When specializing LOAD_ATTR_SLOT, we don't check whether the given member descriptor is valid for the type we got it from.

Here is a problematic example, where one class "borrows" a slot from another:

>>> class Class:
...     __slots__ = ("slot",)
... 
>>> class Sneaky:
...     borrowed = Class.slot
... 
>>> def f(o):
...     return o.borrowed
... 
>>> o = Sneaky()

The unspecialized code behaves correctly:

>>> f(o)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in f
TypeError: descriptor 'slot' for 'Class' objects doesn't apply to a 'Sneaky' object

However, the specialized code crashes, since it is accessing memory past the end of the object:

>>> f(o)
Segmentation fault

We can fix this by performing the same check that the member descriptor performs (PyObject_TypeCheck(obj, descr->d_type)) when specializing.

CC @markshannon

• PR: GH-99257: Check the owner's type when specializing slots #99258

• PR: [3.11] GH-99257: Check the owner's type when specializing slots (GH-99258) #99324