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

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Message-ID: <20130807162147.GA31460@redhat.com>
Date:	Wed, 7 Aug 2013 18:21:47 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Michael Kerrisk <mtk.manpages@...il.com>
Cc:	Chen Gang <gang.chen@...anux.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 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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