From: David Howells <dhowells@redhat.com>
In-Reply-To: <20130802095555.07a2cda3@tlielax.poochiereds.net>
References: <20130802095555.07a2cda3@tlielax.poochiereds.net> <20130801173846.28023.19009.stgit@warthog.procyon.org.uk> <20130801173902.28023.68819.stgit@warthog.procyon.org.uk>
To: Jeff Layton <jlayton@redhat.com>, simo@redhat.com
Cc: dhowells@redhat.com, keyrings@linux-nfs.org, linux-nfs@vger.kernel.org,
        krbdev@mit.edu, "Serge E. Hallyn" <serge.hallyn@ubuntu.com>,
        linux-kernel@vger.kernel.org,
        "Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH 2/2] KEYS: Add per-user_namespace registers for persistent per-UID kerberos caches
Date: Fri, 02 Aug 2013 17:53:25 +0100
Message-ID: <7136.1375462405@warthog.procyon.org.uk>
Sender: linux-nfs-owner@vger.kernel.org

Jeff Layton <jlayton@redhat.com> wrote:

> > +	/* -1 indicates the current user */
> > +	if (_uid == (uid_t)-1) {
> > +		uid = current_uid();
>
> Isn't it possible to have a valid uid of (unsigned int)-1? I know that
> at least some sites use that for "nobody". Why not just require passing
> in the correct UID?

See setresuid() and co. - there -1 is "don't change".

> Looks good overall, but I share Daniel's concerns about making
> krb5-specific infrastructure like this. Essentially this is just a
> persistent keyring that's associated with a kuid, right? Perhaps this
> could be done in such a way that it could be usable for other
> applications in the future?

It's not too hard, I suppose:

	keyctl_get_persistent(uid, prefix, destring)

eg:

	keyctl_get_persistent(-1, "_krb.", KEYCTL_SPEC_PROCESS_KEYRING)

giving:

	struct user_namespace
	  \___ .krb_cache keyring
		\___ _krb.0 keyring
		\___ _krb.5000 keyring
		\___ _krb.5001 keyring
		|	\___ tkt785 big_key
		|	\___ tkt12345 big_key
		\___ _afs.5000 keyring
			\___ afs.redhat.com rxrpc

The other way to do it is create one keyring per user and let userspace create
subkeyrings under that:

	struct user_namespace
	  \___ .krb_cache keyring
		\___ _uid_p.0 keyring
		\___ _uid_p.5000 keyring
		\___ _uid_p.5001 keyring
			\___ krb keyring
			|	\___ tkt785 big_key
			|	\___ tkt12345 big_key
			\___ afs keyring
				\___ afs.redhat.com rxrpc

In the above scheme, it might be worth just making these the same as the user
keyring - which means KEYCTL_SPEC_USER_KEYRING will automatically target it.

Simo:  I believe the problem you have with the user keyring is that it's not
persistent beyond the life of the processes of that UID, right?

David