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

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Message-ID: <CALCETrWWt33=03gbBs73NkBOunZU+req1BLgUNcEMfh3T1AXUA@mail.gmail.com>
Date:   Wed, 14 Dec 2016 08:22:52 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     David Howells <dhowells@...hat.com>
Cc:     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

On Wed, Dec 14, 2016 at 12:37 AM, David Howells <dhowells@...hat.com> wrote:
> 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.

It was the memset that threw me for a loop.

David, are these encrypted keys ever exported anywhere?  If not, could
the code use a mode that doesn't need padding?

--Andy

>
> David



-- 
Andy Lutomirski
AMA Capital Management, LLC