Summary I'm trying to deploy a Python code execution service using nsjail for sandboxing on Google Cloud Run, but nsjail fails with `prctl(PR_SET_SECUREBITS)` errors even with minimal configuration. Is there a working nsjail configuration for Cloud Run's gVisor environment? Environment Platform: Google Cloud Run (managed, gVisor-based) Base Image: python:3.11-slim nsjail: Latest from GitHub (built from source) Deployment: gcloud run deploy with 1GB memory, no special flags ## What I'm Trying To Do Execute untrusted Python scripts safely using nsjail for resource limiting (CPU, memory) and filesystem isolation. ## The Problem nsjail fails to start with this error: [E][2025-11-24T23:58:07+0000][11] initNsFromChild():265 prctl(PR_SET_SECUREBITS, SECBIT_KEEP_CAPS | SECBIT_NO_SETUID_FIXUP): Invalid argument What I've Tried Configuration 1: Minimal nsjail (all namespaces disabled) name: "python-sandbox" mode: ONCE time_limit: 5 # All disabled to avoid namespace errors clone_newnet: false clone_newuser: false clone_newns: false clone_newpid: false clone_newipc: false clone_newuts: false clone_newcgroup: false # Only resource limits rlimit_as: 512 rlimit_cpu: 10 rlimit_nofile: 64 rlimit_nproc: 32 Result: Still fails with prctl() error Configuration 2: With disable_no_new_privs # ... same as above plus: keep_caps: false disable_no_new_privs: true Result: Same error Configuration 3: Full nsjail with namespaces clone_newnet: true clone_newuser: true # ... etc Result: Fails earlier with: [W] clone(flags=CLONE_NEWNS|CLONE_NEWCGROUP|...) failed: Invalid argument Dockerfile FROM python:3.11-slim # Build nsjail RUN apt-get update && apt-get install -y \ build-essential pkg-config libnl-route-3-dev \ libnl-3-dev libprotobuf-dev protobuf-compiler \ bison flex git && \ git clone --depth 1 https://github.com/google/nsjail.git /tmp/nsjail && \ cd /tmp/nsjail && make && \ cp /tmp/nsjail/nsjail /usr/bin/nsjail && \ chmod +x /usr/bin/nsjail # ... rest of setup CMD ["gunicorn", "--bind", "0.0.0.0:8080", "app:app"] Execution Command subprocess.run([ '/usr/bin/nsjail', '--config', '/app/config/nsjail.cfg', '--', '/usr/local/bin/python3', 'script.py' ], timeout=5) What Works Locally with Docker: Works perfectly with docker run --privileged Basic execution: Python scripts run fine without nsjail wrapper Questions Is it possible to run nsjail on Cloud Run at all? I've been told it is, but can't find working configs Is there a Cloud Run deployment flag to allow prctl() syscalls? Is there a modified nsjail build that works without PR_SET_SECUREBITS? What I Need A working nsjail configuration for Cloud Run References nsjail GitHub Cloud Run container contract Similar sandboxing: Windmill (also uses nsjail but unclear if it works on Cloud Run) Continue reading...
