linux-kernel - Re: [PATCH 1/2] autofs4: allow autofs to work outside the initial PID namespace

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Date:	Sat, 24 Nov 2012 22:12:58 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Ian Kent <raven@...maw.net>, autofs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	sukadev@...ux.vnet.ibm.com, serge.hallyn@...onical.com
Subject: Re: [PATCH 1/2] autofs4: allow autofs to work outside the initial PID namespace

On Sat, Nov 24, 2012 at 1:07 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Ian Kent <raven@...maw.net> writes:
>
>> On Sat, 2012-11-24 at 10:23 +0800, Ian Kent wrote:
>>> On Fri, 2012-11-23 at 15:30 +0100, Miklos Szeredi wrote:

>>> AFAICS autofs mounts mounted with MS_PRIVATE in the initial namespace do
>>> propagate to the clone when it's created so I'm assuming subsequent
>>> mounts would also. If these mounts are busy in some way they can't be
>>> umounted in the clone unless "/" is marked private before attempting the
>>> umount.
>>
>> This may sound stupid but if there something like, say, MS_NOPROPAGATE
>> then the problem I see would pretty much just go away. No more need to
>> umount existing mounts and container instances would be isolated. But, I
>> guess, I'm not considering the possibility of cloned of processes as
>> well .... if that makes sense, ;)
>
> Something is very weird is going on.  MS_PRIVATE should be the
> MS_NOPROPOGATE you are looking for.  There is also MS_UNBINDABLE.
> which is a stronger form of MS_PRIVATE and probably worth play with.
>

MS_UNBINDABLE says:  skip this mount when copying a mount tree, such
as when the mount namespace is cloned.

If you set MS_UNBINDABLE on autofs mounts then they will simply not
appear in a cloned namespace.  Which sounds like a good idea,  no?

Thanks,
Miklos
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