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

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Message-ID: <20200605004336.GC148196@sol.localdomain>
Date:   Thu, 4 Jun 2020 17:43:36 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Stephan Müller <smueller@...onox.de>
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

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?

- Eric