Adds client uid validation to XPC server.

[jglogan]

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Motivation and Context

When a user performs an su the effective UID changes but the bootstrap mach port does not, so that if container is running as alice from a GUI login session, it's possible to su bob and continue running container. While this doesn't pose a significant security risk as it's necessary for Alice to know Bob's password and manually enter it with su, this change closes the loophole by validating that client UID from the caller's audit token matches that of the API server.

Testing

• Tested locally
• Added/updated tests
• Added/updated docs

% container ls -a
ID        IMAGE                                               OS     ARCH   STATE    ADDR  CPUS  MEMORY
buildkit  ghcr.io/apple/container-builder-shim/builder:0.7.0  linux  arm64  stopped        2     2048 MB

% su bob
Password:
Restored session: Tue Nov 18 12:29:29 -03 2025

bob:container % container ls -a
Error: internalError: "failed to list containers" (cause: "invalidState: "unauthorized request"")

bob:container % exit

Saving session...
...saving history...truncating history files...
...completed.

% su - bob
Password:

bob:~ % container ls -a
Error: interrupted: "internalError: "failed to list containers" (cause: "interrupted: "XPC connection error: Connection invalid"")
Ensure container system service has been started with `container system start`."

[dkovba]

Should we add automated tests for the UID validation?

[jglogan]

Should we add automated tests for the UID validation?

Thoughts on how we do that? Would these only run locally? How would we change id without running as root to set UID programmatically, require user interaction, or modify a sudoers file?

[dkovba]

Agree that testing would be more complex than the code itself.

[dkovba]

👍