Bug report

Bug description:

AsObj() and TupleAsObj() in Modules/_tkinter.c convert nested lists and tuples to Tcl lists by plain C recursion with no depth limit, so a recursive or very deeply nested list passed to tk.call(), setvar(), Variable.set() or a widget option overflows the C stack and segfaults.

import tkinter
v = ['a']
v.append(v)
tkinter.Tcl().setvar('x', v)  # Segmentation fault

The same happens with a list nested about 50,000 levels deep (for example one returned by json.loads()), and in the other direction when getvar() reads a Tcl list nested a few hundred thousand levels deep (FromObj()). I'd expect an exception, as _flatten() in the same file already gives with ValueError: nesting too deep in _flatten.

The recursion is old; gh-143310 fixed a different crash in the same code and was backported.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-160176: Fix crash in tkinter on deeply nested or recursive lists #160177