after external calls to transfer() to feeReceiver lines 403
   If loanToken or collateralToken are callback tokens when transferred out they may be sent to a contract that can callback into the same function before the first event is emmitted. This results in wen function completes emitting incorrect or inconsistent event data as it will always miss emitting the first states, information, data that were suppposed to be emitted but was missed due to reentrancy

Impact

Medium: This results in incorrect events and missed event emission information for offchain tooling, monitoring, analysis, front ends. Users may act on protocol on faulty information from these events

Tools Used

Manual Analysis

Recommendations

1. It is recommended to follow Checks Effects Interactions patterns CEI pattern to ensure state updates and events are emitted before external calls to ensure accurate information. Move the events above the transfers

2. It may be ideal to make use of Reentrancy Guards e.g OpenZeppelin nonreentrant modifiers on affected functions

3. It may be ideal to whitelist allowed tokens for loanToken and collateralTokens and not allow callback, hook, tokens such as ERC777, ERC1363,