linux-kernel - Re: [PATCH] devpts: Make ptmx be owned by the userns owner instead of userns-local 0

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Date:	Tue, 15 Mar 2016 11:21:23 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Serge Hallyn <serge.hallyn@...ntu.com>
Cc:	gnome-os-list@...me.org,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	mclasen@...hat.com,
	Linux Containers <containers@...ts.linux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] devpts: Make ptmx be owned by the userns owner instead of
 userns-local 0

On Mar 14, 2016 1:35 AM, "Serge Hallyn" <serge.hallyn@...ntu.com> wrote:
>
> Quoting Andy Lutomirski (luto@...nel.org):
> > We used to have ptmx be owned by the inner uid and gid 0.  Change
> > this: if the owner and group are both mapped but are not both 0,
> > then use the owner instead.
> >
> > For container-style namespaces (LXC, etc), this should have no
> > effect -- UID 0 is will either be the owner or will be unmapped.
>
> This doesn't seem right - it's often the case that the owner is mapped
> in as non-0 uid, safe or not.  The actual namespace root uid should be
> the owner (so long as it exists).
>
> Why not reverse the cases?  If 0 is not mapped, then check whether the
> current_user_ns()->owner is mapped?

Good point, and less chance of breakage that way as well.

--Andy