/usr/share/arm/resources/torrcOverride/override.py is in tor-arm 1.4.5.0-1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
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"""
This overwrites the system wide torrc, located at /etc/tor/torrc, with the
contents of the ARM_CONFIG_FILE. The system wide torrc is owned by root so
this will effectively need root permissions and for us to be in GROUP.
This file is completely unusable until we make a tor-arm user and perform
other prep by running with the '--init' argument.
After that's done this is meant to either be used by arm automatically after
writing a torrc to ARM_CONFIG_FILE or by users manually. For arm to use this
automatically you'll either need to...
- compile override.c, setuid on the binary, and move it to your path
cd /usr/share/arm/resources/torrcOverride
make
chown root:tor-arm override
chmod 04750 override
mv override /usr/bin/torrc-override
- allow passwordless sudo for this script
edit /etc/sudoers and add a line with:
<arm user> ALL= NOPASSWD: /usr/share/arm/resources/torrcOverride/override.py
To perform this manually run:
/usr/share/arm/resources/torrcOverride/override.py
pkill -sighup tor
"""
import os
import re
import sys
import grp
import pwd
import time
import shutil
import tempfile
import signal
USER = "tor-arm"
GROUP = "tor-arm"
TOR_CONFIG_FILE = "/etc/tor/torrc"
ARM_CONFIG_FILE = "/var/lib/tor-arm/torrc"
RUN_VERIFY = True # use 'tor --verify-config' to check the torrc
# regex patterns for options the wizard may include
WIZARD_OPT = ("^DataDirectory \S+$",
"^Log notice file \S+$",
"^ControlPort 9052$",
"^CookieAuthentication 1$",
"^RunAsDaemon 1$",
"^User \S+$",
"^ORPort (443|9001)$",
"^DirPort (80|9030)$",
"^Nickname ",
"^ContactInfo ",
"^BridgeRelay 1$",
"^PublishServerDescriptor 0$",
"^RelayBandwidthRate ",
"^RelayBandwidthBurst ",
"^AccountingMax ",
"^SocksPort 0$",
"^PortForwarding 1$",
"^ExitPolicy (accept|reject) \S+$",
"^DirPortFrontPage \S+$",
"^ClientOnly 1$",
"^MaxCircuitDirtiness ",
"^UseBridges 1$",
"^Bridge ")
HELP_MSG = """Usage %s [OPTION]
Backup the system wide torrc (%s) and replace it with the
contents of %s.
--init creates the necessary user and paths
--remove reverts changes made with --init
--validate PATH checks if the given file is wizard generated
""" % (os.path.basename(sys.argv[0]), TOR_CONFIG_FILE, ARM_CONFIG_FILE)
def init():
"""
Performs system preparation needed for this script to run, adding the tor-arm
user and setting up paths/permissions.
"""
# the following is just here if we have a custom destination directory (which
# arm doesn't currently account for)
if not os.path.exists("/bin/"):
print "making '/bin'..."
os.mkdir("/bin")
if not os.path.exists("/var/lib/tor-arm/"):
print "making '/var/lib/tor-arm'..."
os.makedirs("/var/lib/tor-arm")
if not os.path.exists("/var/lib/tor-arm/torrc"):
print "making '/var/lib/tor-arm/torrc'..."
open("/var/lib/tor-arm/torrc", 'w').close()
try: gid = grp.getgrnam(GROUP).gr_gid
except KeyError:
print "adding %s group..." % GROUP
os.system("addgroup --quiet --system %s" % GROUP)
gid = grp.getgrnam(GROUP).gr_gid
print " done, gid: %s" % gid
try: pwd.getpwnam(USER).pw_uid
except KeyError:
print "adding %s user..." % USER
os.system("adduser --quiet --ingroup %s --no-create-home --home /var/lib/tor-arm/ --shell /bin/sh --system %s" % (GROUP, USER))
uid = pwd.getpwnam(USER).pw_uid
print " done, uid: %s" % uid
os.chown("/bin", 0, 0)
os.chown("/var/lib/tor-arm", 0, gid)
os.chmod("/var/lib/tor-arm", 0750)
os.chown("/var/lib/tor-arm/torrc", 0, gid)
os.chmod("/var/lib/tor-arm/torrc", 0760)
def remove():
"""
Reverts the changes made by init, and also removes the optional
/bin/torrc-override binary if it exists.
"""
print "removing %s user..." % USER
os.system("deluser --quiet %s" % USER)
print "removing %s group..." % GROUP
os.system("delgroup --quiet %s" % GROUP)
if os.path.exists("/bin/torrc-override"):
try:
print "removing '/bin/torrc-override'..."
os.remove("/bin/torrc-override")
except OSError, exc:
print " unsuccessful: %s" % exc
if os.path.exists("/var/lib/tor-arm/"):
try:
print "removing '/var/lib/tor-arm'..."
shutil.rmtree("/var/lib/tor-arm/")
except Exception, exc:
print " unsuccessful: %s" % exc
def replaceTorrc():
# TODO: The setresgid and setresuid functions are only available in
# python 2.7 (arm aims for 2.5 compatability). I'm not spotting a method
# for setting the saved user id without it, though. :/
majorVersion, minorVersion = sys.version_info[:2]
canSetSavedUid = majorVersion >= 3 or (majorVersion == 2 and minorVersion >= 7)
orig_uid = os.getuid()
orig_euid = os.geteuid()
# the USER and GROUP must exist on this system
try:
dropped_uid = pwd.getpwnam(USER).pw_uid
dropped_gid = grp.getgrnam(GROUP).gr_gid
dropped_euid, dropped_egid = dropped_uid, dropped_gid
except KeyError:
print "tor-arm user and group was not found, have you run this script with '--init'?"
exit(1)
# if we're actually root, we skip this group check
# root can get away with all of this
if orig_uid != 0:
# check that the user is in GROUP
if not dropped_gid in os.getgroups():
print "Your user needs to be a member of the %s group for this to work" % GROUP
sys.exit(1)
# drop to the unprivileged group, and lose the rest of the groups
os.setgid(dropped_gid)
os.setegid(dropped_egid)
if canSetSavedUid:
# only usable in python 2.7 or later
os.setresgid(dropped_gid, dropped_egid, dropped_gid)
else:
os.setregid(dropped_gid, dropped_egid)
os.setgroups([dropped_gid])
# make a tempfile and write out the contents
try:
tf = tempfile.NamedTemporaryFile(delete=False) # uses mkstemp internally
# allows our child process to write to tf.name (not only if their uid matches, not their gid)
os.chown(tf.name, dropped_uid, orig_euid)
except:
print "We were unable to make a temporary file"
sys.exit(1)
fork_pid = os.fork()
# open the suspect config after we drop privs
# we assume the dropped privs are still enough to write to the tf
if (fork_pid == 0):
signal.signal(signal.SIGCHLD, signal.SIG_IGN)
# Drop privs forever in the child process
# I believe this drops os.setfsuid os.setfsgid stuff
# Clear all other supplemental groups for dropped_uid
os.setgroups([dropped_gid])
if canSetSavedUid:
# only usable in python 2.7 or later
os.setresgid(dropped_gid, dropped_egid, dropped_gid)
os.setresuid(dropped_uid, dropped_euid, dropped_uid)
else:
os.setregid(dropped_gid, dropped_egid)
os.setreuid(dropped_uid, dropped_euid)
os.setgid(dropped_gid)
os.setegid(dropped_egid)
os.setuid(dropped_uid)
os.seteuid(dropped_euid)
try:
af = open(ARM_CONFIG_FILE) # this is totally unpriv'ed
# ensure that the fd we opened has the properties we requrie
configStat = os.fstat(af.fileno()) # this happens on the unpriv'ed FD
if configStat.st_gid != dropped_gid:
print "Arm's configuration file (%s) must be owned by the group %s" % (ARM_CONFIG_FILE, GROUP)
sys.exit(1)
# if everything checks out, we're as safe as we're going to get
armConfig = af.read(1024 * 1024) # limited read but not too limited
af.close()
tf.file.write(armConfig)
tf.flush()
except:
print "Unable to open the arm config as unpriv'ed user"
sys.exit(1)
finally:
tf.close()
sys.exit(0)
else:
# If we're here, we're in the parent waiting for the child's death
# man, unix is really weird...
_, status = os.waitpid(fork_pid, 0)
if status != 0 or not os.path.exists(tf.name):
print "The child seems to have failed; exiting!"
tf.close()
sys.exit(1)
# attempt to verify that the config is OK
if RUN_VERIFY:
# raise privilages to drop them with 'su'
os.setuid(0)
os.seteuid(0)
os.setgid(0)
os.setegid(0)
# drop privilages and exec tor to verify it as the dropped_uid
print "Using Tor to verify that arm will not break Tor's config:"
verifyCmd = "su -c 'tor --verify-config -f %s' %s" % (tf.name, USER)
success = os.system(verifyCmd)
if success != 0:
print "Tor says the new configuration file is invalid: %s (%s)" % (ARM_CONFIG_FILE, tf.name)
sys.exit(1)
# validates that the torrc matches what the wizard could produce
torrcFile = open(tf.name)
torrcContents = torrcFile.readlines()
torrcFile.close()
if not isWizardGenerated(torrcContents):
print "torrc doesn't match what we'd expect from the setup wizard"
sys.exit(1)
# backup the previous tor config
if os.path.exists(TOR_CONFIG_FILE):
try:
backupFilename = "%s_backup_%i" % (TOR_CONFIG_FILE, int(time.time()))
shutil.copy(TOR_CONFIG_FILE, backupFilename)
except IOError, exc:
print "Unable to backup %s (%s)" % (TOR_CONFIG_FILE, exc)
sys.exit(1)
# overwrites TOR_CONFIG_FILE with ARM_CONFIG_FILE as loaded into tf.name
try:
shutil.copy(tf.name, TOR_CONFIG_FILE)
print "Successfully reconfigured Tor"
except IOError, exc:
print "Unable to copy %s to %s (%s)" % (tf.name, TOR_CONFIG_FILE, exc)
sys.exit(1)
# unlink our temp file
try:
os.remove(tf.name)
except:
print "Unable to close temp file %s" % tf.name
sys.exit(1)
sys.exit(0)
def isWizardGenerated(torrcLines):
"""
True if the given torrc contents could be generated by the wizard, false
otherwise. This just checks the basic format and options used, not the
validity of most generated values so this could still be rejected by tor.
"""
wizardPatterns = [re.compile(opt) for opt in WIZARD_OPT]
for line in torrcLines:
commentStart = line.find("#")
if commentStart != -1: line = line[:commentStart]
line = line.strip()
if not line: continue # blank line
isRecognized = False
for pattern in wizardPatterns:
if pattern.match(line):
isRecognized = True
break
if not isRecognized:
print "Unrecognized torrc contents: %s" % line
return False
return True
if __name__ == "__main__":
# sanity check that we're on linux
if os.name != "posix":
print "This is a script specifically for configuring Linux"
sys.exit(1)
if len(sys.argv) == 3 and sys.argv[1] == "--validate":
torrcFile = open(sys.argv[2])
torrcContents = torrcFile.readlines()
torrcFile.close()
isValid = isWizardGenerated(torrcContents)
if isValid: print "torrc validated"
else: print "torrc invalid"
sys.exit(0)
# check that we're running effectively as root
if os.geteuid() != 0:
print "This script needs to be run as root"
sys.exit(1)
if len(sys.argv) < 2:
replaceTorrc()
elif len(sys.argv) == 2 and sys.argv[1] == "--init":
init()
elif len(sys.argv) == 2 and sys.argv[1] == "--remove":
remove()
else:
print HELP_MSG
sys.exit(1)
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