[Patch net] net_sched: check noop_qdisc before qdisc_hash_add()

[Cong Wang]

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 <dvyu...@google.com>
Cc: Jiri Kosina <jkos...@suse.cz>
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
---
 net/sched/sch_generic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index b052b27..1a2f9e9 100644
--- 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
 }
-- 
2.5.5