plugins/python: autodetect ClassName field

If "ClassName" is not specified, load the one and only sudo.Plugin from
the module (if so), otherwise display which plugins are available from
which the system admin can choose.

plugins/python/python_plugin_common.c

@@ -399,6 +399,82 @@ _python_plugin_set_path(struct PluginContext *plugin_ctx, const char *path)
     return SUDO_RC_OK;
 }
 
+/* Returns the list of sudo.Plugins in a module */
+static PyObject *
+_python_plugin_class_list(PyObject *py_module) {
+    PyObject *py_module_dict = PyModule_GetDict(py_module);  // Note: borrowed
+    PyObject *key, *value; // Note: borrowed
+    Py_ssize_t pos = 0;
+    PyObject *py_plugin_list = PyList_New(0);
+
+    while (PyDict_Next(py_module_dict, &pos, &key, &value)) {
+        if (PyObject_IsSubclass(value, (PyObject *)sudo_type_Plugin) == 1) {
+            if (PyList_Append(py_plugin_list, key) != 0)
+                goto cleanup;
+        } else {
+            PyErr_Clear();
+        }
+    }
+
+cleanup:
+    if (PyErr_Occurred()) {
+        Py_CLEAR(py_plugin_list);
+    }
+    return py_plugin_list;
+}
+
+/* Gets a sudo.Plugin class from the specified module. The argument "plugin_class"
+ * can be NULL in which case it loads the one and only "sudo.Plugin" present
+ * in the module (if so), or displays helpful error message. */
+static PyObject *
+_python_plugin_get_class(const char *plugin_path, PyObject *py_module, const char *plugin_class)
+{
+    debug_decl(python_plugin_init, PYTHON_DEBUG_PLUGIN_LOAD);
+    PyObject *py_plugin_list = NULL, *py_class = NULL;
+
+    if (plugin_class == NULL) {
+        py_plugin_list = _python_plugin_class_list(py_module);
+        if (py_plugin_list == NULL) {
+            goto cleanup;
+        }
+
+        if (PyList_Size(py_plugin_list) == 1) {
+            PyObject *py_plugin_name = PyList_GetItem(py_plugin_list, 0); // Note: borrowed
+            plugin_class = PyUnicode_AsUTF8(py_plugin_name);
+        }
+    }
+
+    if (plugin_class == NULL) {
+        py_sudo_log(SUDO_CONV_ERROR_MSG, "No plugin class is specified for python module '%s'. "
+                    "Use 'ClassName' configuration option in 'sudo.conf'\n", plugin_path);
+        if (py_plugin_list != NULL) {
+            char *possible_plugins = py_join_str_list(py_plugin_list, ", ");
+            if (possible_plugins != NULL) {
+                py_sudo_log(SUDO_CONV_ERROR_MSG, "Possible plugins: %s\n", possible_plugins);
+                free(possible_plugins);
+            }
+        }
+        goto cleanup;
+    }
+
+    sudo_debug_printf(SUDO_DEBUG_DEBUG, "Using plugin class '%s'", plugin_class);
+    py_class = PyObject_GetAttrString(py_module, plugin_class);
+    if (py_class == NULL) {
+        py_sudo_log(SUDO_CONV_ERROR_MSG, "Failed to find plugin class '%s'\n", plugin_class);
+        goto cleanup;
+    }
+
+    if (!PyObject_IsSubclass(py_class, (PyObject *)sudo_type_Plugin)) {
+        py_sudo_log(SUDO_CONV_ERROR_MSG, "Plugin class '%s' does not inherit from 'sudo.Plugin'\n", plugin_class);
+        Py_CLEAR(py_class);
+        goto cleanup;
+    }
+
+cleanup:
+    Py_CLEAR(py_plugin_list);
+    debug_return_ptr(py_class);
+}
+
 int
 python_plugin_init(struct PluginContext *plugin_ctx, char * const plugin_options[],
                    unsigned int version)
@@ -419,8 +495,7 @@ python_plugin_init(struct PluginContext *plugin_ctx, char * const plugin_options
     PyThreadState_Swap(plugin_ctx->py_interpreter);
 
     if (!sudo_conf_developer_mode() && sudo_module_register_importblocker() < 0) {
-        py_log_last_error(NULL);
-        debug_return_int(SUDO_RC_ERROR);
+        goto cleanup;
     }
 
     if (_python_plugin_set_path(plugin_ctx, _lookup_value(plugin_options, "ModulePath")) != SUDO_RC_OK) {
@@ -433,23 +508,9 @@ python_plugin_init(struct PluginContext *plugin_ctx, char * const plugin_options
         goto cleanup;
     }
 
-    const char *plugin_class = _lookup_value(plugin_options, "ClassName");
-    if (plugin_class == NULL) {
-        py_sudo_log(SUDO_CONV_ERROR_MSG, "No plugin class is specified for python module '%s'. "
-                    "Use 'ClassName' configuration option in 'sudo.conf'\n", plugin_ctx->plugin_path);
-        goto cleanup;
-    }
-
-    sudo_debug_printf(SUDO_DEBUG_DEBUG, "Using plugin class '%s'", plugin_class);
-    plugin_ctx->py_class = PyObject_GetAttrString(plugin_ctx->py_module, plugin_class);
+    plugin_ctx->py_class = _python_plugin_get_class(plugin_ctx->plugin_path, plugin_ctx->py_module,
+                                                    _lookup_value(plugin_options, "ClassName"));
     if (plugin_ctx->py_class == NULL) {
-        py_sudo_log(SUDO_CONV_ERROR_MSG, "Failed to find plugin class '%s'\n", plugin_class);
-        goto cleanup;
-    }
-
-    if (!PyObject_IsSubclass(plugin_ctx->py_class, (PyObject *)sudo_type_Plugin)) {
-        py_sudo_log(SUDO_CONV_ERROR_MSG, "Plugin class '%s' does not inherit from 'sudo.Plugin'\n", plugin_class);
-        Py_CLEAR(plugin_ctx->py_class);
         goto cleanup;
     }
 

plugins/python/regress/check_python_examples.c

@@ -584,10 +584,31 @@ check_loading_fails_with_missing_path(void)
 }
 
 int
-check_loading_fails_with_missing_classname(void)
+check_loading_succeeds_with_missing_classname(void)
 {
     str_array_free(&data.plugin_options);
     data.plugin_options = create_str_array(2, "ModulePath=" SRC_DIR "/example_debugging.py", NULL);
+
+    const char *errstr = NULL;
+
+    VERIFY_INT(python_io->open(SUDO_API_VERSION, fake_conversation, fake_printf, data.settings,
+                              data.user_info, data.command_info, data.plugin_argc, data.plugin_argv,
+                              data.user_env, data.plugin_options, &errstr), SUDO_RC_OK);
+    VERIFY_PTR(errstr, NULL);
+    VERIFY_INT(python_io->show_version(1), SUDO_RC_OK);
+    python_io->close(0, 0);
+
+    VERIFY_STDOUT(expected_path("check_loading_succeeds_with_missing_classname.stdout"));
+    VERIFY_STR(data.stderr_str, "");
+
+    return true;
+}
+
+int
+check_loading_fails_with_missing_classname(void)
+{
+    str_array_free(&data.plugin_options);
+    data.plugin_options = create_str_array(2, "ModulePath=" SRC_DIR "/regress/plugin_errorstr.py", NULL);
     return check_loading_fails("missing_classname");
 }
 
@@ -1511,6 +1532,7 @@ main(int argc, char *argv[])
     RUN_TEST(check_plugin_unload());
 
     RUN_TEST(check_loading_fails_with_missing_path());
+    RUN_TEST(check_loading_succeeds_with_missing_classname());
     RUN_TEST(check_loading_fails_with_missing_classname());
     RUN_TEST(check_loading_fails_with_wrong_classname());
     RUN_TEST(check_loading_fails_with_wrong_path());

plugins/python/regress/testdata/check_loading_fails_missing_classname.stderr

@@ -1,2 +1,3 @@
-No plugin class is specified for python module 'SRC_DIR/example_debugging.py'. Use 'ClassName' configuration option in 'sudo.conf'
+No plugin class is specified for python module 'SRC_DIR/regress/plugin_errorstr.py'. Use 'ClassName' configuration option in 'sudo.conf'
+Possible plugins: ErrorMsgPlugin, ConstructErrorPlugin
 Failed during loading plugin class

plugins/python/regress/testdata/check_loading_succeeds_with_missing_classname.stdout

@@ -0,0 +1 @@
+Python io plugin (API 1.0): DebugDemoPlugin (loaded from 'SRC_DIR/example_debugging.py')