# Copyright 2015, Tresys Technology, LLC
# Copyright 2016, 2018, Chris PeBenito <pebenito@ieee.org>
#
# SPDX-License-Identifier: LGPL-2.1-only
#
"""
SETools descriptors.
These classes override how a class's attributes are get/set/deleted.
This is how the @property decorator works.
See https://docs.python.org/3/howto/descriptor.html
for more details.
"""
import re
from abc import ABC, abstractmethod
from collections import defaultdict
from collections.abc import Collection
from enum import Enum
from typing import Any, Callable, MutableMapping, Optional, Type, Union
from weakref import WeakKeyDictionary
from .util import validate_perms_any
#
# Query criteria descriptors
#
# Implementation note: if the name_regex attribute value
# is changed the criteria must be reset.
#
class CriteriaDescriptor:
"""
Single item criteria descriptor.
Keyword Parameters:
name_regex The name of instance's regex setting attribute;
used as name_regex below. If unset,
regular expressions will never be used.
lookup_function The name of the SELinuxPolicy lookup function,
e.g. lookup_type or lookup_boolean.
default_value The default value of the criteria. The default
is None.
enum_class The class of enumeration which supports a
lookup class method.
Read-only instance attribute use (obj parameter):
policy The instance of SELinuxPolicy
name_regex This attribute is read to determine if
the criteria should be looked up or
compiled into a regex. If the attribute
does not exist, False is assumed.
"""
def __init__(self, name_regex: Optional[str] = None,
lookup_function: Optional[Union[Callable, str]] = None,
default_value=None, enum_class: Optional[Type[Enum]] = None) -> None:
assert name_regex or lookup_function or enum_class, \
"A simple attribute should be used if there is no regex, lookup function, or enum."
assert not (lookup_function and enum_class), \
"Lookup functions and enum classes are mutually exclusive."
self.regex: Optional[str] = name_regex
self.default_value = default_value
self.lookup_function: Optional[Union[Callable, str]] = lookup_function
self.enum_class = enum_class
self.name: str = ""
# use weak references so instances can be
# garbage collected, rather than unnecessarily
# kept around due to this descriptor.
self.instances: MutableMapping = WeakKeyDictionary()
def __set_name__(self, owner, name):
self.name = name
def __get__(self, obj, objtype=None):
if obj is None:
return self
return self.instances.setdefault(obj, self.default_value)
def __set__(self, obj, value):
if not value:
self.instances[obj] = self.default_value
elif self.regex and getattr(obj, self.regex, False):
self.instances[obj] = re.compile(value)
elif self.lookup_function:
if callable(self.lookup_function):
lookup = self.lookup_function
else:
lookup = getattr(obj.policy, self.lookup_function)
self.instances[obj] = lookup(value)
elif self.enum_class:
self.instances[obj] = self.enum_class.lookup(value)
else:
self.instances[obj] = value
class CriteriaSetDescriptor(CriteriaDescriptor):
"""Descriptor for a set of criteria."""
def __set__(self, obj, value):
if not value:
self.instances[obj] = self.default_value
elif self.regex and getattr(obj, self.regex, False):
self.instances[obj] = re.compile(value)
elif self.lookup_function:
if callable(self.lookup_function):
lookup = self.lookup_function
else:
lookup = getattr(obj.policy, self.lookup_function)
self.instances[obj] = frozenset(lookup(v) for v in value)
elif self.enum_class:
self.instances[obj] = frozenset(self.enum_class.lookup(v) for v in value)
else:
self.instances[obj] = frozenset(value)
class CriteriaPermissionSetDescriptor(CriteriaDescriptor):
"""
Descriptor for a set of permissions criteria.
name_regex The name of instance's regex setting attribute;
used as name_regex below. If unset,
regular expressions will never be used.
default_value The default value of the criteria. The default
is None.
Read-only instance attribute use (obj parameter):
policy The instance of SELinuxPolicy
tclass If it exists, it will be used to validate the
permissions. See validate_perms_any()
tclass_regex If tclass is a regex, the above permission validation
will not use tclass: permissions are verified to be in
at least one class in the policy but not verified that the
permissions are in classes that the regex matches. Assumes False
if the attribute doesn't exist.
"""
def __init__(self, name_regex: Optional[str] = None, default_value=None) -> None:
self.regex: Optional[str] = name_regex
self.default_value = default_value
self.name: str = ""
# use weak references so instances can be
# garbage collected, rather than unnecessarily
# kept around due to this descriptor.
self.instances: MutableMapping = WeakKeyDictionary()
def __set__(self, obj, value):
if not value:
self.instances[obj] = self.default_value
elif self.regex and getattr(obj, self.regex, False):
self.instances[obj] = re.compile(value)
else:
perms = frozenset(v for v in value)
if getattr(obj, "tclass_regex", False):
tclass = None
else:
tclass = getattr(obj, "tclass", None)
if tclass and not isinstance(tclass, Collection):
tclass = frozenset((tclass,))
validate_perms_any(perms,
tclass=tclass,
policy=obj.policy)
self.instances[obj] = perms
#
# NetworkX Graph Descriptors
#
# These descriptors are used to simplify all
# of the dictionary use in the NetworkX graph.
#
class NetworkXGraphEdgeDescriptor(ABC):
"""
Descriptor abstract base class for NetworkX graph edge attributes.
Parameter:
name The edge property name
Instance class attribute use (obj parameter):
G The NetworkX graph
source The edge's source node
target The edge's target node
"""
def __init__(self, propname: str) -> None:
self.name = propname
def __get__(self, obj, objtype=None):
if obj is None:
return self
try:
return obj.G[obj.source][obj.target][self.name]
except KeyError:
raise AttributeError(self.name)
@abstractmethod
def __set__(self, obj, value):
pass
@abstractmethod
def __delete__(self, obj):
pass
class EdgeAttrDict(NetworkXGraphEdgeDescriptor):
"""A descriptor for edge attributes that are dictionaries."""
def __set__(self, obj, value):
# None is a special value to initialize the attribute
if value is None:
obj.G[obj.source][obj.target][self.name] = defaultdict(list)
else:
raise AttributeError("{0} dictionaries should not be assigned directly".
format(self.name))
def __delete__(self, obj):
obj.G[obj.source][obj.target][self.name].clear()
class EdgeAttrIntMax(NetworkXGraphEdgeDescriptor):
"""
A descriptor for edge attributes that are non-negative integers that always
keep the max assigned value until re-initialized.
"""
def __set__(self, obj, value):
# None is a special value to initialize
if value is None:
obj.G[obj.source][obj.target][self.name] = 0
else:
current_value = obj.G[obj.source][obj.target][self.name]
obj.G[obj.source][obj.target][self.name] = max(current_value, value)
def __delete__(self, obj):
obj.G[obj.source][obj.target][self.name] = 0
class EdgeAttrList(NetworkXGraphEdgeDescriptor):
"""A descriptor for edge attributes that are lists."""
def __set__(self, obj, value):
# None is a special value to initialize
if value is None:
obj.G[obj.source][obj.target][self.name] = []
else:
raise ValueError("{0} lists should not be assigned directly".format(self.name))
def __delete__(self, obj):
obj.G[obj.source][obj.target][self.name].clear()
#
# Permission map descriptors
#
class PermissionMapDescriptor:
"""
Descriptor for Permission Map mappings.
Parameter:
name The map setting name.
validator A callable for validating the setting.
Instance class attribute use (obj parameter):
_perm_map The full permission map.
class_ The mapping's object class
perm The mapping's permission
"""
def __init__(self, propname: str, validator: Callable):
self.name: str = propname
self.validator: Callable = validator
def __get__(self, obj, objtype=None):
if obj is None:
return self
return obj._perm_map[obj.class_][obj.perm][self.name]
def __set__(self, obj, value):
obj._perm_map[obj.class_][obj.perm][self.name] = self.validator(value)
def __delete__(self, obj):
raise AttributeError
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