bpo-34651: Only allow the main interpreter to fork. (gh-9279)

When os.fork() is called (on platforms that support it) all threads but the current one are destroyed in the child process. Consequently we must ensure that all but the associated interpreter are likewise destroyed. The main interpreter is critical for runtime operation, so we must ensure that fork only happens in the main interpreter.

https://bugs.python.org/issue34651

1 files changed, 14 insertions, 0 deletions

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 2fddd95..0ac0042 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -32,6 +32,7 @@
 #else
 #include "winreparse.h"
 #endif
+#include "internal/pystate.h"
 
 /* On android API level 21, 'AT_EACCESS' is not declared although
  * HAVE_FACCESSAT is defined. */
@@ -420,6 +421,7 @@ void
 PyOS_AfterFork_Child(void)
 {
     _PyGILState_Reinit();
+    _PyInterpreterState_DeleteExceptMain();
     PyEval_ReInitThreads();
     _PyImport_ReInitLock();
     _PySignal_AfterFork();
@@ -5790,6 +5792,10 @@ os_fork1_impl(PyObject *module)
 {
     pid_t pid;
 
+    if (_PyInterpreterState_Get() != PyInterpreterState_Main()) {
+        PyErr_SetString(PyExc_RuntimeError, "fork not supported for subinterpreters");
+        return NULL;
+    }
     PyOS_BeforeFork();
     pid = fork1();
     if (pid == 0) {
@@ -5821,6 +5827,10 @@ os_fork_impl(PyObject *module)
 {
     pid_t pid;
 
+    if (_PyInterpreterState_Get() != PyInterpreterState_Main()) {
+        PyErr_SetString(PyExc_RuntimeError, "fork not supported for subinterpreters");
+        return NULL;
+    }
     PyOS_BeforeFork();
     pid = fork();
     if (pid == 0) {
@@ -6416,6 +6426,10 @@ os_forkpty_impl(PyObject *module)
     int master_fd = -1;
     pid_t pid;
 
+    if (_PyInterpreterState_Get() != PyInterpreterState_Main()) {
+        PyErr_SetString(PyExc_RuntimeError, "fork not supported for subinterpreters");
+        return NULL;
+    }
     PyOS_BeforeFork();
     pid = forkpty(&master_fd, NULL, NULL, NULL);
     if (pid == 0) {