netdev - Re: [PATCH 3/3] selinux: Add SELinux GTP support

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Date:   Wed, 30 Sep 2020 13:25:27 +0100
From:   Richard Haines <richard_c_haines@...nternet.com>
To:     Harald Welte <laforge@...monks.org>
Cc:     selinux@...r.kernel.org, linux-security-module@...r.kernel.org,
        osmocom-net-gprs@...ts.osmocom.org, netdev@...r.kernel.org,
        stephen.smalley.work@...il.com, paul@...l-moore.com,
        pablo@...filter.org, jmorris@...ei.org
Subject: Re: [PATCH 3/3] selinux: Add SELinux GTP support

On Wed, 2020-09-30 at 13:01 +0200, Harald Welte wrote:
> Hi Richard,
> 
> I don't fully understand in which context you need / use those
> SELinux GTP hooks,

As in the reply to Pablo, I did it for no particular reason other than
idle curiosity, and given the attempted move to Open 5G I thought
adding MAC support might be useful somewhere along the line.

> however one comment from the point of view of somebody who is working
> on GGSN/P-GW
> software using the GTP kernel module:
> 
> On Wed, Sep 30, 2020 at 10:49:34AM +0100, Richard Haines wrote:
> > +selinux_gtp_dev_cmd()
> > +~~~~~~~~~~~~~~~~~~~~~
> > +Validate if the caller (current SID) and the GTP device SID have
> > the required
> > +permission to perform the operation. The GTP/SELinux permission
> > map is
> > +as follow::
> > +
> > +    GTP_CMD_NEWPDP = gtp { add }
> > +    GTP_CMD_DELPDP = gtp { del }
> > +    GTP_CMD_GETPDP = gtp { get }
> 
> Wouldn't it make sense to differentiate between:
> 
> a) add/del/get on the GTP netdev
> b) add/del/get on the indivudual PDP wihin the GTP netdev
> 
> 'a' is typically only created once at startup of a GGSN/P-GW
> software, or is
> done even at system stat-up time.
> 
> 'b' is performed frequently during runtime as the GGSN/P-GW function
> runs, as
> subscribers attach to / detach from the cellular network.
> 
> By differentiating between those two, one could further constrain the
> permissions
> required at runtime.

Yes, at first I did separate them (add_dev, del_dev, add_pkt, del_pkt,
get_pkt), so if this patchset goes anywhere then I can change it no
problem. I guess the '*_pkt' permissions would cover PDP for 3G and PDR
& FAR for 5G ?.
I didn't implement 'get_dev' but thought it could be useful for
retrieving the security context of a device, but that requires passing
it back via netlink so thought I would leave it until later.

>