netdev - Re: [patch] net_sched: stack info leak in cbq_dump

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Date:	Mon, 29 Jul 2013 14:17:25 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	joe@...ches.com
Cc:	dan.carpenter@...cle.com, jhs@...atatu.com, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

From: Joe Perches <joe@...ches.com>
Date: Mon, 29 Jul 2013 13:12:31 -0700

> On Mon, 2013-07-29 at 23:01 +0300, Dan Carpenter wrote:
>> On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
>> > On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
>> > > opt.__reserved isn't cleared so we leak a byte of stack information.
>> > []
>> > > diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
>> > []
>> > > @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
>> > >  	opt.allot = cl->allot;
>> > >  	opt.priority = cl->priority + 1;
>> > >  	opt.cpriority = cl->cpriority + 1;
>> > > +	opt.__reserved = 0;
>> > >  	opt.weight = cl->weight;
>> > >  	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
>> > >  		goto nla_put_failure;
>> > 
>> > Alignment isn't guaranteed here so it'd
>> > probably be better with a memset.
>> > 
>> 
>> Hm...  Which arches would align it differently?
> 
> Hey Dan.
> 
> None so far as I know, but what difference does it make
> when it's a general correctness issue?

Should see if the compiler optimizes the spurious stores away,
and if not we can use an initializer.


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