fix(core): prevent race condition in policy persistence

[braddux]

Fixes #18504. Implements a sequential queue and unique temp files for policy writes.

[gemini-code-assist]

Summary of Changes

Hello @braddux, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical race condition in the policy persistence mechanism. By implementing a sequential queue for write operations and improving the robustness of atomic file writes with unique temporary file names, it ensures that policy updates are applied consistently and reliably, preventing data loss due to concurrent events.

Highlights

• Race Condition Fix: Introduced a sequential promise queue (persistenceQueue) to serialize policy write operations, preventing concurrent updates from overwriting each other and leading to lost data.
• Atomic File Write Improvement: Enhanced the atomic file write mechanism by generating unique temporary file names using a timestamp and random string. This prevents potential ENOENT errors during fs.rename when multiple processes attempt to write temporary files concurrently.

Changelog

• packages/core/src/policy/config.ts
  • Added a persistenceQueue (a Promise chain) to ensure that policy persistence operations are executed sequentially, preventing race conditions.
  • Wrapped the existing policy persistence logic within the persistenceQueue.then() block to serialize writes.
  • Modified the temporary file naming convention for atomic writes to include a unique suffix (Date.now().Math.random()) to avoid conflicts when multiple temporary files are created concurrently.

Activity

• The pull request was created by braddux to fix issue Race Condition in Policy Persistence leads to ENOENT error #18504, addressing a race condition in policy persistence.

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[gemini-code-assist]

Code Review

This pull request effectively addresses a race condition in policy persistence by introducing a sequential queue for write operations and using unique temporary files. However, a critical vulnerability exists where the temporary file creation uses a predictable random number generator, making it susceptible to symlink attacks in shared directories. Furthermore, the persistence of unvalidated regular expressions in policy rules introduces a risk of persistent Regular Expression Denial of Service (ReDoS). There is also a suggestion to make the generation of unique filenames even more robust.

[braddux]

I have addressed the security concerns raised in the review:

1. Secure Temp File Creation: Implemented cryptographically secure random suffixes and used the 'wx' flag with fs.open to ensure exclusive, atomic file creation, preventing symlink attacks.
2. ReDoS Protection: Added a heuristic isSafeRegExp check to validate regular expressions for potential catastrophic backtracking (nested quantifiers, etc.) before they are used or persisted.
3. Validation: Integrated these checks into both the dynamic policy updater and the TOML loader.

I've also updated the tests to verify these security measures. Please let me know if there's anything else!

[allenhutchison]

This looks great. Thanks for fixing this issue.