qemu/authz/listfile.c
Daniel P. Berrangé b4682a63f8 filemon: fix watch IDs to avoid potential wraparound issues
Watch IDs are allocated from incrementing a int counter against
the QFileMonitor object. In very long life QEMU processes with
a huge amount of USB MTP activity creating & deleting directories
it is just about conceivable that the int counter can wrap
around. This would result in incorrect behaviour of the file
monitor watch APIs due to clashing watch IDs.

Instead of trying to detect this situation, this patch changes
the way watch IDs are allocated. It is turned into an int64_t
variable where the high 32 bits are set from the underlying
inotify "int" ID. This gives an ID that is guaranteed unique
for the directory as a whole, and we can rely on the kernel
to enforce this. QFileMonitor then sets the low 32 bits from
a per-directory counter.

The USB MTP device only sets watches on the directory as a
whole, not files within, so there is no risk of guest
triggered wrap around on the low 32 bits.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
2019-04-02 13:52:02 +01:00

284 lines
7.3 KiB
C

/*
* 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(int64_t 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);