linux-kernel - Re: [PATCH v2] xattr: Enable security.capability in user namespaces

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Message-ID: <20170713212111.GC6167@mail.hallyn.com>
Date:   Thu, 13 Jul 2017 16:21:11 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Theodore Ts'o <tytso@....edu>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        containers@...ts.linux-foundation.org, lkp@...org,
        linux-kernel@...r.kernel.org, zohar@...ux.vnet.ibm.com,
        tycho@...ker.com, James.Bottomley@...senPartnership.com,
        vgoyal@...hat.com, christian.brauner@...lbox.org,
        amir73il@...il.com, linux-security-module@...r.kernel.org,
        casey@...aufler-ca.com
Subject: Re: [PATCH v2] xattr: Enable security.capability in user namespaces

Quoting Stefan Berger (stefanb@...ux.vnet.ibm.com):
> For virtualizing the xattrs on the 'value' side I was looking for
> whether there's something like a 'wrapper' structure around the
> actual value of the xattr so that that wrapper could be extended to
> support different values at different uids and applied to any xattr.
> Unfortunately there's no such 'wrapper'.

I believe my very first implementation did essentially this - it used
the not uncommon structure of (mostly making this up):

struct ns_vfs_cap {
	int magic;
	int ncaps;
	struct ns_vfs_cap_data data[0];
};

with (ncaps * sizeof(ns_vfs_cap_data)) following that.

I didn't like it.

-serge