netdev - Re: sha512: make it work, undo percpu message schedule

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Message-ID: <20120113062256.GC12501@secunet.com>
Date:	Fri, 13 Jan 2012 07:22:56 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
	ken@...elabs.ch
Subject: Re: sha512: make it work, undo percpu message schedule

On Wed, Jan 11, 2012 at 11:36:11AM +1100, Herbert Xu wrote:
> On Wed, Jan 11, 2012 at 03:00:40AM +0300, Alexey Dobriyan wrote:
> > commit f9e2bca6c22d75a289a349f869701214d63b5060
> > aka "crypto: sha512 - Move message schedule W[80] to static percpu area"
> > created global message schedule area.
> > 
> > If sha512_update will ever be entered twice, hilarity ensures.
> 
> Hmm, do you know why this happens? On the face of it this shouldn't
> be possible as preemption is disabled.
> 

I did not try to reproduce, but this looks like a race of the 'local out'
and the receive packet path. On 'lokal out' bottom halves are enabled,
so could be interrupted by the NET_RX_SOFTIRQ while doing a sha512_update.
The NET_RX_SOFTIRQ could invoke sha512_update too, that would corrupt the
hash value. My guess could be checked easily by disabling the bottom halves
before the percpu value is fetched.
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