linux-kernel - Re: [RFC] Create an audit record of USB specific details

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Date:	Tue, 5 Apr 2016 09:44:27 -0400
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Burn Alting <burn@...f.dyndns.org>
Cc:	Steve Grubb <sgrubb@...hat.com>, linux-audit@...hat.com,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC] Create an audit record of USB specific details

On Tue, Apr 05, 2016 at 11:07:48PM +1000, Burn Alting wrote:
> On Mon, 2016-04-04 at 14:53 -0700, Greg KH wrote:
> > On Mon, Apr 04, 2016 at 02:48:43PM -0700, Greg KH wrote:
> > > On Mon, Apr 04, 2016 at 05:33:10PM -0400, Steve Grubb wrote:
> > > > On Monday, April 04, 2016 05:56:26 AM Greg KH wrote:
> > > > > On Mon, Apr 04, 2016 at 12:02:42AM -0400, wmealing wrote:
> > > > > > From: Wade Mealing <wmealing@...hat.com>
> > > > > > 
> > > > > > Gday,
> > > > > > 
> > > > > > I'm looking to create an audit trail for when devices are added or removed
> > > > > > from the system.
> > > > > 
> > > > > Then please do it in userspace, as I suggested before, that way you
> > > > > catch all types of devices, not just USB ones.
> > > > > 
> > > > > Also I don't think you realize that USB interfaces are what are bound to
> > > > > drivers, not USB devices, so that is going to mess with any attempted
> > > > > audit trails here.  How are you going to distinguish between the 5
> > > > > different devices that just got plugged in that all have 0000/0000 as
> > > > > vid/pid for them because they are "cheap" devices from China, yet do
> > > > > totally different things because they are different _types_ of devices?
> > > > 
> > > > This sounds like vid/pid should be captured in the event.
> > > 
> > > The code did that, the point is, vid/pid means nothing in the real
> > > world.  So why are you going to audit anything based on it? :)
> > 
> > Oh wait, it's worse, it is logging strings, which are even more
> > unreliable than vid/pid values.  It's pretty obvious this has not been
> > tested on any large batch of real-world devices, or thought through as
> > to why any of this is even needed at all.
> > 
> > So why is this being added?  Who needs/wants this?  What are their
> > requirements here? 
> 
> As a consumer of auditd events for security purposes, the questions I
> would like answered via the sort of audit framework Wade is putting
> together are
> 
> - when was a (possible) removable media device plugged into a system and
> what were the device details - perhaps my corporation has a policy on
> what devices are 'official' and hence one looks for alternatives,
> and/or,

How do you determine if a USB device is "official" or not?  What
attribute(s) are you going to care about that can't be trivially
spoofed?

> - was it there at boot ? (in case someone adds and removes such devices
> when powered off), and eventually

What if you booted off of it?

> - has an open for write (or other system calls) occurred on designated
> removable media? (i.e. what may have been written to removable media -
> cooked or raw) - Yes, this infers a baseline of what's connected or an
> efficient means of working out if a device is 'removable' at system call
> time.

Yes, determining "removable" is non-trivial, good luck with that :)

thanks,

greg k-h