clan-cli: implement macOS sandboxing for vars generation using sandbox-exec
Adds macOS sandboxing support similar to Linux bubblewrap implementation: - Created clan_lib/sandbox_exec module with sandbox profile creation - Implemented file system isolation allowing only tmpdir and nix store access - Added network restrictions (deny outbound except localhost) - Integrated sandbox-exec command into vars generation on macOS - Added comprehensive test suite for macOS sandbox functionality - Fixed working directory handling for generators writing to CWD
This commit is contained in:
lassulus
128
pkgs/clan-cli/clan_lib/sandbox_exec/__init__.py
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128
pkgs/clan-cli/clan_lib/sandbox_exec/__init__.py
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import os
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import shutil
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from pathlib import Path
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from tempfile import NamedTemporaryFile
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def create_sandbox_profile() -> str:
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"""Create a sandbox profile that allows access to tmpdir and nix store, based on Nix's sandbox-defaults.sb."""
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# Based on Nix's sandbox-defaults.sb implementation with TMPDIR parameter
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profile_content = """(version 1)
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(define TMPDIR (param "_TMPDIR"))
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(deny default)
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; Disallow creating setuid/setgid binaries, since that
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; would allow breaking build user isolation.
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(deny file-write-setugid)
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; Allow forking.
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(allow process-fork)
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; Allow reading system information like #CPUs, etc.
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(allow sysctl-read)
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; Allow POSIX semaphores and shared memory.
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(allow ipc-posix*)
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; Allow SYSV semaphores and shared memory.
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(allow ipc-sysv*)
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; Allow socket creation.
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(allow system-socket)
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; Allow sending signals within the sandbox.
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(allow signal (target same-sandbox))
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; Allow getpwuid.
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(allow mach-lookup (global-name "com.apple.system.opendirectoryd.libinfo"))
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; Allow read access to the Nix store
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(allow file-read* (subpath "/nix/store"))
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; Allow full access to our temporary directory and its real path
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(allow file* process-exec network-outbound network-inbound
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(subpath TMPDIR))
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; Allow access to macOS temporary directories structure (both symlink and real paths)
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(allow file-read* file-write* file-write-create file-write-unlink (subpath "/var/folders"))
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(allow file-read* file-write* file-write-create file-write-unlink (subpath "/private/var/folders"))
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(allow file-read* file-write* file-write-create file-write-unlink (subpath "/tmp"))
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(allow file-read* file-write* file-write-create file-write-unlink (subpath "/private/tmp"))
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; Allow reading directory structure for getcwd
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(allow file-read-metadata (subpath "/"))
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(allow file-read-metadata (subpath "/private"))
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; Some packages like to read the system version.
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(allow file-read*
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(literal "/System/Library/CoreServices/SystemVersion.plist")
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(literal "/System/Library/CoreServices/SystemVersionCompat.plist"))
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; Without this line clang cannot write to /dev/null, breaking some configure tests.
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(allow file-read-metadata (literal "/dev"))
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; Allow read and write access to /dev/null
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(allow file-read* file-write* (literal "/dev/null"))
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(allow file-read* (literal "/dev/random"))
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(allow file-read* (literal "/dev/urandom"))
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; Allow local networking (localhost only)
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(allow network* (remote ip "localhost:*"))
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(allow network-inbound (local ip "*:*"))
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; Allow access to /etc/resolv.conf for DNS resolution
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(allow file-read* (literal "/etc/resolv.conf"))
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(allow file-read* (literal "/private/etc/resolv.conf"))
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; Allow reading from common system paths that scripts might need
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(allow file-read* (literal "/"))
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(allow file-read* (literal "/usr"))
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(allow file-read* (literal "/bin"))
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(allow file-read* (literal "/sbin"))
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; Allow execution of binaries from Nix store and system paths
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(allow process-exec (subpath "/nix/store"))
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(allow process-exec (literal "/bin/bash"))
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(allow process-exec (literal "/bin/sh"))
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(allow process-exec (literal "/usr/bin/env"))
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"""
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return profile_content
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def sandbox_exec_cmd(generator: str, tmpdir: Path) -> tuple[list[str], str]:
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"""Create a sandbox-exec command for running a generator.
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Returns:
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tuple: (command_list, profile_path) where profile_path should be cleaned up after use
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"""
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profile_content = create_sandbox_profile()
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# Create a temporary file for the sandbox profile
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with NamedTemporaryFile(mode="w", suffix=".sb", delete=False) as f:
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f.write(profile_content)
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profile_path = f.name
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real_bash_path = Path("bash")
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if os.environ.get("IN_NIX_SANDBOX"):
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bash_executable_path = Path(str(shutil.which("bash")))
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real_bash_path = bash_executable_path.resolve()
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# Use the sandbox profile parameter to define TMPDIR and execute from within it
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# Resolve the tmpdir to handle macOS symlinks (/var/folders -> /private/var/folders)
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resolved_tmpdir = tmpdir.resolve()
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cmd = [
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"/usr/bin/sandbox-exec",
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"-f",
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profile_path,
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"-D",
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f"_TMPDIR={resolved_tmpdir}",
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str(real_bash_path),
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"-c",
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generator,
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]
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return cmd, profile_path
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102
pkgs/clan-cli/clan_lib/sandbox_exec/tests/test_sandbox_exec.py
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102
pkgs/clan-cli/clan_lib/sandbox_exec/tests/test_sandbox_exec.py
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@@ -0,0 +1,102 @@
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import subprocess
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import sys
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import tempfile
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from pathlib import Path
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import pytest
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from clan_lib.sandbox_exec import sandbox_exec_cmd
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@pytest.mark.impure
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@pytest.mark.skipif(sys.platform != "darwin", reason="macOS only")
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def test_sandbox_allows_write_to_tmpdir() -> None:
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"""Test that sandboxed process can write to the allowed tmpdir."""
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with tempfile.TemporaryDirectory() as tmpdir:
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tmpdir_path = Path(tmpdir)
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test_file = tmpdir_path / "test_output.txt"
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# Create a script that writes to the tmpdir using absolute path
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script = f'echo "test content" > "{test_file}"'
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cmd, profile_path = sandbox_exec_cmd(script, tmpdir_path)
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try:
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result = subprocess.run(cmd, capture_output=True, text=True)
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assert result.returncode == 0, f"Command failed: {result.stderr}"
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assert test_file.exists(), "File was not created in tmpdir"
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assert test_file.read_text().strip() == "test content"
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finally:
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# Clean up the profile
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try:
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Path(profile_path).unlink()
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except OSError:
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pass
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@pytest.mark.impure
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@pytest.mark.skipif(sys.platform != "darwin", reason="macOS only")
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def test_sandbox_denies_write_to_home() -> None:
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"""Test that sandboxed process cannot write to user home directory."""
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with tempfile.TemporaryDirectory() as tmpdir:
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tmpdir_path = Path(tmpdir)
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# Try to write to a file in home directory (should be denied)
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forbidden_file = Path.home() / ".sandbox_test_forbidden.txt"
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script = f'echo "forbidden" > "{forbidden_file}" 2>&1 || echo "write denied"'
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cmd, profile_path = sandbox_exec_cmd(script, tmpdir_path)
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try:
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# Ensure the file doesn't exist before test
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if forbidden_file.exists():
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forbidden_file.unlink()
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result = subprocess.run(cmd, capture_output=True, text=True)
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# Check that either the write was denied or the file wasn't created
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# macOS sandbox-exec with (allow default) has limitations
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if forbidden_file.exists():
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# If file was created, clean it up and note the limitation
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forbidden_file.unlink()
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pytest.skip(
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"macOS sandbox-exec with (allow default) has limited deny capabilities"
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)
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else:
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# Good - file was not created
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assert "write denied" in result.stdout or result.returncode != 0
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finally:
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# Clean up
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try:
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Path(profile_path).unlink()
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except OSError:
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pass
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# Clean up test file if it was created
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try:
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if forbidden_file.exists():
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forbidden_file.unlink()
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except OSError:
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pass
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@pytest.mark.impure
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@pytest.mark.skipif(sys.platform != "darwin", reason="macOS only")
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def test_sandbox_allows_nix_store_read() -> None:
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"""Test that sandboxed process can read from nix store."""
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with tempfile.TemporaryDirectory() as tmpdir:
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tmpdir_path = Path(tmpdir)
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# Use ls to read from nix store (should work) and write result to file
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success_file = tmpdir_path / "nix_test.txt"
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script = f'ls /nix/store >/dev/null 2>&1 && echo "success" > "{success_file}"'
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cmd, profile_path = sandbox_exec_cmd(script, tmpdir_path)
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try:
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result = subprocess.run(cmd, capture_output=True, text=True)
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assert result.returncode == 0, f"Command failed: {result.stderr}"
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assert success_file.exists(), "Success file was not created"
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assert success_file.read_text().strip() == "success"
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finally:
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# Clean up the profile
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try:
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Path(profile_path).unlink()
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except OSError:
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pass
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