linux-kernel - Re: [PATCH 1/2] kernel/sys.c: return the current gid when error occurs

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Date:	Wed, 7 Aug 2013 18:35:30 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Al Viro <viro@...iv.linux.org.uk>, holt@....com,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] kernel/sys.c: return the current gid when error occurs

On Wed, Aug 7, 2013 at 6:30 PM, Chen Gang <gang.chen@...anux.com> wrote:
> On 08/08/2013 12:58 AM, Andy Lutomirski wrote:
>> On Wed, Aug 7, 2013 at 9:21 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>>> On 08/06, Andy Lutomirski wrote:
>>>>
>>>> I assume that what the man page means is that the return value is
>>>> whatever fsgid was prior to the call.  On error, fsgid isn't changed, so
>>>> the return value is still "current".
>>>
>>> Probably... Still
>>>
>>>         On success, the previous value of fsuid is returned.
>>>         On error, the current value of fsuid is returned.
>>>
>>> looks confusing. sys_setfsuid() always returns the old value.
>>>
>>>> (FWIW, this behavior is awful and is probably the cause of a security
>>>> bug or three, since success and failure are indistinguishable.
>>>
>>> At least this all looks strange.
>>>
>>> I dunno if we can change this old behaviour. I won't be surprized
>>> if someone already uses setfsuid(-1) as getfsuid().
>>
>
> Oh, really it is.
>
> Hmm... as a pair function, we need add getfsuid() too, if we do not add
> it, it will make negative effect with setfsuid().
>
> Since it is a system call, we have to keep compitable.
>
> So in my opinion, better add getfsuid2()/setfsuid2() instead of current
> setfsuid()

How about getfsuid() and setfsuid2()?

--Andy
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