From: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
To: Gao feng <gaofeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
Cc: Linux FS Devel
<linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Linux Containers
<containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>,
"Eric W. Biederman"
<ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
Subject: Re: [REVIEW][PATCH 1/2] userns: Better restrictions on when proc and sysfs can be mounted
Date: Thu, 14 Nov 2013 08:54:24 -0800 [thread overview]
Message-ID: <CALCETrXtWtF=JgiwENNzh7UZKnXijHauOQ5ZjHYxYJC-BAU5Aw@mail.gmail.com> (raw)
In-Reply-To: <5284AF90.7060506-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
On Thu, Nov 14, 2013 at 3:10 AM, Gao feng <gaofeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org> wrote:
> On 11/13/2013 03:26 PM, Gao feng wrote:
>> On 11/09/2013 01:42 PM, Eric W. Biederman wrote:
>>> Right now I would rather not have the empty directory exception than
>>> remove this code.
>>>
>>> The test is a little trickier to write than it might otherwise be
>>> because /proc and /sys tend to be slightly imperfect filesystems.
>>>
>>> I think the only way to really test that is to call readdir on the
>>> directory itself :( I don't like that thought.
>>>
>>> I don't know what I was thinking when I wrote that test but I definitely
>>> goofed up. Grr!
>>>
>>> I can certainly filter out any directory with nlink > 2. That would be
>>> an easy partial step forward.
>>>
>>> The real question though is how do I detect directories it is safe to
>>> mount on where there will not be files in them. I can't call iterate
>>> with the namespace_lock held so things are a bit tricky.
>>>
>>
>> I know this problem is not easy to be resolved. why not let the user
>> make the decision? maybe we can introduce a new mount option MS_LOCK,
>> if user wants to use mount to hide something, he should use mount with
>> option MS_LOCK. so the unpriviged user can't umount this filesystem and
>> fail to mount the filesystem if one of it's child mount is mounted with
>> MS_LOCK option otherwise he use MS_REC too.
>>
>
> Something like this.
>
> From 437f33ea366623c7a9d557b2e84cae424876a44f Mon Sep 17 00:00:00 2001
> From: Gao feng <gaofeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
> Date: Wed, 13 Nov 2013 16:06:46 +0800
> Subject: [PATCH] userns: introduce new mount option MS_LOCK
>
> After commit 5ff9d8a65ce80efb509ce4e8051394e9ed2cd942
> vfs: Lock in place mounts from more privileged users,
> in userns, the mounts of child mntns which copied from
> parent mntns is locked and user has no rights to umount/move
> them, it's too strict.
>
> The core purpose of above commit is trying to prevent
> unprivileged user from accessing files hidden by mount.
> This patch introduces a new mount option MS_LOCK, this
> gives user the capable to mount filesystem as the type
> of lock if he wants to use mount to hide something.
>
This is bad -- if something was secure in old kernels, it needs to
stay secure. If you had MS_NOT_A_LOCK, that would be okay, but it
might not solve your problem.
--Andy
next prev parent reply other threads:[~2013-11-14 16:54 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-27 21:44 [REVIEW][PATCH 1/2] userns: Better restrictions on when proc and sysfs can be mounted Eric W. Biederman
[not found] ` <878uzmhkqg.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2013-08-27 21:46 ` [REVIEW][PATCH 2/2] sysfs: Restrict mounting sysfs Eric W. Biederman
[not found] ` <874naahkng.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2013-08-28 19:00 ` Greg Kroah-Hartman
2013-09-23 10:33 ` James Hogan
[not found] ` <524018EA.9070202-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
2013-09-23 21:41 ` [PATCH] sysfs: Allow mounting without CONFIG_NET Eric W. Biederman
[not found] ` <87ioxrrzb6.fsf_-_-HxuHnoDHeQZYhcs0q7wBk77fW72O3V7zAL8bYrjMMd8@public.gmane.org>
2013-09-24 11:25 ` James Hogan
2013-08-27 21:47 ` [REVIEW][PATCH 1/2] userns: Better restrictions on when proc and sysfs can be mounted Andy Lutomirski
[not found] ` <CALCETrWPDzuoaJp2ko5jAbwYUBqSdPjvO5uGo-gZVsS4Wm1PKQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2013-08-27 21:57 ` Eric W. Biederman
2013-09-01 4:45 ` Eric W. Biederman
[not found] ` <87eh99noa0.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2013-09-03 17:40 ` Andy Lutomirski
2013-11-02 6:06 ` Gao feng
[not found] ` <52749663.2000701-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
2013-11-04 7:00 ` Janne Karhunen
[not found] ` <CAE=NcrY+CzX+H4XQTdGj7CSZ98a5T=bNgT6=jGZzcjyaHb-ttw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2013-11-09 5:22 ` Eric W. Biederman
2013-11-08 2:33 ` Gao feng
[not found] ` <527C4D88.10907-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
2013-11-09 5:42 ` Eric W. Biederman
[not found] ` <87k3gigmgj.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2013-11-13 7:26 ` Gao feng
[not found] ` <5283299B.8080702-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
2013-11-14 11:10 ` Gao feng
[not found] ` <5284AF90.7060506-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
2013-11-14 16:54 ` Andy Lutomirski [this message]
2013-11-15 1:16 ` Gao feng
[not found] ` <528575EC.2030309-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
2013-11-15 4:54 ` Eric W. Biederman
[not found] ` <87txfexo25.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2013-11-15 6:14 ` Gao feng
[not found] ` <5285BBE2.7010001-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
2013-11-15 8:37 ` Eric W. Biederman
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