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

From: Andy Lutomirski <luto amacapital net>
To: Andy Lutomirski <luto kernel org>
Cc: gnome-os-list gnome org, Linux Containers <containers lists linux-foundation org>, Serge Hallyn <serge hallyn ubuntu com>, "linux-kernel vger kernel org" <linux-kernel vger kernel org>, James Bottomley <James Bottomley hansenpartnership com>, mclasen redhat com, "Eric W. Biederman" <ebiederm xmission com>, Linux FS Devel <linux-fsdevel vger kernel org>
Subject: Re: [PATCH v2] devpts: Make ptmx be owned by the userns owner as a fallback
Date: Fri, 29 Apr 2016 09:22:24 -0700

On Tue, Mar 15, 2016 at 1:05 PM, Andy Lutomirski <luto kernel 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

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