[syslog-ng] [PATCH] afmongodb: Fix a race condition in the queue handling.

[Gergely Nagy]

There is a race condition between afmongodb_dd_queue() and
afmongodb_worker_insert(), that can trigger an assertion when the rate
of incoming messages is very high.

The scenario that triggers this is like this:

* We receive a message, put it in our internal queue, and notify the
  worker thread.
* The worker thread resets the queue's parallel_push.
* We receive another message, notice that the queue is empty, so we
  insert it, and set parallel_push at the same time.
* The worker thread tries to pop the queue's head, but that triggers
  an assert, because parallel_push is set.

The root cause of the problem is that afmongodb_dd_queue() modifies
the queue without locking the queue_mutex. This patch corrects that
problem.

Reported-By: Costa Farber <costaf at wix.com>
Signed-off-by: Gergely Nagy <algernon at balabit.hu>
---
 modules/afmongodb/afmongodb.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/modules/afmongodb/afmongodb.c b/modules/afmongodb/afmongodb.c
index cbd0d16..a88aeaa 100644
--- a/modules/afmongodb/afmongodb.c
+++ b/modules/afmongodb/afmongodb.c
@@ -530,7 +530,9 @@ afmongodb_dd_queue(LogPipe *s, LogMessage *msg, const LogPathOptions *path_optio
   g_mutex_lock(self->suspend_mutex);
   if (queue_was_empty && !self->writer_thread_suspended)
     {
+      g_mutex_lock(self->queue_mutex);
       log_queue_set_parallel_push(self->queue, 1, afmongodb_dd_queue_notify, self, NULL);
+      g_mutex_unlock(self->queue_mutex);
     }
   g_mutex_unlock(self->suspend_mutex);
 }
-- 
1.7.7.3