net_sched: check noop_qdisc before qdisc_hash_add()

Dmitry reported a crash when injecting faults in
attach_one_default_qdisc() and dev->qdisc is still
a noop_disc, the check before qdisc_hash_add() fails
to catch it because it tests NULL. We should test
against noop_qdisc since it is the default qdisc
at this point.

Fixes: 59cc1f61f09c ("net: sched: convert qdisc linked list to hashtable")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index b052b27a984e39c244c94132f1162a7033e5cc63..1a2f9e964330a5cd0c0b9a5cac91807221b0ffd9 100644 (file)
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -794,7 +794,7 @@ static void attach_default_qdiscs(struct net_device *dev)
                }
        }
 #ifdef CONFIG_NET_SCHED
-       if (dev->qdisc)
+       if (dev->qdisc != &noop_qdisc)
                qdisc_hash_add(dev->qdisc);
 #endif
 }