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

Eric Biggers
2020-06-05T06:16:49Z

On Fri, Jun 05, 2020 at 07:58:15AM +0200, Stephan Mueller wrote:
> 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@syzkaller.appspotmail.com
> > > Fixes: 97f2650e5040 ("crypto: drbg - always seeded with SP800-90B ...")
> > > Signed-off-by: Stephan Mueller <smueller@chronox.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.
> >

drbg_seed() and drbg_async_seed() check for drbg->jent being NULL.

Will that now break due it drbg->jent possibly being an ERR_PTR()?

Hence why I'm asking whether drbg_uninstantiate() should set it to NULL.

- Eric