gh-144100: Fix crash for POINTER(str) used in ctypes argtypes by VanshAgarwal24036 · Pull Request #144108 · python/cpython

VanshAgarwal24036 · 2026-01-21T14:15:57Z

It fixes a crash in ctypes that occur when a deprecated POINTER(str) type was used in argtypes.

When such a pointer type was encountered during argument conversion, ctypes would hit an internal assertion and abort the interpreter in debug builds.
This PR replaces the assertion with proper error handling and raises a Python exception instead.

Issue: Assertion failed: typeinfo->proto in PyCPointerType_from_param_impl when using deprecated POINTER(str) in argtypes #144100

VanshAgarwal24036 · 2026-01-23T15:35:40Z

@vstinner This is my proposed solution if you have time please review it.

vstinner · 2026-01-23T17:00:55Z

Lib/test/test_ctypes/test_pointers.py

+        with self.assertWarns(DeprecationWarning):
+            BadType = ctypes.POINTER("BugTrigger")


I would prefer to avoid deprecated code path. You should be able to use:

Suggested change

with self.assertWarns(DeprecationWarning):

BadType = ctypes.POINTER("BugTrigger")

class BadType(ctypes._Pointer):

# _type_ is not defined on purpose

pass

vstinner · 2026-01-23T17:02:21Z

Lib/test/test_ctypes/test_pointers.py

+        if os.name == "nt":
+            libc = ctypes.WinDLL("kernel32.dll")
+            func = libc.GetCurrentProcessId
+        else:
+            libc = ctypes.CDLL(None)
+            func = libc.getpid
+
+        func.argtypes = (BadType,)


You can use the Python C API:

Suggested change

if os.name == "nt":

libc = ctypes.WinDLL("kernel32.dll")

func = libc.GetCurrentProcessId

else:

libc = ctypes.CDLL(None)

func = libc.getpid

func.argtypes = (BadType,)

func = ctypes.pythonapi.Py_GetVersion

func.argtypes = (BadType,)

vstinner · 2026-01-23T17:03:12Z

Lib/test/test_ctypes/test_pointers.py

        ptr.set_type(c_int)
        self.assertIs(ptr._type_, c_int)

+class TestPointerStringProto(unittest.TestCase):


I would prefer to add the test to the end of PointersTestCase, instead of adding a new test case.

Modules/_ctypes/_ctypes.c

vstinner · 2026-01-23T17:05:47Z

Lib/test/test_ctypes/test_pointers.py

 import gc
 import sys
 import unittest
+import os


This import can be removed with my proposed code.

Co-authored-by: Victor Stinner <vstinner@python.org>

vstinner

LGTM

miss-islington-app · 2026-01-26T12:27:46Z

Thanks @VanshAgarwal24036 for the PR, and @vstinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

…ythonGH-144108) (cherry picked from commit 8f45925) Co-authored-by: VanshAgarwal24036 <148854295+VanshAgarwal24036@users.noreply.github.com> Co-authored-by: Victor Stinner <vstinner@python.org>

miss-islington-app · 2026-01-26T12:27:54Z

Sorry, @VanshAgarwal24036 and @vstinner, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 8f459255eba2b6639f1912e5c5e318a7cdafada1 3.13

bedevere-app · 2026-01-26T12:27:59Z

GH-144244 is a backport of this pull request to the 3.14 branch.

bedevere-app · 2026-01-26T12:30:40Z

GH-144245 is a backport of this pull request to the 3.13 branch.

vstinner · 2026-01-26T12:32:07Z

Merged. Thanks for the fix.

VanshAgarwal24036 · 2026-01-26T12:36:24Z

Thanks for guidance and review

…H-144108) (#144244) gh-144100: Fix crash for POINTER(str) used in ctypes argtypes (GH-144108) (cherry picked from commit 8f45925) Co-authored-by: VanshAgarwal24036 <148854295+VanshAgarwal24036@users.noreply.github.com> Co-authored-by: Victor Stinner <vstinner@python.org>

…144108) (#144245) gh-144100: Fix crash for POINTER(str) used in ctypes argtypes (#144108) (cherry picked from commit 8f45925) Co-authored-by: VanshAgarwal24036 <148854295+VanshAgarwal24036@users.noreply.github.com>

…ython#144108) Co-authored-by: Victor Stinner <vstinner@python.org>

pythongh-144100: Fix crash for POINTER(str) used in ctypes argtypes

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bedevere-app bot mentioned this pull request Jan 21, 2026

Assertion failed: typeinfo->proto in PyCPointerType_from_param_impl when using deprecated POINTER(str) in argtypes #144100

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bedevere-app bot added the awaiting review label Jan 21, 2026

Test corrected

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vstinner reviewed Jan 23, 2026

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VanshAgarwal24036 and others added 5 commits January 23, 2026 23:14

Update Modules/_ctypes/_ctypes.c

1685958

Co-authored-by: Victor Stinner <vstinner@python.org>

Update Modules/_ctypes/_ctypes.c

5587067

Co-authored-by: Victor Stinner <vstinner@python.org>

Update test file

e948a1a

Update test file

8a05d9e

Fx error fail

138e52d

VanshAgarwal24036 requested a review from vstinner January 24, 2026 02:08

vstinner approved these changes Jan 26, 2026

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bedevere-app bot added awaiting merge and removed awaiting review labels Jan 26, 2026

vstinner added needs backport to 3.13 bugs and security fixes needs backport to 3.14 bugs and security fixes labels Jan 26, 2026

vstinner merged commit 8f45925 into python:main Jan 26, 2026
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miss-islington-app bot assigned vstinner Jan 26, 2026

bedevere-app bot removed the needs backport to 3.14 bugs and security fixes label Jan 26, 2026

bedevere-app bot removed the needs backport to 3.13 bugs and security fixes label Jan 26, 2026

VanshAgarwal24036 deleted the gh-144100-ctypes-pointer-protol branch January 26, 2026 12:36

thunder-coding pushed a commit to thunder-coding/cpython that referenced this pull request Feb 15, 2026

pythongh-144100: Fix crash for POINTER(str) used in ctypes argtypes (p…

20baa49

…ython#144108) Co-authored-by: Victor Stinner <vstinner@python.org>

		with self.assertWarns(DeprecationWarning):
		BadType = ctypes.POINTER("BugTrigger")

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