xref: /third_party/jinja2/sandbox.py (revision e31aef6a)

"""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
from collections import deque
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 inspect_format_method(callable: t.Callable) -> t.Optional[str]:
    if not isinstance(
        callable, (types.MethodType, types.BuiltinMethodType)
    ) or callable.__name__ not in ("format", "format_map"):
        return None

    obj = callable.__self__

    if isinstance(obj, str):
        return obj

    return None


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:
                        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:
            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 format_string(
        self,
        s: str,
        args: t.Tuple[t.Any, ...],
        kwargs: t.Dict[str, t.Any],
        format_func: t.Optional[t.Callable] = None,
    ) -> str:
        """If a format call is detected, then this is routed through this
        method so that our safety sandbox can be used for it.
        """
        formatter: SandboxedFormatter
        if isinstance(s, Markup):
            formatter = SandboxedEscapeFormatter(self, escape=s.escape)
        else:
            formatter = SandboxedFormatter(self)

        if format_func is not None and format_func.__name__ == "format_map":
            if len(args) != 1 or kwargs:
                raise TypeError(
                    "format_map() takes exactly one argument"
                    f" {len(args) + (kwargs is not None)} given"
                )

            kwargs = args[0]
            args = ()

        rv = formatter.vformat(s, args, kwargs)
        return type(s)(rv)

    def call(
        __self,  # noqa: B902
        __context: Context,
        __obj: t.Any,
        *args: t.Any,
        **kwargs: t.Any,
    ) -> t.Any:
        """Call an object from sandboxed code."""
        fmt = inspect_format_method(__obj)
        if fmt is not None:
            return __self.format_string(fmt, args, kwargs, __obj)

        # 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