Summary

Two integration tests in src/boxlite/tests/jailer.rs fail on hosts where unprivileged user namespaces are blocked by the kernel or AppArmor:

• jailer::jailer_creates_isolated_mount_namespace
• jailer::jailer_enabled_box_starts_and_executes

The failure surfaces during the box start preflight as:

called `Result::unwrap()` on an `Err` value:
Config(\"Sandbox preflight failed: bwrap cannot create user namespaces.

failed to run bwrap: Permission denied (os error 13)\")

Kernel audit log on a fresh Ubuntu 24.04 dev host:

audit: type=1400 apparmor=\"DENIED\" operation=\"capable\"
profile=\"unprivileged_userns\" capability=21 capname=\"sys_admin\"

Reproduction

# fresh Ubuntu 24.04 EC2 host (kernel 7.0.0-1004-aws)
git clone https://github.com/boxlite-ai/boxlite
cd boxlite
make setup
make runtime:debug
make test:integration:rust FILTER=jailer_enabled_box

bwrap --unshare-user --bind / / true succeeds in isolation, but the libcontainer-driven preflight in the jailer requires CAP_SYS_ADMIN inside the userns and that is denied by the unprivileged_userns AppArmor profile that ships in apparmor ≥ 4.0 (Ubuntu 24+ default).

Setting:

• kernel.unprivileged_userns_clone=1
• kernel.apparmor_restrict_unprivileged_userns=0
• apparmor_parser -R /etc/apparmor.d/unprivileged_userns

does not unblock the preflight on this host. The kernel/AppArmor stack appears to require additional unconfinement for bwrap.

Decision (this PR)

These two tests are marked #[ignore] until a portable fix lands. The skip reason is encoded in the #[ignore] attribute so it shows up in test output. Run them explicitly with:

cargo nextest run -p boxlite --features krun,gvproxy --test jailer --run-ignored only

Options for a real fix

1. Test-side preflight — detect userns availability at test start, skip with clear logging on unsupported hosts. Keeps the signal in CI runners with permissive kernels.
2. Run jailer tests in a privileged container in CI (the runc / youki convention).
3. Document a setup script that installs an AppArmor allowlist for the test bwrap binary, similar to bubblewrap-userns-restrict overrides for snap.

Tracking under this issue. Likely going with (1) + (2) for CI.

Context

These two tests were among the originally-reported 14 failures in make test:all; the other 12 had different root causes (engine registration + PID validation) addressed in PR for fix/shim-required-features-and-pid-validation. With that fix, 9/14 pass on a clean dev box; the remaining 5 are environment-dependent (these 2 jailer tests + 3 flaky zygote concurrency tests, see separate issue).