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

On April 4, 2016 6:17:23 PM Greg KH <gregkh(a)linuxfoundation.org&gt; 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&gt; > > > > > > > > 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.