Description

serhiy-storchaka

opened on Aug 20, 2026

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Crash report

del ptr.contents crashes the free-threaded build.

>>> from ctypes import POINTER, c_int
>>> ptr = POINTER(c_int)(c_int(42))
>>> del ptr.contents
Segmentation fault

Pointer_set_contents() passes the new value to Py_BEGIN_CRITICAL_SECTION2(), which dereferences it to get the mutex, but the value is NULL when the attribute is deleted. The check for NULL is in Pointer_set_contents_lock_held(), which is only called after the critical section is entered.

With the GIL it raises TypeError: Pointer does not support item deletion.

The critical section was added in gh-128182, so this affects 3.14 and newer.

Linked PRs

• gh-156124: Fix a crash when deleting ctypes Pointer.contents #156125
• [3.15] gh-156124: Fix a crash when deleting ctypes Pointer.contents (GH-156125) #156153
• [3.14] gh-156124: Fix a crash when deleting ctypes Pointer.contents (GH-156125) #156154

Activity

1. serhiy-storchaka

   added

   3.14bugs and security fixesbugs and security fixes

   3.15bugs and security fixesbugs and security fixes

   3.16new features, bugs and security fixesnew features, bugs and security fixes

   extension-modulesC modules in the Modules dirC modules in the Modules dir

   topic-free-threading

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

   on Aug 20, 2026
2. serhiy-storchaka

   added a parent issue on Aug 20, 2026

   • Add tests for setting and deleting attributes defined in C #156106
3. serhiy-storchaka

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

   gh-156124: Fix a crash when deleting ctypes Pointer.contents (GH-156125)

   ca6e733
4. serhiy-storchaka

   closed this as completedon Aug 21, 2026
5. serhiy-storchaka

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

   [3.14] gh-156124: Fix a crash when deleting ctypes Pointer.contents (G…

   a434d87
6. serhiy-storchaka

   added a commit that references this issue on Oct 10, 2026

   [3.15] gh-156124: Fix a crash when deleting ctypes Pointer.contents (G…

   7681a44

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