ipc/sem.c: fully initialize sem_array before making it visible

commit e8577d1f upstream.

ipc_addid() makes a new ipc identifier visible to everyone.  New objects
start as locked, so that the caller can complete the initialization
after the call.  Within struct sem_array, at least sma->sem_base and
sma->sem_nsems are accessed without any locks, therefore this approach
doesn't work.

Thus: Move the ipc_addid() to the end of the initialization.
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Reported-by: Rik van Riel <riel@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2:
 - Adjust context
 - The error path being moved looks a little different]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

ipc/sem.c

@@ -314,14 +314,6 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 		return retval;
 	}
 
-	id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
-	if (id < 0) {
-		security_sem_free(sma);
-		ipc_rcu_putref(sma);
-		return id;
-	}
-	ns->used_sems += nsems;
-
 	sma->sem_base = (struct sem *) &sma[1];
 
 	for (i = 0; i < nsems; i++)
@@ -332,6 +324,15 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 	INIT_LIST_HEAD(&sma->list_id);
 	sma->sem_nsems = nsems;
 	sma->sem_ctime = get_seconds();
+
+	id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
+	if (id < 0) {
+		security_sem_free(sma);
+		ipc_rcu_putref(sma);
+		return id;
+	}
+	ns->used_sems += nsems;
+
 	sem_unlock(sma);
 
 	return sma->sem_perm.id;