Re: [RFC] Create an audit record of USB specific details
On April 4, 2016 6:17:23 PM Greg KH <gregkh(a)linuxfoundation.org> wrote:
On Mon, Apr 04, 2016 at 05:37:58PM -0400, Paul Moore 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(a)redhat.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.
>
> Audit has some odd requirements placed on it by some of its users. I think
> most notable in this particular case is the need to take specific actions,
> including panicking the system, when audit records can't be sent to userspace
> and are "lost". Granted, it's an odd requirement, definitely not the
> norm/default configuration, but supporting weird stuff like this has allowed
> Linux to be used on some pretty interesting systems that wouldn't have been
> possible otherwise. Looking quickly at some of the kobject/uvent code, it
> doesn't appear that the uevent/netlink channel has this capability.
Are you sure you can loose netlink messages? If you do, you know you
lost them, so isn't that good enough?
Last I checked netlink didn't have a provision for panicking the system, so
no :)
> It also just noticed that it looks like userspace can send fake
uevent
> messages;
That's how your machine boots properly :)
Yes, it looks like that is how the initial devices are handled, right?
Allowing something like that is probably okay for a variety of reasons, but
I expect users would want to restrict access beyond this single trusted
process. The good news is that I think you should be able to do that with
a combination of DAC and MAC.
> I haven't looked at it closely enough yet, but that may be a
concern
> for users which restrict/subdivide root using a LSM ... although it is
> possible that the LSM policy could help here. I'm thinking aloud a bit right
> now, but for SELinux the netlink controls aren't very granular and sysfs can
> be tricky so I can't say for certain about blocking fake events from userspace
> using LSMs/SELinux.
uevents are not tied into LSMs from what I can tell, so I don't
understand wht you are talking about here, sorry.
Perhaps I'm mistaken, but uevents are sent to userspace via netlink which
does have LSM controls. There also appears to be a file I/O mechanism via
sysfs which also has LSM controls.
--
paul moore
www.paul-moore.com