Date: Wed, 7 Aug 2013 18:21:47 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>,
        Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Chen Gang <gang.chen@asianux.com>, Kees Cook <keescook@chromium.org>,
        Al Viro <viro@zeniv.linux.org.uk>, holt@sgi.com,
        Andrew Morton <akpm@linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] kernel/sys.c: return the current gid when error
	occurs
Message-ID: <20130807162147.GA31460@redhat.com>
References: <5200AD26.8070701@asianux.com> <5200AD67.1030109@asianux.com> <52015ADB.30408@mit.edu>
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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().

And perhaps the man page should be changed. Add Michael.

Oleg.

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