left4me/l4d2host/tests/test_overlay_helper.py

import os
import shlex
import subprocess
import sys
from pathlib import Path

import pytest


HELPER_SOURCE = (
    Path(__file__).resolve().parents[2]
    / "deploy"
    / "files"
    / "usr"
    / "local"
    / "libexec"
    / "left4me"
    / "left4me-overlay"
)


def _setup_instance(root: Path, name: str = "alpha", lowerdirs: list[str] | None = None) -> None:
    """Create the on-disk shape the helper expects."""
    (root / "installation").mkdir(parents=True, exist_ok=True)
    (root / "overlays" / "workshop").mkdir(parents=True, exist_ok=True)
    if lowerdirs is None:
        lowerdirs = [str(root / "overlays" / "workshop"), str(root / "installation")]
    inst_dir = root / "instances" / name
    inst_dir.mkdir(parents=True)
    (inst_dir / "instance.env").write_text(
        f"L4D2_PORT=27015\nL4D2_ARGS=-tickrate 100\nL4D2_LOWERDIRS={':'.join(lowerdirs)}\n"
    )
    runtime = root / "runtime" / name
    (runtime / "upper").mkdir(parents=True)
    (runtime / "work").mkdir(parents=True)
    (runtime / "merged").mkdir(parents=True)


def _run(args: list[str], root: Path, extra_env: dict[str, str] | None = None) -> subprocess.CompletedProcess:
    env = {
        **os.environ,
        "LEFT4ME_ROOT": str(root),
        "LEFT4ME_OVERLAY_PRINT_ONLY": "1",
    }
    if extra_env:
        env.update(extra_env)
    return subprocess.run(
        [sys.executable, str(HELPER_SOURCE), *args],
        env=env,
        capture_output=True,
        text=True,
    )


def test_mount_prints_expected_nsenter_command(tmp_path: Path) -> None:
    _setup_instance(tmp_path)

    result = _run(["mount", "alpha"], tmp_path)

    assert result.returncode == 0, result.stderr
    parts = shlex.split(result.stdout.strip())
    assert parts[0] == "/usr/bin/nsenter"
    assert parts[1] == "--mount=/proc/1/ns/mnt"
    assert parts[2] == "--"
    assert parts[3] == "/bin/mount"
    assert parts[4:6] == ["-t", "overlay"]
    assert parts[6] == "overlay"
    assert parts[7] == "-o"
    options = parts[8]
    assert f"upperdir={tmp_path}/runtime/alpha/upper" in options
    assert f"workdir={tmp_path}/runtime/alpha/work" in options
    assert f"lowerdir={tmp_path}/overlays/workshop:{tmp_path}/installation" in options
    assert parts[9] == str(tmp_path / "runtime" / "alpha" / "merged")


def test_umount_prints_expected_nsenter_command(tmp_path: Path) -> None:
    _setup_instance(tmp_path)

    result = _run(["umount", "alpha"], tmp_path)

    assert result.returncode == 0, result.stderr
    parts = shlex.split(result.stdout.strip())
    assert parts == [
        "/usr/bin/nsenter",
        "--mount=/proc/1/ns/mnt",
        "--",
        "/bin/umount",
        str(tmp_path / "runtime" / "alpha" / "merged"),
    ]


@pytest.mark.parametrize("bad_name", ["..", "../escape", "FOO", "foo bar", "foo/bar", ""])
def test_rejects_bad_instance_name(tmp_path: Path, bad_name: str) -> None:
    result = _run(["mount", bad_name], tmp_path)
    assert result.returncode != 0
    assert "invalid instance name" in result.stderr or "usage:" in result.stderr


def test_rejects_lowerdir_outside_allowlist(tmp_path: Path) -> None:
    _setup_instance(tmp_path, lowerdirs=["/etc"])
    result = _run(["mount", "alpha"], tmp_path)
    assert result.returncode != 0
    assert "outside the permitted roots" in result.stderr


def test_rejects_lowerdir_traversal(tmp_path: Path) -> None:
    # An overlay subdirectory whose path uses .. to escape the overlays root.
    _setup_instance(tmp_path, lowerdirs=[str(tmp_path / "overlays" / "..") + "/etc"])
    result = _run(["mount", "alpha"], tmp_path)
    assert result.returncode != 0
    assert "outside the permitted roots" in result.stderr or "path does not exist" in result.stderr


def test_rejects_lowerdir_symlink_escape(tmp_path: Path) -> None:
    _setup_instance(tmp_path)
    sneaky = tmp_path / "overlays" / "sneaky"
    os.symlink("/etc", sneaky)
    # rewrite instance.env to point at the symlink
    inst_env = tmp_path / "instances" / "alpha" / "instance.env"
    inst_env.write_text(f"L4D2_LOWERDIRS={sneaky}\n")
    result = _run(["mount", "alpha"], tmp_path)
    assert result.returncode != 0
    assert "outside the permitted roots" in result.stderr


def test_rejects_missing_instance_env(tmp_path: Path) -> None:
    (tmp_path / "instances" / "alpha").mkdir(parents=True)
    runtime = tmp_path / "runtime" / "alpha"
    (runtime / "upper").mkdir(parents=True)
    (runtime / "work").mkdir(parents=True)
    (runtime / "merged").mkdir(parents=True)
    result = _run(["mount", "alpha"], tmp_path)
    assert result.returncode != 0
    assert "instance.env not found" in result.stderr


def test_rejects_lowerdir_count_over_cap(tmp_path: Path) -> None:
    (tmp_path / "installation").mkdir()
    many = [str(tmp_path / "installation")] * 501
    _setup_instance(tmp_path, lowerdirs=many)
    result = _run(["mount", "alpha"], tmp_path)
    assert result.returncode != 0
    assert "501 entries" in result.stderr


def test_rejects_empty_lowerdir_entry(tmp_path: Path) -> None:
    (tmp_path / "installation").mkdir()
    _setup_instance(
        tmp_path,
        lowerdirs=[str(tmp_path / "installation"), "", str(tmp_path / "installation")],
    )
    result = _run(["mount", "alpha"], tmp_path)
    assert result.returncode != 0
    assert "empty entry" in result.stderr


@pytest.mark.skipif(sys.platform != "linux", reason="user.* xattrs are Linux-only")
def test_rejects_upperdir_with_fuseoverlayfs_xattr(tmp_path: Path) -> None:
    _setup_instance(tmp_path)
    tainted = tmp_path / "runtime" / "alpha" / "upper" / "deleted-thing"
    tainted.write_bytes(b"")
    try:
        os.setxattr(tainted, "user.fuseoverlayfs.opaque", b"y")
    except OSError:
        pytest.skip("filesystem doesn't support user.* xattrs")
    result = _run(["mount", "alpha"], tmp_path)
    assert result.returncode != 0
    assert "fuse-overlayfs xattr" in result.stderr