linux-kernel - Re: race condition in crypto larval handling

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Message-ID: <20130908045422.GA31896@gondor.apana.org.au>
Date:	Sun, 8 Sep 2013 14:54:22 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Kees Cook <keescook@...omium.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-crypto@...r.kernel.org, Tyler Hicks <tyhicks@...onical.com>
Subject: Re: race condition in crypto larval handling

On Sun, Sep 08, 2013 at 02:37:03PM +1000, Herbert Xu wrote:
> On Sat, Sep 07, 2013 at 08:34:15PM -0700, Kees Cook wrote:
> >
> > However, I noticed on the "good" path (even without the above patch),
> > I sometimes see a double-kfree triggered by the modprobe process. I
> > can't, however, see how that's happening, since larval_destroy should
> > only be called when refcnt == 0.
> 
> Do you still see this double free with this patch? Without the
> patch it is completely expected as killing the same lavral twice
> will cause memory corruption leading to all sorts of weirdness,
> even if you stop it from deleting the list entry twice.

Actually I know what it is.  sha512 registers two algorithms.
Therefore, it will create two larvals in sequence and then destroy
them in turn.  So it's not a double free at all.  If you put a
printk in crypto_larval_alloc that should confirm this.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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