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 18:05:26 +0100
From:	David Howells <dhowells@...hat.com>
To:	ebiederm@...ssion.com (Eric W. Biederman)
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, simo@...hat.com
Subject: Re: [PATCH 2/2] KEYS: Add per-user_namespace registers for persistent per-UID kerberos caches

Eric W. Biederman <ebiederm@...ssion.com> wrote:

> > The cache returned is a keyring named "_krb.<uid>" that the possessor can
> > read, search, clear, invalidate, unlink from and add links to.  SELinux
> > and co. get a say as to whether this call will succeed as the caller must
> > have LINK permission on the cache keyring.
> 
> I think it would be more accurate to say you use the existing LSM
> security hooks for security keys.

Yes.

> Calling out SELinux in particular just seems odd as there is absolutely
> nothing SELinux specific in this patch.

Sorry, I normally think of SELinux as that's what I usually deal with.  Yes,
any and all LSMs.

> > +		    !nsown_capable(CAP_SETUID))
>
> You you make this ns_capable(ns, CAP_SETUID);
> 
> nsown_capable is the right thing here but I am trying to remove the
> function because it makes it too easy to not think about which
> user namespace you are in.

Okay.

> > +	index_key.desc_len = sprintf(buf, "_krb.%u", __kuid_val(uid));
> 
> Please don't use the implementation detail __kuid_val.  Please use
> from_kuid(&init_user_ns, uid) instead so it is explicitly documented
> which user namespace you are using.

Actually, I don't want that either.  I want the user-visible UID from the
namespace.

David
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