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

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Date:   Wed, 14 Dec 2016 13:04:04 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        David Howells <dhowells@...hat.com>, keyrings@...r.kernel.org,
        Eric Biggers <ebiggers3@...il.com>,
        linux-crypto@...r.kernel.org, Stephan Mueller <smueller@...onox.de>
Subject: Re: [PATCH v2] keys/encrypted: Fix two crypto-on-the-stack bugs

On Tue, Dec 13, 2016 at 06:53:03PM -0800, Andy Lutomirski wrote:
> On Tue, Dec 13, 2016 at 6:48 PM, Andy Lutomirski <luto@...nel.org> wrote:
> > The driver put a constant buffer of all zeros on the stack and
> > pointed a scatterlist entry at it in two places.  This doesn't work
> > with virtual stacks.  Use ZERO_PAGE instead.
> 
> Wait a second...
> 
> > -       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.

It's decrypting so I presume it just needs to the extra space for
the padding and the result will be thrown away.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt