Fix for bug 113934. string*n and unicode*n did no overflow checking at

all, either to see whether the # of chars fit in an int, or that the
amount of memory needed fit in a size_t.  Checking these is expensive, but
the alternative is silently wrong answers (as in the bug report) or
core dumps (which were easy to provoke using Unicode strings).

Objects/stringobject.c

@@ -393,16 +393,31 @@ string_repeat(register PyStringObject *a, register int n)
 	register int i;
 	register int size;
 	register PyStringObject *op;
+	size_t nbytes;
 	if (n < 0)
 		n = 0;
+	/* watch out for overflows:  the size can overflow int,
+	 * and the # of bytes needed can overflow size_t
+	 */
 	size = a->ob_size * n;
+	if (n && size / n != a->ob_size) {
+		PyErr_SetString(PyExc_OverflowError,
+			"repeated string is too long");
+		return NULL;
+	}
 	if (size == a->ob_size) {
 		Py_INCREF(a);
 		return (PyObject *)a;
 	}
-	/* PyObject_NewVar is inlined */
+	nbytes = size * sizeof(char);
+	if (nbytes / sizeof(char) != (size_t)size ||
+	    nbytes + sizeof(PyStringObject) <= nbytes) {
+		PyErr_SetString(PyExc_OverflowError,
+			"repeated string is too long");
+		return NULL;
+	}
 	op = (PyStringObject *)
-		PyObject_MALLOC(sizeof(PyStringObject) + size * sizeof(char));
+		PyObject_MALLOC(sizeof(PyStringObject) + nbytes);
 	if (op == NULL)
 		return PyErr_NoMemory();
 	PyObject_INIT_VAR(op, &PyString_Type, size);

Objects/unicodeobject.c

@@ -3993,6 +3993,8 @@ unicode_repeat(PyUnicodeObject *str, int len)
 {
     PyUnicodeObject *u;
     Py_UNICODE *p;
+    int nchars;
+    size_t nbytes;
 
     if (len < 0)
         len = 0;
@@ -4003,7 +4005,22 @@ unicode_repeat(PyUnicodeObject *str, int len)
         return (PyObject*) str;
     }
 
-    u = _PyUnicode_New(len * str->length);
+    /* ensure # of chars needed doesn't overflow int and # of bytes
+     * needed doesn't overflow size_t
+     */
+    nchars = len * str->length;
+    if (len && nchars / len != str->length) {
+        PyErr_SetString(PyExc_OverflowError,
+                        "repeated string is too long");
+        return NULL;
+    }
+    nbytes = (nchars + 1) * sizeof(Py_UNICODE);
+    if (nbytes / sizeof(Py_UNICODE) != (size_t)(nchars + 1)) {
+        PyErr_SetString(PyExc_OverflowError,
+                        "repeated string is too long");
+        return NULL;
+    }
+    u = _PyUnicode_New(nchars);
     if (!u)
         return NULL;