linux-kernel - Re: [PATCH v2] crypto: DRBG - always try to free Jitter RNG instance

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Date:   Fri, 05 Jun 2020 07:58:15 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>, davem@...emloft.net,
        herbert@...dor.apana.org.au, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        syzbot <syzbot+2e635807decef724a1fa@...kaller.appspotmail.com>
Subject: Re: [PATCH v2] crypto: DRBG - always try to free Jitter RNG instance

Am Freitag, 5. Juni 2020, 02:43:36 CEST schrieb Eric Biggers:

Hi Eric,

> On Thu, Jun 04, 2020 at 08:41:00AM +0200, Stephan Müller wrote:
> > The Jitter RNG is unconditionally allocated as a seed source follwoing
> > the patch 97f2650e5040. Thus, the instance must always be deallocated.
> > 
> > Reported-by: syzbot+2e635807decef724a1fa@...kaller.appspotmail.com
> > Fixes: 97f2650e5040 ("crypto: drbg - always seeded with SP800-90B ...")
> > Signed-off-by: Stephan Mueller <smueller@...onox.de>
> > ---
> > 
> >  crypto/drbg.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/crypto/drbg.c b/crypto/drbg.c
> > index 37526eb8c5d5..8a0f16950144 100644
> > --- a/crypto/drbg.c
> > +++ b/crypto/drbg.c
> > @@ -1631,6 +1631,9 @@ static int drbg_uninstantiate(struct drbg_state
> > *drbg)> 
> >  	if (drbg->random_ready.func) {
> >  	
> >  		del_random_ready_callback(&drbg->random_ready);
> >  		cancel_work_sync(&drbg->seed_work);
> > 
> > +	}
> > +
> > +	if (!IS_ERR_OR_NULL(drbg->jent)) {
> > 
> >  		crypto_free_rng(drbg->jent);
> >  		drbg->jent = NULL;
> >  	
> >  	}
> 
> It it okay that ->jent can be left as an ERR_PTR() value?
> 
> Perhaps it should always be set to NULL?

The error value is used in the drbg_instantiate function. There it is checked 
whether -ENOENT (i.e. the cipher is not available) or any other error is 
present. I am not sure we should move that check.

Thanks for the review.
> 
> - Eric


Ciao
Stephan