bpo-34410: Fix a crash in the tee iterator when re-enter it. (GH-15625)

RuntimeError is now raised in this case.
(cherry picked from commit 526a01467b3277f9fcf7f91e66c23321caa1245d)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index 22c04f2..eba59ba 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -443,6 +443,7 @@ typedef struct {
     PyObject_HEAD
     PyObject *it;
     int numread;                /* 0 <= numread <= LINKCELLS */
+    int running;
     PyObject *nextlink;
     PyObject *(values[LINKCELLS]);
 } teedataobject;
@@ -465,6 +466,7 @@ teedataobject_newinternal(PyObject *it)
     if (tdo == NULL)
         return NULL;
 
+    tdo->running = 0;
     tdo->numread = 0;
     tdo->nextlink = NULL;
     Py_INCREF(it);
@@ -493,7 +495,14 @@ teedataobject_getitem(teedataobject *tdo, int i)
     else {
         /* this is the lead iterator, so fetch more data */
         assert(i == tdo->numread);
+        if (tdo->running) {
+            PyErr_SetString(PyExc_RuntimeError,
+                            "cannot re-enter the tee iterator");
+            return NULL;
+        }
+        tdo->running = 1;
         value = PyIter_Next(tdo->it);
+        tdo->running = 0;
         if (value == NULL)
             return NULL;
         tdo->numread++;