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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+d5870a903591faaca4ae@syzkaller.appspotmail.com,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Jiri Pirko <jiri@resnulli.us>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@mellanox.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.19 12/79] net_sched: let qdisc_put() accept NULL pointer
Date:   Fri, 20 Sep 2019 00:02:57 +0200
Message-Id: <20190919214808.894122058@linuxfoundation.org>
In-Reply-To: <20190919214807.612593061@linuxfoundation.org>
References: <20190919214807.612593061@linuxfoundation.org>
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From: Cong Wang <xiyou.wangcong@gmail.com>

[ Upstream commit 6efb971ba8edfbd80b666f29de12882852f095ae ]

When tcf_block_get() fails in sfb_init(), q->qdisc is still a NULL
pointer which leads to a crash in sfb_destroy(). Similar for
sch_dsmark.

Instead of fixing each separately, Linus suggested to just accept
NULL pointer in qdisc_put(), which would make callers easier.

(For sch_dsmark, the bug probably exists long before commit
6529eaba33f0.)

Fixes: 6529eaba33f0 ("net: sched: introduce tcf block infractructure")
Reported-by: syzbot+d5870a903591faaca4ae@syzkaller.appspotmail.com
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/sched/sch_generic.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -950,6 +950,9 @@ void qdisc_destroy(struct Qdisc *qdisc)
 	const struct Qdisc_ops  *ops = qdisc->ops;
 	struct sk_buff *skb, *tmp;
 
+	if (!qdisc)
+		return;
+
 	if (qdisc->flags & TCQ_F_BUILTIN ||
 	    !refcount_dec_and_test(&qdisc->refcnt))
 		return;