Unshare the FD table when creating threads in init to avoid fd leaks

[OneBlue]

Summary of the Pull Request

This change solves a potential FD leak that can happen if multiple WSLA shells are open at the same time.

The leak happens when threads inside of init create children processes, which inherit all fd from their parents by default. If that happens while an hvsocket is opened, that socket is inherited in the child, which will never close it, causing a hang

PR Checklist

• Closes: Link to issue #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[Copilot]

Pull request overview

This PR aims to prevent file-descriptor inheritance/leaks when WSLA init creates “thread” fork handlers, by detaching the thread’s file-descriptor table so other init threads’ child processes don’t inherit hvsockets opened by the handler thread.

Changes:

• Add unshare(CLONE_FILES) when handling WSLA_FORK::Thread in WSLAInit.cpp to detach the thread’s FD table and reduce FD inheritance.

[benhillis]

This doesn’t seem right to me. Both this thread and the parent have this file descriptor.

[johnstep]

I believe this is correct since the file descriptor here is in a separate table from the parent.

[benhillis]

yeah I couldn't quite follow the logic, this seems right to me.