From mboxrd@z Thu Jan  1 00:00:00 1970
From: ebiederm@xmission.com (Eric W. Biederman)
Subject: Re: [RFC][PATCH 4/3] vfs: Allow rmdir to remove mounts in all but the current mount namespace
Date: Fri, 11 Oct 2013 18:39:53 -0700
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Cc: Andy Lutomirski <luto@amacapital.net>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Linux-Fsdevel <linux-fsdevel@vger.kernel.org>,
	Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Rob Landley <rob@landley.net>,
	Linus Torvalds <torvalds@linux-foundation.org>
To: Miklos Szeredi <miklos@szeredi.hu>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <87iox38fkv.fsf@xmission.com> (Eric W. Biederman's message of
	"Fri, 11 Oct 2013 18:04:32 -0700")
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

ebiederm@xmission.com (Eric W. Biederman) writes:

> Miklos Szeredi <miklos@szeredi.hu> writes:
>
>> On Thu, Oct 10, 2013 at 1:43 PM, Eric W. Biederman
>>> Miklos if you as the fuse maintainer aren't worried about network
>>> filesystems, and multiple namespaces I won't worry either.  Especially
>>> since modern versions of fuse aren't affected.
>>
>> I think the above conditions (local mount blocks unlink/rename) are
>> enough to prevent most of the problems, of which there aren't many in
>> any case.
>
> Dumb question.
>
> What prevents someone setting up a race between the fusermount
> permission checks and replacing the destination with a symlink, perhaps
> to /etc/shadow?
>
> Do we need a MS_NOFOLLOW?

Doh!  mount(".",...) works just fine..

My apologies for the silly question.

Eric