Source code for plinth.actions

# SPDX-License-Identifier: AGPL-3.0-or-later
"""Framework to run specified actions with elevated privileges."""

import functools
import importlib
import inspect
import json
import logging
import os
import subprocess
import threading

from plinth import cfg

logger = logging.getLogger(__name__)

[docs]def privileged(func): """Mark a method as allowed to be run as privileged method. This decorator is to mark any method as needing to be executed with superuser privileges. This is necessary because the primary FreedomBox service daemon runs as a regular user and has no special privileges. When performing system operations, FreedomBox service will either communicate with privileged daemons such as NetworkManager and systemd, or spawns a separate process with higher privileges. When spawning a separate process all the action parameters need to serialized, communicated to the process and then de-serialized inside the process. The return value also need to undergo such serialization and de-serialization. This decorator makes this task simpler. A call to a decorated method will be serialized into a sudo call (or later into a D-Bus call). The method arguments are turned to JSON and method is called with superuser privileges. As arguments are de-serialized, they are verified for type before the actual call as superuser. Return values are serialized and returned where they are de-serialized. Exceptions are also serialized and de-serialized. The decorator wrapper code will either return the value or raise exception. For a method to be decorated, the method must have type annotations for all of its parameters and should not use keyword-only arguments. It must also be in a module named directly under the application similar to, and Currently supported types are bool, int, float, str, dict/Dict, list/List, Optional and Union. Privileged methods many not output to the stdout as it interferes with the serialization and de-serialization process. """ setattr(func, '_privileged', True) _check_privileged_action_arguments(func) @functools.wraps(func) def wrapper(*args, **kwargs): module_name = _get_privileged_action_module_name(func) action_name = func.__name__ return _run_privileged_method_as_process(module_name, action_name, args, kwargs) return wrapper
def _run_privileged_method_as_process(module_name, action_name, args, kwargs): """Execute the privileged method in a sub-process with sudo.""" run_as_user = kwargs.pop('_run_as_user', None) run_in_background = kwargs.pop('_run_in_background', False) raw_output = kwargs.pop('_raw_output', False) log_error = kwargs.pop('_log_error', True) read_fd, write_fd = os.pipe() os.set_inheritable(write_fd, True) # Prepare the command command = ['sudo', '--non-interactive', '--close-from', str(write_fd + 1)] if run_as_user: command += ['--user', run_as_user] if cfg.develop: command += [f'PYTHONPATH={cfg.file_root}'] command += [ os.path.join(cfg.actions_dir, 'actions'), module_name, action_name, '--write-fd', str(write_fd) ] proc_kwargs = { 'stdin': subprocess.PIPE, 'stdout': subprocess.PIPE, 'stderr': subprocess.PIPE, 'shell': False, 'pass_fds': [write_fd], } if cfg.develop: # In development mode pass on local pythonpath to access Plinth proc_kwargs['env'] = {'PYTHONPATH': cfg.file_root} _log_action(module_name, action_name, run_as_user, run_in_background) proc = subprocess.Popen(command, **proc_kwargs) os.close(write_fd) if raw_output: input_ = json.dumps({'args': args, 'kwargs': kwargs}).encode() return proc, read_fd, input_ buffers = [] # XXX: Use async to avoid creating a thread. read_thread = threading.Thread(target=_thread_reader, args=(read_fd, buffers)) read_thread.start() wait_args = (module_name, action_name, args, kwargs, log_error, proc, command, read_fd, read_thread, buffers) if not run_in_background: return _wait_for_return(*wait_args) wait_thread = threading.Thread(target=_wait_for_return, args=wait_args) wait_thread.start() def _wait_for_return(module_name, action_name, args, kwargs, log_error, proc, command, read_fd, read_thread, buffers): """Communicate with the subprocess and wait for its return.""" json_args = json.dumps({'args': args, 'kwargs': kwargs}) output, error = proc.communicate(input=json_args.encode()) read_thread.join() if proc.returncode != 0: logger.error('Error executing command - %s, %s, %s', command, output, error) raise subprocess.CalledProcessError(proc.returncode, command) try: return_value = json.loads(b''.join(buffers)) except json.JSONDecodeError: logger.error( 'Error decoding action return value %s..%s(*%s, **%s): %s', module_name, action_name, args, kwargs, return_value) raise if return_value['result'] == 'success': return return_value['return'] module = importlib.import_module(return_value['exception']['module']) exception_class = getattr(module, return_value['exception']['name']) exception = exception_class(*return_value['exception']['args'], output, error) if log_error: logger.error('Error running action %s..%s(*%s, **%s): %s %s %s', module_name, action_name, args, kwargs, exception, exception.args, return_value['exception']['traceback']) raise exception def _thread_reader(read_fd, buffers): """Read from the pipe in a separate thread.""" while True: buffer =, 10240) if not buffer: break buffers.append(buffer) os.close(read_fd) def _check_privileged_action_arguments(func): """Check that a privileged action has well defined types.""" argspec = inspect.getfullargspec(func) if (argspec.varargs or argspec.varkw or argspec.kwonlyargs or argspec.kwonlydefaults): raise SyntaxError('Actions must not have variable args') for arg in argspec.args: if arg not in argspec.annotations: raise SyntaxError('All arguments must be annotated') def _get_privileged_action_module_name(func): """Figure out the module name of a privileged action.""" module_name = func.__module__ while module_name: module_name, _, last = module_name.rpartition('.') if last == 'privileged': break if not module_name: raise ValueError('Privileged actions must be placed under a ' 'package/module named privileged') return module_name.rpartition('.')[2] def _log_action(module_name, action_name, run_as_user, run_in_background): """Log an action in a compact format.""" prompt = f'({run_as_user})$' if run_as_user else '#' suffix = '&' if run_in_background else '''%s %s..%s(…) %s', prompt, module_name, action_name, suffix)