On Fri, 02 Aug 2013 17:53:25 +0100
David Howells <dhowells@xxxxxxxxxx> wrote:
> Jeff Layton <jlayton@xxxxxxxxxx> 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".
>
<facepalm>
Good point. I got confused between -1 and -2. I think Solaris uses
(uid_t)-2 for nobody. Using -1 in this case should be fine.
> > 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
>
That's probably what I'd suggest. Allow one persistent keyring per
user, and expect userland to organize things sanely under it.
nit: I probably wouldn't call the top-level keyring "krb_cache"
though ;)
> 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?
>
Possibly. It really comes down to what sort of lifecycle you expect here.
Some applications might be caught by surprise if the per-user keyring
was already populated in certain situations. OTOH, they have the same
problem if there's even one running process with that uid so maybe it's
not a big deal.
If you do this, it might make sense to allow the admin to tune the
expiry sysctl in such a way that user keyrings go away as soon as
the last reference is gone (maybe by setting it to 0?).
--
Jeff Layton <jlayton@xxxxxxxxxx>
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