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

Stephan Mueller
2020-06-03T11:41:01Z

Am Mittwoch, 3. Juni 2020, 13:09:19 CEST schrieb Dan Carpenter:

Hi Dan,

> On Wed, Jun 03, 2020 at 10:08:56AM +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..33d28016da2d 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 (drbg->jent) {
> >
> > crypto_free_rng(drbg->jent);
> > drbg->jent = NULL;
> >
> > }
>
> free_everything functions never work. For example, "drbg->jent" can be
> an error pointer at this point.
>
> crypto/drbg.c
> 1577 if (!drbg->core) {
> 1578 drbg->core = &drbg_cores[coreref];
> 1579 drbg->pr = pr;
> 1580 drbg->seeded = false;
> 1581 drbg->reseed_threshold = drbg_max_requests(drbg);
> 1582
> 1583 ret = drbg_alloc_state(drbg);
> 1584 if (ret)
> 1585 goto unlock;
> 1586
> 1587 ret = drbg_prepare_hrng(drbg);
> 1588 if (ret)
> 1589 goto free_everything;
> ^^^^^^^^^^^^^^^^^^^^
> If we hit two failures inside drbg_prepare_hrng() then "drbg->jent" can
> be an error pointer.
>
> 1590
> 1591 if (IS_ERR(drbg->jent)) {
> 1592 ret = PTR_ERR(drbg->jent);
> 1593 drbg->jent = NULL;
> 1594 if (fips_enabled || ret != -ENOENT)
> 1595 goto free_everything;
> 1596 pr_info("DRBG: Continuing without Jitter
> RNG\n"); 1597 }
> 1598
> 1599 reseed = false;
> 1600 }
> 1601
> 1602 ret = drbg_seed(drbg, pers, reseed);
> 1603
> 1604 if (ret && !reseed)
> 1605 goto free_everything;
> 1606
> 1607 mutex_unlock(&drbg->drbg_mutex);
> 1608 return ret;
> 1609
> 1610 unlock:
> 1611 mutex_unlock(&drbg->drbg_mutex);
> 1612 return ret;
> 1613
> 1614 free_everything:
> 1615 mutex_unlock(&drbg->drbg_mutex);
> 1616 drbg_uninstantiate(drbg);
> ^^^^
> Leading to an Oops.

Thanks a lot for the hint - a version 2 should come shortly.
>
> 1617 return ret;
> 1618 }
>
> regards,
> dan carpenter

Ciao
Stephan