kerberos-identity: Ensure idles queued to main thread are property synchronized

Kerberos identities are refreshed on a helper thread, and the state of
those identities are exported over the user bus on the main thread.

Since the main consumer of an identity's properties is the bus service
running on the main thread, to simplify things, property notifications
are dispatched from the main thread as well (even though the underlying
state is changed on a worker thread).

The mechanism to dispatch property notifies to the main thread is an
idle handler. The logic for doing the dispatch has a concurrency
bug however. In order to coaelsce multiple notifies that happen in
quick succession, the dispatch code checks for a preexisting idle id
associated with the given property. That idle id is set from the worker
thread when the idle is queued, and it's cleared from the main thread
when the idle is dispatched. The bug is that the main thread could in
theory clear the idle id immediately after the worker thread decided
there was already a notify queued, leading to a notify getting
completely dropped.

This commit addresses the bug by adding appropriate locking.

Closes https://gitlab.gnome.org/GNOME/gnome-online-accounts/-/issues/160


(cherry picked from commit 709e1db83ebf8980f4367d548f12d25a69e77955)

1 files changed, 3 insertions, 0 deletions

diff --git a/src/goaidentity/goakerberosidentity.c b/src/goaidentity/goakerberosidentity.c
index d5eaeed..6994ad6 100644
--- a/src/goaidentity/goakerberosidentity.c
+++ b/src/goaidentity/goakerberosidentity.c
@@ -520,7 +520,10 @@ typedef struct
 static void
 clear_idle_id (NotifyRequest *request)
 {
+  G_LOCK (identity_lock);
   *request->idle_id = 0;
+  G_UNLOCK (identity_lock);
+
   g_object_unref (request->self);
   g_slice_free (NotifyRequest, request);
 }