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# Authors: Karl MacMillan <kmacmillan@mentalrootkit.com>
#
# Copyright (C) 2006 Red Hat
# see file 'COPYING' for use and warranty information
#
# This program 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; version 2 only
#
# This program 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 this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
#
"""
Classes representing basic access.
SELinux - at the most basic level - represents access as
the 4-tuple subject (type or context), target (type or context),
object class, permission. The policy language elaborates this basic
access to faciliate more concise rules (e.g., allow rules can have multiple
source or target types - see refpolicy for more information).
This module has objects for representing the most basic access (AccessVector)
and sets of that access (AccessVectorSet). These objects are used in Madison
in a variety of ways, but they are the fundamental representation of access.
"""
import refpolicy
def is_idparam(id):
"""Determine if an id is a paramater in the form $N, where N is
an integer.
Returns:
True if the id is a paramater
False if the id is not a paramater
"""
if len(id) > 1 and id[0] == '$':
try:
int(id[1:])
except ValueError:
return False
return True
else:
return False
class AccessVector:
"""
An access vector is the basic unit of access in SELinux.
Access vectors are the most basic representation of access within
SELinux. It represents the access a source type has to a target
type in terms of an object class and a set of permissions.
Access vectors are distinct from AVRules in that they can only
store a single source type, target type, and object class. The
simplicity of AccessVectors makes them useful for storing access
in a form that is easy to search and compare.
The source, target, and object are stored as string. No checking
done to verify that the strings are valid SELinux identifiers.
Identifiers in the form $N (where N is an integer) are reserved as
interface parameters and are treated as wild cards in many
circumstances.
Properties:
.src_type - The source type allowed access. [String or None]
.tgt_type - The target type to which access is allowed. [String or None]
.obj_class - The object class to which access is allowed. [String or None]
.perms - The permissions allowed to the object class. [IdSet]
.audit_msgs - The audit messages that generated this access vector [List of strings]
"""
def __init__(self, init_list=None):
if init_list:
self.from_list(init_list)
else:
self.src_type = None
self.tgt_type = None
self.obj_class = None
self.perms = refpolicy.IdSet()
self.audit_msgs = []
# The direction of the information flow represented by this
# access vector - used for matching
self.info_flow_dir = None
def from_list(self, list):
"""Initialize an access vector from a list.
Initialize an access vector from a list treating the list as
positional arguments - i.e., 0 = src_type, 1 = tgt_type, etc.
All of the list elements 3 and greater are treated as perms.
For example, the list ['foo_t', 'bar_t', 'file', 'read', 'write']
would create an access vector list with the source type 'foo_t',
target type 'bar_t', object class 'file', and permissions 'read'
and 'write'.
This format is useful for very simple storage to strings or disc
(see to_list) and for initializing access vectors.
"""
if len(list) < 4:
raise ValueError("List must contain at least four elements %s" % str(list))
self.src_type = list[0]
self.tgt_type = list[1]
self.obj_class = list[2]
self.perms = refpolicy.IdSet(list[3:])
def to_list(self):
"""
Convert an access vector to a list.
Convert an access vector to a list treating the list as positional
values. See from_list for more information on how an access vector
is represented in a list.
"""
l = [self.src_type, self.tgt_type, self.obj_class]
l.extend(self.perms)
return l
def __str__(self):
return self.to_string()
def to_string(self):
return "allow %s %s : %s %s;" % (self.src_type, self.tgt_type,
self.obj_class, self.perms.to_space_str())
def __cmp__(self, other):
if self.src_type != other.src_type:
return cmp(self.src_type, other.src_type)
if self.tgt_type != other.tgt_type:
return cmp(self.tgt_type, other.tgt_type)
if self.obj_class != self.obj_class:
return cmp(self.obj_class, other.obj_class)
if len(self.perms) != len(other.perms):
return cmp(len(self.perms), len(other.perms))
x = list(self.perms)
x.sort()
y = list(other.perms)
y.sort()
for pa, pb in zip(x, y):
if pa != pb:
return cmp(pa, pb)
return 0
def avrule_to_access_vectors(avrule):
"""Convert an avrule into a list of access vectors.
AccessVectors and AVRules are similary, but differ in that
an AVRule can more than one source type, target type, and
object class. This function expands a single avrule into a
list of one or more AccessVectors representing the access
defined in the AVRule.
"""
if isinstance(avrule, AccessVector):
return [avrule]
a = []
for src_type in avrule.src_types:
for tgt_type in avrule.tgt_types:
for obj_class in avrule.obj_classes:
access = AccessVector()
access.src_type = src_type
access.tgt_type = tgt_type
access.obj_class = obj_class
access.perms = avrule.perms.copy()
a.append(access)
return a
class AccessVectorSet:
"""A non-overlapping set of access vectors.
An AccessVectorSet is designed to store one or more access vectors
that are non-overlapping. Access can be added to the set
incrementally and access vectors will be added or merged as
necessary. For example, adding the following access vectors using
add_av:
allow $1 etc_t : read;
allow $1 etc_t : write;
allow $1 var_log_t : read;
Would result in an access vector set with the access vectors:
allow $1 etc_t : { read write};
allow $1 var_log_t : read;
"""
def __init__(self):
"""Initialize an access vector set.
"""
self.src = {}
# The information flow direction of this access vector
# set - see objectmodel.py for more information. This
# stored here to speed up searching - see matching.py.
self.info_dir = None
def __iter__(self):
"""Iterate over all of the unique access vectors in the set."""
for tgts in self.src.values():
for objs in tgts.values():
for av in objs.values():
yield av
def __len__(self):
"""Return the number of unique access vectors in the set.
Because of the inernal representation of the access vector set,
__len__ is not a constant time operation. Worst case is O(N)
where N is the number of unique access vectors, but the common
case is probably better.
"""
l = 0
for tgts in self.src.values():
for objs in tgts.values():
l += len(objs)
return l
def to_list(self):
"""Return the unique access vectors in the set as a list.
The format of the returned list is a set of nested lists,
each access vector represented by a list. This format is
designed to be simply serializable to a file.
For example, consider an access vector set with the following
access vectors:
allow $1 user_t : file read;
allow $1 etc_t : file { read write};
to_list would return the following:
[[$1, user_t, file, read]
[$1, etc_t, file, read, write]]
See AccessVector.to_list for more information.
"""
l = []
for av in self:
l.append(av.to_list())
return l
def from_list(self, l):
"""Add access vectors stored in a list.
See to list for more information on the list format that this
method accepts.
This will add all of the access from the list. Any existing
access vectors in the set will be retained.
"""
for av in l:
self.add_av(AccessVector(av))
def add(self, src_type, tgt_type, obj_class, perms, audit_msg=None):
"""Add an access vector to the set.
"""
tgt = self.src.setdefault(src_type, { })
cls = tgt.setdefault(tgt_type, { })
if cls.has_key(obj_class):
access = cls[obj_class]
else:
access = AccessVector()
access.src_type = src_type
access.tgt_type = tgt_type
access.obj_class = obj_class
cls[obj_class] = access
access.perms.update(perms)
if audit_msg:
access.audit_msgs.append(audit_msg)
def add_av(self, av, audit_msg=None):
"""Add an access vector to the set."""
self.add(av.src_type, av.tgt_type, av.obj_class, av.perms)
def avs_extract_types(avs):
types = refpolicy.IdSet()
for av in avs:
types.add(av.src_type)
types.add(av.tgt_type)
return types
def avs_extract_obj_perms(avs):
perms = { }
for av in avs:
if perms.has_key(av.obj_class):
s = perms[av.obj_class]
else:
s = refpolicy.IdSet()
perms[av.obj_class] = s
s.update(av.perms)
return perms
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