2012-04-29 02:07:25 +04:00
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#! /usr/bin/python
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"""
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privilege.py
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Copyright (c) 2009-2010, Travis H.
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License terms: Same as those of Python itself.
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This module is designed to implement the privilege-dropping API
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described here:
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http://www.cs.berkeley.edu/~daw/papers/setuid-usenix02.pdf
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http://www.cs.berkeley.edu/~daw/papers/setuid-login08b.pdf
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This topic is complex so you should read at least the second paper
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before trying to understand why I'm doing this.
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NOTE: This code does not (yet) attempt to work on Solaris and AIX.
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That is, you must have getres[ug]id and setres[ug]id to use it.
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TODO:
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I have added setres[ug]id to python; unsure of when it will
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appear; make a future version of this will check for its presence.
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Make interface more OO, less imperative.
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Implement drop_priv_temp, restore_priv.
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Implement on systems without setres[ug]id
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Contributors:
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Kevin Gilette
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"""
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from ctypes import *
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from ctypes.util import find_library
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import os
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import pwd
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import grp
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# Get the name of the Operating System
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os_kernel = os.uname()[0]
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class PrivilegeFail(Exception):
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pass
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clib = CDLL(find_library("c"))
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# Tested on x86-64 -- all tests pass when run as root
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__uid_t = c_uint
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__gid_t = c_uint
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_getresuid = clib.getresuid
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def getresuid():
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"""Get the real, effective, and saved user IDs"""
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# Create some memory locations for getresuid to write to.
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r = __uid_t()
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e = __uid_t()
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s = __uid_t()
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# Call getresuid syscall, passing by reference.
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res = _getresuid(byref(r), byref(e), byref(s))
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if res < 0: raise pythonapi.PyErr_SetFromErrno(py_object(OSError))
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# Convert to python integers.
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return r.value, e.value, s.value
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_getresgid = clib.getresgid
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def getresgid():
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"""Get the real, effective, and saved group IDs"""
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r = __gid_t()
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e = __gid_t()
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s = __gid_t()
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# Call getresgid syscall, passing by reference.
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res = _getresgid(byref(r), byref(e), byref(s))
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if res < 0: raise pythonapi.PyErr_SetFromErrno(py_object(OSError))
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# Convert to python integers.
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return r.value, e.value, s.value
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# Import the setresuid system call using ctypes
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_setresuid = clib.setresuid
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_setresuid.argttypes = [__uid_t, __uid_t, __uid_t]
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_setresuid.resttype = c_int
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# Import the setresgid system call using ctypes
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_setresgid = clib.setresgid
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_setresgid.argttypes = [__gid_t, __gid_t, __gid_t]
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_setresgid.resttype = c_int
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def setresuid(ruid, euid, suid):
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"""Set the real, effective, and saved user IDs"""
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res = _setresuid(__uid_t(ruid), __uid_t(euid), __uid_t(suid))
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if res < 0: raise pythonapi.PyErr_SetFromErrno(py_object(OSError))
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def setresgid(rgid, egid, sgid):
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"""Set the real, effecive, and saved group IDs"""
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res = _setresgid(__gid_t(rgid), __gid_t(egid), __gid_t(sgid))
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if res < 0: raise pythonapi.PyErr_SetFromErrno(py_object(OSError))
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def sort_uniq(args):
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"""Sort a sequence, discarding duplicates."""
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return sorted(set(args))
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class user_credentials:
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"""
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This represents the credentials associated with a user.
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User ID
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Group ID
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Supplementary Groups
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This is used as an argument to drop_permanently
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"""
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def __init__(self, uid, gid, sups):
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# -1 has special meaning for several set*id calls (ignore)
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if uid == -1: raise PrivilegeFail
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if gid == -1: raise PrivilegeFail
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nm = os.sysconf('SC_NGROUPS_MAX')
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if nm < 0 or nm < len(sups): raise PrivilegeFail
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self.uid = uid
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self.gid = gid
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self.sups = sort_uniq(sups)
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def eql_sups(current, target):
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"""
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Compare two supplementary group lists, and ignore if effective GID is in current but not target.
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Prerequisite: The supplementary group lists are sorted and filtered for duplicates.
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"""
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egid = os.getegid()
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my_current = sort_uniq(current)
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# Instead of tediously ignoring this value, if it's in the current list, then go ahead
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# and add it to the target list
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if egid in current:
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my_target = target + [ egid ]
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else:
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my_target = target
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my_target = sort_uniq(my_target)
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return my_current == my_target
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def get_sups():
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"""This is here to give us a layer of abstraction relative to system calls"""
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return os.getgroups()
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def set_sups(target_sups):
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"""
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This is designed to give us a layer of abstraction from the system calls.
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2013-03-03 20:27:39 +04:00
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It also accommodates FreeBSD's idiosyncrasy (which is POSIX-compliant) of
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2012-04-29 02:07:25 +04:00
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keeping the egid in the supplementary groups list.
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It also makes an effort to not call the setgroups routine if the target
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group list is identical to the current one in force.
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"""
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global os_kernel
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if os_kernel == 'FreeBSD':
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target_sups = [ os.getegid() ] + target_sups
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if os.geteuid() == 0:
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# This will raise an OSError exception if it fails
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os.setgroups(target_sups)
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else:
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cur_sups = get_sups()
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# This will probably fail
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if not eql_sups(cur_sups, target_sups):
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# This will raise an OSError exception if it fails
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os.setgroups(target_sups)
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return True
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def set_gids(r, e, s):
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"""This is here to give us a layer of abstraction relative to system calls"""
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setresgid(r, e, s)
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def set_uids(r, e, s):
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"""This is here to give us a layer of abstraction relative to system calls"""
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setresuid(r, e, s)
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class res_ids:
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"""
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This represents the three IDs (group or user) associated with a process.
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"""
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def __init__(self, real, effective, saved):
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self.r = real
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self.e = effective
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self.s = saved
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class proc_credentials:
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"""
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This obtains and represents the credentials associated with a process.
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"""
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def __init__(self):
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2017-05-18 07:41:34 +03:00
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self.uids = res_ids(*getresuid())
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self.gids = res_ids(*getresgid())
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2012-04-29 02:07:25 +04:00
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self.sups = sort_uniq(os.getgroups())
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def get_fs_ids():
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"""Get filesystem IDs - applies only to Linux"""
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uid = None
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gid = None
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file = open('/proc/self/status', 'r')
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for line in file:
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fields = line.split()
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if fields[0] == 'Uid:':
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uid = int(fields[4])
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elif fields[0] == 'Gid:':
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gid = int(fields[4])
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return uid, gid
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def coerce_user(user):
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if hasattr(user, '__int__'):
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return int(user)
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return pwd.getpwnam(user).pw_uid
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def coerce_group(group):
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if hasattr(group, '__int__'):
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return int(group)
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return grp.getgrnam(group).gr_gid
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def drop_privileges_permanently(uid, gid, sups):
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"""
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This routine is designed to permanently drop all privileges to the
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user, group, and supplementary groups specified.
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"""
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uid = coerce_user(uid)
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gid = coerce_group(gid)
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sups = list(map(coerce_group, sups))
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2012-04-29 02:07:25 +04:00
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# This does some syntax checking
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ucred = user_credentials(uid, gid, sups)
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# This is for our convenience
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u = uid
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g = gid
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# Order is important in these three calls
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set_sups(ucred.sups)
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set_gids(g, g, g) # real, effective, saved
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set_uids(u, u, u) # real, effective, saved
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# Check that we actually did what we expected or throw exception.
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pc = proc_credentials()
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# Portably compare the supplementary group list
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if not eql_sups(pc.sups, ucred.sups): raise PrivilegeFail
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# Check all the gids
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if not (g == pc.gids.r and g == pc.gids.e and g == pc.gids.s):
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raise PrivilegeFail
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# Check all the uids
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if not (u == pc.uids.r and u == pc.gids.e and u == pc.uids.s):
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raise PrivilegeFail
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global os_kernel
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if os_kernel == 'Linux':
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if get_fs_ids() != (u, g): raise PrivilegeFail
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# This is all test code
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# It is run if this script is invoked directly
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if __name__ == '__main__':
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import unittest
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class test_getresXid(unittest.TestCase):
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"""Test the calls to getresXid"""
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def test__getresuid(self):
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# TODO: is there any way to avoid redefining this here? I tried a global but it didn't
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# work.
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# Note: the double-leading underscore may be getting special-cased by python.
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__uid_t = c_int
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r = __uid_t()
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e = __uid_t()
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s = __uid_t()
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ret = _getresuid(byref(r), byref(e), byref(s))
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self.assertEqual(ret, 0)
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self.assertEqual(r.value, os.getuid())
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self.assertEqual(e.value, os.geteuid())
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# NOTE: no other portable way to get saved UID
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def test_getresuid(self):
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(r, e, s) = getresuid()
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self.assertEqual(r, os.getuid())
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self.assertEqual(e, os.geteuid())
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# NOTE: no other portable way to get saved UID
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def test__getresgid(self):
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__gid_t = c_int
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r = __gid_t()
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e = __gid_t()
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s = __gid_t()
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ret = _getresgid(byref(r), byref(e), byref(s))
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self.assertEqual(ret, 0)
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self.assertEqual(r.value, os.getgid())
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self.assertEqual(e.value, os.getegid())
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# NOTE: no other portable way to get saved GID
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def test_getresgid(self):
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(r, e, s) = getresgid()
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self.assertEqual(r, os.getgid())
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self.assertEqual(e, os.getegid())
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# NOTE: no other portable way to get saved GID
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class test_setresuid(unittest.TestCase):
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"""Test the call to setresuid"""
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def setUp(self):
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self.uid = os.geteuid()
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def test__setresuid(self):
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__uid_t = c_int
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r1 = __uid_t(1)
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e1 = __uid_t(1)
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# Must save root UID so that we can reset UIDs for other tests
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s1 = __uid_t(0)
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if self.uid == 0:
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rv = _setresuid(r1, e1, s1)
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self.assertEqual(rv, 0)
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(r2, e2, s2) = getresuid()
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self.assertEqual(r1.value, r2)
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self.assertEqual(e1.value, e2)
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self.assertEqual(s1.value, s2)
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else:
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rv = _setresuid(r1, e1, s1)
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self.assertEqual(rv, -1)
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def test_setresuid(self):
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if self.uid == 0:
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setresuid(1,1,0)
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(r, e, s) = getresuid()
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self.assertEqual(r, 1)
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self.assertEqual(e, 1)
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self.assertEqual(s, 0)
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else:
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self.assertRaises(OSError, setresuid, 1, 1, 1)
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def tearDown(self):
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if self.uid == 0:
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# Restore UIDs for next test
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_setresuid(0, 0, 0)
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class test_setresgid(unittest.TestCase):
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"""Test the call to setresgid"""
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def setUp(self):
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self.uid = os.geteuid()
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def test__setresgid(self):
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__gid_t = c_int
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r1 = __gid_t(1)
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e1 = __gid_t(1)
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s1 = __gid_t(1)
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if self.uid == 0:
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rv = _setresgid(r1, e1, s1)
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self.assertEqual(rv, 0)
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(r2, e2, s2) = getresgid()
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self.assertEqual(r1.value, r2)
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self.assertEqual(e1.value, e2)
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self.assertEqual(s1.value, s2)
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else:
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rv = _setresgid(r1, e1, s1)
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self.assertEqual(rv, -1)
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def test_setresgid(self):
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if self.uid == 0:
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setresgid(1,1,1)
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(r, e, s) = getresgid()
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self.assertEqual(r, 1)
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self.assertEqual(e, 1)
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self.assertEqual(s, 1)
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else:
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self.assertRaises(OSError, setresgid, 1, 1, 1)
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class test_sort_uniq(unittest.TestCase):
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def test_sort_uniq(self):
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l = [ 'c', 'a', 'b', 'a' ]
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self.assertEqual(sort_uniq(l), [ 'a', 'b', 'c'])
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class test_user_credentials(unittest.TestCase):
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def test_negatives(self):
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self.assertRaises(PrivilegeFail, user_credentials, -1, 0, [])
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self.assertRaises(PrivilegeFail, user_credentials, 0, -1, [])
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uc = user_credentials(0, 0, [0, 1])
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class test_eql_sups(unittest.TestCase):
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def test_equal(self):
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self.assert_(eql_sups([0, 1, 2], [0, 1, 2]))
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def test_contains_egid(self):
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self.assert_(eql_sups(sort_uniq([0, 1, 2, os.getegid()]), [0, 1, 2]))
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self.assert_(eql_sups(sort_uniq([0, 1, os.getegid(), 9999]), [0, 1, 9999]))
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class test_get_sups(unittest.TestCase):
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def test(self):
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self.assertEqual(os.getgroups(), get_sups())
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class test_set_sups(unittest.TestCase):
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def test_equal(self):
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sups = os.getgroups()
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set_sups(sups)
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self.assertEqual(sups, os.getgroups())
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def test_unequal(self):
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old_sups = os.getgroups()
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sups = [ 1, 2, 3 ]
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if os.geteuid() == 0:
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set_sups(sups)
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self.assert_(eql_sups(os.getgroups(), sups))
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# Clean up by resetting supplementary groups
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set_sups(old_sups)
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else:
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self.assertRaises(OSError, set_sups, sups)
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class test_res_ids(unittest.TestCase):
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def test_res_ids(self):
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ids = res_ids(1, 2, 3)
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self.assertEqual(ids.r, 1)
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self.assertEqual(ids.e, 2)
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self.assertEqual(ids.s, 3)
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class test_proc_credentials(unittest.TestCase):
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def test_pc(self):
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pc = proc_credentials()
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self.assertEqual(pc.uids.r, os.getuid())
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self.assertEqual(pc.uids.e, os.geteuid())
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self.assertEqual(pc.uids.s, (getresuid())[2])
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self.assertEqual(pc.gids.r, os.getgid())
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self.assertEqual(pc.gids.e, os.getegid())
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self.assertEqual(pc.gids.s, (getresgid())[2])
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self.assertEqual(pc.sups, sort_uniq(os.getgroups()))
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class test_get_fs_ids(unittest.TestCase):
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def test_get_fs_ids(self):
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uid, gid = get_fs_ids()
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self.assertEqual(uid, os.getuid())
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self.assertEqual(gid, os.getgid())
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class test_drop_privs(unittest.TestCase):
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def test_drop_privs(self):
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"""This test must be run last"""
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if os.geteuid() == 0:
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drop_privileges_permanently(1, 1, [1])
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suite = unittest.TestSuite()
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suite.addTest(unittest.makeSuite(test_getresXid))
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suite.addTest(unittest.makeSuite(test_setresuid))
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suite.addTest(unittest.makeSuite(test_setresgid))
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suite.addTest(unittest.makeSuite(test_sort_uniq))
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suite.addTest(unittest.makeSuite(test_user_credentials))
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suite.addTest(unittest.makeSuite(test_eql_sups))
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suite.addTest(unittest.makeSuite(test_set_sups))
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suite.addTest(unittest.makeSuite(test_res_ids))
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suite.addTest(unittest.makeSuite(test_proc_credentials))
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suite.addTest(unittest.makeSuite(test_get_fs_ids))
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suite.addTest(unittest.makeSuite(test_drop_privs))
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unittest.TextTestRunner().run(suite)
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