gh-112723: Call `PyThreadState_Clear()` from the correct interpreter (#112776)

The `PyThreadState_Clear()` function must only be called with the GIL
held and must be called from the same interpreter as the passed in
thread state. Otherwise, any Python objects on the thread state may be
destroyed using the wrong interpreter, leading to memory corruption.

This is also important for `Py_GIL_DISABLED` builds because free lists
will be associated with PyThreadStates and cleared in
`PyThreadState_Clear()`.

This fixes two places that called `PyThreadState_Clear()` from the wrong
interpreter and adds an assertion to `PyThreadState_Clear()`.

1 files changed, 26 insertions, 46 deletions

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index b5c7dc5da59..0ec29846b08 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -576,44 +576,33 @@ init_interp_settings(PyInterpreterState *interp,
         interp->feature_flags |= Py_RTFLAGS_MULTI_INTERP_EXTENSIONS;
     }
 
-    /* We check "gil" in init_interp_create_gil(). */
+    switch (config->gil) {
+    case PyInterpreterConfig_DEFAULT_GIL: break;
+    case PyInterpreterConfig_SHARED_GIL: break;
+    case PyInterpreterConfig_OWN_GIL: break;
+    default:
+        return _PyStatus_ERR("invalid interpreter config 'gil' value");
+    }
 
     return _PyStatus_OK();
 }
 
 
-static PyStatus
+static void
 init_interp_create_gil(PyThreadState *tstate, int gil)
 {
-    PyStatus status;
-
     /* finalize_interp_delete() comment explains why _PyEval_FiniGIL() is
        only called here. */
     // XXX This is broken with a per-interpreter GIL.
     _PyEval_FiniGIL(tstate->interp);
 
     /* Auto-thread-state API */
-    status = _PyGILState_SetTstate(tstate);
-    if (_PyStatus_EXCEPTION(status)) {
-        return status;
-    }
+    _PyGILState_SetTstate(tstate);
 
-    int own_gil;
-    switch (gil) {
-    case PyInterpreterConfig_DEFAULT_GIL: own_gil = 0; break;
-    case PyInterpreterConfig_SHARED_GIL: own_gil = 0; break;
-    case PyInterpreterConfig_OWN_GIL: own_gil = 1; break;
-    default:
-        return _PyStatus_ERR("invalid interpreter config 'gil' value");
-    }
+    int own_gil = (gil == PyInterpreterConfig_OWN_GIL);
 
     /* Create the GIL and take it */
-    status = _PyEval_InitGIL(tstate, own_gil);
-    if (_PyStatus_EXCEPTION(status)) {
-        return status;
-    }
-
-    return _PyStatus_OK();
+    _PyEval_InitGIL(tstate, own_gil);
 }
 
 
@@ -657,10 +646,7 @@ pycore_create_interpreter(_PyRuntimeState *runtime,
     }
     _PyThreadState_Bind(tstate);
 
-    status = init_interp_create_gil(tstate, config.gil);
-    if (_PyStatus_EXCEPTION(status)) {
-        return status;
-    }
+    init_interp_create_gil(tstate, config.gil);
 
     *tstate_p = tstate;
     return _PyStatus_OK();
@@ -2099,28 +2085,21 @@ new_interpreter(PyThreadState **tstate_p, const PyInterpreterConfig *config)
         return _PyStatus_OK();
     }
 
-    PyThreadState *tstate = _PyThreadState_New(interp,
-                                               _PyThreadState_WHENCE_INTERP);
-    if (tstate == NULL) {
-        PyInterpreterState_Delete(interp);
-        *tstate_p = NULL;
-        return _PyStatus_OK();
-    }
-    _PyThreadState_Bind(tstate);
-
+    // XXX Might new_interpreter() have been called without the GIL held?
     PyThreadState *save_tstate = _PyThreadState_GET();
-    int has_gil = 0;
+    PyThreadState *tstate = NULL;
 
     /* From this point until the init_interp_create_gil() call,
        we must not do anything that requires that the GIL be held
        (or otherwise exist).  That applies whether or not the new
        interpreter has its own GIL (e.g. the main interpreter). */
+    if (save_tstate != NULL) {
+        _PyThreadState_Detach(save_tstate);
+    }
 
     /* Copy the current interpreter config into the new interpreter */
     const PyConfig *src_config;
     if (save_tstate != NULL) {
-        // XXX Might new_interpreter() have been called without the GIL held?
-        _PyThreadState_Detach(save_tstate);
         src_config = _PyInterpreterState_GetConfig(save_tstate->interp);
     }
     else
@@ -2142,11 +2121,14 @@ new_interpreter(PyThreadState **tstate_p, const PyInterpreterConfig *config)
         goto error;
     }
 
-    status = init_interp_create_gil(tstate, config->gil);
-    if (_PyStatus_EXCEPTION(status)) {
+    tstate = _PyThreadState_New(interp, _PyThreadState_WHENCE_INTERP);
+    if (tstate == NULL) {
+        status = _PyStatus_NO_MEMORY();
         goto error;
     }
-    has_gil = 1;
+
+    _PyThreadState_Bind(tstate);
+    init_interp_create_gil(tstate, config->gil);
 
     /* No objects have been created yet. */
 
@@ -2165,16 +2147,14 @@ new_interpreter(PyThreadState **tstate_p, const PyInterpreterConfig *config)
 
 error:
     *tstate_p = NULL;
-
-    /* Oops, it didn't work.  Undo it all. */
-    if (has_gil) {
+    if (tstate != NULL) {
+        PyThreadState_Clear(tstate);
         _PyThreadState_Detach(tstate);
+        PyThreadState_Delete(tstate);
     }
     if (save_tstate != NULL) {
         _PyThreadState_Attach(save_tstate);
     }
-    PyThreadState_Clear(tstate);
-    PyThreadState_Delete(tstate);
     PyInterpreterState_Delete(interp);
 
     return status;