Re: [RFC PATCH ghak90 (was ghak32) V3 04/10] audit: add support for non-syscall auxiliary records

[Richard Guy Briggs]

On 2018-07-24 17:57, Paul Moore wrote:
> On Tue, Jul 24, 2018 at 3:40 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> > On 2018-07-20 18:14, Paul Moore wrote:
> > > On Wed, Jun 6, 2018 at 1:01 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> > > > Standalone audit records have the timestamp and serial number generated
> > > > on the fly and as such are unique, making them standalone.  This new
> > > > function audit_alloc_local() generates a local audit context that will
> > > > be used only for a standalone record and its auxiliary record(s).  The
> > > > context is discarded immediately after the local associated records are
> > > > produced.
> > > >
> > > > Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> > > > ---
> > > >  include/linux/audit.h |  8 ++++++++
> > > >  kernel/auditsc.c      | 25 +++++++++++++++++++++++--
> > > >  2 files changed, 31 insertions(+), 2 deletions(-)
> 
> ...
> 
> > > > +       struct audit_context *context;
> > > > +
> > > > +       if (!audit_ever_enabled)
> > > > +               return NULL; /* Return if not auditing. */
> > > > +
> > > > +       context = audit_alloc_context(AUDIT_RECORD_CONTEXT);
> > > > +       if (!context)
> > > > +               return NULL;
> > > > +       context->serial = audit_serial();
> > > > +       context->ctime = current_kernel_time64();
> > > > +       context->in_syscall = 1;
> > >
> > > Setting in_syscall is both interesting and a bit troubling, if for no
> > > other reason than I expect most (all?) callers to be in an interrupt
> > > context when audit_alloc_local() is called.  Setting in_syscall would
> > > appear to be conceptually in this case.  Can you help explain why this
> > > is the right thing to do, or necessary to ensure things are handled
> > > correctly?
> >
> > I'll admit this is cheating a bit, but seemed harmless.  It is needed so
> > that auditsc_get_stamp() from audit_get_stamp() from audit_log_start()
> > doesn't bail on me without giving me its already assigned time and
> > serial values rather than generating a new one.  I did look to see if
> > there were any other undesireable side effects and found none, so I'm
> > tmepted to rename the ->in_syscall to something a bit more helpful.  I
> > could add a new audit_context structure member to make
> > auditsc_get_stamp() co-operative, but this seems wasteful and
> > unnecessary.
> 
> That's what I suspected.
> 
> Let's look into renaming the "in_syscall" field, it borderline
> confusing now, and hijacking it for something which is very obviously
> not "in syscall" is A Very Bad Thing.

Ok, looking more carefully, I'm not going to touch in_syscall, since it
does more than I remember discovering when investigating why the
existing stamp wasn't being used.  I don't want to change the existing
behaviour.  I'll somewhat reluctantly grow the context struct and add a
"local" boolean to it so that auditsc_get_stamp knows to use the
existing stamp in both the in_syscall and local cases.

> paul moore

- RGB

--
Richard Guy Briggs <rgb@xxxxxxxxxx>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635