From: David Howells <dhowells@redhat.com>
Subject: Re: [PATCH v2] keys/encrypted: Fix two crypto-on-the-stack bugs
Date: Wed, 14 Dec 2016 08:37:59 +0000
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Cc: dhowells@redhat.com, Andy Lutomirski <luto@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>, keyrings@vger.kernel.org,
        Eric Biggers <ebiggers3@gmail.com>,
        linux-crypto@vger.kernel.org,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Stephan Mueller <smueller@chronox.de>
To: Andy Lutomirski <luto@amacapital.net>
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Andy Lutomirski <luto@amacapital.net> wrote:

> > -       sg_set_buf(&sg_out[1], pad, sizeof pad);
> > +       sg_set_buf(&sg_out[1], empty_zero_page, 16);
> 
> My fix here is obviously bogus (I meant to use ZERO_PAGE(0)), but what
> exactly is the code trying to do?  The old code makes no sense.  It's
> setting the *output* buffer to zeroed padding.

Padding goes into the encrypt function and is going to come out of the decrypt
function.  Possibly derived_key_decrypt() should be checking that the padding
that comes out is actually a bunch of zeros.  Maybe we don't actually need to
get the padding out, but I'm not sure whether the crypto layer will
malfunction if we don't give it a buffer for the padding.

David