JelleZijlstra · May 20, 2023 · Apr 29, 2023 · Apr 29, 2023 · Apr 29, 2023 · Apr 29, 2023
diff --git a/Lib/test/test_mmap.py b/Lib/test/test_mmap.py
@@ -264,6 +264,57 @@ def test_bad_file_desc(self):
         # Try opening a bad file descriptor...
         self.assertRaises(OSError, mmap.mmap, -2, 4096)
 
+    def test_unexpected_mmap_close_scenario_1(self):
+        # See gh-103987
+        with open(TESTFN, "wb+") as f:
+            data = b'aabaac\x00deef\x00\x00aa\x00'
+            n = len(data)
+            f.write(data)
+            f.flush()
+
+            class X:
+                def __index__(self):
+                    m.close()
+                    return 1
+
+            m = mmap.mmap(f.fileno(), n, access=mmap.ACCESS_READ)
+
+        self.assertEqual(m[1], 97)
+        with self.assertRaises(ValueError):
+            m[X()] # should not crash
+
+        with self.assertRaises(ValueError):
+            m[X():5] # should not crash
+
+        with self.assertRaises(ValueError):
+            m[X()] = 1
+            m[X()] # should through ValueError
+
+        with self.assertRaises(ValueError):
+            m[X():5] = b'abcde'
+            m[X():5] # should through ValueError
+
+        m.close() # first CHECK_VALID will pick and raise ValueError
+        with self.assertRaises(ValueError):
+            m[0:5] # should not crash
+
+
+    def test_unexpected_mmap_close_scenario_2(self):
+
+        with open(TESTFN, "wb+") as f:
+            data = b'aabaac\x00deef\x00\x00aa\x00'
+            n = len(data)
+            f.write(data)
+            f.flush()
+
+            m = mmap.mmap(f.fileno(), n, access=mmap.ACCESS_READ)
+
+        m.close()
+        with self.assertRaises(ValueError):
+            m["abc"] # first CHECK_VALID will pick and raise ValueError
+
+
+
     def test_tougher_find(self):
         # Do a tougher .find() test.  SF bug 515943 pointed out that, in 2.2,
         # searching for data with embedded \0 bytes didn't work.

diff --git a/Misc/NEWS.d/next/Library/2023-04-29-18-23-16.gh-issue-103987.sRgALL.rst b/Misc/NEWS.d/next/Library/2023-04-29-18-23-16.gh-issue-103987.sRgALL.rst
@@ -0,0 +1 @@
+Fix ``mmap_subscript`` in mmapmodule.c to avoid segmentation fault
diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
@@ -945,6 +945,7 @@ mmap_subscript(mmap_object *self, PyObject *item)
                 "mmap index out of range");
             return NULL;
         }
+        CHECK_VALID(NULL);
         return PyLong_FromLong(Py_CHARMASK(self->data[i]));
     }
     else if (PySlice_Check(item)) {
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fix ``mmap_subscript`` in mmapmodule.c to avoid segmentation fault
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