Date:   Thu, 12 Nov 2020 13:39:26 -0500
From:   Chuck Lever <chuck.lever@...cle.com>
To:     Bruce Fields <bfields@...ldses.org>
Cc:     David Howells <dhowells@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        linux-crypto@...r.kernel.org, linux-afs@...ts.infradead.org,
        CIFS <linux-cifs@...r.kernel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 00/18] crypto: Add generic Kerberos library



> On Nov 12, 2020, at 1:37 PM, J. Bruce Fields <bfields@...ldses.org> wrote:
> 
> On Thu, Nov 12, 2020 at 12:57:45PM +0000, David Howells wrote:
>> 
>> Hi Herbert, Bruce,
>> 
>> Here's my first cut at a generic Kerberos crypto library in the kernel so
>> that I can share code between rxrpc and sunrpc (and cifs?).
>> 
>> I derived some of the parts from the sunrpc gss library and added more
>> advanced AES and Camellia crypto.  I haven't ported across the DES-based
>> crypto yet - I figure that can wait a bit till the interface is sorted.
>> 
>> Whilst I have put it into a directory under crypto/, I haven't made an
>> interface that goes and loads it (analogous to crypto_alloc_skcipher,
>> say).  Instead, you call:
>> 
>>        const struct krb5_enctype *crypto_krb5_find_enctype(u32 enctype);
>> 
>> to go and get a handler table and then use a bunch of accessor functions to
>> jump through the hoops.  This is basically the way the sunrpc gsslib does
>> things.  It might be worth making it so you do something like:
>> 
>> 	struct crypto_mech *ctx = crypto_mech_alloc("krb5(18)");
>> 
>> to get enctype 18, but I'm not sure if it's worth the effort.  Also, I'm
>> not sure if there are any alternatives to kerberos we will need to support.
> 
> We did have code for a non-krb5 mechanism at some point, but it was torn
> out.  So I don't think that's a priority.
> 
> (Chuck, will RPC-over-SSL need a new non-krb5 mechanism?)

No, RPC-over-TLS does not involve the GSS infrastructure in any way.


>> There are three main interfaces to it:
>> 
>> (*) I/O crypto: encrypt, decrypt, get_mic and verify_mic.
>> 
>>     These all do in-place crypto, using an sglist to define the buffer
>>     with the data in it.  Is it necessary to make it able to take separate
>>     input and output buffers?
> 
> I don't know.  My memory is that the buffer management in the existing
> rpcsec_gss code is complex and fragile.  See e.g. the long comment in
> gss_krb5_remove_padding.

And even worse, the buffer handling is slightly different in the NFS
client and server code paths.


> --b.
> 
>> (*) PRF+ calculation for key derivation.
>> (*) Kc, Ke, Ki derivation.
>> 
>>     These use krb5_buffer structs to pass objects around.  This is akin to
>>     the xdr_netobj, but has a void* instead of a u8* data pointer.
>> 
>> In terms of rxrpc's rxgk, there's another step in key derivation that isn't
>> part of the kerberos standard, but uses the PRF+ function to generate a key
>> that is then used to generate Kc, Ke and Ki.  Is it worth putting this into
>> the directory or maybe having a callout to insert an intermediate step in
>> key derivation?
>> 
>> Note that, for purposes of illustration, I've included some rxrpc patches
>> that use this interface to implement the rxgk Rx security class.  The
>> branch also is based on some rxrpc patches that are a prerequisite for
>> this, but the crypto patches don't need it.
>> 
>> ---
>> The patches can be found here also:
>> 
>> 	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=crypto-krb5
>> 
>> David
>> ---
>> David Howells (18):
>>      crypto/krb5: Implement Kerberos crypto core
>>      crypto/krb5: Add some constants out of sunrpc headers
>>      crypto/krb5: Provide infrastructure and key derivation
>>      crypto/krb5: Implement the Kerberos5 rfc3961 key derivation
>>      crypto/krb5: Implement the Kerberos5 rfc3961 encrypt and decrypt functions
>>      crypto/krb5: Implement the Kerberos5 rfc3961 get_mic and verify_mic
>>      crypto/krb5: Implement the AES enctypes from rfc3962
>>      crypto/krb5: Implement crypto self-testing
>>      crypto/krb5: Implement the AES enctypes from rfc8009
>>      crypto/krb5: Implement the AES encrypt/decrypt from rfc8009
>>      crypto/krb5: Add the AES self-testing data from rfc8009
>>      crypto/krb5: Implement the Camellia enctypes from rfc6803
>>      rxrpc: Add the security index for yfs-rxgk
>>      rxrpc: Add YFS RxGK (GSSAPI) security class
>>      rxrpc: rxgk: Provide infrastructure and key derivation
>>      rxrpc: rxgk: Implement the yfs-rxgk security class (GSSAPI)
>>      rxrpc: rxgk: Implement connection rekeying
>>      rxgk: Support OpenAFS's rxgk implementation
>> 
>> 
>> crypto/krb5/Kconfig              |    9 +
>> crypto/krb5/Makefile             |   11 +-
>> crypto/krb5/internal.h           |  101 +++
>> crypto/krb5/kdf.c                |  223 ++++++
>> crypto/krb5/main.c               |  190 +++++
>> crypto/krb5/rfc3961_simplified.c |  732 ++++++++++++++++++
>> crypto/krb5/rfc3962_aes.c        |  140 ++++
>> crypto/krb5/rfc6803_camellia.c   |  249 ++++++
>> crypto/krb5/rfc8009_aes2.c       |  440 +++++++++++
>> crypto/krb5/selftest.c           |  543 +++++++++++++
>> crypto/krb5/selftest_data.c      |  289 +++++++
>> fs/afs/misc.c                    |   13 +
>> include/crypto/krb5.h            |  100 +++
>> include/keys/rxrpc-type.h        |   17 +
>> include/trace/events/rxrpc.h     |    4 +
>> include/uapi/linux/rxrpc.h       |   17 +
>> net/rxrpc/Kconfig                |   10 +
>> net/rxrpc/Makefile               |    5 +
>> net/rxrpc/ar-internal.h          |   20 +
>> net/rxrpc/conn_object.c          |    2 +
>> net/rxrpc/key.c                  |  319 ++++++++
>> net/rxrpc/rxgk.c                 | 1232 ++++++++++++++++++++++++++++++
>> net/rxrpc/rxgk_app.c             |  424 ++++++++++
>> net/rxrpc/rxgk_common.h          |  164 ++++
>> net/rxrpc/rxgk_kdf.c             |  271 +++++++
>> net/rxrpc/security.c             |    6 +
>> 26 files changed, 5530 insertions(+), 1 deletion(-)
>> create mode 100644 crypto/krb5/kdf.c
>> create mode 100644 crypto/krb5/rfc3961_simplified.c
>> create mode 100644 crypto/krb5/rfc3962_aes.c
>> create mode 100644 crypto/krb5/rfc6803_camellia.c
>> create mode 100644 crypto/krb5/rfc8009_aes2.c
>> create mode 100644 crypto/krb5/selftest.c
>> create mode 100644 crypto/krb5/selftest_data.c
>> create mode 100644 net/rxrpc/rxgk.c
>> create mode 100644 net/rxrpc/rxgk_app.c
>> create mode 100644 net/rxrpc/rxgk_common.h
>> create mode 100644 net/rxrpc/rxgk_kdf.c

--
Chuck Lever

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