netdev - Re: [PATCH ipsec] xfrm: prevent ipcomp scratch buffer race condition

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Date:	Tue, 15 Oct 2013 22:55:10 +0200
From:	Michal Kubecek <mkubecek@...e.cz>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH ipsec] xfrm: prevent ipcomp scratch buffer race condition

On Tue, Oct 15, 2013 at 10:33:48AM +0200, Steffen Klassert wrote:
> > diff --git a/net/xfrm/xfrm_ipcomp.c b/net/xfrm/xfrm_ipcomp.c
> > index 2906d52..96946fb 100644
> > --- a/net/xfrm/xfrm_ipcomp.c
> > +++ b/net/xfrm/xfrm_ipcomp.c
> > @@ -48,9 +48,11 @@ static int ipcomp_decompress(struct xfrm_state *x, struct sk_buff *skb)
> >  	const int cpu = get_cpu();
> >  	u8 *scratch = *per_cpu_ptr(ipcomp_scratches, cpu);
> >  	struct crypto_comp *tfm = *per_cpu_ptr(ipcd->tfms, cpu);
> > -	int err = crypto_comp_decompress(tfm, start, plen, scratch, &dlen);
> > +	int err;
> >  	int len;
> >  
> > +	local_bh_disable();
> 
> Maybe we could disable the BHs before we fetch the percpu pointers.
> Then we can use smp_processor_id() to get the cpu. With that we
> could get rid of a (now useless) preempt_disable()/preempt_enable()
> pair. Same could be done in ipcomp_compress().

Sounds like a good idea. I'll send v2 after some basic testing.

                                                 Michal Kubecek

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