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infoflow.py
# Copyright 2014-2015, Tresys Technology, LLC # # This file is part of SETools. # # SETools is free software: you can redistribute it and/or modify # it under the terms of the GNU Lesser General Public License as # published by the Free Software Foundation, either version 2.1 of # the License, or (at your option) any later version. # # SETools 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 Lesser General Public License for more details. # # You should have received a copy of the GNU Lesser General Public # License along with SETools. If not, see # <http://www.gnu.org/licenses/>. # import itertools import logging from contextlib import suppress import networkx as nx from networkx.exception import NetworkXError, NetworkXNoPath from .descriptors import EdgeAttrIntMax, EdgeAttrList from .exception import RuleNotConditional from .policyrep import TERuletype __all__ = ['InfoFlowAnalysis'] class InfoFlowAnalysis: """Information flow analysis.""" def __init__(self, policy, perm_map, min_weight=1, exclude=None, booleans=None): """ Parameters: policy The policy to analyze. perm_map The permission map or path to the permission map file. minweight The minimum permission weight to include in the analysis. (default is 1) exclude The types excluded from the information flow analysis. (default is none) booleans If None, all rules will be added to the analysis (default). otherwise it should be set to a dict with keys corresponding to boolean names and values of True/False. Any unspecified booleans will use the policy's default values. """ self.log = logging.getLogger(__name__) self.policy = policy self.min_weight = min_weight self.perm_map = perm_map self.exclude = exclude self.booleans = booleans self.rebuildgraph = True self.rebuildsubgraph = True self.G = nx.DiGraph() self.subG = None @property def min_weight(self): return self._min_weight @min_weight.setter def min_weight(self, weight): if not 1 <= weight <= 10: raise ValueError( "Min information flow weight must be an integer 1-10.") self._min_weight = weight self.rebuildsubgraph = True @property def perm_map(self): return self._perm_map @perm_map.setter def perm_map(self, perm_map): self._perm_map = perm_map self.rebuildgraph = True self.rebuildsubgraph = True @property def exclude(self): return self._exclude @exclude.setter def exclude(self, types): if types: self._exclude = [self.policy.lookup_type(t) for t in types] else: self._exclude = [] self.rebuildsubgraph = True def shortest_path(self, source, target): """ Generator which yields one shortest path between the source and target types (there may be more). Parameters: source The source type. target The target type. Yield: generator(steps) steps Yield: tuple(source, target, rules) source The source type for this step of the information flow. target The target type for this step of the information flow. rules The list of rules creating this information flow step. """ s = self.policy.lookup_type(source) t = self.policy.lookup_type(target) if self.rebuildsubgraph: self._build_subgraph() self.log.info("Generating one shortest information flow path from {0} to {1}...". format(s, t)) with suppress(NetworkXNoPath): # NodeNotFound: the type is valid but not in graph, e.g. # excluded or disconnected due to min weight # NetworkXNoPath: no paths or the target type is # not in the graph yield self.__generate_steps(nx.shortest_path(self.subG, s, t)) def all_paths(self, source, target, maxlen=2): """ Generator which yields all paths between the source and target up to the specified maximum path length. This algorithm tends to get very expensive above 3-5 steps, depending on the policy complexity. Parameters: source The source type. target The target type. maxlen Maximum length of paths. Yield: generator(steps) steps Yield: tuple(source, target, rules) source The source type for this step of the information flow. target The target type for this step of the information flow. rules The list of rules creating this information flow step. """ if maxlen < 1: raise ValueError("Maximum path length must be positive.") s = self.policy.lookup_type(source) t = self.policy.lookup_type(target) if self.rebuildsubgraph: self._build_subgraph() self.log.info("Generating all information flow paths from {0} to {1}, max length {2}...". format(s, t, maxlen)) with suppress(NetworkXNoPath): # NodeNotFound: the type is valid but not in graph, e.g. # excluded or disconnected due to min weight # NetworkXNoPath: no paths or the target type is # not in the graph for path in nx.all_simple_paths(self.subG, s, t, maxlen): yield self.__generate_steps(path) def all_shortest_paths(self, source, target): """ Generator which yields all shortest paths between the source and target types. Parameters: source The source type. target The target type. Yield: generator(steps) steps Yield: tuple(source, target, rules) source The source type for this step of the information flow. target The target type for this step of the information flow. rules The list of rules creating this information flow step. """ s = self.policy.lookup_type(source) t = self.policy.lookup_type(target) if self.rebuildsubgraph: self._build_subgraph() self.log.info("Generating all shortest information flow paths from {0} to {1}...". format(s, t)) with suppress(NetworkXNoPath): # NodeNotFound: the type is valid but not in graph, e.g. # excluded or disconnected due to min weight # NetworkXNoPath: no paths or the target type is # not in the graph for path in nx.all_shortest_paths(self.subG, s, t): yield self.__generate_steps(path) def infoflows(self, type_, out=True): """ Generator which yields all information flows in/out of a specified source type. Parameters: source The starting type. Keyword Parameters: out If true, information flows out of the type will be returned. If false, information flows in to the type will be returned. Default is true. Yield: generator(steps) steps A generator that returns the tuple of source, target, and rules for each information flow. """ s = self.policy.lookup_type(type_) if self.rebuildsubgraph: self._build_subgraph() self.log.info("Generating all information flows {0} {1}". format("out of" if out else "into", s)) with suppress(NetworkXError): # NetworkXError: the type is valid but not in graph, e.g. # excluded or disconnected due to min weight if out: flows = self.subG.out_edges(s) else: flows = self.subG.in_edges(s) for source, target in flows: yield Edge(self.subG, source, target) def get_stats(self): # pragma: no cover """ Get the information flow graph statistics. Return: str """ if self.rebuildgraph: self._build_graph() return nx.info(self.G) # # Internal functions follow # def __generate_steps(self, path): """ Generator which returns the source, target, and associated rules for each information flow step. Parameter: path A list of graph node names representing an information flow path. Yield: tuple(source, target, rules) source The source type for this step of the information flow. target The target type for this step of the information flow. rules The list of rules creating this information flow step. """ for s in range(1, len(path)): yield Edge(self.subG, path[s - 1], path[s]) # # # Graph building functions # # # 1. _build_graph determines the flow in each direction for each TE # rule and then expands the rule. All information flows are # included in this main graph: memory is traded off for efficiency # as the main graph should only need to be rebuilt if permission # weights change. # 2. _build_subgraph derives a subgraph which removes all excluded # types (nodes) and edges (information flows) which are below the # minimum weight. This subgraph is rebuilt only if the main graph # is rebuilt or the minimum weight or excluded types change. def _build_graph(self): self.G.clear() self.G.name = "Information flow graph for {0}.".format(self.policy) self.perm_map.map_policy(self.policy) self.log.info("Building information flow graph from {0}...".format(self.policy)) for rule in self.policy.terules(): if rule.ruletype != TERuletype.allow: continue (rweight, wweight) = self.perm_map.rule_weight(rule) for s, t in itertools.product(rule.source.expand(), rule.target.expand()): # only add flows if they actually flow # in or out of the source type type if s != t: if wweight: edge = Edge(self.G, s, t, create=True) edge.rules.append(rule) edge.weight = wweight if rweight: edge = Edge(self.G, t, s, create=True) edge.rules.append(rule) edge.weight = rweight self.rebuildgraph = False self.rebuildsubgraph = True self.log.info("Completed building information flow graph.") self.log.debug("Graph stats: nodes: {0}, edges: {1}.".format( nx.number_of_nodes(self.G), nx.number_of_edges(self.G))) def _build_subgraph(self): if self.rebuildgraph: self._build_graph() self.log.info("Building information flow subgraph...") self.log.debug("Excluding {0!r}".format(self.exclude)) self.log.debug("Min weight {0}".format(self.min_weight)) self.log.debug("Exclude disabled conditional policy: {0}".format( self.booleans is not None)) # delete excluded types from subgraph nodes = [n for n in self.G.nodes() if n not in self.exclude] self.subG = self.G.subgraph(nodes).copy() # delete edges below minimum weight. # no need if weight is 1, since that # does not exclude any edges. if self.min_weight > 1: delete_list = [] for s, t in self.subG.edges(): edge = Edge(self.subG, s, t) if edge.weight < self.min_weight: delete_list.append(edge) self.subG.remove_edges_from(delete_list) if self.booleans is not None: delete_list = [] for s, t in self.subG.edges(): edge = Edge(self.subG, s, t) # collect disabled rules rule_list = [] # pylint: disable=not-an-iterable for rule in edge.rules: if not rule.enabled(**self.booleans): rule_list.append(rule) deleted_rules = [] for rule in rule_list: if rule not in deleted_rules: edge.rules.remove(rule) deleted_rules.append(rule) if not edge.rules: delete_list.append(edge) self.subG.remove_edges_from(delete_list) self.rebuildsubgraph = False self.log.info("Completed building information flow subgraph.") self.log.debug("Subgraph stats: nodes: {0}, edges: {1}.".format( nx.number_of_nodes(self.subG), nx.number_of_edges(self.subG))) class Edge: """ A graph edge. Also used for returning information flow steps. Parameters: graph The NetworkX graph. source The source type of the edge. target The target type of the edge. Keyword Parameters: create (T/F) create the edge if it does not exist. The default is False. """ rules = EdgeAttrList('rules') # use capacity to store the info flow weight so # we can use network flow algorithms naturally. # The weight for each edge is 1 since each info # flow step is no more costly than another # (see below add_edge() call) weight = EdgeAttrIntMax('capacity') def __init__(self, graph, source, target, create=False): self.G = graph self.source = source self.target = target if not self.G.has_edge(source, target): if create: self.G.add_edge(source, target, weight=1) self.rules = None self.weight = None else: raise ValueError("Edge does not exist in graph") def __getitem__(self, key): # This is implemented so this object can be used in NetworkX # functions that operate on (source, target) tuples if isinstance(key, slice): return [self._index_to_item(i) for i in range(* key.indices(2))] else: return self._index_to_item(key) def _index_to_item(self, index): """Return source or target based on index.""" if index == 0: return self.source elif index == 1: return self.target else: raise IndexError("Invalid index (edges only have 2 items): {0}".format(index))
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