dnssd: Prevent crashes after releasing resolvergnome-3-34

The following error often happens when mounting dav+sd share (e.g. created
over gnome-user-media) and the mount operation fails for some reason:

dbus[47482]: arguments to dbus_connection_unref() were incorrect,
assertion "connection->generation == _dbus_current_generation" failed
in file ../../dbus/dbus-connection.c line 2823. This is normally a bug
in some application using the D-Bus library.

This is because avahi is not thread-safe and our resolver doesn't use
mutexes. But it seems to me that mutexes are not necessarily needed if
everything would work as expected. Unfortunately, changes made by commit
3384af8 causes that start_avahi_resolver is being called multiple times
by mistake, which also calls avahi_service_resolver_new multiple times.
Consequently, it may crash when resolver is beeing freed too early as
there might still be unexpected pending operations using avahi client.

Fixes: GNOME/gvfs#449


(cherry picked from commit c8f8f345a0c88e68dd21f6b548ab1cfba56732e9)

1 files changed, 6 insertions, 2 deletions

diff --git a/common/gvfsdnssdresolver.c b/common/gvfsdnssdresolver.c
index 0f0f5f60..be062227 100644
--- a/common/gvfsdnssdresolver.c
+++ b/common/gvfsdnssdresolver.c
@@ -81,6 +81,7 @@ struct _GVfsDnsSdResolver
   char **txt_records;
 
   AvahiServiceResolver *avahi_resolver;
+  guint start_avahi_resolver_id;
 };
 
 
@@ -241,6 +242,7 @@ start_avahi_resolver (gpointer user_data)
                                                          resolver);
 
 out:
+  resolver->start_avahi_resolver_id = 0;
   g_object_unref (resolver);
   return FALSE;
 }
@@ -248,10 +250,10 @@ out:
 static void
 ensure_avahi_resolver (GVfsDnsSdResolver  *resolver)
 {
-  if (resolver->avahi_resolver != NULL)
+  if (resolver->avahi_resolver != NULL || resolver->start_avahi_resolver_id != 0)
     return;
 
-  g_idle_add (start_avahi_resolver, g_object_ref (resolver));
+  resolver->start_avahi_resolver_id = g_idle_add (start_avahi_resolver, g_object_ref (resolver));
 }
 
 static void
@@ -373,6 +375,8 @@ g_vfs_dns_sd_resolver_finalize (GObject *object)
   if (resolver->avahi_resolver != NULL)
     avahi_service_resolver_free (resolver->avahi_resolver);
 
+  if (resolver->start_avahi_resolver_id != 0)
+    g_source_remove (resolver->start_avahi_resolver_id);
 
   resolvers = g_list_remove (resolvers, resolver);