linux-kernel - Re: [PATCH v2] devpts: Make ptmx be owned by the userns owner as a fallback

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Message-ID: <CALCETrUJFgOHE5S2Drg1TiXjJFCNC2CKWerSEj_wk9Rrdv1JFg@mail.gmail.com>
Date:	Fri, 29 Apr 2016 09:22:24 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	gnome-os-list@...me.org,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Alexander Larsson <alexl@...hat.com>, mclasen@...hat.com,
	Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH v2] devpts: Make ptmx be owned by the userns owner as a fallback

On Tue, Mar 15, 2016 at 1:05 PM, Andy Lutomirski <luto@...nel.org> wrote:
> New devpts instances have ptmx owned by the inner uid and gid 0.
>
> For container-style namespaces (LXC, etc), this should have no
> effect, this is fine.
>
> For sandbox-style namespaces (xdg-app and similar), this is
> problematic -- there may not be an inner 0:0.  If that happens,
> devpts mounts will fail.
>
> Fix it by adding a fallback: if 0:0 is not mapped but the userns
> owner and group are mapped, then ptmx will be owned by the namespace
> owner.
>
> This won't change behavior except in cases where mount would
> currently return -EINVAL.

Eric, this patch is straightforward, fixes a real problem, and is
mostly orthogonal to the devpts stuff you're working on.  Could you
apply it for 4.7?

--Andy