lkml.org 
[lkml]   [2014]   [Oct]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] [RFC] mnt: add ability to clone mntns starting with the current root
On Tue, Oct 7, 2014 at 2:50 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
> Andy Lutomirski <luto@amacapital.net> writes:
>
>> On Tue, Oct 7, 2014 at 2:26 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
>>> Andy Lutomirski <luto@amacapital.net> writes:
>>>
>>>> Why should MNT_LOCKED on submounts be enforced?
>>>>
>>>> Is it because, if you retain a reference to the detached tree, then
>>>> you can see under the submounts?
>>>
>>> Yes. MNT_DETACH is a recursive operation that detaches all of the mount
>>> and all of it's submounts. Which means you can see under the submounts
>>> if you have a reference to a detached mount.
>>>
>>>> If so, let's fix *that*. Because
>>>> otherwise the whole model of pivot_root + detach will break.
>>>
>>> I am not certain what you are referring to. pivot_root doesn't
>>> manipulate the mount tree so you can see under anything.
>>>
>>> What I believe is the appropriate fix is to fail umount2(...,MNT_DETACH)
>>> if there are any referenced mount points being detached that have a
>>> locked submount.
>>
>> Most of the container-using things do, roughly:
>>
>> Unshare userns and mountns
>> Mount some new stuff
>> pivot_root to the new stuff
>> MNT_DETACH the old.
>>
>> That last step will almost always fail if you make this change.
>
> I don't think so.
>
> I expect I could add full busy detection of normal umounts and those
> applications would not fail.
>
> What I am proposing is a more targeted version of busy detection that
> looks at each mount in the set that detach will unmount. For each mount
> if it is busy with non-submount references and it has at least one
> locked submount fail the detach with -EBUSY.
>
> Do you really think we have userspace references to the one or more of the
> mounts under old?
>

I suspect that we have a userspace reference to old itself.

--Andy

> Eric



--
Andy Lutomirski
AMA Capital Management, LLC


\
 
 \ /
  Last update: 2014-10-08 00:21    [W:0.108 / U:0.068 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site