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

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Date:	Fri, 2 Aug 2013 15:20:07 -0500
From:	Nico Williams <nico@...ptonector.com>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	David Howells <dhowells@...hat.com>, keyrings@...ux-nfs.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>, simo@...hat.com,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	linux-nfs@...r.kernel.org, krbdev@....edu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] KEYS: Add per-user_namespace registers for persistent
 per-UID kerberos caches

On Fri, Aug 2, 2013 at 8:55 AM, Jeff Layton <jlayton@...hat.com> wrote:
> 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?

POSIX requires valid UIDs to be non-nengative.  POSIX does not require
uid_t to be signed or unsigned.  POSIX does make use of (uid_t)-1 as a
sentinel (e.g., in setreuid(2)).  (uid_t)-1 is special.  Do not use
it.

As an aside, note that on Solaris 10 and less uid_t was signed, so
UIDs 2^31..2^32-2 were unusable.  Interop with S10 and less requires
that you not use such UIDs.  Ditto gid_t and GIDs.

Also note that in Solaris 11 uid_t is unsigned BUT the range of UIDs
2^31..2^32-2 is still reserved (for automatic, on-demand,
non-persistent allocation for ID mapping purposes).  Interop with S11
requires that you not use such UIDs.  Ditto gid_t and GIDs.

Nico
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