linux-kernel - Re: Doing crypto in small stack buffers (bluetooth vs vmalloc-stack crash, etc)

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Message-ID: <CALCETrUWyNz91WO6O3dNb+YELeZy5q4+oTo6dLRR67P2WvBB8g@mail.gmail.com>
Date:	Wed, 22 Jun 2016 14:48:24 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Andy Lutomirski <luto@...nel.org>, linux-bluetooth@...r.kernel.org,
	Johan Hedberg <johan.hedberg@...il.com>,
	Gustavo Padovan <gustavo@...ovan.org>,
	Marcel Holtmann <marcel@...tmann.org>,
	linux-crypto@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Doing crypto in small stack buffers (bluetooth vs vmalloc-stack
 crash, etc)

On Tue, Jun 21, 2016 at 5:52 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Tue, Jun 21, 2016 at 5:42 PM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
>> On Tue, Jun 21, 2016 at 10:43:40AM -0700, Andy Lutomirski wrote:
>>>
>>> Is there a straightforward way that bluetooth and, potentially, other
>>> drivers can just do synchronous crypto in a small buffer specified by
>>> its virtual address?  The actual cryptography part of the crypto code
>>> already works this way, but I can't find an API for it.
>>
>> Yes, single block users should use crypto_cipher_encrypt_one, an
>> example would be drivers/md/dm-crypt.c.
>>
>
> Aha!  I expected something like that to exist, but I couldn't find it.
> I'll change the two offenders I've found so far to use it.
>

Before I do this, can you explain what the difference is between
crypto_cipher and crypto_skcipher?  net/bluetooth/smp.c currently uses
crypto_alloc_skcipher, which you added in:

commit 71af2f6bb22a4bf42663e10f1d8913d4967ed07f
Author: Herbert Xu <herbert@...dor.apana.org.au>
Date:   Sun Jan 24 21:18:30 2016 +0800

    Bluetooth: Use skcipher and hash

Am I just supposed to replace "skcipher" with "cipher" everywhere?

--Andy