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gdbusconnection: Disallow subscribers for implicit match rules

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While it's true that GDBus makes no ordering guarantees about
the order of callbacks for signals subscriptions for the same
signal, it's still a good idea not to change the order if we
don't have to.

Since g_dbus_connection_signal_subscribe started tracking name
owners itself, the order of NameOwnerChanged handlers can
change counterintuitively because that tracking creates a match
rule implicitly, that future subscribers can use for their
subscriptions.

This commit just adds a minor change to the syntax for those
implicit match rules, so explicit match rules will always be
treated distinctly. The change is to add a leading "*" to the
match rule that later gets filtered out when sending the match
rule to the bus.
This commit is contained in:
Ray Strode 2024-05-06 19:48:07 -04:00
parent 47866d252f
commit 19a5ce6a14
1 changed files with 17 additions and 3 deletions
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20
gio/gdbusconnection.c
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@ -3603,13 +3603,14 @@ args_to_rule (const gchar *sender,
const gchar *member,
const gchar *object_path,
const gchar *arg0,
const gchar header_tag,
GDBusSignalFlags flags)
{
GString *rule;
rule = g_string_new ("type='signal'");
if (flags & G_DBUS_SIGNAL_FLAGS_NO_MATCH_RULE)
g_string_prepend_c (rule, '-');
if (header_tag != '\0')
g_string_prepend_c (rule, header_tag);
if (sender != NULL)
g_string_append_printf (rule, ",sender='%s'", sender);
if (interface_name != NULL)
@ -3646,6 +3647,9 @@ add_match_rule (GDBusConnection *connection,
GError *error;
GDBusMessage *message;
if (match_rule[0] == '*')
match_rule++;
if (match_rule[0] == '-')
return;
@ -3677,6 +3681,9 @@ remove_match_rule (GDBusConnection *connection,
GError *error;
GDBusMessage *message;
if (match_rule[0] == '*')
match_rule++;
if (match_rule[0] == '-')
return;
@ -3840,6 +3847,7 @@ g_dbus_connection_signal_subscribe (GDBusConnection *connection,
gpointer user_data,
GDestroyNotify user_data_free_func)
{
gchar header_tag = '\0';
gchar *rule;
SignalData *signal_data;
SignalData *name_watcher = NULL;
@ -3877,7 +3885,9 @@ g_dbus_connection_signal_subscribe (GDBusConnection *connection,
* the usual way, but the '-' prevents the match rule from ever
* actually being send to the bus (either for add or remove).
*/
rule = args_to_rule (sender, interface_name, member, object_path, arg0, flags);
if (flags & G_DBUS_SIGNAL_FLAGS_NO_MATCH_RULE)
header_tag = '-';
rule = args_to_rule (sender, interface_name, member, object_path, arg0, header_tag, flags);
if (sender != NULL && (g_dbus_is_unique_name (sender) || g_strcmp0 (sender, "org.freedesktop.DBus") == 0))
sender_is_its_own_owner = TRUE;
@ -3926,11 +3936,15 @@ g_dbus_connection_signal_subscribe (GDBusConnection *connection,
/* We already checked that sender != NULL implies MESSAGE_BUS_CONNECTION */
g_assert (connection->flags & G_DBUS_CONNECTION_FLAGS_MESSAGE_BUS_CONNECTION);
/* We pass a prefix of "*" to mean it's an internal match rule and shouldn't gain
* subscribers
*/
name_owner_rule = args_to_rule (DBUS_SERVICE_DBUS,
DBUS_INTERFACE_DBUS,
"NameOwnerChanged",
DBUS_PATH_DBUS,
sender,
'*',
G_DBUS_SIGNAL_FLAGS_NONE);
name_watcher = g_hash_table_lookup (connection->map_rule_to_signal_data, name_owner_rule);