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Editing: avc_audit.py
# Authors: John Dennis <jdennis@redhat.com> # # Copyright (C) 2006,2007,2008 Red Hat, Inc. # # 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; either version 2 of the License, or # (at your option) any later version. # # 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., 675 Mass Ave, Cambridge, MA 02139, USA. # __all__ = [ 'AuditSocketReceiverThread', 'AuditRecordReceiver', # FIXME, do we really want to export this? 'verify_avc', ] from builtins import str from builtins import object import syslog import audit import select import selinux import socket as Socket import fcntl from six.moves import _thread import threading import time from functools import cmp_to_key from setroubleshoot.config import get_config from setroubleshoot.errcode import * from setroubleshoot.util import * from setroubleshoot.audit_data import * try: getattr(audit, 'AUDIT_EOE') except AttributeError: audit.AUDIT_EOE = 1320 #------------------------------------------------------------------------------ my_context = AvcContext(selinux.getcon()[1]) def verify_avc(avc): if avc.scontext.type == None or avc.tcontext.type == None: return False if my_context.type == avc.scontext.type: syslog.syslog(syslog.LOG_ERR, "setroubleshoot generated AVC, exiting to avoid recursion, context=%s, AVC scontext=%s" % (my_context, avc.scontext)) syslog.syslog(syslog.LOG_ERR, "audit event\n%s" % (avc.audit_event.format())) import sys sys.exit(0) return True #------------------------------------------------------------------------------ class AuditRecordReceiver(object): """ The audit system emits messages about a single event independently. Thus one single auditable event may be composed from one or more individual audit messages. Each audit message is prefixed with a unique event id, which includes a timestamp. The last audit message associated with an event is not marked in any fashion. Audit messages for a specific event may arrive interleaved with audit messages for other events. It is the job of higher level software (this code) to assemble the audit messages into events. The AuditEvent class is used for assembly. When a new event id is seen a new AuditEvent object is created, then every time an audit message arrives with that event id it is added to that object. The AuditEvent object contains the timestamp associated with the audit event as well as other data items useful for processing and handling the event. The audit system does not tell us when the last message belonging to an event has been emitted so we have no explicit way of knowing when the audit event has been fully assembled from its constituent message parts. We use the heuristic if a sufficient length of time has expired since we last saw a message for this event, then it must be complete Thus when audit events are created we place them in a cache where they will reside until their time to live has expired at which point we will assume they are complete and emit the event. Events are expired in the flush_cache() method. The events resident in the cache are sorted by their timestamps. A time threshold is established. Any events in the cache older than the time threshold are flushed from the cache as complete events. When should flushes be performed? The moment when a new message is added would seem a likely candidate moment to perform a sweep of the cache. But this is costly and does not improve how quickly events are expired. We could wait some interval of time (something much greater than how long we expect it would take for messages percolate) and this has good behavior, except for the following case. Sometimes messages are emitted by audit in rapid succession. If we swept the cache once a second then the cache may have grown quite large. Since it is very likely that any given audit event is complete by the time the next several events start arriving we can optimize by tracking how many messages have arrived since the last time we swept the cache. The the heuristic for when to sweep the cache becomes: If we've seen a sufficient number of messages then sweep -or- if a sufficient length of time has elapsed then we sweep Note that when audit messages are injected via log file scanning elapsed wall clock time has no meaning relative to when to perform the cache sweep. However, the timestamp for an event remains a critical factor when deciding if an event is complete (have we scanned far enough ahead such we're confident we won't see any more messages for this event?). Thus the threshold for when to expire an event from the cache during static log file scanning is determined not by wall clock time but rather by the oldest timestamp in the cache (e.g.there is enough spread between timestamps in the cache its reasonable to assume the event is complete). One might ask in the case of log file scanning why not fill the cache until EOF is reached and then sweep the cache? Because in log files it is not unusual to have thousands or tens of thousands of events and the cache would grown needlessly large. Because we have to deal with the real time case we already have code to keep only the most recent events in the cache so we might as well use that logic, keep the code paths the same and minimize resource usage. """ # number of seconds an event must reside in the cache until its # considered complete cache_time_to_live = 0.005 def __init__(self): self.flush_size = 30 self.flush_count = 0 self.cache = {} self.events = [] self.reset_statistics() def num_cached_events(self): return len(self.cache) def reset_statistics(self): self.max_cache_length = 0 self.event_count = 0 def insert_new_event(self, record): audit_event = AuditEvent() self.cache[str(record.event_id)] = audit_event return audit_event def get_event_from_record(self, record): return self.cache.get(str(record.event_id), None) def add_record_to_cache(self, record): log_debug("%s.add_record_to_cache(): %s" % (self.__class__.__name__, record)) audit_event = self.get_event_from_record(record) if record.record_type == 'EOE': if audit_event: self.flush_event(audit_event) return if audit_event is None: audit_event = self.insert_new_event(record) audit_event.add_record(record) def emit_event(self, audit_event): self.event_count += 1 self.events.insert(0, audit_event) def flush_event(self, audit_event): self.emit_event(audit_event) del(self.cache[str(audit_event.event_id)]) def flush_cache(self, threshold_age=None): '''Flush events from the cache if they are older than the threshold age. If the threshold age is None then the threshold age is set to the age of the newest event in the cache minus the cache time to live, in other words anything in the cache which is older than the time to live relative to the most current event is flushed. ''' # no events, nothing to do if len(self.cache) == 0: return if len(self.cache) > self.max_cache_length: self.max_cache_length = len(self.cache) event_ids = list(self.cache.keys()) # flush everything if threshold_age == 0: for event_id in event_ids: audit_event = self.cache[event_id] self.flush_event(audit_event) return # flush old events event_ids.sort(key=cmp_to_key(lambda a, b: self.cache[a].timestamp < self.cache[b].timestamp)) if threshold_age is None: threshold_age = self.cache[event_ids[-1]].timestamp - self.cache_time_to_live for event_id in event_ids: audit_event = self.cache[event_id] if audit_event.timestamp < threshold_age: self.flush_event(audit_event) def flush(self, threshold_age=None): self.flush_cache(threshold_age) self.flush_count = 0 while len(self.events) > 0: audit_event = self.events.pop() yield audit_event def close(self): """Emit every event in the cache irrespective of its timestamp. This means we're done, nothing should remain buffered.""" for audit_event in self.flush(0): yield audit_event def feed(self, record): 'Accept a new audit record into the system for processing.' self.flush_count += 1 if record.record_type in ('AVC', 'AVC_PATH', 'SYSCALL', 'CWD', 'PATH', 'EOE', "1400", "1107"): self.add_record_to_cache(record) # If we've seen enough messages then sweep the event cache and flush what we can if self.flush_count > self.flush_size: for audit_event in self.flush(): yield audit_event while len(self.events) > 0: audit_event = self.events.pop() yield audit_event #------------------------------------------------------------------------------ class AuditSocketReceiverThread(threading.Thread): def __init__(self, queue, report_receiver): # parent class constructor threading.Thread.__init__(self) self.queue = queue self.report_receiver = report_receiver self.record_receiver = AuditRecordReceiver() self.retry_interval = get_config('audit', 'retry_interval', int) self.get_socket_paths() self.timeout_interval = 2 self.has_audit_eoe = False def get_socket_paths(self): self.audit_socket_paths = [] audit_socket_path = get_config('audit', 'text_protocol_socket_path') self.audit_socket_paths.append(audit_socket_path) audit_socket_path = get_config('audit', 'binary_protocol_socket_path') self.audit_socket_paths.append(audit_socket_path) def connect(self): while True: try: for self.audit_socket_path in self.audit_socket_paths: if self.audit_socket_path is not None: try: record_format = derive_record_format(self.audit_socket_path) self.record_reader = AuditRecordReader(record_format) self.audit_socket = Socket.socket(Socket.AF_UNIX, Socket.SOCK_STREAM) fcntl.fcntl(self.audit_socket.fileno(), fcntl.F_SETFD, fcntl.FD_CLOEXEC) self.audit_socket.connect(self.audit_socket_path) self.audit_socket_fd = self.audit_socket.makefile() log_debug("audit socket (%s) connected" % self.audit_socket_path) return except Socket.error as e: errno, strerror = get_error_from_socket_exception(e) log_debug("attempt to open audit socket (%s) failed, error='%s'" % (self.audit_socket_path, strerror)) log_debug("could not open any audit sockets (%s), retry in %d seconds" % (', '.join(self.audit_socket_paths), self.retry_interval)) except Socket.error as e: errno, strerror = get_error_from_socket_exception(e) log_debug("audit socket (%s) failed, error='%s', retry in %d seconds" % (self.audit_socket_path, strerror, self.retry_interval)) except OSError as e: log_debug("audit socket (%s) failed, error='%s', retry in %d seconds" % (self.audit_socket_path, e[1], self.retry_interval)) time.sleep(self.retry_interval) def new_audit_record_handler(self, record_type, event_id, body_text, fields, line_number): 'called to enter a new audit record' audit_record = AuditRecord(record_type, event_id, body_text, fields, line_number) audit_record.audispd_rectify() for audit_event in self.record_receiver.feed(audit_record): self.new_audit_event_handler(audit_event) def new_audit_event_handler(self, audit_event): if audit_event.is_avc() and not audit_event.is_granted() and audit_event.num_records() > 0: avcs = compute_avcs(audit_event) for avc in avcs: if verify_avc(avc): self.queue.put((avc, self.report_receiver)) def run(self): self.connect() timeout = self.timeout_interval while True: inList, outList, errList = select.select([self.audit_socket], [], [], timeout) try: if self.audit_socket in inList: import os new_data = os.read(self.audit_socket_fd.fileno(), 1024) if new_data == '': log_debug("audit socket connection dropped") self.connect() else: log_debug("cached audit event count = %d" % (self.record_receiver.num_cached_events())) if not self.has_audit_eoe: timeout = self.timeout_interval for (record_type, event_id, body_text, fields, line_number) in self.record_reader.feed(new_data): if record_type == 'EOE': self.has_audit_eoe = True timeout = None self.new_audit_record_handler(record_type, event_id, body_text, fields, line_number) else: # timeout, anything waiting in our event cache? for audit_event in self.record_receiver.flush(time.time() - self.timeout_interval): self.new_audit_event_handler(audit_event) if self.record_receiver.num_cached_events() == 0: timeout = None except KeyboardInterrupt as e: log_debug("KeyboardInterrupt exception in %s" % self.__class__.__name__) _thread.interrupt_main() except SystemExit as e: log_debug("SystemExit exception in %s" % self.__class__.__name__) _thread.interrupt_main() except Exception as e: import traceback syslog_trace(traceback.format_exc()) syslog.syslog(syslog.LOG_ERR, "exception %s: %s" % (e.__class__.__name__, str(e))) return
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