#!/usr/bin/env python2.4
#
# Copyright 2006 sense.lab e.V.
# 
# This file is part of the CryptoBox.
#
# The CryptoBox is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
# 
# The CryptoBox is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with the CryptoBox; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#


"""module for executing the programs, that need root privileges

Syntax:
	- program
	- device
	- [action]
	- [action args]

this script will always return with an exitcode 0 (true), if "check" is the only argument
"""

__revision__ = "$Id"

import os
import sys
import subprocess
import pwd
import grp
import types

allowedProgs = {
	"sfdisk":	"/sbin/sfdisk",
	"cryptsetup":	"/sbin/cryptsetup",
	"mount":	"/bin/mount",
	"umount":	"/bin/umount",
	"blkid":	"/sbin/blkid",
	}


DEV_TYPES = { "pipe":1, "char":2, "dir":4, "block":6, "file":8, "link":10, "socket":12}
EVENT_MARKER = '_event_marker_'


def checkIfFileIsSafe(fname):
	"""check if the file and its parents are only writeable for root"""
	#FIXME: for now we may skip this test - but users will not like it this way :)
	return True
	props = os.stat(fname)
	## check if it is owned by non-root
	if props.st_uid != 0: return False
	## check group-write permission if gid is not zero
	if (props.st_gid != 0) and (props.st_mode % 32 / 16 > 0): return False
	## check if it is world-writeable
	if props.st_mode % 4 / 2 > 0: return False
	## are we at root-level (directory-wise)? If yes, then we are ok ...
	if fname == os.path.sep: return True
	## check if the parent directory is ok - recursively :)
	return checkIfFileIsSafe(os.path.dirname(os.path.abspath(fname)))


def	checkIfPluginIsValid(plugin):
	import imp
	try:
		x = imp.load_source("cbox_plugin",plugin)
	#TODO: no wildcard catches, please!
	except Exception:
		return False
	try:
		if getattr(x, "PLUGIN_TYPE") == "cryptobox":
			return True
		else:
			return False
	except Exception:
		return False


def	checkIfEventScriptIsValid(plugin):
	event_dir = os.path.dirname(plugin)
	if os.path.exists(os.path.join(event_dir, EVENT_MARKER)):
		return True
	else:
		return False


def call_plugin(args):
	"""check if the plugin may be called - and do it finally ..."""
	plugin = os.path.abspath(args[0])
	del args[0]
	## check existence and if it is executable
	if not os.access(plugin, os.X_OK):
		raise Exception, "could not find executable plugin (%s)" % plugin
	## check if the plugin (and its parents) are only writeable for root
	if not checkIfFileIsSafe(plugin):
		raise Exception, "the plugin (%s) is not safe - check its (and its parents') permissions" % plugin
	## check if the plugin is a python program, that is marked as a cryptobox plugin
	if not checkIfPluginIsValid(plugin):
		raise Exception, "the plugin (%s) is not a correctly marked python script" % plugin
	args.insert(0, plugin)
	proc = subprocess.Popen(
		shell = False,
		args = args)
	proc.wait()
	return proc.returncode == 0


def call_event(args):
	"""check if the event script may be called - and do it finally ..."""
	event = os.path.abspath(args[0])
	del args[0]
	## check existence and if it is executable
	if not os.access(event, os.X_OK):
		raise Exception, "could not find executable event script (%s)" % event
	## check if the script is valid (the marker file must be in the same directory)
	if not checkIfEventScriptIsValid(event):
		raise Exception, "the event script (%s) does not reside in a directory with the marker file (%s) - this is not allowed due to abuse prevention" % (event, EVENT_MARKER)
	## check if the event (and its parents) are only writeable for root
	if not checkIfFileIsSafe(event):
		raise Exception, "the event (%s) is not safe - check its (and its parents') permissions" % event
	args.insert(0, event)
	proc = subprocess.Popen(
		shell = False,
		args = args)
	proc.wait()
	return proc.returncode == 0


def isWriteable(device, force_dev_type=None):
	"""check if the calling user (not root!) has write access to the device/file

	the real (not the effictive) user id is used for the check
	additionally the permissions of the default groups of the real uid are checked
	this check works nicely together with "super", as it changes (by default) only
	the effective uid (not the real uid)
	"""
	# first check, if the device/file exists
	if not os.path.exists(device):
		return False
	# check the type of the device - if necessary
	if not force_dev_type is None:
		dev_type = os.stat(device).st_mode % 65536 / 4096
		if dev_type != force_dev_type: return False
	# retrieve the information for the real user id
	(trustUserName, trustUID, groupsOfTrustUser) = getUserInfo(os.getuid())
	# set the default groups of the caller for the check (restore them later)
	savedGroups = os.getgroups()
	os.setgroups(groupsOfTrustUser)
	# check permissions
	result = os.access(device, os.W_OK) and os.access(device, os.R_OK)
	# reset the groups of this process
	os.setgroups(savedGroups)
	return result


def run_cryptsetup(args):
	"""execute cryptsetup as root

	@args: list of arguments - they will be treated accordingly to the first element
		of this list (the action)"""
	if not args: raise "WrongArguments", "no action for cryptsetup supplied"
	if type(args) != types.ListType: raise "WrongArguments", "invalid arguments supplied: %s" % (args, )
	try:
		action = args[0]
		del args[0]
		device = None
		cmd_args = []
		if action == "luksFormat":
			device = args[0]; del args[0]
			cmd_args.append(action)
			cmd_args.append(device)
		elif action == "luksUUID":
			device = args[0]; del args[0]
			cmd_args.append(action)
			cmd_args.append(device)
		elif action == "luksOpen":
			if len(args) < 2: raise "WrongArguments", "missing arguments"
			device = args[0]; del args[0]
			destination = args[0]; del args[0]
			cmd_args.append(action)
			cmd_args.append(device)
			cmd_args.append(destination)
		elif action == "luksClose":
			if len(args) < 1: raise "WrongArguments", "missing arguments"
			destination = args[0]; del args[0]
			# maybe add a check for the mapped device's permissions?
			# dmsetup deps self.device
			cmd_args.append(action)
			cmd_args.append(destination)
		elif action == "luksAddKey":
			device = args[0]; del args[0]
			cmd_args.append(action)
			cmd_args.append(device)
		elif action == "luksDelKey":
			if len(args) < 2: raise "WrongArguments", "missing arguments"
			device = args[0]; del args[0]
			cmd_args.insert(-1, action)
			cmd_args.insert(-1, device)
		elif action == "isLuks":
			device = args[0]; del args[0]
			cmd_args.append(action)
			cmd_args.append(device)
		else: raise "WrongArguments", "invalid action supplied: %s" % (action, )
		# check if a device was defined - and check it
		if (not device is None) and (not isWriteable(device, DEV_TYPES["block"])):
			raise "WrongArguments", "%s is not a writeable block device" % (device, )
		cs_args = [allowedProgs["cryptsetup"]]
		cs_args.extend(args)
		cs_args.extend(cmd_args)
	except (TypeError, IndexError):
		raise "WrongArguments", "invalid arguments supplied: %s" % (args, )
	# execute cryptsetup with the given parameters
	proc = subprocess.Popen(
		shell = False,
		args = cs_args)
	proc.wait()
	## chown the devmapper block device to the cryptobox user
	if (proc.returncode == 0) and (action == "luksOpen"):
		os.chown(os.path.join(os.path.sep, "dev", "mapper", destination), os.getuid(), os.getgid())
	return proc.returncode == 0


def run_sfdisk(args):
	"""execute sfdisk for partitioning

	not implemented yet"""
	print "ok - you are free to call sfdisk ..."
	print "  not yet implemented ..."
	return True


def getFSType(device):
	"""get the filesystem type of a device"""
	proc = subprocess.Popen(
		shell = False,
		stdout	= subprocess.PIPE,
		args = [ allowedProgs["blkid"],
			"-s", "TYPE",
			"-o", "value",
			"-c", os.devnull,
			"-w", os.devnull,
			device])
	(stdout, stderr) = proc.communicate()
	if proc.returncode != 0:
		return None
	return stdout.strip()


def run_mount(args):
	"""execute mount
	"""
	if not args: raise "WrongArguments", "no destination for mount supplied"
	if type(args) != types.ListType: raise "WrongArguments", "invalid arguments supplied: %s" % (args, )
	try:
		device = args[0]
		del args[0]
		destination = args[0]
		del args[0]
		# check permissions for the device
		if not isWriteable(device, DEV_TYPES["block"]):
			raise "WrongArguments", "%s is not a writeable block device" % (device, )
		## check permissions for the mountpoint
		if not isWriteable(destination, DEV_TYPES["dir"]):
			raise "WrongArguments", "the mountpoint (%s) is not writeable" % (destination, )
		# check for additional (not allowed) arguments
		if len(args) != 0:
			raise "WrongArguments", "too many arguments for 'mount': %s" % (args, )
	except TypeError:
		raise "WrongArguments", "invalid arguments supplied: %s" % (args, )
	# execute mount with the given parameters
	# first overwrite the real uid, as 'mount' wants this to be zero (root)
	savedUID = os.getuid()
	os.setuid(os.geteuid())
	## we have to change the permissions of the mounted directory - otherwise it will
	## not be writeable for the cryptobox user
	## for 'vfat' we have to do this during mount
	## for ext2/3 we have to do it afterward
	## first: get the user/group of the target
	(trustUserName, trustUID, groupsOfTrustUser) = getUserInfo(savedUID)
	trustGID = groupsOfTrustUser[0]
	fsType = getFSType(device)
	## define arguments
	if fsType == "vfat":
		## add the "uid/gid" arguments to the mount call
		mount_args = [allowedProgs["mount"],
			"-o", "uid=%d,gid=%d" % (trustUID, trustGID),
			device,
			destination]
	else:
		## all other filesystem types will be handled after mount
		mount_args = [allowedProgs["mount"], device, destination]
	# execute mount
	proc = subprocess.Popen(
		shell = False,
		args = mount_args)
	proc.wait()
	## return in case of an error
	if proc.returncode != 0:
		return False
	## for vfat: we are done
	if fsType == "vfat": return True
	## for all other filesystem types: chown the mount directory
	try:
		os.chown(destination, trustUID, groupsOfTrustUser[0])
	except OSError, errMsg:
		sys.stderr.write("could not chown the mount destination (%s) to the specified user (%d/%d): %s\n" % (destination, trustUID, groupsOfTrustUser[0], errMsg))
		sys.stderr.write("UID: %d\n" % (os.geteuid(),))
		return False
	## BEWARE: it would be nice, if we could restore the previous uid (not euid) but
	## this would also override the euid (see 'man 2 setuid') - any ideas?
	return True


def run_umount(args):
	"""execute mount
	"""
	if not args: raise "WrongArguments", "no mountpoint for umount supplied"
	if type(args) != types.ListType: raise "WrongArguments", "invalid arguments supplied"
	try:
		destination = args[0]
		del args[0]
		# check permissions for the destination
		if not isWriteable(os.path.dirname(destination), DEV_TYPES["dir"]):
			raise "WrongArguments", "the parent of the mountpoint (%s) is not writeable" % (destination, )
		if len(args) != 0: raise "WrongArguments", "umount does not allow arguments"
	except TypeError:
		raise "WrongArguments", "invalid arguments supplied"
	# execute umount with the given parameters
	# first overwrite the real uid, as 'umount' wants this to be zero (root)
	savedUID = os.getuid()
	os.setuid(os.geteuid())
	# execute umount (with the parameter '-l' - lazy umount)
	proc = subprocess.Popen(
		shell = False,
		args = [allowedProgs["umount"], "-l", destination])
	proc.wait()
	# restore previous real uid
	os.setuid(savedUID)
	return proc.returncode == 0


def getUserInfo(user):
	"""return information about the specified user

	@user:		(uid or name)
	@return:	tuple of (name, uid, (groups))
	"""
	if user is None: raise "KeyError", "no user supplied"
	# first check, if 'user' contains an id - then check for a name
	try:
		userinfo = pwd.getpwuid(user)
	except TypeError:
		# if a KeyError is raised again, then the supplied user was invalid
		userinfo = pwd.getpwnam(user)
	u_groups = [one_group.gr_gid
		for one_group in grp.getgrall()
		if userinfo.pw_name in one_group.gr_mem]
	if not userinfo.pw_gid in u_groups: u_groups.append(userinfo.pw_gid)
	return (userinfo.pw_name, userinfo.pw_uid, u_groups)


# **************** main **********************

# prevent import
if __name__ == "__main__":

	# do we have root privileges (effective uid is zero)?
	if os.geteuid() != 0:
		sys.stderr.write("the effective uid is not zero - you should use 'super' to call this script (%s)" % sys.argv[0])
		sys.exit(100)

	# remove program name
	args = sys.argv[1:]

	# do not allow to use root permissions (real uid may not be zero)
	#if os.getuid() == 0:
	#	sys.stderr.write("the uid of the caller is zero (root) - this is not allowed\n")
	#	sys.exit(100)
	
	# check if there were arguments
	if (len(args) == 0):
		sys.stderr.write("No arguments supplied\n")
		sys.exit(100)

	# did the user call the "check" action?
	if (len(args) == 1) and (args[0].lower() == "check"):
		# exit silently
		sys.exit(0)
	
	if args[0].lower() == "plugin":
		del args[0]
		try:
			isOK = call_plugin(args)
		except Exception, errMsg:
			sys.stderr.write("Execution of plugin failed: %s\n" % errMsg)
			sys.exit(100)
		if isOK:
			sys.exit(0)
		else:
			sys.exit(1)

	if args[0].lower() == "event":
		del args[0]
		try:
			isOK = call_event(args)
		except Exception, errMsg:
			sys.stderr.write("Execution of event script failed: %s\n" % errMsg)
			sys.exit(100)
		if isOK:
			sys.exit(0)
		else:
			sys.exit(1)

	# check parameters count
	if len(args) < 2:
		sys.stderr.write("Not enough arguments supplied (%s)!\n" % " ".join(args))
		sys.exit(100)

	progRequest = args[0]
	del args[0]

	if not progRequest in allowedProgs.keys():
		sys.stderr.write("Invalid program requested: %s\n" % progRequest)
		sys.exit(100)

	if progRequest == "cryptsetup":	runner = run_cryptsetup
	elif progRequest == "sfdisk":	runner = run_sfdisk
	elif progRequest == "mount":	runner = run_mount
	elif progRequest == "umount":	runner = run_umount
	else:
		sys.stderr.write("The interface for this program (%s) is not yet implemented!\n" % progRequest)
		sys.exit(100)
	try:
		if runner(args):
			sys.exit(0)
		else:
			sys.exit(1)
	except "WrongArguments", errstr:
		sys.stderr.write("Execution failed: %s\n" % errstr)
		sys.exit(100)