Repository navigation
PyErr_GivenExceptionMatches crashes with SIGSEGV on deeply nested tuple targets #156204
Description
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]
Activity
pythongh-156204: Safely skip ctypes test on mobile/wasm and reduce tu…
pythongh-156204: address review feedback
pythongh-156204: drop docs change
picnixz commentedon Aug 22, 2026
I think it's not a real use-case here but since we document that recursion is supported, let's fix this. Is there a noticable effect on performances for regular code or not at all? Because
PyErr_GivenExceptionMatchesis AFAIR used in hot paths (loops, iterators, coroutines, etc).pythongh-156204: convert test helper to Argument Clinic
pythongh-156204: remove comment
pythongh-156204: report recursion overflow as unraisable
gh-156204: Guard recursion in `PyErr_GivenExceptionMatches` (GH-156205)
[3.14] gh-156204: Guard recursion in `PyErr_GivenExceptionMatches` (G…
ZeroIntensity commentedon Oct 2, 2026
The 3.15 backport will be merged later. Thanks @BHUVANSH855 for the report and the fix.
[3.15] gh-156204: Guard recursion in `PyErr_GivenExceptionMatches` (G…