krun: stop using set_workdir

[slp]

Stop using set_workdir, which can be dangerous, and rely exclusively on the config file for setting up the workdir in the container.

Fixes: #1691

Summary by Sourcery

Remove the use of set_workdir function in krun handler, relying exclusively on the config file for setting up the container's working directory.

Bug Fixes:

• Eliminate potentially dangerous direct workdir setting in the krun handler, addressing a potential security or configuration inconsistency

Enhancements:

• Simplify the krun handler by removing direct workdir configuration method

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request removes the usage of set_workdir in libkrun_exec. The working directory is now exclusively configured via the config file.

Sequence diagram for libkrun_exec function call flow (after removal of set_workdir)

sequenceDiagram
  participant libkrun_exec
  participant krun_set_root
  participant libkrun_configure_vm

  libkrun_exec->>krun_set_root: krun_set_root (ctx_id, "/")
  activate krun_set_root
  krun_set_root-->>libkrun_exec: returns ret
  deactivate krun_set_root
  libkrun_exec->>libkrun_configure_vm: libkrun_configure_vm (ctx_id, handle, &configured, &err)
  activate libkrun_configure_vm
  libkrun_configure_vm-->>libkrun_exec: returns ret
  deactivate libkrun_configure_vm

Loading

File-Level Changes

Change	Details	Files
Removed the krun_set_workdir function from libkrun_exec.	Removed the declaration of krun_set_workdir. Removed the dlsym call to load krun_set_workdir. Removed the call to krun_set_workdir.	src/libcrun/handlers/krun.c

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[sourcery-ai]

Hey @slp - I've reviewed your changes - here's some feedback:

Overall Comments:

• Consider adding a comment explaining why krun_set_workdir is considered dangerous.
• It might be worth adding a check to ensure that the config file is actually setting the workdir.

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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[giuseppe]

LGTM

[rhatdan]

/lgtm

[slp]

Side note, dangerous was probably a bit of an exaggeration on my part. In the crun-krun execution model, the guest's kernel is simply part of the untrusted workload, and it's not considered by any means a protection layer on top of the userspace component. In fact, we now allow users to provide their own kernels.

The protection is provided by the combination of HW Virtualization on top of the usual container-based protections (cgroups, namespaces, selinux, etc...).