Description

ashm-dev

opened on Feb 19, 2026

Issue body actions

Bug description

atexit_register() in Modules/atexitmodule.c leaks memory on every call. PyTuple_GetSlice() returns a new reference, but the result is never decref'd after being packed into the callback tuple via PyTuple_Pack().

Additionally, there is no NULL check after PyTuple_GetSlice(), which could lead to undefined behavior if the allocation fails.

// Modules/atexitmodule.c, atexit_register()
PyObject *func_args = PyTuple_GetSlice(args, 1, PyTuple_GET_SIZE(args));
// BUG 1: missing NULL check
PyObject *func_kwargs = kwargs;
...
PyObject *callback = PyTuple_Pack(3, func, func_args, func_kwargs);
// BUG 2: missing Py_DECREF(func_args) — leaks the tuple

The leak is detected by AddressSanitizer/LeakSanitizer when running test_atexit on an ASAN build, causing 3 test failures: test_shutdown, test_atexit_instances, and test_general (subprocess exits with code 1 due to LSAN reporting 240 bytes leaked in 4 allocations).

Fix:

PyObject *func_args = PyTuple_GetSlice(args, 1, PyTuple_GET_SIZE(args));
if (func_args == NULL) {
    return NULL;
}
...
PyObject *callback = PyTuple_Pack(3, func, func_args, func_kwargs);
Py_DECREF(func_args);

CPython versions tested on

CPython main branch

Operating systems tested on

Linux

Linked PRs

• gh-144986: Fix memory leak in atexit.register() #144987
• [3.14] gh-144986: Fix memory leak in atexit.register() (GH-144987) #145020

Activity

1. ashm-dev

   added 3 commits that reference this issue on Feb 19, 2026

   pythongh-144986: Fix memory leak in atexit.register()

   2191c56

   Add NEWS entry for pythongh-144986

   7e3dd83

   Merge branch 'main' into pythongh-144986-fix-atexit-memleak

   1f1e8b1
2. sergey-miryanov

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   3.14bugs and security fixesbugs and security fixes

   3.15bugs and security fixesbugs and security fixes

   on Feb 19, 2026
3. StanFromIreland

   added

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

   on Feb 19, 2026
4. ashm-dev

   added 3 commits that reference this issue on Feb 19, 2026

   Add NEWS entry for pythongh-144986

   28e4533

   Merge branch 'main' into pythongh-144986-fix-atexit-memleak

   aad8a59

   Merge branch 'main' into pythongh-144986-fix-atexit-memleak

   c3152f0
5. pablogsal

   added a commit that references this issue on Feb 19, 2026

   gh-144986: Fix memory leak in atexit.register() (#144987)

   50c1471
6. miss-islington

   added a commit that references this issue on Feb 19, 2026

   pythongh-144986: Fix memory leak in atexit.register() (pythonGH-144987)

   2065be9
7. brijkapadia

   added a commit that references this issue on Feb 28, 2026

   pythongh-144986: Fix memory leak in atexit.register() (python#144987)

   8e04b79
8. kumaraditya303

   added a commit that references this issue on Mar 16, 2026

   [3.14] gh-144986: Fix memory leak in atexit.register() (GH-144987) (#…

   a1f2fef
9. kumaraditya303

   closed this as completedon Mar 16, 2026
10. ljfp

    added a commit that references this issue on Apr 25, 2026

    pythongh-144986: Fix memory leak in atexit.register() (python#144987)

    9dbbcf8

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