commit f02d1a43c6be658cd279edb90e8e96c99e1127e7
author Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> Fri May 17 00:33:10 2019 -0700
committer GitHub <noreply@github.com> Fri May 17 00:33:10 2019 -0700
tree c27f46c3ad004c5a96eeb1b498076dabd7788350
parent aa73841a8fdded4a462d045d1eb03899cbeecd65

bpo-36946: Fix possible signed integer overflow when handling slices. (GH-13375)


The final addition (cur += step) may overflow, so use size_t for "cur".
"cur" is always positive (even for negative steps), so it is safe to use
size_t here.

Co-Authored-By: Martin Panter <vadmium+py@gmail.com>
(cherry picked from commit 14514d9084a40f599c57da853a305aa264562a43)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>

Modules/mmapmodule.c

diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
index f957e2c..223afac 100644
--- a/Modules/mmapmodule.c
+++ b/Modules/mmapmodule.c
@@ -790,7 +790,8 @@
                                               slicelen);
         else {
             char *result_buf = (char *)PyMem_Malloc(slicelen);
-            Py_ssize_t cur, i;
+            size_t cur;
+            Py_ssize_t i;
             PyObject *result;
 
             if (result_buf == NULL)
@@ -910,7 +911,8 @@
             memcpy(self->data + start, vbuf.buf, slicelen);
         }
         else {
-            Py_ssize_t cur, i;
+            size_t cur;
+            Py_ssize_t i;
 
             for (cur = start, i = 0;
                  i < slicelen;