linux-kernel - Re: [RFC][PATCH 4/3] vfs: Allow rmdir to remove mounts in all but the current mount namespace

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Message-ID: <87iox38fkv.fsf@xmission.com>
Date:	Fri, 11 Oct 2013 18:04:32 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Andy Lutomirski <luto@...capital.net>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rob Landley <rob@...dley.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC][PATCH 4/3] vfs: Allow rmdir to remove mounts in all but the current mount namespace

Miklos Szeredi <miklos@...redi.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?

Eric

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