netdev - [Patch net] net_sched: check noop_qdisc before qdisc_hash

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Message-Id: <1491357091-27064-1-git-send-email-xiyou.wangcong@gmail.com>
Date:   Tue,  4 Apr 2017 18:51:30 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     dvyukov@...gle.com, edumazet@...gle.com,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Kosina <jkosina@...e.cz>
Subject: [Patch net] 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@...gle.com>
Cc: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.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