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

From: David Howells
Date: Fri Aug 02 2013 - 12:53:42 EST

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".

> 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)


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


struct user_namespace
\___ .krb_cache keyring
\___ _krb.0 keyring
\___ _krb.5000 keyring
\___ _krb.5001 keyring
| \___ tkt785 big_key
| \___ tkt12345 big_key
\___ _afs.5000 keyring
\___ 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
\___ 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?

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