# Copyright 2020, Microsoft Corporation
#
# SPDX-License-Identifier: LGPL-2.1-only
#
import logging
from collections import defaultdict
from typing import Dict, List, Set
from ..policyrep import AnyTERule, Type
from ..terulequery import TERuleQuery
from .checkermodule import CheckerModule
from .descriptors import ConfigSetDescriptor
EXEMPT_WRITE = "exempt_write_domain"
EXEMPT_EXEC = "exempt_exec_domain"
EXEMPT_FILE = "exempt_file"
class ReadOnlyExecutables(CheckerModule):
"""Checker module for asserting all executable files are read-only."""
check_type = "ro_execs"
check_config = frozenset((EXEMPT_WRITE, EXEMPT_EXEC, EXEMPT_FILE))
exempt_write_domain = ConfigSetDescriptor("lookup_type_or_attr", strict=False, expand=True)
exempt_file = ConfigSetDescriptor("lookup_type_or_attr", strict=False, expand=True)
exempt_exec_domain = ConfigSetDescriptor("lookup_type_or_attr", strict=False, expand=True)
def __init__(self, policy, checkname, config) -> None:
super().__init__(policy, checkname, config)
self.log = logging.getLogger(__name__)
self.exempt_write_domain = config.get(EXEMPT_WRITE)
self.exempt_file = config.get(EXEMPT_FILE)
self.exempt_exec_domain = config.get(EXEMPT_EXEC)
def _collect_executables(self) -> Dict[Type, Set[AnyTERule]]:
self.log.debug("Collecting list of executable file types.")
self.log.debug("Ignore exec domains: {!r}".format(self.exempt_exec_domain))
query = TERuleQuery(self.policy,
ruletype=("allow",),
tclass=("file",),
perms=("execute", "execute_no_trans"))
collected = defaultdict(set)
for rule in query.results():
sources = set(rule.source.expand()) - self.exempt_exec_domain
targets = set(rule.target.expand()) - self.exempt_file
# ignore rule if source or target is an empty attr
if not sources or not targets:
self.log.debug("Ignoring execute rule: {}".format(rule))
continue
for t in targets:
self.log.debug("Determined {} is executable by: {}".format(t, rule))
collected[t].add(rule)
return collected
def run(self) -> List:
self.log.info("Checking executables are read-only.")
query = TERuleQuery(self.policy,
ruletype=("allow",),
tclass=("file",),
perms=("write", "append"))
executables = self._collect_executables()
failures = defaultdict(set)
for exec_type in executables.keys():
self.log.debug("Checking if executable type {} is writable.".format(exec_type))
query.target = exec_type
for rule in sorted(query.results()):
if set(rule.source.expand()) - self.exempt_write_domain:
failures[exec_type].add(rule)
for exec_type in sorted(failures.keys()):
self.output.write("\n------------\n\n")
self.output.write("Executable type {} is writable.\n\n".format(exec_type))
self.output.write("Execute rules:\n")
for rule in sorted(executables[exec_type]):
self.output.write(" * {}\n".format(rule))
self.output.write("\nWrite rules:\n")
for rule in sorted(failures[exec_type]):
self.log_fail(str(rule))
self.log.debug("{} failure(s)".format(len(failures)))
return sorted(failures.keys())
