linux-kernel - Re: [PATCH] selinux: enable per-file labeling for functionfs

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Message-ID: <CAEjxPJ6iFrfVxbRM71b9G0+59L+vxNiJ1mpeXSGwuG_n+D15Lw@mail.gmail.com>
Date: Thu, 21 Aug 2025 09:03:49 -0400
From: Stephen Smalley <stephen.smalley.work@...il.com>
To: Neill Kapron <nkapron@...gle.com>
Cc: Paul Moore <paul@...l-moore.com>, Ondrej Mosnacek <omosnace@...hat.com>, kernel-team@...roid.com, 
	selinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selinux: enable per-file labeling for functionfs

On Thu, Aug 21, 2025 at 8:59 AM Stephen Smalley
<stephen.smalley.work@...il.com> wrote:
>
> On Wed, Aug 20, 2025 at 5:23 PM Neill Kapron <nkapron@...gle.com> wrote:
> >
> > This patch adds support for genfscon per-file labeling of functionfs
> > files as well as support for userspace to apply labels after new
> > functionfs endpoints are created.
> >
> > This allows for separate labels and therefore access control on a
> > per-endpoint basis. An example use case would be for the default
> > endpoint EP0 used as a restricted control endpoint, and additional
> > usb endpoints to be used by other more permissive domains.
> >
> > It should be noted that if there are multiple functionfs mounts on a
> > system, genfs file labels will apply to all mounts, and therefore will not
> > likely be as useful as the userspace relabeling portion of this patch -
> > the addition to selinux_is_genfs_special_handling().
> >
> > Signed-off-by: Neill Kapron <nkapron@...gle.com>
>
> Did you confirm that functionfs is safe wrt genfscon-based and
> userspace labeling, as per:
> https://github.com/SELinuxProject/selinux-kernel/issues/2
>
> Also as per that longstanding open issue, we'd welcome patches to
> generalize the current hardcoded list of filesystem types to
> instead lookup the filesystem type in the policy to see if it should
> support genfscon and/or userspace labeling.

Also, do we need a new policycap to conditionally enable this new
labeling behavior to avoid any regressions?
See the corresponding checks for cgroup labeling and
https://github.com/SELinuxProject/selinux-kernel/wiki/Getting-Started#adding-a-new-selinux-policy-capability