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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, Eric Dumazet <edumazet@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 205/220] net: sched: avoid writing on noop_qdisc
Date:   Fri, 22 Nov 2019 11:29:30 +0100
Message-Id: <20191122100928.564216161@linuxfoundation.org>
In-Reply-To: <20191122100912.732983531@linuxfoundation.org>
References: <20191122100912.732983531@linuxfoundation.org>
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From: Eric Dumazet <edumazet@google.com>

[ Upstream commit f98ebd47fd0da1717267ce1583a105d8cc29a16a ]

While noop_qdisc.gso_skb and noop_qdisc.skb_bad_txq are not used
in other places, it seems not correct to overwrite their fields
in dev_init_scheduler_queue().

noop_qdisc is essentially a shared and read-only object, even if
it is not marked as const because of some implementation detail.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/sched/sch_generic.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 30e32df5f84a7..8a4d01e427a22 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -577,6 +577,18 @@ struct Qdisc noop_qdisc = {
 	.dev_queue	=	&noop_netdev_queue,
 	.running	=	SEQCNT_ZERO(noop_qdisc.running),
 	.busylock	=	__SPIN_LOCK_UNLOCKED(noop_qdisc.busylock),
+	.gso_skb = {
+		.next = (struct sk_buff *)&noop_qdisc.gso_skb,
+		.prev = (struct sk_buff *)&noop_qdisc.gso_skb,
+		.qlen = 0,
+		.lock = __SPIN_LOCK_UNLOCKED(noop_qdisc.gso_skb.lock),
+	},
+	.skb_bad_txq = {
+		.next = (struct sk_buff *)&noop_qdisc.skb_bad_txq,
+		.prev = (struct sk_buff *)&noop_qdisc.skb_bad_txq,
+		.qlen = 0,
+		.lock = __SPIN_LOCK_UNLOCKED(noop_qdisc.skb_bad_txq.lock),
+	},
 };
 EXPORT_SYMBOL(noop_qdisc);
 
@@ -1253,8 +1265,6 @@ static void dev_init_scheduler_queue(struct net_device *dev,
 
 	rcu_assign_pointer(dev_queue->qdisc, qdisc);
 	dev_queue->qdisc_sleeping = qdisc;
-	__skb_queue_head_init(&qdisc->gso_skb);
-	__skb_queue_head_init(&qdisc->skb_bad_txq);
 }
 
 void dev_init_scheduler(struct net_device *dev)
-- 
2.20.1