gh-104690 Disallow thread creation and fork at interpreter finalization (#104826)

Disallow thread creation and fork at interpreter finalization.

in the following functions, check if interpreter is finalizing and raise `RuntimeError` with appropriate message:
* `_thread.start_new_thread` and thus `threading`
* `posix.fork`
* `posix.fork1`
* `posix.forkpty`
* `_posixsubprocess.fork_exec` when a `preexec_fn=` is supplied.

---------

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index 3647080..2d88f5e 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -5,6 +5,7 @@
 
 #include "Python.h"
 #include "pycore_fileutils.h"
+#include "pycore_pystate.h"
 #if defined(HAVE_PIPE2) && !defined(_GNU_SOURCE)
 # define _GNU_SOURCE
 #endif
@@ -943,6 +944,11 @@ subprocess_fork_exec_impl(PyObject *module, PyObject *process_args,
     Py_ssize_t fds_to_keep_len = PyTuple_GET_SIZE(py_fds_to_keep);
 
     PyInterpreterState *interp = PyInterpreterState_Get();
+    if ((preexec_fn != Py_None) && interp->finalizing) {
+        PyErr_SetString(PyExc_RuntimeError,
+                        "preexec_fn not supported at interpreter shutdown");
+        return NULL;
+    }
     if ((preexec_fn != Py_None) && (interp != PyInterpreterState_Main())) {
         PyErr_SetString(PyExc_RuntimeError,
                         "preexec_fn not supported within subinterpreters");