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

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Date:	Tue, 01 Dec 2015 15:10:31 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cong Wang <cwang@...pensource.com>
Cc:	pageexec@...email.hu, Daniele Fucini <dfucini@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	David Miller <davem@...emloft.net>, spender@...ecurity.net,
	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 14:47 -0800, Cong Wang wrote:
> On Tue, Dec 1, 2015 at 2:33 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Hmm... it looks like we have a much more serious bug :
> >
> > qdisc_lookup() calls qdisc_match_from_root(dev->qdisc, handle) without
> > proper lock being held, so we might actually crash the host,
> > if qdisc_tree_decrease_qlen() happens at the time qdiscs are changed.
> >
> > qdisc_tree_decrease_qlen() needs serious care :(
> 
> Convert qdisc list to RCU protected?

Yes, or/and add a per txqueue list, to shorten lookup times !

If we have a per txqueue list, we do not need RCU as we already own the
qdisc lock.



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