linux-kernel - Re: [PATCH v2] keys/encrypted: Fix two crypto-on-the-stack bugs

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Message-ID: <18039.1481704679@warthog.procyon.org.uk>
Date:   Wed, 14 Dec 2016 08:37:59 +0000
From:   David Howells <dhowells@...hat.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     dhowells@...hat.com, Andy Lutomirski <luto@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>, keyrings@...r.kernel.org,
        Eric Biggers <ebiggers3@...il.com>,
        linux-crypto@...r.kernel.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Stephan Mueller <smueller@...onox.de>
Subject: Re: [PATCH v2] keys/encrypted: Fix two crypto-on-the-stack bugs

Andy Lutomirski <luto@...capital.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