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

Dan Carpenter
2020-06-03T11:09:48Z

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.

1617 return ret;
1618 }

regards,
dan carpenter