authz: add QAuthZListFile object type for a file access control list

Add a QAuthZListFile object type that implements the QAuthZ interface. This
built-in implementation is a proxy around the QAuthZList object type,
initializing it from an external file, and optionally, automatically
reloading it whenever it changes.

To create an instance of this object via the QMP monitor, the syntax
used would be:

      {
        "execute": "object-add",
        "arguments": {
          "qom-type": "authz-list-file",
          "id": "authz0",
          "props": {
            "filename": "/etc/qemu/vnc.acl",
	    "refresh": true
          }
        }
      }

If "refresh" is "yes", inotify is used to monitor the file,
automatically reloading changes. If an error occurs during reloading,
all authorizations will fail until the file is next successfully
loaded.

The /etc/qemu/vnc.acl file would contain a JSON representation of a
QAuthZList object

    {
      "rules": [
         { "match": "fred", "policy": "allow", "format": "exact" },
         { "match": "bob", "policy": "allow", "format": "exact" },
         { "match": "danb", "policy": "deny", "format": "glob" },
         { "match": "dan*", "policy": "allow", "format": "exact" },
      ],
      "policy": "deny"
    }

This sets up an authorization rule that allows 'fred', 'bob' and anyone
whose name starts with 'dan', except for 'danb'. Everyone unmatched is
denied.

The object can be loaded on the comand line using

   -object authz-list-file,id=authz0,filename=/etc/qemu/vnc.acl,refresh=yes

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

authz/Makefile.objs

@@ -1,3 +1,4 @@
 authz-obj-y += base.o
 authz-obj-y += simple.o
 authz-obj-y += list.o
+authz-obj-y += listfile.o

authz/listfile.c

@@ -0,0 +1,283 @@
+/*
+ * QEMU access control list file authorization driver
+ *
+ * Copyright (c) 2018 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "authz/listfile.h"
+#include "authz/trace.h"
+#include "qemu/error-report.h"
+#include "qemu/main-loop.h"
+#include "qemu/sockets.h"
+#include "qemu/filemonitor.h"
+#include "qom/object_interfaces.h"
+#include "qapi/qapi-visit-authz.h"
+#include "qapi/qmp/qjson.h"
+#include "qapi/qmp/qobject.h"
+#include "qapi/qmp/qerror.h"
+#include "qapi/qobject-input-visitor.h"
+
+
+static bool
+qauthz_list_file_is_allowed(QAuthZ *authz,
+                            const char *identity,
+                            Error **errp)
+{
+    QAuthZListFile *fauthz = QAUTHZ_LIST_FILE(authz);
+    if (fauthz->list) {
+        return qauthz_is_allowed(fauthz->list, identity, errp);
+    }
+
+    return false;
+}
+
+
+static QAuthZ *
+qauthz_list_file_load(QAuthZListFile *fauthz, Error **errp)
+{
+    GError *err = NULL;
+    gchar *content = NULL;
+    gsize len;
+    QObject *obj = NULL;
+    QDict *pdict;
+    Visitor *v = NULL;
+    QAuthZ *ret = NULL;
+
+    trace_qauthz_list_file_load(fauthz, fauthz->filename);
+    if (!g_file_get_contents(fauthz->filename, &content, &len, &err)) {
+        error_setg(errp, "Unable to read '%s': %s",
+                   fauthz->filename, err->message);
+        goto cleanup;
+    }
+
+    obj = qobject_from_json(content, errp);
+    if (!obj) {
+        goto cleanup;
+    }
+
+    pdict = qobject_to(QDict, obj);
+    if (!pdict) {
+        error_setg(errp, QERR_INVALID_PARAMETER_TYPE, "obj", "dict");
+        goto cleanup;
+    }
+
+    v = qobject_input_visitor_new(obj);
+
+    ret = (QAuthZ *)user_creatable_add_type(TYPE_QAUTHZ_LIST,
+                                            NULL, pdict, v, errp);
+
+ cleanup:
+    visit_free(v);
+    qobject_unref(obj);
+    if (err) {
+        g_error_free(err);
+    }
+    g_free(content);
+    return ret;
+}
+
+
+static void
+qauthz_list_file_event(int wd G_GNUC_UNUSED,
+                       QFileMonitorEvent ev G_GNUC_UNUSED,
+                       const char *name G_GNUC_UNUSED,
+                       void *opaque)
+{
+    QAuthZListFile *fauthz = opaque;
+    Error *err = NULL;
+
+    if (ev != QFILE_MONITOR_EVENT_MODIFIED &&
+        ev != QFILE_MONITOR_EVENT_CREATED) {
+        return;
+    }
+
+    object_unref(OBJECT(fauthz->list));
+    fauthz->list = qauthz_list_file_load(fauthz, &err);
+    trace_qauthz_list_file_refresh(fauthz,
+                                   fauthz->filename, fauthz->list ? 1 : 0);
+    if (!fauthz->list) {
+        error_report_err(err);
+    }
+}
+
+static void
+qauthz_list_file_complete(UserCreatable *uc, Error **errp)
+{
+    QAuthZListFile *fauthz = QAUTHZ_LIST_FILE(uc);
+    gchar *dir = NULL, *file = NULL;
+
+    fauthz->list = qauthz_list_file_load(fauthz, errp);
+
+    if (!fauthz->refresh) {
+        return;
+    }
+
+    fauthz->file_monitor = qemu_file_monitor_new(errp);
+    if (!fauthz->file_monitor) {
+        return;
+    }
+
+    dir = g_path_get_dirname(fauthz->filename);
+    if (g_str_equal(dir, ".")) {
+        error_setg(errp, "Filename must be an absolute path");
+        goto cleanup;
+    }
+    file = g_path_get_basename(fauthz->filename);
+    if (g_str_equal(file, ".")) {
+        error_setg(errp, "Path has no trailing filename component");
+        goto cleanup;
+    }
+
+    fauthz->file_watch = qemu_file_monitor_add_watch(
+        fauthz->file_monitor, dir, file,
+        qauthz_list_file_event, fauthz, errp);
+    if (fauthz->file_watch < 0) {
+        goto cleanup;
+    }
+
+ cleanup:
+    g_free(file);
+    g_free(dir);
+}
+
+
+static void
+qauthz_list_file_prop_set_filename(Object *obj,
+                                   const char *value,
+                                   Error **errp G_GNUC_UNUSED)
+{
+    QAuthZListFile *fauthz = QAUTHZ_LIST_FILE(obj);
+
+    g_free(fauthz->filename);
+    fauthz->filename = g_strdup(value);
+}
+
+
+static char *
+qauthz_list_file_prop_get_filename(Object *obj,
+                                   Error **errp G_GNUC_UNUSED)
+{
+    QAuthZListFile *fauthz = QAUTHZ_LIST_FILE(obj);
+
+    return g_strdup(fauthz->filename);
+}
+
+
+static void
+qauthz_list_file_prop_set_refresh(Object *obj,
+                                  bool value,
+                                  Error **errp G_GNUC_UNUSED)
+{
+    QAuthZListFile *fauthz = QAUTHZ_LIST_FILE(obj);
+
+    fauthz->refresh = value;
+}
+
+
+static bool
+qauthz_list_file_prop_get_refresh(Object *obj,
+                                  Error **errp G_GNUC_UNUSED)
+{
+    QAuthZListFile *fauthz = QAUTHZ_LIST_FILE(obj);
+
+    return fauthz->refresh;
+}
+
+
+static void
+qauthz_list_file_finalize(Object *obj)
+{
+    QAuthZListFile *fauthz = QAUTHZ_LIST_FILE(obj);
+
+    object_unref(OBJECT(fauthz->list));
+    g_free(fauthz->filename);
+    qemu_file_monitor_free(fauthz->file_monitor);
+}
+
+
+static void
+qauthz_list_file_class_init(ObjectClass *oc, void *data)
+{
+    UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
+    QAuthZClass *authz = QAUTHZ_CLASS(oc);
+
+    ucc->complete = qauthz_list_file_complete;
+
+    object_class_property_add_str(oc, "filename",
+                                  qauthz_list_file_prop_get_filename,
+                                  qauthz_list_file_prop_set_filename,
+                                  NULL);
+    object_class_property_add_bool(oc, "refresh",
+                                   qauthz_list_file_prop_get_refresh,
+                                   qauthz_list_file_prop_set_refresh,
+                                   NULL);
+
+    authz->is_allowed = qauthz_list_file_is_allowed;
+}
+
+
+static void
+qauthz_list_file_init(Object *obj)
+{
+    QAuthZListFile *authz = QAUTHZ_LIST_FILE(obj);
+
+    authz->file_watch = -1;
+#ifdef CONFIG_INOTIFY1
+    authz->refresh = TRUE;
+#endif
+}
+
+
+QAuthZListFile *qauthz_list_file_new(const char *id,
+                                     const char *filename,
+                                     bool refresh,
+                                     Error **errp)
+{
+    return QAUTHZ_LIST_FILE(
+        object_new_with_props(TYPE_QAUTHZ_LIST_FILE,
+                              object_get_objects_root(),
+                              id, errp,
+                              "filename", filename,
+                              "refresh", refresh ? "yes" : "no",
+                              NULL));
+}
+
+
+static const TypeInfo qauthz_list_file_info = {
+    .parent = TYPE_QAUTHZ,
+    .name = TYPE_QAUTHZ_LIST_FILE,
+    .instance_init = qauthz_list_file_init,
+    .instance_size = sizeof(QAuthZListFile),
+    .instance_finalize = qauthz_list_file_finalize,
+    .class_size = sizeof(QAuthZListFileClass),
+    .class_init = qauthz_list_file_class_init,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_USER_CREATABLE },
+        { }
+    }
+};
+
+
+static void
+qauthz_list_file_register_types(void)
+{
+    type_register_static(&qauthz_list_file_info);
+}
+
+
+type_init(qauthz_list_file_register_types);

authz/trace-events

@@ -9,3 +9,7 @@ qauthz_simple_is_allowed(void *authz, const char *wantidentity, const char *goti
 # auth/list.c
 qauthz_list_check_rule(void *authz, const char *identity, const char *rule, int format, int policy) "AuthZ list %p check rule=%s identity=%s format=%d policy=%d"
 qauthz_list_default_policy(void *authz, const char *identity, int policy) "AuthZ list %p default identity=%s policy=%d"
+
+# auth/listfile.c
+qauthz_list_file_load(void *authz, const char *filename) "AuthZ file %p load filename=%s"
+qauthz_list_file_refresh(void *authz, const char *filename, int success) "AuthZ file %p load filename=%s success=%d"