PyErr_GivenExceptionMatches crashes with SIGSEGV on deeply nested tuple targets

Crash report

What happened?

Problem Description

PyErr_GivenExceptionMatches(err, exc) in Python/errors.c recursively iterates through nested tuple exception targets without guarding recursion depth via Py_EnterRecursiveCall() / Py_LeaveRecursiveCall().

When evaluating deeply nested tuple structures passed through C API extensions or dynamic tuple composition, unbounded native C call stack growth leads to stack exhaustion and an immediate SIGSEGV crash.

Steps to Reproduce

import ctypes

lib = ctypes.pythonapi
lib.PyErr_GivenExceptionMatches.argtypes = [ctypes.py_object, ctypes.py_object]
lib.PyErr_GivenExceptionMatches.restype = ctypes.c_int

# Construct deeply nested tuple target
tup = (1, ValueError)
for _ in range(1_000_000):
    tup = (1, tup)

# Trigger exception matching traversal
res = lib.PyErr_GivenExceptionMatches(TypeError(), tup)

Actual Result

Segmentation fault (core dumped)

Program received signal SIGSEGV, Segmentation fault.
PyTuple_Size (op=op@entry=0x7ffff2beda30) at Objects/tupleobject.c:100
100             return Py_SIZE(op);
#0  PyTuple_Size (op=op@entry=0x7ffff2beda30) at Objects/tupleobject.c:100
#1  0x0000555555824f63 in PyErr_GivenExceptionMatches (err=err@entry=0x7ffff78ea900, exc=0x7ffff2beda30) at Python/errors.c:339
#2  0x0000555555824fb0 in PyErr_GivenExceptionMatches (err=err@entry=0x7ffff78ea900, exc=0x7ffff2beda90) at Python/errors.c:342
#3  0x0000555555824fb0 in PyErr_GivenExceptionMatches (err=err@entry=0x7ffff78ea900, exc=0x7ffff2bedaf0) at Python/errors.c:342
#4  0x0000555555824fb0 in PyErr_GivenExceptionMatches (err=err@entry=0x7ffff78ea900, exc=0x7ffff2bedb50) at Python/errors.c:342
...
rsp             0x7fffff7ff000      0x7fffff7ff000

Expected Result

PyErr_GivenExceptionMatches should guard recursion with Py_EnterRecursiveCall() / Py_LeaveRecursiveCall(), setting a RecursionError and returning 0 safely when recursion depth is exceeded instead of crashing the interpreter.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.16.0a0 (heads/fix-err-given-exception-matches-recursion:999a046b24c, Aug 21 2026, 18:34:) [GCC 13.3.0]

Linked PRs

• gh-156205

Commencez dans Python/errors.c, au niveau de PyErr_GivenExceptionMatches, et reproduisez le cas de tuple profondément imbriqué de l’issue. Vérifiez les conventions existantes de protection contre la récursion, puis vérifiez qu’un imbrication excessive lève RecursionError et retourne sans danger au lieu de provoquer un crash ; la PR liée gh-156205 indique que le travail est déjà en cours.