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from inspect import signature, Signature
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from typing import (
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Any,
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Callable,
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Dict,
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Set,
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Sequence,
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Tuple,
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NamedTuple,
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Type,
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Literal,
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Union,
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TYPE_CHECKING,
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)
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import ast
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import builtins
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import collections
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import operator
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import sys
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from functools import cached_property
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from dataclasses import dataclass, field
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from types import MethodDescriptorType, ModuleType
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from IPython.utils.docs import GENERATING_DOCUMENTATION
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from IPython.utils.decorators import undoc
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if TYPE_CHECKING or GENERATING_DOCUMENTATION:
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from typing_extensions import Protocol
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else:
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# do not require on runtime
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Protocol = object # requires Python >=3.8
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@undoc
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class HasGetItem(Protocol):
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def __getitem__(self, key) -> None:
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...
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@undoc
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class InstancesHaveGetItem(Protocol):
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def __call__(self, *args, **kwargs) -> HasGetItem:
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...
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@undoc
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class HasGetAttr(Protocol):
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def __getattr__(self, key) -> None:
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...
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@undoc
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class DoesNotHaveGetAttr(Protocol):
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pass
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# By default `__getattr__` is not explicitly implemented on most objects
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MayHaveGetattr = Union[HasGetAttr, DoesNotHaveGetAttr]
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def _unbind_method(func: Callable) -> Union[Callable, None]:
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"""Get unbound method for given bound method.
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Returns None if cannot get unbound method, or method is already unbound.
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"""
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owner = getattr(func, "__self__", None)
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owner_class = type(owner)
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name = getattr(func, "__name__", None)
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instance_dict_overrides = getattr(owner, "__dict__", None)
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if (
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owner is not None
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and name
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and (
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not instance_dict_overrides
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or (instance_dict_overrides and name not in instance_dict_overrides)
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)
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):
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return getattr(owner_class, name)
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return None
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@undoc
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@dataclass
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class EvaluationPolicy:
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"""Definition of evaluation policy."""
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allow_locals_access: bool = False
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allow_globals_access: bool = False
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allow_item_access: bool = False
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allow_attr_access: bool = False
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allow_builtins_access: bool = False
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allow_all_operations: bool = False
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allow_any_calls: bool = False
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allowed_calls: Set[Callable] = field(default_factory=set)
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def can_get_item(self, value, item):
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return self.allow_item_access
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def can_get_attr(self, value, attr):
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return self.allow_attr_access
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def can_operate(self, dunders: Tuple[str, ...], a, b=None):
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if self.allow_all_operations:
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return True
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def can_call(self, func):
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if self.allow_any_calls:
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return True
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if func in self.allowed_calls:
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return True
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owner_method = _unbind_method(func)
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if owner_method and owner_method in self.allowed_calls:
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return True
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def _get_external(module_name: str, access_path: Sequence[str]):
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"""Get value from external module given a dotted access path.
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Raises:
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* `KeyError` if module is removed not found, and
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* `AttributeError` if acess path does not match an exported object
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"""
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member_type = sys.modules[module_name]
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for attr in access_path:
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member_type = getattr(member_type, attr)
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return member_type
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def _has_original_dunder_external(
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value,
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module_name: str,
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access_path: Sequence[str],
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method_name: str,
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):
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if module_name not in sys.modules:
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# LBYLB as it is faster
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return False
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try:
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member_type = _get_external(module_name, access_path)
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value_type = type(value)
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if type(value) == member_type:
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return True
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if method_name == "__getattribute__":
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# we have to short-circuit here due to an unresolved issue in
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# `isinstance` implementation: https://bugs.python.org/issue32683
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return False
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if isinstance(value, member_type):
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method = getattr(value_type, method_name, None)
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member_method = getattr(member_type, method_name, None)
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if member_method == method:
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return True
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except (AttributeError, KeyError):
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return False
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def _has_original_dunder(
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value, allowed_types, allowed_methods, allowed_external, method_name
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):
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# note: Python ignores `__getattr__`/`__getitem__` on instances,
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# we only need to check at class level
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value_type = type(value)
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# strict type check passes â no need to check method
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if value_type in allowed_types:
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return True
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method = getattr(value_type, method_name, None)
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if method is None:
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return None
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if method in allowed_methods:
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return True
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for module_name, *access_path in allowed_external:
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if _has_original_dunder_external(value, module_name, access_path, method_name):
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return True
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return False
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@undoc
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@dataclass
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class SelectivePolicy(EvaluationPolicy):
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allowed_getitem: Set[InstancesHaveGetItem] = field(default_factory=set)
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allowed_getitem_external: Set[Tuple[str, ...]] = field(default_factory=set)
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allowed_getattr: Set[MayHaveGetattr] = field(default_factory=set)
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allowed_getattr_external: Set[Tuple[str, ...]] = field(default_factory=set)
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allowed_operations: Set = field(default_factory=set)
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allowed_operations_external: Set[Tuple[str, ...]] = field(default_factory=set)
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_operation_methods_cache: Dict[str, Set[Callable]] = field(
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default_factory=dict, init=False
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)
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def can_get_attr(self, value, attr):
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has_original_attribute = _has_original_dunder(
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value,
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allowed_types=self.allowed_getattr,
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allowed_methods=self._getattribute_methods,
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allowed_external=self.allowed_getattr_external,
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method_name="__getattribute__",
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)
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has_original_attr = _has_original_dunder(
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value,
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allowed_types=self.allowed_getattr,
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allowed_methods=self._getattr_methods,
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allowed_external=self.allowed_getattr_external,
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method_name="__getattr__",
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)
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accept = False
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# Many objects do not have `__getattr__`, this is fine.
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if has_original_attr is None and has_original_attribute:
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accept = True
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else:
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# Accept objects without modifications to `__getattr__` and `__getattribute__`
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accept = has_original_attr and has_original_attribute
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if accept:
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# We still need to check for overriden properties.
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value_class = type(value)
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if not hasattr(value_class, attr):
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return True
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class_attr_val = getattr(value_class, attr)
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is_property = isinstance(class_attr_val, property)
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if not is_property:
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return True
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# Properties in allowed types are ok (although we do not include any
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# properties in our default allow list currently).
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if type(value) in self.allowed_getattr:
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return True # pragma: no cover
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# Properties in subclasses of allowed types may be ok if not changed
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for module_name, *access_path in self.allowed_getattr_external:
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try:
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external_class = _get_external(module_name, access_path)
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external_class_attr_val = getattr(external_class, attr)
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except (KeyError, AttributeError):
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return False # pragma: no cover
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return class_attr_val == external_class_attr_val
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return False
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def can_get_item(self, value, item):
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"""Allow accessing `__getiitem__` of allow-listed instances unless it was not modified."""
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return _has_original_dunder(
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value,
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allowed_types=self.allowed_getitem,
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allowed_methods=self._getitem_methods,
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allowed_external=self.allowed_getitem_external,
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method_name="__getitem__",
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)
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def can_operate(self, dunders: Tuple[str, ...], a, b=None):
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objects = [a]
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if b is not None:
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objects.append(b)
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return all(
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[
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_has_original_dunder(
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obj,
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allowed_types=self.allowed_operations,
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allowed_methods=self._operator_dunder_methods(dunder),
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allowed_external=self.allowed_operations_external,
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method_name=dunder,
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)
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for dunder in dunders
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for obj in objects
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]
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)
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def _operator_dunder_methods(self, dunder: str) -> Set[Callable]:
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if dunder not in self._operation_methods_cache:
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self._operation_methods_cache[dunder] = self._safe_get_methods(
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self.allowed_operations, dunder
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)
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return self._operation_methods_cache[dunder]
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@cached_property
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def _getitem_methods(self) -> Set[Callable]:
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return self._safe_get_methods(self.allowed_getitem, "__getitem__")
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@cached_property
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def _getattr_methods(self) -> Set[Callable]:
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return self._safe_get_methods(self.allowed_getattr, "__getattr__")
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@cached_property
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def _getattribute_methods(self) -> Set[Callable]:
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return self._safe_get_methods(self.allowed_getattr, "__getattribute__")
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def _safe_get_methods(self, classes, name) -> Set[Callable]:
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return {
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method
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for class_ in classes
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for method in [getattr(class_, name, None)]
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if method
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}
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class _DummyNamedTuple(NamedTuple):
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"""Used internally to retrieve methods of named tuple instance."""
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class EvaluationContext(NamedTuple):
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#: Local namespace
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locals: dict
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#: Global namespace
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globals: dict
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#: Evaluation policy identifier
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evaluation: Literal[
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"forbidden", "minimal", "limited", "unsafe", "dangerous"
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] = "forbidden"
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#: Whether the evalution of code takes place inside of a subscript.
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#: Useful for evaluating ``:-1, 'col'`` in ``df[:-1, 'col']``.
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in_subscript: bool = False
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class _IdentitySubscript:
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"""Returns the key itself when item is requested via subscript."""
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def __getitem__(self, key):
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return key
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IDENTITY_SUBSCRIPT = _IdentitySubscript()
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SUBSCRIPT_MARKER = "__SUBSCRIPT_SENTINEL__"
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UNKNOWN_SIGNATURE = Signature()
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class GuardRejection(Exception):
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"""Exception raised when guard rejects evaluation attempt."""
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pass
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def guarded_eval(code: str, context: EvaluationContext):
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"""Evaluate provided code in the evaluation context.
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If evaluation policy given by context is set to ``forbidden``
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no evaluation will be performed; if it is set to ``dangerous``
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standard :func:`eval` will be used; finally, for any other,
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policy :func:`eval_node` will be called on parsed AST.
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"""
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locals_ = context.locals
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if context.evaluation == "forbidden":
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raise GuardRejection("Forbidden mode")
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# note: not using `ast.literal_eval` as it does not implement
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# getitem at all, for example it fails on simple `[0][1]`
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if context.in_subscript:
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# syntatic sugar for ellipsis (:) is only available in susbcripts
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# so we need to trick the ast parser into thinking that we have
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# a subscript, but we need to be able to later recognise that we did
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# it so we can ignore the actual __getitem__ operation
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if not code:
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return tuple()
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locals_ = locals_.copy()
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locals_[SUBSCRIPT_MARKER] = IDENTITY_SUBSCRIPT
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code = SUBSCRIPT_MARKER + "[" + code + "]"
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context = EvaluationContext(**{**context._asdict(), **{"locals": locals_}})
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if context.evaluation == "dangerous":
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return eval(code, context.globals, context.locals)
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expression = ast.parse(code, mode="eval")
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return eval_node(expression, context)
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BINARY_OP_DUNDERS: Dict[Type[ast.operator], Tuple[str]] = {
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ast.Add: ("__add__",),
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ast.Sub: ("__sub__",),
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ast.Mult: ("__mul__",),
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ast.Div: ("__truediv__",),
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ast.FloorDiv: ("__floordiv__",),
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ast.Mod: ("__mod__",),
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ast.Pow: ("__pow__",),
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ast.LShift: ("__lshift__",),
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ast.RShift: ("__rshift__",),
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ast.BitOr: ("__or__",),
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ast.BitXor: ("__xor__",),
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ast.BitAnd: ("__and__",),
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ast.MatMult: ("__matmul__",),
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}
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COMP_OP_DUNDERS: Dict[Type[ast.cmpop], Tuple[str, ...]] = {
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ast.Eq: ("__eq__",),
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ast.NotEq: ("__ne__", "__eq__"),
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ast.Lt: ("__lt__", "__gt__"),
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ast.LtE: ("__le__", "__ge__"),
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ast.Gt: ("__gt__", "__lt__"),
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ast.GtE: ("__ge__", "__le__"),
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ast.In: ("__contains__",),
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# Note: ast.Is, ast.IsNot, ast.NotIn are handled specially
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}
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UNARY_OP_DUNDERS: Dict[Type[ast.unaryop], Tuple[str, ...]] = {
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ast.USub: ("__neg__",),
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ast.UAdd: ("__pos__",),
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# we have to check both __inv__ and __invert__!
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ast.Invert: ("__invert__", "__inv__"),
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ast.Not: ("__not__",),
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}
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|
|
|
|
|
|
class Duck:
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|
"""A dummy class used to create objects of other classes without calling their ``__init__``"""
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|
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def _find_dunder(node_op, dunders) -> Union[Tuple[str, ...], None]:
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dunder = None
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for op, candidate_dunder in dunders.items():
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if isinstance(node_op, op):
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dunder = candidate_dunder
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return dunder
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|
|
|
|
|
|
def eval_node(node: Union[ast.AST, None], context: EvaluationContext):
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|
|
"""Evaluate AST node in provided context.
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|
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|
|
Applies evaluation restrictions defined in the context. Currently does not support evaluation of functions with keyword arguments.
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|
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|
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|
Does not evaluate actions that always have side effects:
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|
|
|
- class definitions (``class sth: ...``)
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|
|
- function definitions (``def sth: ...``)
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|
|
- variable assignments (``x = 1``)
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|
|
- augmented assignments (``x += 1``)
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|
- deletions (``del x``)
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|
Does not evaluate operations which do not return values:
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|
- assertions (``assert x``)
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|
- pass (``pass``)
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|
- imports (``import x``)
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|
|
- control flow:
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|
|
- conditionals (``if x:``) except for ternary IfExp (``a if x else b``)
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|
|
- loops (``for`` and ``while``)
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|
|
- exception handling
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The purpose of this function is to guard against unwanted side-effects;
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it does not give guarantees on protection from malicious code execution.
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"""
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policy = EVALUATION_POLICIES[context.evaluation]
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if node is None:
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return None
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if isinstance(node, ast.Expression):
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return eval_node(node.body, context)
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if isinstance(node, ast.BinOp):
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left = eval_node(node.left, context)
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right = eval_node(node.right, context)
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dunders = _find_dunder(node.op, BINARY_OP_DUNDERS)
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if dunders:
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if policy.can_operate(dunders, left, right):
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return getattr(left, dunders[0])(right)
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else:
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raise GuardRejection(
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f"Operation (`{dunders}`) for",
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type(left),
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f"not allowed in {context.evaluation} mode",
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)
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if isinstance(node, ast.Compare):
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left = eval_node(node.left, context)
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all_true = True
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negate = False
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for op, right in zip(node.ops, node.comparators):
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right = eval_node(right, context)
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dunder = None
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dunders = _find_dunder(op, COMP_OP_DUNDERS)
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if not dunders:
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if isinstance(op, ast.NotIn):
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dunders = COMP_OP_DUNDERS[ast.In]
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negate = True
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if isinstance(op, ast.Is):
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dunder = "is_"
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if isinstance(op, ast.IsNot):
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dunder = "is_"
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negate = True
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if not dunder and dunders:
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dunder = dunders[0]
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if dunder:
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a, b = (right, left) if dunder == "__contains__" else (left, right)
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if dunder == "is_" or dunders and policy.can_operate(dunders, a, b):
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result = getattr(operator, dunder)(a, b)
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if negate:
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result = not result
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if not result:
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all_true = False
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left = right
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else:
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raise GuardRejection(
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f"Comparison (`{dunder}`) for",
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type(left),
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f"not allowed in {context.evaluation} mode",
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)
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else:
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raise ValueError(
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f"Comparison `{dunder}` not supported"
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) # pragma: no cover
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return all_true
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if isinstance(node, ast.Constant):
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return node.value
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if isinstance(node, ast.Tuple):
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return tuple(eval_node(e, context) for e in node.elts)
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if isinstance(node, ast.List):
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return [eval_node(e, context) for e in node.elts]
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if isinstance(node, ast.Set):
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return {eval_node(e, context) for e in node.elts}
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if isinstance(node, ast.Dict):
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return dict(
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zip(
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[eval_node(k, context) for k in node.keys],
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[eval_node(v, context) for v in node.values],
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)
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)
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if isinstance(node, ast.Slice):
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return slice(
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eval_node(node.lower, context),
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eval_node(node.upper, context),
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eval_node(node.step, context),
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)
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if isinstance(node, ast.UnaryOp):
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value = eval_node(node.operand, context)
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dunders = _find_dunder(node.op, UNARY_OP_DUNDERS)
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if dunders:
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if policy.can_operate(dunders, value):
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return getattr(value, dunders[0])()
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else:
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raise GuardRejection(
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f"Operation (`{dunders}`) for",
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type(value),
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f"not allowed in {context.evaluation} mode",
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)
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if isinstance(node, ast.Subscript):
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value = eval_node(node.value, context)
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slice_ = eval_node(node.slice, context)
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if policy.can_get_item(value, slice_):
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return value[slice_]
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raise GuardRejection(
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"Subscript access (`__getitem__`) for",
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type(value), # not joined to avoid calling `repr`
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f" not allowed in {context.evaluation} mode",
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)
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if isinstance(node, ast.Name):
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if policy.allow_locals_access and node.id in context.locals:
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return context.locals[node.id]
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if policy.allow_globals_access and node.id in context.globals:
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return context.globals[node.id]
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if policy.allow_builtins_access and hasattr(builtins, node.id):
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# note: do not use __builtins__, it is implementation detail of cPython
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return getattr(builtins, node.id)
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if not policy.allow_globals_access and not policy.allow_locals_access:
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raise GuardRejection(
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f"Namespace access not allowed in {context.evaluation} mode"
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)
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else:
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raise NameError(f"{node.id} not found in locals, globals, nor builtins")
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if isinstance(node, ast.Attribute):
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value = eval_node(node.value, context)
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if policy.can_get_attr(value, node.attr):
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return getattr(value, node.attr)
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raise GuardRejection(
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"Attribute access (`__getattr__`) for",
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type(value), # not joined to avoid calling `repr`
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f"not allowed in {context.evaluation} mode",
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)
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if isinstance(node, ast.IfExp):
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test = eval_node(node.test, context)
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if test:
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return eval_node(node.body, context)
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else:
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return eval_node(node.orelse, context)
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if isinstance(node, ast.Call):
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func = eval_node(node.func, context)
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if policy.can_call(func) and not node.keywords:
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args = [eval_node(arg, context) for arg in node.args]
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return func(*args)
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try:
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sig = signature(func)
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except ValueError:
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sig = UNKNOWN_SIGNATURE
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# if annotation was not stringized, or it was stringized
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# but resolved by signature call we know the return type
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not_empty = sig.return_annotation is not Signature.empty
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not_stringized = not isinstance(sig.return_annotation, str)
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if not_empty and not_stringized:
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duck = Duck()
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# if allow-listed builtin is on type annotation, instantiate it
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if policy.can_call(sig.return_annotation) and not node.keywords:
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args = [eval_node(arg, context) for arg in node.args]
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return sig.return_annotation(*args)
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try:
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# if custom class is in type annotation, mock it;
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# this only works for heap types, not builtins
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duck.__class__ = sig.return_annotation
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return duck
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except TypeError:
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pass
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raise GuardRejection(
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"Call for",
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func, # not joined to avoid calling `repr`
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f"not allowed in {context.evaluation} mode",
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)
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raise ValueError("Unhandled node", ast.dump(node))
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SUPPORTED_EXTERNAL_GETITEM = {
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("pandas", "core", "indexing", "_iLocIndexer"),
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("pandas", "core", "indexing", "_LocIndexer"),
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("pandas", "DataFrame"),
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("pandas", "Series"),
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("numpy", "ndarray"),
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("numpy", "void"),
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}
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BUILTIN_GETITEM: Set[InstancesHaveGetItem] = {
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dict,
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str, # type: ignore[arg-type]
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bytes, # type: ignore[arg-type]
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list,
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tuple,
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collections.defaultdict,
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collections.deque,
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collections.OrderedDict,
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collections.ChainMap,
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collections.UserDict,
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collections.UserList,
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collections.UserString, # type: ignore[arg-type]
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_DummyNamedTuple,
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_IdentitySubscript,
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}
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def _list_methods(cls, source=None):
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"""For use on immutable objects or with methods returning a copy"""
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return [getattr(cls, k) for k in (source if source else dir(cls))]
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dict_non_mutating_methods = ("copy", "keys", "values", "items")
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list_non_mutating_methods = ("copy", "index", "count")
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set_non_mutating_methods = set(dir(set)) & set(dir(frozenset))
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dict_keys: Type[collections.abc.KeysView] = type({}.keys())
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NUMERICS = {int, float, complex}
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ALLOWED_CALLS = {
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bytes,
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*_list_methods(bytes),
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dict,
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*_list_methods(dict, dict_non_mutating_methods),
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dict_keys.isdisjoint,
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list,
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*_list_methods(list, list_non_mutating_methods),
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set,
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*_list_methods(set, set_non_mutating_methods),
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frozenset,
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*_list_methods(frozenset),
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range,
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str,
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*_list_methods(str),
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tuple,
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*_list_methods(tuple),
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*NUMERICS,
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*[method for numeric_cls in NUMERICS for method in _list_methods(numeric_cls)],
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collections.deque,
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*_list_methods(collections.deque, list_non_mutating_methods),
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collections.defaultdict,
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*_list_methods(collections.defaultdict, dict_non_mutating_methods),
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collections.OrderedDict,
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*_list_methods(collections.OrderedDict, dict_non_mutating_methods),
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collections.UserDict,
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*_list_methods(collections.UserDict, dict_non_mutating_methods),
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collections.UserList,
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*_list_methods(collections.UserList, list_non_mutating_methods),
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collections.UserString,
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*_list_methods(collections.UserString, dir(str)),
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collections.Counter,
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*_list_methods(collections.Counter, dict_non_mutating_methods),
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collections.Counter.elements,
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collections.Counter.most_common,
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}
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BUILTIN_GETATTR: Set[MayHaveGetattr] = {
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*BUILTIN_GETITEM,
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set,
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frozenset,
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object,
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type, # `type` handles a lot of generic cases, e.g. numbers as in `int.real`.
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*NUMERICS,
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dict_keys,
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MethodDescriptorType,
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ModuleType,
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}
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BUILTIN_OPERATIONS = {*BUILTIN_GETATTR}
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EVALUATION_POLICIES = {
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"minimal": EvaluationPolicy(
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allow_builtins_access=True,
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allow_locals_access=False,
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allow_globals_access=False,
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allow_item_access=False,
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allow_attr_access=False,
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allowed_calls=set(),
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allow_any_calls=False,
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allow_all_operations=False,
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),
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"limited": SelectivePolicy(
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allowed_getitem=BUILTIN_GETITEM,
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allowed_getitem_external=SUPPORTED_EXTERNAL_GETITEM,
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allowed_getattr=BUILTIN_GETATTR,
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allowed_getattr_external={
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|
# pandas Series/Frame implements custom `__getattr__`
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("pandas", "DataFrame"),
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("pandas", "Series"),
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},
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allowed_operations=BUILTIN_OPERATIONS,
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allow_builtins_access=True,
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allow_locals_access=True,
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allow_globals_access=True,
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allowed_calls=ALLOWED_CALLS,
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|
),
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"unsafe": EvaluationPolicy(
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|
allow_builtins_access=True,
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allow_locals_access=True,
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allow_globals_access=True,
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|
allow_attr_access=True,
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allow_item_access=True,
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allow_any_calls=True,
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allow_all_operations=True,
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),
|
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|
}
|
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|
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|
|
|
__all__ = [
|
|
|
"guarded_eval",
|
|
|
"eval_node",
|
|
|
"GuardRejection",
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|
"EvaluationContext",
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|
"_unbind_method",
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]
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