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510 lines
17 KiB
510 lines
17 KiB
# -*- coding: utf-8 -*-
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"""A sandbox layer that ensures unsafe operations cannot be performed.
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Useful when the template itself comes from an untrusted source.
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"""
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import operator
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import types
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import warnings
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from collections import deque
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from string import Formatter
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from markupsafe import EscapeFormatter
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from markupsafe import Markup
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from ._compat import abc
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from ._compat import PY2
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from ._compat import range_type
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from ._compat import string_types
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from .environment import Environment
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from .exceptions import SecurityError
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#: maximum number of items a range may produce
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MAX_RANGE = 100000
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#: attributes of function objects that are considered unsafe.
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if PY2:
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UNSAFE_FUNCTION_ATTRIBUTES = {
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"func_closure",
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"func_code",
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"func_dict",
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"func_defaults",
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"func_globals",
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}
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else:
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# On versions > python 2 the special attributes on functions are gone,
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# but they remain on methods and generators for whatever reason.
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UNSAFE_FUNCTION_ATTRIBUTES = set()
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#: unsafe method attributes. function attributes are unsafe for methods too
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UNSAFE_METHOD_ATTRIBUTES = {"im_class", "im_func", "im_self"}
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#: unsafe generator attributes.
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UNSAFE_GENERATOR_ATTRIBUTES = {"gi_frame", "gi_code"}
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#: unsafe attributes on coroutines
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UNSAFE_COROUTINE_ATTRIBUTES = {"cr_frame", "cr_code"}
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#: unsafe attributes on async generators
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UNSAFE_ASYNC_GENERATOR_ATTRIBUTES = {"ag_code", "ag_frame"}
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# make sure we don't warn in python 2.6 about stuff we don't care about
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warnings.filterwarnings(
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"ignore", "the sets module", DeprecationWarning, module=__name__
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)
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_mutable_set_types = (set,)
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_mutable_mapping_types = (dict,)
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_mutable_sequence_types = (list,)
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# on python 2.x we can register the user collection types
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try:
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from UserDict import UserDict, DictMixin
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from UserList import UserList
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_mutable_mapping_types += (UserDict, DictMixin)
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_mutable_set_types += (UserList,)
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except ImportError:
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pass
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# if sets is still available, register the mutable set from there as well
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try:
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from sets import Set
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_mutable_set_types += (Set,)
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except ImportError:
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pass
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#: register Python 2.6 abstract base classes
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_mutable_set_types += (abc.MutableSet,)
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_mutable_mapping_types += (abc.MutableMapping,)
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_mutable_sequence_types += (abc.MutableSequence,)
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_mutable_spec = (
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(
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_mutable_set_types,
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frozenset(
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[
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"add",
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"clear",
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"difference_update",
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"discard",
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"pop",
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"remove",
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"symmetric_difference_update",
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"update",
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]
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),
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),
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(
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_mutable_mapping_types,
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frozenset(["clear", "pop", "popitem", "setdefault", "update"]),
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),
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(
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_mutable_sequence_types,
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frozenset(["append", "reverse", "insert", "sort", "extend", "remove"]),
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),
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(
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deque,
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frozenset(
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[
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"append",
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"appendleft",
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"clear",
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"extend",
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"extendleft",
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"pop",
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"popleft",
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"remove",
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"rotate",
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]
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),
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),
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)
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class _MagicFormatMapping(abc.Mapping):
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"""This class implements a dummy wrapper to fix a bug in the Python
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standard library for string formatting.
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See https://bugs.python.org/issue13598 for information about why
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this is necessary.
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"""
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def __init__(self, args, kwargs):
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self._args = args
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self._kwargs = kwargs
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self._last_index = 0
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def __getitem__(self, key):
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if key == "":
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idx = self._last_index
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self._last_index += 1
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try:
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return self._args[idx]
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except LookupError:
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pass
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key = str(idx)
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return self._kwargs[key]
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def __iter__(self):
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return iter(self._kwargs)
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def __len__(self):
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return len(self._kwargs)
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def inspect_format_method(callable):
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if not isinstance(
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callable, (types.MethodType, types.BuiltinMethodType)
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) or callable.__name__ not in ("format", "format_map"):
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return None
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obj = callable.__self__
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if isinstance(obj, string_types):
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return obj
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def safe_range(*args):
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"""A range that can't generate ranges with a length of more than
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MAX_RANGE items.
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"""
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rng = range_type(*args)
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if len(rng) > MAX_RANGE:
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raise OverflowError(
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"Range too big. The sandbox blocks ranges larger than"
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" MAX_RANGE (%d)." % MAX_RANGE
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)
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return rng
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def unsafe(f):
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"""Marks a function or method as unsafe.
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::
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@unsafe
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def delete(self):
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pass
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"""
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f.unsafe_callable = True
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return f
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def is_internal_attribute(obj, attr):
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"""Test if the attribute given is an internal python attribute. For
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example this function returns `True` for the `func_code` attribute of
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python objects. This is useful if the environment method
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:meth:`~SandboxedEnvironment.is_safe_attribute` is overridden.
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>>> from jinja2.sandbox import is_internal_attribute
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>>> is_internal_attribute(str, "mro")
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True
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>>> is_internal_attribute(str, "upper")
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False
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"""
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if isinstance(obj, types.FunctionType):
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if attr in UNSAFE_FUNCTION_ATTRIBUTES:
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return True
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elif isinstance(obj, types.MethodType):
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if attr in UNSAFE_FUNCTION_ATTRIBUTES or attr in UNSAFE_METHOD_ATTRIBUTES:
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return True
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elif isinstance(obj, type):
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if attr == "mro":
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return True
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elif isinstance(obj, (types.CodeType, types.TracebackType, types.FrameType)):
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return True
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elif isinstance(obj, types.GeneratorType):
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if attr in UNSAFE_GENERATOR_ATTRIBUTES:
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return True
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elif hasattr(types, "CoroutineType") and isinstance(obj, types.CoroutineType):
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if attr in UNSAFE_COROUTINE_ATTRIBUTES:
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return True
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elif hasattr(types, "AsyncGeneratorType") and isinstance(
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obj, types.AsyncGeneratorType
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):
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if attr in UNSAFE_ASYNC_GENERATOR_ATTRIBUTES:
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return True
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return attr.startswith("__")
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def modifies_known_mutable(obj, attr):
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"""This function checks if an attribute on a builtin mutable object
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(list, dict, set or deque) would modify it if called. It also supports
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the "user"-versions of the objects (`sets.Set`, `UserDict.*` etc.) and
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with Python 2.6 onwards the abstract base classes `MutableSet`,
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`MutableMapping`, and `MutableSequence`.
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>>> modifies_known_mutable({}, "clear")
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True
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>>> modifies_known_mutable({}, "keys")
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False
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>>> modifies_known_mutable([], "append")
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True
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>>> modifies_known_mutable([], "index")
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False
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If called with an unsupported object (such as unicode) `False` is
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returned.
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>>> modifies_known_mutable("foo", "upper")
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False
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"""
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for typespec, unsafe in _mutable_spec:
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if isinstance(obj, typespec):
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return attr in unsafe
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return False
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class SandboxedEnvironment(Environment):
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"""The sandboxed environment. It works like the regular environment but
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tells the compiler to generate sandboxed code. Additionally subclasses of
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this environment may override the methods that tell the runtime what
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attributes or functions are safe to access.
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If the template tries to access insecure code a :exc:`SecurityError` is
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raised. However also other exceptions may occur during the rendering so
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the caller has to ensure that all exceptions are caught.
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"""
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sandboxed = True
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#: default callback table for the binary operators. A copy of this is
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#: available on each instance of a sandboxed environment as
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#: :attr:`binop_table`
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default_binop_table = {
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"+": operator.add,
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"-": operator.sub,
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"*": operator.mul,
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"/": operator.truediv,
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"//": operator.floordiv,
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"**": operator.pow,
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"%": operator.mod,
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}
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#: default callback table for the unary operators. A copy of this is
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#: available on each instance of a sandboxed environment as
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#: :attr:`unop_table`
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default_unop_table = {"+": operator.pos, "-": operator.neg}
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#: a set of binary operators that should be intercepted. Each operator
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#: that is added to this set (empty by default) is delegated to the
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#: :meth:`call_binop` method that will perform the operator. The default
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#: operator callback is specified by :attr:`binop_table`.
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#:
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#: The following binary operators are interceptable:
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#: ``//``, ``%``, ``+``, ``*``, ``-``, ``/``, and ``**``
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#:
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#: The default operation form the operator table corresponds to the
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#: builtin function. Intercepted calls are always slower than the native
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#: operator call, so make sure only to intercept the ones you are
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#: interested in.
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#:
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#: .. versionadded:: 2.6
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intercepted_binops = frozenset()
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#: a set of unary operators that should be intercepted. Each operator
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#: that is added to this set (empty by default) is delegated to the
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#: :meth:`call_unop` method that will perform the operator. The default
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#: operator callback is specified by :attr:`unop_table`.
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#:
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#: The following unary operators are interceptable: ``+``, ``-``
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#:
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#: The default operation form the operator table corresponds to the
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#: builtin function. Intercepted calls are always slower than the native
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#: operator call, so make sure only to intercept the ones you are
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#: interested in.
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#:
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#: .. versionadded:: 2.6
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intercepted_unops = frozenset()
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def intercept_unop(self, operator):
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"""Called during template compilation with the name of a unary
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operator to check if it should be intercepted at runtime. If this
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method returns `True`, :meth:`call_unop` is executed for this unary
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operator. The default implementation of :meth:`call_unop` will use
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the :attr:`unop_table` dictionary to perform the operator with the
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same logic as the builtin one.
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The following unary operators are interceptable: ``+`` and ``-``
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Intercepted calls are always slower than the native operator call,
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so make sure only to intercept the ones you are interested in.
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.. versionadded:: 2.6
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"""
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return False
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def __init__(self, *args, **kwargs):
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Environment.__init__(self, *args, **kwargs)
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self.globals["range"] = safe_range
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self.binop_table = self.default_binop_table.copy()
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self.unop_table = self.default_unop_table.copy()
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def is_safe_attribute(self, obj, attr, value):
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"""The sandboxed environment will call this method to check if the
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attribute of an object is safe to access. Per default all attributes
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starting with an underscore are considered private as well as the
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special attributes of internal python objects as returned by the
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:func:`is_internal_attribute` function.
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"""
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return not (attr.startswith("_") or is_internal_attribute(obj, attr))
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def is_safe_callable(self, obj):
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"""Check if an object is safely callable. Per default a function is
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considered safe unless the `unsafe_callable` attribute exists and is
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True. Override this method to alter the behavior, but this won't
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affect the `unsafe` decorator from this module.
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"""
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return not (
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getattr(obj, "unsafe_callable", False) or getattr(obj, "alters_data", False)
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)
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def call_binop(self, context, operator, left, right):
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"""For intercepted binary operator calls (:meth:`intercepted_binops`)
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this function is executed instead of the builtin operator. This can
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be used to fine tune the behavior of certain operators.
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.. versionadded:: 2.6
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"""
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return self.binop_table[operator](left, right)
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def call_unop(self, context, operator, arg):
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"""For intercepted unary operator calls (:meth:`intercepted_unops`)
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this function is executed instead of the builtin operator. This can
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be used to fine tune the behavior of certain operators.
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.. versionadded:: 2.6
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"""
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return self.unop_table[operator](arg)
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def getitem(self, obj, argument):
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"""Subscribe an object from sandboxed code."""
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try:
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return obj[argument]
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except (TypeError, LookupError):
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if isinstance(argument, string_types):
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try:
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attr = str(argument)
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except Exception:
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pass
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else:
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try:
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value = getattr(obj, attr)
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except AttributeError:
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pass
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else:
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if self.is_safe_attribute(obj, argument, value):
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return value
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return self.unsafe_undefined(obj, argument)
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return self.undefined(obj=obj, name=argument)
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def getattr(self, obj, attribute):
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"""Subscribe an object from sandboxed code and prefer the
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attribute. The attribute passed *must* be a bytestring.
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"""
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try:
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value = getattr(obj, attribute)
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except AttributeError:
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try:
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return obj[attribute]
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except (TypeError, LookupError):
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pass
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else:
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if self.is_safe_attribute(obj, attribute, value):
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return value
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return self.unsafe_undefined(obj, attribute)
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return self.undefined(obj=obj, name=attribute)
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def unsafe_undefined(self, obj, attribute):
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"""Return an undefined object for unsafe attributes."""
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return self.undefined(
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"access to attribute %r of %r "
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"object is unsafe." % (attribute, obj.__class__.__name__),
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name=attribute,
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obj=obj,
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exc=SecurityError,
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)
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def format_string(self, s, args, kwargs, format_func=None):
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"""If a format call is detected, then this is routed through this
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method so that our safety sandbox can be used for it.
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"""
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if isinstance(s, Markup):
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formatter = SandboxedEscapeFormatter(self, s.escape)
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else:
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formatter = SandboxedFormatter(self)
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if format_func is not None and format_func.__name__ == "format_map":
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if len(args) != 1 or kwargs:
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raise TypeError(
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"format_map() takes exactly one argument %d given"
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% (len(args) + (kwargs is not None))
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)
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kwargs = args[0]
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args = None
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kwargs = _MagicFormatMapping(args, kwargs)
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rv = formatter.vformat(s, args, kwargs)
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return type(s)(rv)
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def call(__self, __context, __obj, *args, **kwargs): # noqa: B902
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"""Call an object from sandboxed code."""
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fmt = inspect_format_method(__obj)
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if fmt is not None:
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return __self.format_string(fmt, args, kwargs, __obj)
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# the double prefixes are to avoid double keyword argument
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# errors when proxying the call.
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if not __self.is_safe_callable(__obj):
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raise SecurityError("%r is not safely callable" % (__obj,))
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return __context.call(__obj, *args, **kwargs)
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class ImmutableSandboxedEnvironment(SandboxedEnvironment):
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"""Works exactly like the regular `SandboxedEnvironment` but does not
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permit modifications on the builtin mutable objects `list`, `set`, and
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`dict` by using the :func:`modifies_known_mutable` function.
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"""
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def is_safe_attribute(self, obj, attr, value):
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if not SandboxedEnvironment.is_safe_attribute(self, obj, attr, value):
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return False
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return not modifies_known_mutable(obj, attr)
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# This really is not a public API apparently.
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try:
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from _string import formatter_field_name_split
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except ImportError:
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def formatter_field_name_split(field_name):
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return field_name._formatter_field_name_split()
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|
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class SandboxedFormatterMixin(object):
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def __init__(self, env):
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self._env = env
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def get_field(self, field_name, args, kwargs):
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first, rest = formatter_field_name_split(field_name)
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obj = self.get_value(first, args, kwargs)
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for is_attr, i in rest:
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if is_attr:
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obj = self._env.getattr(obj, i)
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else:
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obj = self._env.getitem(obj, i)
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return obj, first
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class SandboxedFormatter(SandboxedFormatterMixin, Formatter):
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def __init__(self, env):
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SandboxedFormatterMixin.__init__(self, env)
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Formatter.__init__(self)
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class SandboxedEscapeFormatter(SandboxedFormatterMixin, EscapeFormatter):
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def __init__(self, env, escape):
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SandboxedFormatterMixin.__init__(self, env)
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EscapeFormatter.__init__(self, escape)
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|