linux-kernel - Re: [PATCH v4 03/21] fs: Allow sysfs and cgroupfs to share super blocks between user namespaces

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Date:	Wed, 18 May 2016 11:27:12 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Seth Forshee <seth.forshee@...onical.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Miklos Szeredi <mszeredi@...hat.com>,
	Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
	linux-kernel@...r.kernel.org, linux-bcache@...r.kernel.org,
	dm-devel@...hat.com, linux-raid@...r.kernel.org,
	linux-mtd@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
	fuse-devel@...ts.sourceforge.net,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
	cgroups@...r.kernel.org
Subject: Re: [PATCH v4 03/21] fs: Allow sysfs and cgroupfs to share super blocks between user namespaces

Seth Forshee <seth.forshee@...onical.com> writes:

> On Wed, May 18, 2016 at 10:45:31AM -0500, Eric W. Biederman wrote:
>> > But if we do that it violates some of the assumptions of the patch to
>> > rework MNT_NODEV on your testing branch (and also those behind patch 2
>> > in this series). Something will need to be changed there to prevent a
>> > regression in mount behavior when a user ns tries to mount without
>> > MNT_NODEV when the mount inherited from its parent has it set.
>> 
>> Thank you for pointing that out.  I will look into that.
>> 
>> I believe I know exactly what you are talking about.  Of the choices I
>> think it is better to a minor localized change in the fs_fully_visible
>> logic than it is to cause problems elsewhere.
>
> Agreed.
>
>> >> Apologies for not catching this earlier.
>> >
>> > Actually this is a more recent patch, so you possibly hadn't seen it
>> > before.
>> >
>> >> I am looking at folding all of this into the patch that introduces
>> >> sget_userns so that even bisects won't have regresssions.
>> >
>> > That's fine with me.
>> 
>> And thank you for keeping everything as separate patches.  That is at
>> least helping me catch up.  Even if I don't agree that these things
>> should be separate come merge time.
>
> Honestly I probably would have squashed some of them into that first
> patch myself if you hadn't already applied it to your testing branch, so
> that's all just luck.
>
> Keep in mind that I also have that patch for mqueue that isn't in this
> series, and I haven't yet checked to see if the 4.7 merges introduce
> anything which is going to require updating these patches. I was
> planning to wait and send out updates after -rc1, but if you want that
> stuff sooner just let me know.

As unfortunately I don't have anything going into -rc1 I am working on
this right now.

Let me finish sorting out the sget_userns and mnt nodev mess and I will
push something out and then we can compare notes.  I think I have mqueue
covered by other changes.  As it is in the set of filesystems that
should just use sget_userns.

I am sorting through the nodev corner of this now.  It should just be a
day or two.

Eric