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Fix use-after-free when calling g_dbus_connection_flush_sync()

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When the _g_dbus_worker_flush_sync() schedules the 'data' and releases
the worker->write_lock, it is possible for the GDBus worker thread thread
to finish the D-Bus call and acquire the worker->write_lock before
the _g_dbus_worker_flush_sync() re-acquires it in the if (data != NULL) body.
When that happens, the ostream_flush_cb() increases the worker->write_num_messages_flushed
and then releases the worker->write_lock. The write lock is reacquired by
the _g_dbus_worker_flush_sync(), which sees that the while condition is satisfied,
thus it doesn't enter the loop body and immediately clears the data members and
frees the data structure itself. The ostream_flush_cb() is still ongoing, possibly
inside flush_data_list_complete(), where it accesses the FlushData, which can be
in any stage of being freed.

Instead, add an explicit boolean flag indicating when the flush is truly finished.

Closes #1896
This commit is contained in:
Milan Crha 2019-10-10 14:55:20 +00:00 committed by Philip Withnall
parent c97565748a
commit 822f8bae9e
1 changed files with 4 additions and 5 deletions
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9
gio/gdbusprivate.c
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@ -408,6 +408,7 @@ typedef struct
GMutex mutex;
GCond cond;
guint64 number_to_wait_for;
gboolean finished;
GError *error;
} FlushData;
@ -1158,6 +1159,7 @@ flush_data_list_complete (const GList *flushers,
f->error = error != NULL ? g_error_copy (error) : NULL;
g_mutex_lock (&f->mutex);
f->finished = TRUE;
g_cond_signal (&f->cond);
g_mutex_unlock (&f->mutex);
}
@ -1787,6 +1789,7 @@ _g_dbus_worker_flush_sync (GDBusWorker *worker,
g_mutex_init (&data->mutex);
g_cond_init (&data->cond);
data->number_to_wait_for = worker->write_num_messages_written + pending_writes;
data->finished = FALSE;
g_mutex_lock (&data->mutex);
schedule_writing_unlocked (worker, NULL, data, NULL);
@ -1796,14 +1799,10 @@ _g_dbus_worker_flush_sync (GDBusWorker *worker,
if (data != NULL)
{
/* Wait for flush operations to finish. */
g_mutex_lock (&worker->write_lock);
while (worker->write_num_messages_flushed < data->number_to_wait_for)
while (!data->finished)
{
g_mutex_unlock (&worker->write_lock);
g_cond_wait (&data->cond, &data->mutex);
g_mutex_lock (&worker->write_lock);
}
g_mutex_unlock (&worker->write_lock);
g_mutex_unlock (&data->mutex);
g_cond_clear (&data->cond);