netdev - Re: [PATCH net] net: Prevent invalid access to skb->prev in __qdisc_drop

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Date:   Thu, 29 Nov 2018 16:00:42 -0800
From:   Christoph Paasch <christoph.paasch@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Christoph Paasch <cpaasch@...le.com>,
        netdev <netdev@...r.kernel.org>, bhole_prashant_q7@....ntt.co.jp,
        tyhicks@...onical.com
Subject: Re: [PATCH net] net: Prevent invalid access to skb->prev in __qdisc_drop_all

On Thu, Nov 29, 2018 at 3:54 PM David Miller <davem@...emloft.net> wrote:
>
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Thu, 29 Nov 2018 15:09:18 -0800
>
> > diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> > index 2c38e3d0792468162ee0dc4137f1400160ab9276..22cd46a600576f286803536d45875cd9d537cdca 100644
> > --- a/net/sched/sch_netem.c
> > +++ b/net/sched/sch_netem.c
> > @@ -431,6 +431,9 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> >         int count = 1;
> >         int rc = NET_XMIT_SUCCESS;
> >
> > +       /* Do not fool qdisc_drop_all() */
> > +       skb->prev = NULL;
> > +
> >         /* Random duplication */
> >         if (q->duplicate && q->duplicate >= get_crandom(&q->dup_cor))
> >                 ++count;
>
> If this works I definitely prefer it to making the entire stack pay the
> price to fix this crash.

Yes, I tried it out and it works.


Christoph