linux-kernel - Re: [PATCH] kernel: user_namespace: always set the return parameter 'new_cred' when call unshare

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Date:	Wed, 21 Aug 2013 13:57:39 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	Serge Hallyn <serge.hallyn@...ntu.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andy Lutomirski <luto@...capital.net>,
	"dhowells@...hat.com" <dhowells@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel: user_namespace: always set the return
	parameter 'new_cred' when call unshare_userns() successfully.

On 08/21, Chen Gang wrote:
>
> On 08/20/2013 10:37 PM, Oleg Nesterov wrote:
> > On 08/20, Serge Hallyn wrote:
> >>
> >>
> >> But the only existing caller (sys_unshare) does in fact initialize it to
> >> NULL.  So while this patch does no harm, is it necessary?
> >
> > Agreed.
> >
> > Plus, with this patch unshare_userns() becomes "inconsistent" compared
> > to other unshare_ helpers.
> >
>
> Hmm... for static functions, they don't need, but for extern functions,
> recommend to do so.
>
>
> For "unshare_ helpers", I find 3 extern functions:
>
>   unshare_files() which already set value.
>   unshare_userns() and unshare_nsproxy_namespaces() which not set.
>
> In my opinion, recommend to always set the return parameter when
> succeed, for the 2 left extern functions.

I do not think that static/extern should make any difference. To me,
the cleanup should make unshare_userns() return "cred *" (or NULL or
ERR_PTR()) But this is subjective and in this case we should change
other unshare_ helpers too. Doesn't worth the trouble.

Oleg.

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