linux-kernel - Re: [PATCH v3 0/1] Relax restrictions on user.* xattr

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Date:   Wed, 8 Sep 2021 09:37:17 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        virtio-fs-list <virtio-fs@...hat.com>,
        Daniel J Walsh <dwalsh@...hat.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Casey Schaufler <casey.schaufler@...el.com>,
        LSM <linux-security-module@...r.kernel.org>,
        SElinux list <selinux@...r.kernel.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        "Fields, Bruce" <bfields@...hat.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Dave Chinner <david@...morbit.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v3 0/1] Relax restrictions on user.* xattr

On Tue, 7 Sept 2021 at 23:40, Vivek Goyal <vgoyal@...hat.com> wrote:
>
> On Mon, Sep 06, 2021 at 04:56:44PM +0200, Miklos Szeredi wrote:
> > On Mon, 6 Sept 2021 at 16:39, Dr. David Alan Gilbert
> > <dgilbert@...hat.com> wrote:
> >
> > > IMHO the real problem here is that the user/trusted/system/security
> > > 'namespaces' are arbitrary hacks rather than a proper namespacing
> > > mechanism that allows you to create new (nested) namespaces and associate
> > > permissions with each one.
> >
> > Indeed.
> >
> > This is what Eric Biederman suggested at some point for supporting
> > trusted xattrs within a user namespace:
> >
> > | For trusted xattrs I think it makes sense in principle.   The namespace
> > | would probably become something like "trusted<ns-root-uid>.".
> >
> > Theory sounds simple enough.  Anyone interested in looking at the details?
>
> So this namespaced trusted.* xattr domain will basically avoid the need
> to have CAP_SYS_ADMIN in init_user_ns, IIUC.  I guess this is better
> than giving CAP_SYS_ADMIN in init_user_ns.

That's the objective, yes.  I think the trick is getting filesystems
to store yet another xattr type.

Thanks,
Miklos