Description

BHUVANSH855

opened on Aug 21, 2026

Issue body actions

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-156204: Guard recursion in PyErr_GivenExceptionMatches #156205
• [3.15] gh-156204: Guard recursion in PyErr_GivenExceptionMatches (GH-156205) #158622
• [3.14] gh-156204: Guard recursion in PyErr_GivenExceptionMatches (GH-156205) #158623

Activity

1. BHUVANSH855

   added

   type-crashA hard crash of the interpreter, possibly with a core dumpA hard crash of the interpreter, possibly with a core dump

   on Aug 21, 2026
2. BHUVANSH855

   added a commit that references this issue on Aug 21, 2026

   pythongh-156204: Safely skip ctypes test on mobile/wasm and reduce tu…

   d0d8595
3. StanFromIreland

   added

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   on Aug 21, 2026
4. BHUVANSH855

   added 2 commits that reference this issue on Aug 21, 2026

   pythongh-156204: address review feedback

   b6be6c5

   pythongh-156204: drop docs change

   170d3c9
5. picnixz commented on Aug 22, 2026

   

   picnixz

   on Aug 22, 2026

   Member

   More actions

   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_GivenExceptionMatches is AFAIR used in hot paths (loops, iterators, coroutines, etc).
6. BHUVANSH855

   added 3 commits that reference this issue on Sep 24, 2026

   pythongh-156204: convert test helper to Argument Clinic

   12ce58f

   pythongh-156204: remove comment

   e7c80b9

   pythongh-156204: report recursion overflow as unraisable

   141b181
7. ZeroIntensity

   added 2 commits that reference this issue on Oct 2, 2026

   gh-156204: Guard recursion in `PyErr_GivenExceptionMatches` (GH-156205)

   20d5e67

   [3.14] gh-156204: Guard recursion in `PyErr_GivenExceptionMatches` (G…

   a9eeb9f
8. ZeroIntensity commented on Oct 2, 2026

   

   ZeroIntensity

   on Oct 2, 2026

   Member

   More actions

   The 3.15 backport will be merged later. Thanks @BHUVANSH855 for the report and the fix.

   Reacted by Bhuvansh
9. ZeroIntensity

   closed this as completedon Oct 2, 2026
10. ZeroIntensity

    added a commit that references this issue on Oct 11, 2026

    [3.15] gh-156204: Guard recursion in `PyErr_GivenExceptionMatches` (G…

    ae21cb7

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