netdev - Re: size overflow in function qdisc_tree_decrease_qlen net/sched/sch

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Date:	Tue, 01 Dec 2015 06:10:11 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Daniele Fucini <dfucini@...il.com>
Cc:	Cong Wang <cwang@...pensource.com>,
	netdev <netdev@...r.kernel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	David Miller <davem@...emloft.net>, spender@...ecurity.net,
	pageexec@...email.hu, re.emese@...il.com
Subject: Re: size overflow in function qdisc_tree_decrease_qlen
 net/sched/sch_api.c

On Tue, 2015-12-01 at 06:06 -0800, Eric Dumazet wrote:
> On Tue, 2015-12-01 at 12:19 +0100, Daniele Fucini wrote:
> > Thanks for the reply. Here's the output of `tc qdisc show`:
> > https://gist.github.com/1847102c8fe08f63e9e7

> Hmm... I do not think we ever took care of MQ in
> qdisc_tree_decrease_qlen()

This looks like a false positive, because MQ recomputes backlog/qlen at
the time (stats) dumps are requested.

I would say there is no bug.

static int mq_dump(struct Qdisc *sch, struct sk_buff *skb)
{
        struct net_device *dev = qdisc_dev(sch);
        struct Qdisc *qdisc;
        unsigned int ntx;

        sch->q.qlen = 0;
        memset(&sch->bstats, 0, sizeof(sch->bstats));
        memset(&sch->qstats, 0, sizeof(sch->qstats));

        for (ntx = 0; ntx < dev->num_tx_queues; ntx++) {
                qdisc = netdev_get_tx_queue(dev, ntx)->qdisc_sleeping;
                spin_lock_bh(qdisc_lock(qdisc));
                sch->q.qlen             += qdisc->q.qlen;
                sch->bstats.bytes       += qdisc->bstats.bytes;
                sch->bstats.packets     += qdisc->bstats.packets;
                sch->qstats.backlog     += qdisc->qstats.backlog;
                sch->qstats.drops       += qdisc->qstats.drops;
                sch->qstats.requeues    += qdisc->qstats.requeues;
                sch->qstats.overlimits  += qdisc->qstats.overlimits;
                spin_unlock_bh(qdisc_lock(qdisc));
        }
        return 0;
}


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