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authentik/passbook/lib/expression/evaluator.py

106 lines
4.0 KiB
Python

"""passbook expression policy evaluator"""
import re
from textwrap import indent
from typing import Any, Dict, Iterable, Optional
from django.core.exceptions import ValidationError
from elasticapm import capture_span
from requests import Session
from structlog import get_logger
from passbook.core.models import User
LOGGER = get_logger()
class BaseEvaluator:
"""Validate and evaluate python-based expressions"""
# Globals that can be used by function
_globals: Dict[str, Any]
# Context passed as locals to exec()
_context: Dict[str, Any]
# Filename used for exec
_filename: str
def __init__(self):
# update passbook/policies/expression/templates/policy/expression/form.html
# update docs/policies/expression/index.md
self._globals = {
"regex_match": BaseEvaluator.expr_filter_regex_match,
"regex_replace": BaseEvaluator.expr_filter_regex_replace,
"pb_is_group_member": BaseEvaluator.expr_func_is_group_member,
"pb_user_by": BaseEvaluator.expr_func_user_by,
"pb_logger": get_logger(),
"requests": Session(),
}
self._context = {}
self._filename = "BaseEvalautor"
@staticmethod
def expr_filter_regex_match(value: Any, regex: str) -> bool:
"""Expression Filter to run re.search"""
return re.search(regex, value) is None
@staticmethod
def expr_filter_regex_replace(value: Any, regex: str, repl: str) -> str:
"""Expression Filter to run re.sub"""
return re.sub(regex, repl, value)
@staticmethod
def expr_func_user_by(**filters) -> Optional[User]:
"""Get user by filters"""
users = User.objects.filter(**filters)
if users:
return users.first()
return None
@staticmethod
def expr_func_is_group_member(user: User, **group_filters) -> bool:
"""Check if `user` is member of group with name `group_name`"""
return user.groups.filter(**group_filters).exists()
def wrap_expression(self, expression: str, params: Iterable[str]) -> str:
"""Wrap expression in a function, call it, and save the result as `result`"""
handler_signature = ",".join(params)
full_expression = ""
full_expression += "from ipaddress import ip_address, ip_network\n"
full_expression += f"def handler({handler_signature}):\n"
full_expression += indent(expression, " ")
full_expression += f"\nresult = handler({handler_signature})"
return full_expression
@capture_span(name="BaseEvaluator", span_type="lib.evaluator.evaluate")
def evaluate(self, expression_source: str) -> Any:
"""Parse and evaluate expression. If the syntax is incorrect, a SyntaxError is raised.
If any exception is raised during execution, it is raised.
The result is returned without any type-checking."""
param_keys = self._context.keys()
ast_obj = compile(
self.wrap_expression(expression_source, param_keys), self._filename, "exec",
)
try:
_locals = self._context
# Yes this is an exec, yes it is potentially bad. Since we limit what variables are
# available here, and these policies can only be edited by admins, this is a risk
# we're willing to take.
# pylint: disable=exec-used
exec(ast_obj, self._globals, _locals) # nosec # noqa
result = _locals["result"]
except Exception as exc:
LOGGER.warning("Expression error", exc=exc)
raise
return result
def validate(self, expression: str) -> bool:
"""Validate expression's syntax, raise ValidationError if Syntax is invalid"""
param_keys = self._context.keys()
try:
compile(
self.wrap_expression(expression, param_keys), self._filename, "exec",
)
return True
except (ValueError, SyntaxError) as exc:
raise ValidationError(f"Expression Syntax Error: {str(exc)}") from exc