linux-kernel - Re: [PATCH v2 15/41] SUNRPC: Enable rpcsec_gss_krb5.ko to be built without CRYPTO

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Message-ID: <CAMuHMdVUMV0grWS7c5N4wCZn+MuN4ysCBqY3zDJjW9q5siBFsQ@mail.gmail.com>
Date:   Mon, 6 Mar 2023 19:01:27 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Chuck Lever III <chuck.lever@...cle.com>
Cc:     Chuck Lever <cel@...nel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        Simo Sorce <simo@...hat.com>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 15/41] SUNRPC: Enable rpcsec_gss_krb5.ko to be built
 without CRYPTO_DES

Hi Chuck,

On Mon, Mar 6, 2023 at 5:17 PM Chuck Lever III <chuck.lever@...cle.com> wrote:
> > On Mar 6, 2023, at 3:16 AM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Sun, 15 Jan 2023, Chuck Lever wrote:
> >> From: Chuck Lever <chuck.lever@...cle.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@...hat.com>
> >> Signed-off-by: Chuck Lever <chuck.lever@...cle.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.
>
> I'm not following. Which CRYPTO_ options trigger the behavior?
> On my test system, CONFIG_RPCSEC_GSS_KRB5=m and the CRYPTO stuff
> is all =y.

On v6.2, "make ARCH=m68k defconfig" gives you
CONFIG_RPCSEC_GSS_KRB5=m
On v6.3, it became builtin, due to dropping the dependencies on
the individual crypto modules.

$ grep -E "CRYPTO_(MD5|DES|CBC|CTS|ECB|HMAC|SHA1|AES)" .config
CONFIG_CRYPTO_AES=y
CONFIG_CRYPTO_AES_TI=m
CONFIG_CRYPTO_DES=m
CONFIG_CRYPTO_CBC=m
CONFIG_CRYPTO_CTS=m
CONFIG_CRYPTO_ECB=m
CONFIG_CRYPTO_HMAC=m
CONFIG_CRYPTO_MD5=m
CONFIG_CRYPTO_SHA1=m

> > This is not necessarily bad in-se, but you might want to be aware of it,
> > and perhaps change the "default y".
>
> Well that might be there to address the need for GSS to be
> enabled if NFSv4 support is built. See commit df486a25900f
> ("NFS: Fix the selection of security flavours in Kconfig")
>
> I'm not claiming I understand exactly how that fix works.

And that was changed again a little bit later in commit
e3b2854faabd1043 ("SUNRPC: Fix the SUNRPC Kerberos V RPCSEC_GSS
module dependencies").

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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