Issue #1621: Fix undefined behaviour from signed overflow in datetime module…

Issue #1621: Fix undefined behaviour from signed overflow in datetime module hashes, array and list iterations, and get_integer (stringlib/string_format.h)

Modules/_datetimemodule.c

@@ -2746,13 +2746,13 @@ static Py_hash_t
 generic_hash(unsigned char *data, int len)
 {
     register unsigned char *p;
-    register Py_hash_t x;
+    register Py_uhash_t x;
 
     p = (unsigned char *) data;
-    x = *p << 7;
+    x = (Py_uhash_t)*p << 7;
     while (--len >= 0)
-        x = (1000003*x) ^ *p++;
-    x ^= len;
+        x = (1000003U*x) ^ (Py_uhash_t)*p++;
+    x ^= (Py_uhash_t)len;
     if (x == -1)
         x = -2;
 

Modules/arraymodule.c

@@ -2351,7 +2351,7 @@ array_ass_subscr(arrayobject* self, PyObject* item, PyObject* value)
                 self->ob_item + (cur + 1) * itemsize,
                 lim * itemsize);
         }
-        cur = start + slicelength * step;
+        cur = start + (size_t)slicelength * step;
         if (cur < (size_t)Py_SIZE(self)) {
             memmove(self->ob_item + (cur-slicelength) * itemsize,
                 self->ob_item + cur * itemsize,

Objects/listobject.c

@@ -2434,7 +2434,7 @@ list_subscript(PyListObject* self, PyObject* item)
             src = self->ob_item;
             dest = ((PyListObject *)result)->ob_item;
             for (cur = start, i = 0; i < slicelength;
-                 cur += step, i++) {
+                 cur += (size_t)step, i++) {
                 it = src[cur];
                 Py_INCREF(it);
                 dest[i] = it;
@@ -2525,7 +2525,7 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
                     self->ob_item + cur + 1,
                     lim * sizeof(PyObject *));
             }
-            cur = start + slicelength*step;
+            cur = start + (size_t)slicelength * step;
             if (cur < (size_t)Py_SIZE(self)) {
                 memmove(self->ob_item + cur - slicelength,
                     self->ob_item + cur,
@@ -2589,7 +2589,7 @@ list_ass_subscript(PyListObject* self, PyObject* item, PyObject* value)
             selfitems = self->ob_item;
             seqitems = PySequence_Fast_ITEMS(seq);
             for (cur = start, i = 0; i < slicelength;
-                 cur += step, i++) {
+                 cur += (size_t)step, i++) {
                 garbage[i] = selfitems[cur];
                 ins = seqitems[i];
                 Py_INCREF(ins);

Objects/stringlib/string_format.h

@@ -209,19 +209,17 @@ get_integer(const SubString *str)
         if (digitval < 0)
             return -1;
         /*
-           This trick was copied from old Unicode format code.  It's cute,
-           but would really suck on an old machine with a slow divide
-           implementation.  Fortunately, in the normal case we do not
-           expect too many digits.
+           Detect possible overflow before it happens:
+
+              accumulator * 10 + digitval > PY_SSIZE_T_MAX if and only if
+              accumulator > (PY_SSIZE_T_MAX - digitval) / 10.
         */
-        oldaccumulator = accumulator;
-        accumulator *= 10;
-        if ((accumulator+10)/10 != oldaccumulator+1) {
+        if (accumulator > (PY_SSIZE_T_MAX - digitval) / 10) {
             PyErr_Format(PyExc_ValueError,
                          "Too many decimal digits in format string");
             return -1;
         }
-        accumulator += digitval;
+        accumulator = accumulator * 10 + digitval;
     }
     return accumulator;
 }