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 <[email protected]>
(cherry picked from commit 14514d9)

Co-authored-by: Zackery Spytz <[email protected]>

Author: miss-islington

Lib/ctypes/test/test_arrays.py

@@ -69,6 +69,17 @@ def test_simple(self):
         from operator import delitem
         self.assertRaises(TypeError, delitem, ca, 0)
 
+    def test_step_overflow(self):
+        a = (c_int * 5)()
+        a[3::sys.maxsize] = (1,)
+        self.assertListEqual(a[3::sys.maxsize], [1])
+        a = (c_char * 5)()
+        a[3::sys.maxsize] = b"A"
+        self.assertEqual(a[3::sys.maxsize], b"A")
+        a = (c_wchar * 5)()
+        a[3::sys.maxsize] = u"X"
+        self.assertEqual(a[3::sys.maxsize], u"X")
+
     def test_numeric_arrays(self):
 
         alen = 5

Lib/test/seq_tests.py

@@ -209,6 +209,7 @@ def test_getslice(self):
         a = self.type2test([0,1,2,3,4])
         self.assertEqual(a[ -pow(2,128): 3 ], self.type2test([0,1,2]))
         self.assertEqual(a[ 3: pow(2,145) ], self.type2test([3,4]))
+        self.assertEqual(a[3::sys.maxsize], self.type2test([3]))
 
     def test_contains(self):
         u = self.type2test([0, 1, 2])

Lib/test/string_tests.py

@@ -1135,7 +1135,7 @@ def test_slice(self):
     def test_extended_getslice(self):
         # Test extended slicing by comparing with list slicing.
         s = string.ascii_letters + string.digits
-        indices = (0, None, 1, 3, 41, -1, -2, -37)
+        indices = (0, None, 1, 3, 41, sys.maxsize, -1, -2, -37)
         for start in indices:
             for stop in indices:
                 # Skip step 0 (invalid)

Lib/test/test_array.py

@@ -745,7 +745,7 @@ def test_extended_getslice(self):
         # Test extended slicing by comparing with list slicing
         # (Assumes list conversion works correctly, too)
         a = array.array(self.typecode, self.example)
-        indices = (0, None, 1, 3, 19, 100, -1, -2, -31, -100)
+        indices = (0, None, 1, 3, 19, 100, sys.maxsize, -1, -2, -31, -100)
         for start in indices:
             for stop in indices:
                 # Everything except the initial 0 (invalid step)
@@ -843,7 +843,7 @@ def test_setslice(self):
         self.assertRaises(TypeError, a.__setitem__, slice(0, 1), b)
 
     def test_extended_set_del_slice(self):
-        indices = (0, None, 1, 3, 19, 100, -1, -2, -31, -100)
+        indices = (0, None, 1, 3, 19, 100, sys.maxsize, -1, -2, -31, -100)
         for start in indices:
             for stop in indices:
                 # Everything except the initial 0 (invalid step)

Lib/test/test_bytes.py

@@ -283,7 +283,7 @@ def test_extended_getslice(self):
         # Test extended slicing by comparing with list slicing.
         L = list(range(255))
         b = self.type2test(L)
-        indices = (0, None, 1, 3, 19, 100, -1, -2, -31, -100)
+        indices = (0, None, 1, 3, 19, 100, sys.maxsize, -1, -2, -31, -100)
         for start in indices:
             for stop in indices:
                 # Skip step 0 (invalid)
@@ -1238,7 +1238,8 @@ def test_del_expand(self):
         self.assertLessEqual(sys.getsizeof(b), size)
 
     def test_extended_set_del_slice(self):
-        indices = (0, None, 1, 3, 19, 300, 1<<333, -1, -2, -31, -300)
+        indices = (0, None, 1, 3, 19, 300, 1<<333, sys.maxsize,
+            -1, -2, -31, -300)
         for start in indices:
             for stop in indices:
                 # Skip invalid step 0

Lib/test/test_mmap.py

@@ -452,7 +452,7 @@ def test_extended_getslice(self):
         m = mmap.mmap(-1, len(s))
         m[:] = s
         self.assertEqual(m[:], s)
-        indices = (0, None, 1, 3, 19, 300, -1, -2, -31, -300)
+        indices = (0, None, 1, 3, 19, 300, sys.maxsize, -1, -2, -31, -300)
         for start in indices:
             for stop in indices:
                 # Skip step 0 (invalid)
@@ -464,7 +464,7 @@ def test_extended_set_del_slice(self):
         # Test extended slicing by comparing with list slicing.
         s = bytes(reversed(range(256)))
         m = mmap.mmap(-1, len(s))
-        indices = (0, None, 1, 3, 19, 300, -1, -2, -31, -300)
+        indices = (0, None, 1, 3, 19, 300, sys.maxsize, -1, -2, -31, -300)
         for start in indices:
             for stop in indices:
                 # Skip invalid step 0

Misc/NEWS.d/next/Core and Builtins/2019-05-16-23-53-45.bpo-36946.qjxr0Y.rst

@@ -0,0 +1 @@
+Fix possible signed integer overflow when handling slices.

Modules/_ctypes/_ctypes.c

@@ -4372,7 +4372,8 @@ Array_subscript(PyObject *myself, PyObject *item)
         StgDictObject *stgdict, *itemdict;
         PyObject *proto;
         PyObject *np;
-        Py_ssize_t start, stop, step, slicelen, cur, i;
+        Py_ssize_t start, stop, step, slicelen, i;
+        size_t cur;
 
         if (PySlice_Unpack(item, &start, &stop, &step) < 0) {
             return NULL;
@@ -4512,7 +4513,8 @@ Array_ass_subscript(PyObject *myself, PyObject *item, PyObject *value)
         return Array_ass_item(myself, i, value);
     }
     else if (PySlice_Check(item)) {
-        Py_ssize_t start, stop, step, slicelen, otherlen, i, cur;
+        Py_ssize_t start, stop, step, slicelen, otherlen, i;
+        size_t cur;
 
         if (PySlice_Unpack(item, &start, &stop, &step) < 0) {
             return -1;

Modules/_elementtree.c

@@ -1771,7 +1771,8 @@ element_subscr(PyObject* self_, PyObject* item)
         return element_getitem(self_, i);
     }
     else if (PySlice_Check(item)) {
-        Py_ssize_t start, stop, step, slicelen, cur, i;
+        Py_ssize_t start, stop, step, slicelen, i;
+        size_t cur;
         PyObject* list;
 
         if (!self->extra)
@@ -1823,7 +1824,8 @@ element_ass_subscr(PyObject* self_, PyObject* item, PyObject* value)
         return element_setitem(self_, i, value);
     }
     else if (PySlice_Check(item)) {
-        Py_ssize_t start, stop, step, slicelen, newlen, cur, i;
+        Py_ssize_t start, stop, step, slicelen, newlen, i;
+        size_t cur;
 
         PyObject* recycle = NULL;
         PyObject* seq;

Modules/arraymodule.c

@@ -2343,7 +2343,8 @@ array_subscr(arrayobject* self, PyObject* item)
         return array_item(self, i);
     }
     else if (PySlice_Check(item)) {
-        Py_ssize_t start, stop, step, slicelength, cur, i;
+        Py_ssize_t start, stop, step, slicelength, i;
+        size_t cur;
         PyObject* result;
         arrayobject* ar;
         int itemsize = self->ob_descr->itemsize;
@@ -2527,7 +2528,8 @@ array_ass_subscr(arrayobject* self, PyObject* item, PyObject* value)
         return 0;
     }
     else {
-        Py_ssize_t cur, i;
+        size_t cur;
+        Py_ssize_t i;
 
         if (needed != slicelength) {
             PyErr_Format(PyExc_ValueError,