gh-122431: Disallow negative values in readline.append_history_file

Lib/test/test_readline.py

@@ -113,6 +113,14 @@ def test_write_read_append(self):
         # write_history_file can create the target
         readline.write_history_file(hfilename)
 
+        # Negative values should be disallowed
+        with self.assertRaises(ValueError):
+            readline.append_history_file(-42, hfilename)
+
+        # See gh-122431, using the minumum signed integer value caused a segfault
+        with self.assertRaises(ValueError):
+            readline.append_history_file(-2147483648, hfilename)
+
     def test_nonascii_history(self):
         readline.clear_history()
         try:

Misc/NEWS.d/next/Library/2024-07-30-11-37-40.gh-issue-122431.lAzVtu.rst

@@ -0,0 +1 @@
+:func:`readline.append_history_file` now raises a :exc:`ValueError` when given a negative value.

Modules/readline.c

@@ -351,6 +351,12 @@ readline_append_history_file_impl(PyObject *module, int nelements,
                                   PyObject *filename_obj)
 /*[clinic end generated code: output=5df06fc9da56e4e4 input=784b774db3a4b7c5]*/
 {
+    if (nelements < 0)
+    {
+        PyErr_SetString(PyExc_ValueError, "nelements cannot be negative");
+        return NULL;
+    }
+
     PyObject *filename_bytes;
     const char *filename;
     int err;