JezK
Edit File: sandbox.py
"""A sandbox layer that ensures unsafe operations cannot be performed. Useful when the template itself comes from an untrusted source. """ import operator import types import typing as t from _string import formatter_field_name_split # type: ignore from collections import abc try: from collections.abc import deque except ImportError: from collections import deque from functools import update_wrapper from string import Formatter from markupsafe import EscapeFormatter from markupsafe import Markup from .environment import Environment from .exceptions import SecurityError from .runtime import Context from .runtime import Undefined F = t.TypeVar("F", bound=t.Callable[..., t.Any]) #: maximum number of items a range may produce MAX_RANGE = 100000 #: Unsafe function attributes. UNSAFE_FUNCTION_ATTRIBUTES: t.Set[str] = set() #: Unsafe method attributes. Function attributes are unsafe for methods too. UNSAFE_METHOD_ATTRIBUTES: t.Set[str] = set() #: unsafe generator attributes. UNSAFE_GENERATOR_ATTRIBUTES = {"gi_frame", "gi_code"} #: unsafe attributes on coroutines UNSAFE_COROUTINE_ATTRIBUTES = {"cr_frame", "cr_code"} #: unsafe attributes on async generators UNSAFE_ASYNC_GENERATOR_ATTRIBUTES = {"ag_code", "ag_frame"} _mutable_spec: t.Tuple[t.Tuple[t.Type, t.FrozenSet[str]], ...] = ( ( abc.MutableSet, frozenset( [ "add", "clear", "difference_update", "discard", "pop", "remove", "symmetric_difference_update", "update", ] ), ), ( abc.MutableMapping, frozenset(["clear", "pop", "popitem", "setdefault", "update"]), ), ( abc.MutableSequence, frozenset(["append", "reverse", "insert", "sort", "extend", "remove"]), ), ( deque, frozenset( [ "append", "appendleft", "clear", "extend", "extendleft", "pop", "popleft", "remove", "rotate", ] ), ), ) def safe_range(*args: int) -> range: """A range that can't generate ranges with a length of more than MAX_RANGE items. """ rng = range(*args) if len(rng) > MAX_RANGE: raise OverflowError( "Range too big. The sandbox blocks ranges larger than" f" MAX_RANGE ({MAX_RANGE})." ) return rng def unsafe(f: F) -> F: """Marks a function or method as unsafe. .. code-block: python @unsafe def delete(self): pass """ f.unsafe_callable = True # type: ignore return f def is_internal_attribute(obj: t.Any, attr: str) -> bool: """Test if the attribute given is an internal python attribute. For example this function returns `True` for the `func_code` attribute of python objects. This is useful if the environment method :meth:`~SandboxedEnvironment.is_safe_attribute` is overridden. >>> from jinja2.sandbox import is_internal_attribute >>> is_internal_attribute(str, "mro") True >>> is_internal_attribute(str, "upper") False """ if isinstance(obj, types.FunctionType): if attr in UNSAFE_FUNCTION_ATTRIBUTES: return True elif isinstance(obj, types.MethodType): if attr in UNSAFE_FUNCTION_ATTRIBUTES or attr in UNSAFE_METHOD_ATTRIBUTES: return True elif isinstance(obj, type): if attr == "mro": return True elif isinstance(obj, (types.CodeType, types.TracebackType, types.FrameType)): return True elif isinstance(obj, types.GeneratorType): if attr in UNSAFE_GENERATOR_ATTRIBUTES: return True elif hasattr(types, "CoroutineType") and isinstance(obj, types.CoroutineType): if attr in UNSAFE_COROUTINE_ATTRIBUTES: return True elif hasattr(types, "AsyncGeneratorType") and isinstance( obj, types.AsyncGeneratorType ): if attr in UNSAFE_ASYNC_GENERATOR_ATTRIBUTES: return True return attr.startswith("__") def modifies_known_mutable(obj: t.Any, attr: str) -> bool: """This function checks if an attribute on a builtin mutable object (list, dict, set or deque) or the corresponding ABCs would modify it if called. >>> modifies_known_mutable({}, "clear") True >>> modifies_known_mutable({}, "keys") False >>> modifies_known_mutable([], "append") True >>> modifies_known_mutable([], "index") False If called with an unsupported object, ``False`` is returned. >>> modifies_known_mutable("foo", "upper") False """ for typespec, unsafe in _mutable_spec: if isinstance(obj, typespec): return attr in unsafe return False class SandboxedEnvironment(Environment): """The sandboxed environment. It works like the regular environment but tells the compiler to generate sandboxed code. Additionally subclasses of this environment may override the methods that tell the runtime what attributes or functions are safe to access. If the template tries to access insecure code a :exc:`SecurityError` is raised. However also other exceptions may occur during the rendering so the caller has to ensure that all exceptions are caught. """ sandboxed = True #: default callback table for the binary operators. A copy of this is #: available on each instance of a sandboxed environment as #: :attr:`binop_table` default_binop_table: t.Dict[str, t.Callable[[t.Any, t.Any], t.Any]] = { "+": operator.add, "-": operator.sub, "*": operator.mul, "/": operator.truediv, "//": operator.floordiv, "**": operator.pow, "%": operator.mod, } #: default callback table for the unary operators. A copy of this is #: available on each instance of a sandboxed environment as #: :attr:`unop_table` default_unop_table: t.Dict[str, t.Callable[[t.Any], t.Any]] = { "+": operator.pos, "-": operator.neg, } #: a set of binary operators that should be intercepted. Each operator #: that is added to this set (empty by default) is delegated to the #: :meth:`call_binop` method that will perform the operator. The default #: operator callback is specified by :attr:`binop_table`. #: #: The following binary operators are interceptable: #: ``//``, ``%``, ``+``, ``*``, ``-``, ``/``, and ``**`` #: #: The default operation form the operator table corresponds to the #: builtin function. Intercepted calls are always slower than the native #: operator call, so make sure only to intercept the ones you are #: interested in. #: #: .. versionadded:: 2.6 intercepted_binops: t.FrozenSet[str] = frozenset() #: a set of unary operators that should be intercepted. Each operator #: that is added to this set (empty by default) is delegated to the #: :meth:`call_unop` method that will perform the operator. The default #: operator callback is specified by :attr:`unop_table`. #: #: The following unary operators are interceptable: ``+``, ``-`` #: #: The default operation form the operator table corresponds to the #: builtin function. Intercepted calls are always slower than the native #: operator call, so make sure only to intercept the ones you are #: interested in. #: #: .. versionadded:: 2.6 intercepted_unops: t.FrozenSet[str] = frozenset() def __init__(self, *args: t.Any, **kwargs: t.Any) -> None: super().__init__(*args, **kwargs) self.globals["range"] = safe_range self.binop_table = self.default_binop_table.copy() self.unop_table = self.default_unop_table.copy() def is_safe_attribute(self, obj: t.Any, attr: str, value: t.Any) -> bool: """The sandboxed environment will call this method to check if the attribute of an object is safe to access. Per default all attributes starting with an underscore are considered private as well as the special attributes of internal python objects as returned by the :func:`is_internal_attribute` function. """ return not (attr.startswith("_") or is_internal_attribute(obj, attr)) def is_safe_callable(self, obj: t.Any) -> bool: """Check if an object is safely callable. By default callables are considered safe unless decorated with :func:`unsafe`. This also recognizes the Django convention of setting ``func.alters_data = True``. """ return not ( getattr(obj, "unsafe_callable", False) or getattr(obj, "alters_data", False) ) def call_binop( self, context: Context, operator: str, left: t.Any, right: t.Any ) -> t.Any: """For intercepted binary operator calls (:meth:`intercepted_binops`) this function is executed instead of the builtin operator. This can be used to fine tune the behavior of certain operators. .. versionadded:: 2.6 """ return self.binop_table[operator](left, right) def call_unop(self, context: Context, operator: str, arg: t.Any) -> t.Any: """For intercepted unary operator calls (:meth:`intercepted_unops`) this function is executed instead of the builtin operator. This can be used to fine tune the behavior of certain operators. .. versionadded:: 2.6 """ return self.unop_table[operator](arg) def getitem( self, obj: t.Any, argument: t.Union[str, t.Any] ) -> t.Union[t.Any, Undefined]: """Subscribe an object from sandboxed code.""" try: return obj[argument] except (TypeError, LookupError): if isinstance(argument, str): try: attr = str(argument) except Exception: pass else: try: value = getattr(obj, attr) except AttributeError: pass else: fmt = self.wrap_str_format(value) if fmt is not None: return fmt if self.is_safe_attribute(obj, argument, value): return value return self.unsafe_undefined(obj, argument) return self.undefined(obj=obj, name=argument) def getattr(self, obj: t.Any, attribute: str) -> t.Union[t.Any, Undefined]: """Subscribe an object from sandboxed code and prefer the attribute. The attribute passed *must* be a bytestring. """ try: value = getattr(obj, attribute) except AttributeError: try: return obj[attribute] except (TypeError, LookupError): pass else: fmt = self.wrap_str_format(value) if fmt is not None: return fmt if self.is_safe_attribute(obj, attribute, value): return value return self.unsafe_undefined(obj, attribute) return self.undefined(obj=obj, name=attribute) def unsafe_undefined(self, obj: t.Any, attribute: str) -> Undefined: """Return an undefined object for unsafe attributes.""" return self.undefined( f"access to attribute {attribute!r} of" f" {type(obj).__name__!r} object is unsafe.", name=attribute, obj=obj, exc=SecurityError, ) def wrap_str_format(self, value: t.Any) -> t.Optional[t.Callable[..., str]]: """If the given value is a ``str.format`` or ``str.format_map`` method, return a new function than handles sandboxing. This is done at access rather than in :meth:`call`, so that calls made without ``call`` are also sandboxed. """ if not isinstance( value, (types.MethodType, types.BuiltinMethodType) ) or value.__name__ not in ("format", "format_map"): return None f_self: t.Any = value.__self__ if not isinstance(f_self, str): return None str_type: t.Type[str] = type(f_self) is_format_map = value.__name__ == "format_map" formatter: SandboxedFormatter if isinstance(f_self, Markup): formatter = SandboxedEscapeFormatter(self, escape=f_self.escape) else: formatter = SandboxedFormatter(self) vformat = formatter.vformat def wrapper(*args: t.Any, **kwargs: t.Any) -> str: if is_format_map: if kwargs: raise TypeError("format_map() takes no keyword arguments") if len(args) != 1: raise TypeError( f"format_map() takes exactly one argument ({len(args)} given)" ) kwargs = args[0] args = () return str_type(vformat(f_self, args, kwargs)) return update_wrapper(wrapper, value) def call( __self, # noqa: B902 __context: Context, __obj: t.Any, *args: t.Any, **kwargs: t.Any, ) -> t.Any: """Call an object from sandboxed code.""" # the double prefixes are to avoid double keyword argument # errors when proxying the call. if not __self.is_safe_callable(__obj): raise SecurityError(f"{__obj!r} is not safely callable") return __context.call(__obj, *args, **kwargs) class ImmutableSandboxedEnvironment(SandboxedEnvironment): """Works exactly like the regular `SandboxedEnvironment` but does not permit modifications on the builtin mutable objects `list`, `set`, and `dict` by using the :func:`modifies_known_mutable` function. """ def is_safe_attribute(self, obj: t.Any, attr: str, value: t.Any) -> bool: if not super().is_safe_attribute(obj, attr, value): return False return not modifies_known_mutable(obj, attr) class SandboxedFormatter(Formatter): def __init__(self, env: Environment, **kwargs: t.Any) -> None: self._env = env super().__init__(**kwargs) def get_field( self, field_name: str, args: t.Sequence[t.Any], kwargs: t.Mapping[str, t.Any] ) -> t.Tuple[t.Any, str]: first, rest = formatter_field_name_split(field_name) obj = self.get_value(first, args, kwargs) for is_attr, i in rest: if is_attr: obj = self._env.getattr(obj, i) else: obj = self._env.getitem(obj, i) return obj, first class SandboxedEscapeFormatter(SandboxedFormatter, EscapeFormatter): pass