Re: [PATCH v2 15/41] SUNRPC: Enable rpcsec_gss_krb5.ko to be built without CRYPTO_DES

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Chuck Lever <cel@kernel.org>
Cc: linux-nfs@vger.kernel.org, dhowells@redhat.com, simo@redhat.com,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 15/41] SUNRPC: Enable rpcsec_gss_krb5.ko to be built without CRYPTO_DES
Date: Mon, 6 Mar 2023 09:16:18 +0100 (CET)	[thread overview]
Message-ID: <1331f5b4-66cb-4afa-4e81-64cf4bc696d@linux-m68k.org> (raw)
In-Reply-To: <167380331214.10651.11224254824457738270.stgit@bazille.1015granger.net>

 	Hi Chuck,

On Sun, 15 Jan 2023, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
>
> Because the DES block cipher has been deprecated by Internet
> standard, highly secure configurations might require that DES
> support be blacklisted or not installed. NFS Kerberos should still
> be able to work correctly with only the AES-based enctypes in that
> situation.
>
> Also note that MIT Kerberos has begun a deprecation process for DES
> encryption types. Their README for 1.19.3 states:
>
>> Beginning with the krb5-1.19 release, a warning will be issued
>> if initial credentials are acquired using the des3-cbc-sha1
>> encryption type.  In future releases, this encryption type will
>> be disabled by default and eventually removed.
>>
>> Beginning with the krb5-1.18 release, single-DES encryption
>> types have been removed.
>
> Aside from the CONFIG option name change, there are two important
> policy changes:
>
> 1. The 'insecure enctype' group is now disabled by default.
>   Distributors have to take action to enable support for deprecated
>   enctypes. Implementation of these enctypes will be removed in a
>   future kernel release.
>
> 2. des3-cbc-sha1 is now considered part of the 'insecure enctype'
>   group, having been deprecated by RFC 8429, and is thus disabled
>   by default
>
> After this patch is applied, SunRPC support can be built with
> Kerberos 5 support but without CRYPTO_DES enabled in the kernel.
> And, when these enctypes are disabled, the Linux kernel's SunRPC
> RPCSEC GSS implementation fully complies with BCP 179 / RFC 6649
> and BCP 218 / RFC 8429.
>
> Tested-by: Scott Mayhew <smayhew@redhat.com>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Thanks for your patch, which is now commit dfe9a123451a6e73 ("SUNRPC:
Enable rpcsec_gss_krb5.ko to be built without CRYPTO_DES") in v6.3-rc1.

> --- a/net/sunrpc/Kconfig
> +++ b/net/sunrpc/Kconfig
> @@ -19,10 +19,10 @@ config SUNRPC_SWAP
> config RPCSEC_GSS_KRB5
> 	tristate "Secure RPC: Kerberos V mechanism"
> 	depends on SUNRPC && CRYPTO
> -	depends on CRYPTO_MD5 && CRYPTO_DES && CRYPTO_CBC && CRYPTO_CTS
> -	depends on CRYPTO_ECB && CRYPTO_HMAC && CRYPTO_SHA1 && CRYPTO_AES
> 	default y
> 	select SUNRPC_GSS
> +	select CRYPTO_SKCIPHER
> +	select CRYPTO_HASH
> 	help
> 	  Choose Y here to enable Secure RPC using the Kerberos version 5
> 	  GSS-API mechanism (RFC 1964).

While updating my defconfigs for v6.3-rc1, I noticed this change has an
interesting side-effect: if any of the CRYPTO_* algorithms were modular
before, RPCSEC_GSS_KRB5 was modular, too.
After this change, RPCSEC_GSS_KRB5 is promoted to builtin.

This is not necessarily bad in-se, but you might want to be aware of it,
and perhaps change the "default y".

Gr{oetje,eeting}s,

 						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
 							    -- Linus Torvalds