Re: [RFC PATCH 0/3] move WEP implementation to skcipher interface

From: Eric Biggers <ebiggers@kernel.org>
To: Denis Kenzior <denkenz@gmail.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Marcel Holtmann <marcel@holtmann.org>,
	"open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
	<linux-crypto@vger.kernel.org>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Johannes Berg <johannes@sipsolutions.net>,
	"open list:NFC SUBSYSTEM" <linux-wireless@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [RFC PATCH 0/3] move WEP implementation to skcipher interface
Date: Fri, 7 Jun 2019 14:15:14 -0700	[thread overview]
Message-ID: <20190607211514.GD648@sol.localdomain> (raw)
In-Reply-To: <f40ad169-93b9-636f-9656-634ff331ee2b@gmail.com>

On Fri, Jun 07, 2019 at 03:45:45PM -0500, Denis Kenzior wrote:
> Hi Ard,
> 
> > 
> > Ah ok, good to know. That does imply that the driver is not entirely
> > broken, which is good news I suppose.
> > 
> 
> Not entirely, but we did have to resort to using multiple sockets, otherwise
> parallel encrypt/decrypt operations on the socket would result in invalid
> behavior.  Probably due to the issue Eric already pointed out.
> 
> No such issue with any other ciphers that we use.
> 
> Regards,
> -Denis

Okay, that sucks, so we do have to keep "ecb(arc4)" in the crypto API then.  And
we can't fix its name to be just "arc4".  It's odd that someone would choose to
use AF_ALG over writing a 20 line arc4_crypt() in userspace, but whatever.

Yes, "ecb(arc4)" isn't currently thread safe.  ARC4 uses a single key whereas
modern stream ciphers use a key + IV.  To comply with the crypto API it would
have to copy the key to a stack buffer for each encryption/decryption.  But it
doesn't; it just updates the key instead, making it non thread safe.  If users
are actually relying on that, we'll have to settle for adding a mutex instead.

In any case, we can still remove the 'cipher' algorithm version as Ard is
suggesting, as well as possibly convert the in-kernel users to use an
arc4_crypt() library function and remove the hardware driver support.

- Eric