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