430 lines
14 KiB
Python
430 lines
14 KiB
Python
"""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 typing as t
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from collections import abc
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from collections import deque
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from string import Formatter
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from _string import formatter_field_name_split # type: ignore
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from markupsafe import EscapeFormatter
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from markupsafe import Markup
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from .environment import Environment
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from .exceptions import SecurityError
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from .runtime import Context
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from .runtime import Undefined
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F = t.TypeVar("F", bound=t.Callable[..., t.Any])
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#: maximum number of items a range may produce
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MAX_RANGE = 100000
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#: Unsafe function attributes.
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UNSAFE_FUNCTION_ATTRIBUTES: t.Set[str] = set()
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#: Unsafe method attributes. Function attributes are unsafe for methods too.
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UNSAFE_METHOD_ATTRIBUTES: t.Set[str] = set()
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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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_mutable_spec: t.Tuple[t.Tuple[t.Type[t.Any], t.FrozenSet[str]], ...] = (
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(
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abc.MutableSet,
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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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abc.MutableMapping,
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frozenset(["clear", "pop", "popitem", "setdefault", "update"]),
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),
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(
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abc.MutableSequence,
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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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def inspect_format_method(callable: t.Callable[..., t.Any]) -> t.Optional[str]:
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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, str):
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return obj
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return None
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def safe_range(*args: int) -> range:
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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(*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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f" MAX_RANGE ({MAX_RANGE})."
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)
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return rng
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def unsafe(f: F) -> F:
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"""Marks a function or method as unsafe.
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.. code-block: python
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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 # type: ignore
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return f
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def is_internal_attribute(obj: t.Any, attr: str) -> bool:
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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: t.Any, attr: str) -> bool:
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"""This function checks if an attribute on a builtin mutable object
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(list, dict, set or deque) or the corresponding ABCs would modify it
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if called.
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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, ``False`` is 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: t.Dict[str, t.Callable[[t.Any, t.Any], t.Any]] = {
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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: t.Dict[str, t.Callable[[t.Any], t.Any]] = {
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"+": operator.pos,
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"-": operator.neg,
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}
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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: t.FrozenSet[str] = 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: t.FrozenSet[str] = frozenset()
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def __init__(self, *args: t.Any, **kwargs: t.Any) -> None:
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super().__init__(*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: t.Any, attr: str, value: t.Any) -> bool:
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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: t.Any) -> bool:
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"""Check if an object is safely callable. By default callables
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are considered safe unless decorated with :func:`unsafe`.
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This also recognizes the Django convention of setting
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``func.alters_data = True``.
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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(
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self, context: Context, operator: str, left: t.Any, right: t.Any
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) -> t.Any:
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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: Context, operator: str, arg: t.Any) -> t.Any:
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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(
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self, obj: t.Any, argument: t.Union[str, t.Any]
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) -> t.Union[t.Any, Undefined]:
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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, str):
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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: t.Any, attribute: str) -> t.Union[t.Any, Undefined]:
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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: t.Any, attribute: str) -> Undefined:
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"""Return an undefined object for unsafe attributes."""
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return self.undefined(
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f"access to attribute {attribute!r} of"
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f" {type(obj).__name__!r} object is unsafe.",
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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(
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self,
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s: str,
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args: t.Tuple[t.Any, ...],
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kwargs: t.Dict[str, t.Any],
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format_func: t.Optional[t.Callable[..., t.Any]] = None,
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) -> str:
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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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formatter: SandboxedFormatter
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if isinstance(s, Markup):
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formatter = SandboxedEscapeFormatter(self, escape=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"
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f" {len(args) + (kwargs is not None)} given"
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)
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kwargs = args[0]
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args = ()
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rv = formatter.vformat(s, args, kwargs)
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return type(s)(rv)
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def call(
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__self, # noqa: B902
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__context: Context,
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__obj: t.Any,
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*args: t.Any,
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**kwargs: t.Any,
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) -> t.Any:
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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(f"{__obj!r} is not safely callable")
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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: t.Any, attr: str, value: t.Any) -> bool:
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if not super().is_safe_attribute(obj, attr, value):
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return False
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return not modifies_known_mutable(obj, attr)
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class SandboxedFormatter(Formatter):
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def __init__(self, env: Environment, **kwargs: t.Any) -> None:
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self._env = env
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super().__init__(**kwargs)
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def get_field(
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self, field_name: str, args: t.Sequence[t.Any], kwargs: t.Mapping[str, t.Any]
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) -> t.Tuple[t.Any, str]:
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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 SandboxedEscapeFormatter(SandboxedFormatter, EscapeFormatter):
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pass
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