# Copyright 2015 Rackspace Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
"""Privilege separation ("privsep") daemon.
To ease transition this supports 2 alternative methods of starting the
daemon, all resulting in a helper process running with elevated
privileges and open socket(s) to the original process:
1. Start via fork()
Assumes process currently has all required privileges and is about
to drop them (perhaps by setuid to an unprivileged user). If the
the initial environment is secure and `PrivContext.start(Method.FORK)`
is called early in `main()`, then this is the most secure and
simplest. In particular, if the initial process is already running
as non-root (but with sufficient capabilities, via eg suitable
systemd service files), then no part needs to involve uid=0 or
sudo.
2. Start via sudo/rootwrap
This starts the privsep helper on first use via sudo and rootwrap,
and communicates via a temporary Unix socket passed on the command
line. The communication channel is briefly exposed in the
filesystem, but is protected with file permissions and connecting
to it only grants access to the unprivileged process. Requires a
suitable entry in sudoers or rootwrap.conf filters.
The privsep daemon exits when the communication channel is closed,
(which usually occurs when the unprivileged process exits).
"""
from concurrent import futures
import enum
import errno
import io
import logging as pylogging
import os
import platform
import socket
import subprocess
import sys
import tempfile
import threading
import eventlet
from oslo_config import cfg
from oslo_log import log as logging
from oslo_utils import encodeutils
from oslo_utils import importutils
import six
from oslo_privsep._i18n import _
from oslo_privsep import capabilities
from oslo_privsep import comm
if platform.system() == 'Linux':
import fcntl
import grp
import pwd
LOG = logging.getLogger(__name__)
@enum.unique
class StdioFd(enum.IntEnum):
# NOTE(gus): We can't use sys.std*.fileno() here. sys.std*
# objects may be random file-like objects that may not match the
# true system std* fds - and indeed may not even have a file
# descriptor at all (eg: test fixtures that monkey patch
# fixtures.StringStream onto sys.stdout). Below we always want
# the _real_ well-known 0,1,2 Unix fds during os.dup2
# manipulation.
STDIN = 0
STDOUT = 1
STDERR = 2
@enum.unique
class Message(enum.IntEnum):
"""Types of messages sent across the communication channel"""
PING = 1
PONG = 2
CALL = 3
RET = 4
ERR = 5
LOG = 6
class FailedToDropPrivileges(Exception):
pass
class ProtocolError(Exception):
pass
def set_cloexec(fd):
flags = fcntl.fcntl(fd, fcntl.F_GETFD)
if (flags & fcntl.FD_CLOEXEC) == 0:
flags |= fcntl.FD_CLOEXEC
fcntl.fcntl(fd, fcntl.F_SETFD, flags)
def setuid(user_id_or_name):
try:
new_uid = int(user_id_or_name)
except (TypeError, ValueError):
new_uid = pwd.getpwnam(user_id_or_name).pw_uid
if new_uid != 0:
try:
os.setuid(new_uid)
except OSError:
msg = _('Failed to set uid %s') % new_uid
LOG.critical(msg)
raise FailedToDropPrivileges(msg)
def setgid(group_id_or_name):
try:
new_gid = int(group_id_or_name)
except (TypeError, ValueError):
new_gid = grp.getgrnam(group_id_or_name).gr_gid
if new_gid != 0:
try:
os.setgid(new_gid)
except OSError:
msg = _('Failed to set gid %s') % new_gid
LOG.critical(msg)
raise FailedToDropPrivileges(msg)
class PrivsepLogHandler(pylogging.Handler):
def __init__(self, channel, processName=None):
super(PrivsepLogHandler, self).__init__()
self.channel = channel
self.processName = processName
def emit(self, record):
# Vaguely based on pylogging.handlers.SocketHandler.makePickle
if self.processName:
record.processName = self.processName
data = dict(record.__dict__)
if record.exc_info:
if not record.exc_text:
fmt = self.formatter or pylogging.Formatter()
data['exc_text'] = fmt.formatException(record.exc_info)
data['exc_info'] = None # drop traceback in favor of exc_text
# serialise msg now so we can drop (potentially unserialisable) args
data['msg'] = record.getMessage()
data['args'] = ()
self.channel.send((None, (Message.LOG, data)))
class _ClientChannel(comm.ClientChannel):
"""Our protocol, layered on the basic primitives in comm.ClientChannel"""
def __init__(self, sock):
super(_ClientChannel, self).__init__(sock)
self.exchange_ping()
def exchange_ping(self):
try:
# exchange "ready" messages
reply = self.send_recv((Message.PING.value,))
success = reply[0] == Message.PONG
except Exception as e:
LOG.exception('Error while sending initial PING to privsep: %s', e)
success = False
if not success:
msg = _('Privsep daemon failed to start')
LOG.critical(msg)
raise FailedToDropPrivileges(msg)
def remote_call(self, name, args, kwargs):
result = self.send_recv((Message.CALL.value, name, args, kwargs))
if result[0] == Message.RET:
# (RET, return value)
return result[1]
elif result[0] == Message.ERR:
# (ERR, exc_type, args)
#
# TODO(gus): see what can be done to preserve traceback
# (without leaking local values)
exc_type = importutils.import_class(result[1])
raise exc_type(*result[2])
else:
raise ProtocolError(_('Unexpected response: %r') % result)
def out_of_band(self, msg):
if msg[0] == Message.LOG:
# (LOG, LogRecord __dict__)
message = {encodeutils.safe_decode(k): v
for k, v in msg[1].items()}
record = pylogging.makeLogRecord(message)
if LOG.isEnabledFor(record.levelno):
LOG.logger.handle(record)
else:
LOG.warning('Ignoring unexpected OOB message from privileged '
'process: %r', msg)
def fdopen(fd, *args, **kwargs):
# NOTE(gus): We can't just use os.fdopen() here and allow the
# regular (optional) monkey_patching to do its thing. Turns out
# that regular file objects (as returned by os.fdopen) on python2
# are broken in lots of ways regarding blocking behaviour. We
# *need* the newer io.* objects on py2 (doesn't matter on py3,
# since the old file code has been replaced with io.*)
if eventlet.patcher.is_monkey_patched('socket'):
return eventlet.greenio.GreenPipe(fd, *args, **kwargs)
else:
return io.open(fd, *args, **kwargs)
def _fd_logger(level=logging.WARN):
"""Helper that returns a file object that is asynchronously logged"""
read_fd, write_fd = os.pipe()
read_end = fdopen(read_fd, 'r', 1)
write_end = fdopen(write_fd, 'w', 1)
def logger(f):
for line in f:
LOG.log(level, 'privsep log: %s', line.rstrip())
t = threading.Thread(
name='fd_logger',
target=logger, args=(read_end,)
)
t.daemon = True
t.start()
return write_end
def replace_logging(handler, log_root=None):
if log_root is None:
log_root = logging.getLogger(None).logger # root logger
for h in log_root.handlers:
log_root.removeHandler(h)
log_root.addHandler(handler)
class ForkingClientChannel(_ClientChannel):
def __init__(self, context):
"""Start privsep daemon using fork()
Assumes we already have required privileges.
"""
sock_a, sock_b = socket.socketpair()
for s in (sock_a, sock_b):
s.setblocking(True)
# Important that these sockets don't get leaked
set_cloexec(s)
# Try to prevent any buffered output from being written by both
# parent and child.
for f in (sys.stdout, sys.stderr):
f.flush()
if os.fork() == 0:
# child
channel = comm.ServerChannel(sock_b)
sock_a.close()
# Replace root logger early (to capture any errors during setup)
replace_logging(PrivsepLogHandler(channel,
processName=str(context)))
Daemon(channel, context=context).run()
LOG.debug('privsep daemon exiting')
os._exit(0)
# parent
sock_b.close()
super(ForkingClientChannel, self).__init__(sock_a)
class RootwrapClientChannel(_ClientChannel):
def __init__(self, context):
"""Start privsep daemon using exec()
Uses sudo/rootwrap to gain privileges.
"""
listen_sock = socket.socket(socket.AF_UNIX)
# Note we listen() on the unprivileged side, and connect to it
# from the privileged process. This means there is no exposed
# attack point on the privileged side.
# NB: Permissions on sockets are not checked on some (BSD) Unices
# so create socket in a private directory for safety. Privsep
# daemon will (initially) be running as root, so will still be
# able to connect to sock path.
tmpdir = tempfile.mkdtemp() # NB: created with 0700 perms
try:
sockpath = os.path.join(tmpdir, 'privsep.sock')
listen_sock.bind(sockpath)
listen_sock.listen(1)
cmd = context.helper_command(sockpath)
LOG.info('Running privsep helper: %s', cmd)
proc = subprocess.Popen(cmd, shell=False, stderr=_fd_logger())
if proc.wait() != 0:
msg = ('privsep helper command exited non-zero (%s)' %
proc.returncode)
LOG.critical(msg)
raise FailedToDropPrivileges(msg)
LOG.info('Spawned new privsep daemon via rootwrap')
sock, _addr = listen_sock.accept()
LOG.debug('Accepted privsep connection to %s', sockpath)
finally:
# Don't need listen_sock anymore, so clean up.
listen_sock.close()
try:
os.unlink(sockpath)
except OSError as e:
if e.errno != errno.ENOENT:
raise
os.rmdir(tmpdir)
super(RootwrapClientChannel, self).__init__(sock)
class Daemon(object):
"""NB: This doesn't fork() - do that yourself before calling run()"""
def __init__(self, channel, context):
self.channel = channel
self.context = context
self.user = context.conf.user
self.group = context.conf.group
self.caps = set(context.conf.capabilities)
self.thread_pool = futures.ThreadPoolExecutor(
context.conf.thread_pool_size)
self.communication_error = None
def run(self):
"""Run request loop. Sets up environment, then calls loop()"""
os.chdir("/")
os.umask(0)
self._drop_privs()
self._close_stdio()
self.loop()
def _close_stdio(self):
with open(os.devnull, 'w+') as devnull:
os.dup2(devnull.fileno(), StdioFd.STDIN)
os.dup2(devnull.fileno(), StdioFd.STDOUT)
# stderr is left untouched
def _drop_privs(self):
try:
# Keep current capabilities across setuid away from root.
capabilities.set_keepcaps(True)
if self.group is not None:
try:
os.setgroups([])
except OSError:
msg = _('Failed to remove supplemental groups')
LOG.critical(msg)
raise FailedToDropPrivileges(msg)
if self.user is not None:
setuid(self.user)
if self.group is not None:
setgid(self.group)
finally:
capabilities.set_keepcaps(False)
LOG.info('privsep process running with uid/gid: %(uid)s/%(gid)s',
{'uid': os.getuid(), 'gid': os.getgid()})
capabilities.drop_all_caps_except(self.caps, self.caps, [])
def fmt_caps(capset):
if not capset:
return 'none'
fc = [capabilities.CAPS_BYVALUE.get(c, str(c))
for c in capset]
fc.sort()
return '|'.join(fc)
eff, prm, inh = capabilities.get_caps()
LOG.info(
'privsep process running with capabilities '
'(eff/prm/inh): %(eff)s/%(prm)s/%(inh)s',
{
'eff': fmt_caps(eff),
'prm': fmt_caps(prm),
'inh': fmt_caps(inh),
})
def _process_cmd(self, msgid, cmd, *args):
"""Executes the requested command in an execution thread.
This executes a call within a thread executor and returns the results
of the execution.
:param msgid: The message identifier.
:param cmd: The `Message` type indicating the command type.
:param args: The function, args, and kwargs if a Message.CALL type.
:return: A tuple of the return status, optional call output, and
optional error information.
"""
if cmd == Message.PING:
return (Message.PONG.value,)
try:
if cmd != Message.CALL:
raise ProtocolError(_('Unknown privsep cmd: %s') % cmd)
# Extract the callable and arguments
name, f_args, f_kwargs = args
func = importutils.import_class(name)
if not self.context.is_entrypoint(func):
msg = _('Invalid privsep function: %s not exported') % name
raise NameError(msg)
ret = func(*f_args, **f_kwargs)
return (Message.RET.value, ret)
except Exception as e:
LOG.debug(
'privsep: Exception during request[%(msgid)s]: '
'%(err)s', {'msgid': msgid, 'err': e}, exc_info=True)
cls = e.__class__
cls_name = '%s.%s' % (cls.__module__, cls.__name__)
return (Message.ERR.value, cls_name, e.args)
def _create_done_callback(self, msgid):
"""Creates a future callback to receive command execution results.
:param msgid: The message identifier.
:return: A future reply callback.
"""
channel = self.channel
def _call_back(result):
"""Future execution callback.
:param result: The `future` execution and its results.
"""
try:
reply = result.result()
LOG.debug('privsep: reply[%(msgid)s]: %(reply)s',
{'msgid': msgid, 'reply': reply})
channel.send((msgid, reply))
except IOError:
self.communication_error = sys.exc_info()
except Exception as e:
LOG.debug(
'privsep: Exception during request[%(msgid)s]: '
'%(err)s', {'msgid': msgid, 'err': e}, exc_info=True)
cls = e.__class__
cls_name = '%s.%s' % (cls.__module__, cls.__name__)
reply = (Message.ERR.value, cls_name, e.args)
try:
channel.send((msgid, reply))
except IOError:
self.communication_error = sys.exc_info()
return _call_back
def loop(self):
"""Main body of daemon request loop"""
LOG.info('privsep daemon running as pid %s', os.getpid())
# We *are* this context now - any calls through it should be
# executed locally.
self.context.set_client_mode(False)
for msgid, msg in self.channel:
error = self.communication_error
if error:
if error[1].errno == errno.EPIPE:
# Write stream closed, exit loop
break
six.reraise(*error)
# Submit the command for execution
future = self.thread_pool.submit(self._process_cmd, msgid, *msg)
future.add_done_callback(self._create_done_callback(msgid))
LOG.debug('Socket closed, shutting down privsep daemon')
def helper_main():
"""Start privileged process, serving requests over a Unix socket."""
cfg.CONF.register_cli_opts([
cfg.StrOpt('privsep_context', required=True),
cfg.StrOpt('privsep_sock_path', required=True),
])
logging.register_options(cfg.CONF)
cfg.CONF(args=sys.argv[1:], project='privsep')
logging.setup(cfg.CONF, 'privsep') # note replace_logging call below
context = importutils.import_class(cfg.CONF.privsep_context)
from oslo_privsep import priv_context # Avoid circular import
if not isinstance(context, priv_context.PrivContext):
LOG.fatal('--privsep_context must be the (python) name of a '
'PrivContext object')
sock = socket.socket(socket.AF_UNIX)
sock.connect(cfg.CONF.privsep_sock_path)
set_cloexec(sock)
channel = comm.ServerChannel(sock)
# Channel is set up, so fork off daemon "in the background" and exit
if os.fork() != 0:
# parent
return
# child
# Note we don't move into a new process group/session like a
# regular daemon might, since we _want_ to remain associated with
# the originating (unprivileged) process.
# Channel is set up now, so move to in-band logging
replace_logging(PrivsepLogHandler(channel))
LOG.info('privsep daemon starting')
try:
Daemon(channel, context).run()
except Exception as e:
LOG.exception(e)
sys.exit(str(e))
LOG.debug('privsep daemon exiting')
sys.exit(0)
if __name__ == '__main__':
helper_main()