The _warnings module did not properly handle cases where strings were not being

passed in as the message to use for a warning. Fixed along with making the code
more robust against other errors where return values were not checked.

Closes issue 3639.
Code review by Benjamin Peterson.

Lib/test/test_warnings.py

@@ -202,6 +202,16 @@ class WarnTests(unittest.TestCase):
                 self.assertEqual(str(w.message), text)
                 self.assert_(w.category is UserWarning)
 
+    # Issue 3639
+    def test_warn_nonstandard_types(self):
+        # warn() should handle non-standard types without issue.
+        for ob in (Warning, None, 42):
+            with support.catch_warning(self.module) as w:
+                self.module.warn(ob)
+                # Don't directly compare objects since
+                # ``Warning() != Warning()``.
+                self.assertEquals(str(w.message), str(UserWarning(ob)))
+
     def test_filename(self):
         with warnings_state(self.module):
             with support.catch_warning(self.module) as w:
@@ -315,7 +325,6 @@ class WarnTests(unittest.TestCase):
                             self.module.warn_explicit,
                             None, Warning, None, 1, registry=42)
 
-
 class CWarnTests(BaseTest, WarnTests):
     module = c_warnings
 

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 3.0 release candidate 1
 Core and Builtins
 -----------------
 
+- Issue 3639: The _warnings module could segfault the interpreter when
+  unexpected types were passed in as arguments.
+
 - Issue #3712: The memoryview object had a reference leak and didn't support
   cyclic garbage collection.
 

Python/_warnings.c

@@ -258,6 +258,8 @@ show_warning(PyObject *filename, int lineno, PyObject *text, PyObject
     /* Print "  source_line\n" */
     if (sourceline) {
         char *source_line_str = _PyUnicode_AsString(sourceline);
+	if (source_line_str == NULL)
+		return;
         while (*source_line_str == ' ' || *source_line_str == '\t' ||
                 *source_line_str == '\014')
             source_line_str++;
@@ -266,8 +268,9 @@ show_warning(PyObject *filename, int lineno, PyObject *text, PyObject
         PyFile_WriteString("\n", f_stderr);
     }
     else
-        _Py_DisplaySourceLine(f_stderr, _PyUnicode_AsString(filename),
+        if (_Py_DisplaySourceLine(f_stderr, _PyUnicode_AsString(filename),
-                              lineno, 2);
+                              lineno, 2) < 0)
+		return;
     PyErr_Clear();
 }
 
@@ -366,8 +369,11 @@ warn_explicit(PyObject *category, PyObject *message,
             PyObject *to_str = PyObject_Str(item);
             const char *err_str = "???";
 
-            if (to_str != NULL)
+            if (to_str != NULL) {
                 err_str = _PyUnicode_AsString(to_str);
+		if (err_str == NULL)
+			goto cleanup;
+	    }
             PyErr_Format(PyExc_RuntimeError,
                         "Unrecognized action (%s) in warnings.filters:\n %s",
                         action, err_str);
@@ -498,7 +504,9 @@ setup_context(Py_ssize_t stack_level, PyObject **filename, int *lineno,
     }
     else {
         const char *module_str = _PyUnicode_AsString(*module);
-        if (module_str && strcmp(module_str, "__main__") == 0) {
+	if (module_str == NULL)
+		goto handle_error;
+        if (strcmp(module_str, "__main__") == 0) {
             PyObject *argv = PySys_GetObject("argv");
             if (argv != NULL && PyList_Size(argv) > 0) {
                 int is_true;