Audit record ordering requirements

[Richard Guy Briggs]

On 2020-03-27 10:08, Steve Grubb wrote:
> On Friday, March 27, 2020 10:03:07 AM EDT Steve Grubb wrote:
> > On Thursday, March 26, 2020 8:28:51 PM EDT Paul Moore wrote:
> > > On Thu, Mar 26, 2020 at 7:49 PM Casey Schaufler <casey at schaufler-ca.com>
> > 
> > wrote:
> > > > I'm looking at adding an audit record type for the case where
> > > > there are multiple security modules providing subject data. There
> > > > are several reasons to create a new record rather than adding the
> > > > additional information to existing records, including possible
> > > > size overflows and format compatibility.
> > > > 
> > > > While working with the code I have found that it is much easier
> > > > if the new record (I'm calling it MAC_TASK_CONTEXTS) can be generated
> > > > before the "base" record, which could be a SYSCALL record, than
> > > > after it. Can I get away with this? I haven't seen any documentation
> > > > that says the CWD record has to follow the event's SYSCALL record,
> > > > but I wouldn't be at all surprised if it's implicitly assumed.
> > > 
> > > From a kernel perspective, as long as the timestamp matches (so it's
> > > considered part of the same "event") I've got no problem with that.
> > > However, Steve's audit userspace has a lot of assumptions about how
> > > things are done so it's probably best that he comments on this so his
> > > tools don't blow up.
> > 
> > There are some assumptions about what record is last in order to speed up
> > "aging" the event during search so that we know the event is complete and
> > ready for processing. We can always change that if needed. But a new kernel
> > won't be compatible with older tools.
> > 
> > The only long term fix for this would be to have something that says how
> > many records are in this event, then add a field for each record saying
> > which one it is. Then we can have a reliable way to decide when we have
> > all records ready for processing. This only affects searching/reporting,
> > not logging.
> 
> Or I can make a change to put EOF to disk. Currently, that is not done to 
> conserve disk space.

I was going to say.  We already had that functionality.  It was recently
deleted.  An EOF isn't a big record.

> > But I think the records are in chronological order as the syscall traverses
> > the various observers in the kernel. And as Paul said, as long as they all
> > have the same timestamp/serial number, userspace will collect them all up.
> > 
> > -Steve

- RGB

--
Richard Guy Briggs <rgb at redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
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