[avahi] [PATCH] D-Bus NameOwnerChanged: better match rule

[Alban Crequy]

When subscribing to the D-Bus signal NameOwnerChanged from the bus driver,
specify the object path and the sender in the match rule. Otherwise, random
connections on the bus could impersonate the bus driver.

In addition, specify the member NameOwnerChanged in the match rules: the other
D-Bus signals received don't require a match rule to be received.
---
 avahi-daemon/dbus-protocol.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/avahi-daemon/dbus-protocol.c b/avahi-daemon/dbus-protocol.c
index eb8a662..03c2930 100644
--- a/avahi-daemon/dbus-protocol.c
+++ b/avahi-daemon/dbus-protocol.c
@@ -1111,7 +1111,16 @@ static int dbus_connect(void) {
         goto fail;
     }
 
-    dbus_bus_add_match(server->bus, "type='signal',""interface='" DBUS_INTERFACE_DBUS  "'", &error);
+    /* Only register the rule for NameOwnerChanged.
+     * NameAcquired and Disconnected don't require a match rule to be received.
+     */
+    dbus_bus_add_match(server->bus,
+                       "type='signal',"
+                       "path='" DBUS_PATH_DBUS "',"
+                       "interface='" DBUS_INTERFACE_DBUS  "',"
+                       "member='NameOwnerChanged',"
+                       "sender='"DBUS_SERVICE_DBUS"'",
+                       &error);
 
     if (dbus_error_is_set(&error)) {
         avahi_log_error("dbus_bus_add_match(): %s", error.message);
-- 
1.8.5.3