linux-kernel - Re: [PATCH] drbd: dynamically allocate shash descriptor

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Message-ID: <CAK8P3a3PDznLXbaQNtFpgtJyP29mh2gGSm8DeSk0NfZCgZQ_kA@mail.gmail.com>
Date:   Mon, 17 Jun 2019 22:38:49 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Roland Kammerer <roland.kammerer@...bit.com>
Cc:     Philipp Reisner <philipp.reisner@...bit.com>,
        Lars Ellenberg <lars.ellenberg@...bit.com>,
        Jens Axboe <axboe@...nel.dk>,
        Eric Biggers <ebiggers@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Kees Cook <keescook@...omium.org>, drbd-dev@...ts.linbit.com,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drbd: dynamically allocate shash descriptor

On Mon, Jun 17, 2019 at 4:36 PM Roland Kammerer
<roland.kammerer@...bit.com> wrote:
> > @@ -5572,6 +5579,7 @@ static int drbd_do_auth(struct drbd_connection *connection)
> >       kfree(response);
> >       kfree(right_response);
> >       shash_desc_zero(desc);
> > +     kfree(desc);
> >
> >       return rv;
> >  }
>
> Hi Arnd,
>
> are you sure your cleanup is okay?
>
> >       shash_desc_zero(desc);
> > +     kfree(desc);
>
> You shash_desc_zero() a potential NULL pointer. memzero_expicit() in the
> function then dereferences it:
>
> memzero_explicit(desc,
>         sizeof(*desc) + crypto_shash_descsize(desc->tfm));
>
> Maybe some if (desc) guard?

Good catch. I guess kzfree() would have been the right thing to call.

        Arnd