pythoncapi
diff --git a/‎Lib/test/test_mmap.py‎
Lines changed: 14 additions & 0 deletions b/‎Lib/test/test_mmap.py‎
Lines changed: 14 additions & 0 deletions
diff --git a/‎Misc/NEWS‎
Lines changed: 3 additions & 0 deletions b/‎Misc/NEWS‎
Lines changed: 3 additions & 0 deletions
@@ -720,6 +720,20 @@ def test_write_returning_the_number_of_bytes_written(self):
         self.assertEqual(mm.write(b"yz"), 2)
         self.assertEqual(mm.write(b"python"), 6)
 
+    @unittest.skipIf(os.name == 'nt', 'cannot resize anonymous mmaps on Windows')
+    def test_resize_past_pos(self):
+        m = mmap.mmap(-1, 8192)
+        self.addCleanup(m.close)
+        m.read(5000)
+        try:
+            m.resize(4096)
+        except SystemError:
+            self.skipTest("resizing not supported")
+        self.assertEqual(m.read(14), b'')
+        self.assertRaises(ValueError, m.read_byte)
+        self.assertRaises(ValueError, m.write_byte, 42)
+        self.assertRaises(ValueError, m.write, b'abc')
+
 
 class LargeMmapTests(unittest.TestCase):
 
 
@@ -404,6 +404,9 @@ Library
   pickling and text representation purposes. Patch by Emanuel Barry and
   Serhiy Storchaka.
 
+- Fix possible integer overflows and crashes in the mmap module with unusual
+  usage patterns.
+
 - Issue #1703178: Fix the ability to pass the --link-objects option to the
   distutils build_ext command.