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From: Andy Lutomirski <luto@amacapital.net>
Date: Wed, 9 Oct 2013 13:09:17 -0700
Message-ID: <CALCETrUqXTj7T_bYOgwMiO_kcU=NPD_+ck+Z=JsmXuUJJGshuQ@mail.gmail.com>
Subject: Re: Grrrr fusermount.
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>, "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>
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On Wed, Oct 9, 2013 at 12:12 PM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
> ebiederm@xmission.com (Eric W. Biederman) writes:
>
>> But I will go through and read the old fusermount code before I get too
>> much farther just so I understand what I am potentially breaking.
>
> Grr.
>
> So I have just read the fusermount umount code and the hack that it uses
> before there was UMOUNT_NOFOLLOW support in the vm.
>
> If I walk this path of lazy unmounts and detaching directories, anyone
> with a new kernel and an old copy of fusermount and a nfs mounted home
> directory will be able to exploit the fusermount umount symlink race.
>
> Unless we can declare that old fusermount binaries are buggy beyond
> supporting this patchset as it exists is dead.

What's the hack that it does?

--Andy