linux-kernel - Re: [PATCH 2/2] KEYS: Add per-user_namespace registers for persistent per-UID kerberos caches

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Date:	Fri, 02 Aug 2013 17:53:25 +0100
From:	David Howells <dhowells@...hat.com>
To:	Jeff Layton <jlayton@...hat.com>, simo@...hat.com
Cc:	dhowells@...hat.com, keyrings@...ux-nfs.org,
	linux-nfs@...r.kernel.org, krbdev@....edu,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH 2/2] KEYS: Add per-user_namespace registers for persistent per-UID kerberos caches

Jeff Layton <jlayton@...hat.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
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