From 265f962f91ebf4ea018fb259f690341059c5c2a7 Mon Sep 17 00:00:00 2001
From: Ammar Askar <ammar@ammaraskar.com>
Date: Thu, 4 Jun 2020 11:59:55 -0700
Subject: [PATCH] Restrict co_code to be under INT_MAX in codeobject

---
 Objects/codeobject.c  | 8 ++++++++
 Objects/frameobject.c | 6 +++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index 737635943aced5..cb4fb681243336 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -166,6 +166,14 @@ PyCode_NewWithPosOnlyArgs(int argcount, int posonlyargcount, int kwonlyargcount,
         return NULL;
     }
 
+    /* Make sure that code is indexable with an int, this is
+       a long running assumption in ceval.c and many parts of
+       the interpreter. */
+    if (PyBytes_GET_SIZE(code) > INT_MAX) {
+        PyErr_SetString(PyExc_OverflowError, "co_code larger than INT_MAX");
+        return NULL;
+    }
+
     /* Check for any inner or outer closure references */
     n_cellvars = PyTuple_GET_SIZE(cellvars);
     if (!n_cellvars && !PyTuple_GET_SIZE(freevars)) {
diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index b6d073bd456d03..5043d0ef424146 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -397,9 +397,9 @@ frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno, void *Py_UNUSED(ignore
         return -1;
     }
 
-    int len = Py_SAFE_DOWNCAST(
-        PyBytes_GET_SIZE(f->f_code->co_code)/sizeof(_Py_CODEUNIT),
-        Py_ssize_t, int);
+    /* PyCode_NewWithPosOnlyArgs limits co_code to be under INT_MAX so this
+     * should never overflow. */
+    int len = (int)(PyBytes_GET_SIZE(f->f_code->co_code) / sizeof(_Py_CODEUNIT));
     int *lines = marklines(f->f_code, len);
     if (lines == NULL) {
         return -1;