gh-128421: add critical section around traceback.tb_next (#131322)

Author: kumaraditya303

Python/clinic/traceback.c.h

@@ -99,10 +99,16 @@ tb_dir(PyObject *Py_UNUSED(self), PyObject *Py_UNUSED(ignored))
 "tb_lasti", "tb_lineno");
 }
 
+/*[clinic input]
+@critical_section
+@getter
+traceback.tb_next
+[clinic start generated code]*/
+
 staticPyObject*
-tb_next_get(PyObject*op, void*Py_UNUSED(_))
+traceback_tb_next_get_impl(PyTracebackObject*self)
+/*[clinic end generated code: output=963634df7d5fc837 input=8f6345f2b73cb965]*/
 {
-PyTracebackObject*self=_PyTracebackObject_CAST(op);
 PyObject*ret= (PyObject*)self->tb_next;
 if (!ret){
 ret=Py_None;
@@ -133,37 +139,48 @@ tb_lineno_get(PyObject *op, void *Py_UNUSED(_))
 returnPyLong_FromLong(lineno);
 }
 
+/*[clinic input]
+@critical_section
+@setter
+traceback.tb_next
+[clinic start generated code]*/
+
 staticint
-tb_next_set(PyObject*op, PyObject*new_next, void*Py_UNUSED(_))
+traceback_tb_next_set_impl(PyTracebackObject*self, PyObject*value)
+/*[clinic end generated code: output=d4868cbc48f2adac input=ce66367f85e3c443]*/
 {
-if (!new_next){
+if (!value){
 PyErr_Format(PyExc_TypeError, "can't delete tb_next attribute");
 return-1;
  }
 
 /* We accept None or a traceback object, and map None -> NULL (inverse of
  tb_next_get) */
-if (new_next==Py_None){
-new_next=NULL;
- } elseif (!PyTraceBack_Check(new_next)){
+if (value==Py_None){
+value=NULL;
+ } elseif (!PyTraceBack_Check(value)){
 PyErr_Format(PyExc_TypeError,
 "expected traceback object, got '%s'",
-Py_TYPE(new_next)->tp_name);
+Py_TYPE(value)->tp_name);
 return-1;
  }
 
 /* Check for loops */
-PyTracebackObject*self=_PyTracebackObject_CAST(op);
-PyTracebackObject*cursor= (PyTracebackObject*)new_next;
+PyTracebackObject*cursor=(PyTracebackObject*)value;
+Py_XINCREF(cursor);
 while (cursor){
 if (cursor==self){
 PyErr_Format(PyExc_ValueError, "traceback loop detected");
+Py_DECREF(cursor);
 return-1;
  }
-cursor=cursor->tb_next;
+Py_BEGIN_CRITICAL_SECTION(cursor);
+Py_XINCREF(cursor->tb_next);
+Py_SETREF(cursor, cursor->tb_next);
+Py_END_CRITICAL_SECTION();
  }
 
-Py_XSETREF(self->tb_next, (PyTracebackObject*)Py_XNewRef(new_next));
+Py_XSETREF(self->tb_next, (PyTracebackObject*)Py_XNewRef(value));
 
 return0;
 }
@@ -181,7 +198,7 @@ static PyMemberDef tb_memberlist[] ={
 };
 
 staticPyGetSetDeftb_getsetters[] ={
-{"tb_next", tb_next_get, tb_next_set, NULL, NULL},
+TRACEBACK_TB_NEXT_GETSETDEF
 {"tb_lineno", tb_lineno_get, NULL, NULL, NULL},
 {NULL} /* Sentinel */
 };