arinc653: avoid array overrun

Incrementing ->sched_index between bounds check and array access may
result in accessing one past the array when that is fully filled
(->num_schedule_entries == ARINC653_MAX_DOMAINS_PER_SCHEDULE).

Fixes: 22787f2e10 ("ARINC 653 scheduler")
Reported-by: Kamil Frankowicz <kamil.frankowicz@cert.pl>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Stewart Hildebrand <stewart@stew.dk>
master commit: 5a1121633f
master date: 2026-03-26 10:47:41 +0100

xen/common/sched/arinc653.c

@@ -550,12 +550,9 @@ a653sched_do_schedule(
 
     /* Switch minor frame or find correct minor frame after a miss */
     while ( (now >= sched_priv->next_switch_time) &&
-        (sched_priv->sched_index < sched_priv->num_schedule_entries) )
-    {
-        sched_priv->sched_index++;
+            (++sched_priv->sched_index < sched_priv->num_schedule_entries) )
         sched_priv->next_switch_time +=
             sched_priv->schedule[sched_priv->sched_index].runtime;
-    }
 
     /*
      * If we exhausted the domains in the schedule and still have time left