Re: [PATCH v6 3/3] fanotify,audit: Allow audit to use the full permission event response

[Richard Guy Briggs]

On 2023-01-20 13:58, Paul Moore wrote:
> On Tue, Jan 17, 2023 at 4:14 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> >
> > This patch passes the full response so that the audit function can use all
> > of it. The audit function was updated to log the additional information in
> > the AUDIT_FANOTIFY record.
> >
> > Currently the only type of fanotify info that is defined is an audit
> > rule number, but convert it to hex encoding to future-proof the field.
> > Hex encoding suggested by Paul Moore <paul@xxxxxxxxxxxxxx>.
> >
> > The {subj,obj}_trust values are {0,1,2}, corresponding to no, yes, unknown.
> >
> > Sample records:
> >   type=FANOTIFY msg=audit(1600385147.372:590): resp=2 fan_type=1 fan_info=3137 subj_trust=3 obj_trust=5
> >   type=FANOTIFY msg=audit(1659730979.839:284): resp=1 fan_type=0 fan_info=3F subj_trust=2 obj_trust=2
> >
> > Suggested-by: Steve Grubb <sgrubb@xxxxxxxxxx>
> > Link: https://lore.kernel.org/r/3075502.aeNJFYEL58@x2
> > Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> > ---
> >  fs/notify/fanotify/fanotify.c |  3 ++-
> >  include/linux/audit.h         |  9 +++++----
> >  kernel/auditsc.c              | 16 +++++++++++++---
> >  3 files changed, 20 insertions(+), 8 deletions(-)
> 
> ...
> 
> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index d1fb821de104..3133c4175c15 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> > @@ -2877,10 +2878,19 @@ void __audit_log_kern_module(char *name)
> >         context->type = AUDIT_KERN_MODULE;
> >  }
> >
> > -void __audit_fanotify(u32 response)
> > +void __audit_fanotify(u32 response, struct fanotify_response_info_audit_rule *friar)
> >  {
> > -       audit_log(audit_context(), GFP_KERNEL,
> > -               AUDIT_FANOTIFY, "resp=%u", response);
> > +       /* {subj,obj}_trust values are {0,1,2}: no,yes,unknown */
> > +       if (friar->hdr.type == FAN_RESPONSE_INFO_NONE) {
> > +               audit_log(audit_context(), GFP_KERNEL, AUDIT_FANOTIFY,
> > +                         "resp=%u fan_type=%u fan_info=3F subj_trust=2 obj_trust=2",
> > +                         response, FAN_RESPONSE_INFO_NONE);
> > +               return;
> > +       }
> > +       audit_log(audit_context(), GFP_KERNEL, AUDIT_FANOTIFY,
> > +                 "resp=%u fan_type=%u fan_info=%X subj_trust=%u obj_trust=%u",
> > +                 response, friar->hdr.type, friar->rule_number,
> > +                 friar->subj_trust, friar->obj_trust);
> >  }
> 
> The only thing that comes to mind might be to convert the if-return
> into a switch statement to make it a bit cleaner and easier to patch
> in the future, but that is soooo far removed from any real concern
> that I debated even mentioning it.  I only bring it up in case the
> "3F" discussion results in a respin, and even then I'm not going to
> hold my ACK over something as silly as a if-return vs switch.
> 
> For clarity, this is what I was thinking:
> 
> void __audit_fanontify(...)
> {
>   switch (type) {
>   case FAN_RESPONSE_INFO_NONE:
>     audit_log(...);
>     break;
>   default:
>     audit_log(...);
>   }
> }

I agree that would be cleaner, but FAN_RESPONSE_INFO_NONE and
FAN_RESPONSE_INFO_AUDIT_RULE would be the two, with default being
ignored since they could be other types unrelated to audit.

There were a number of bits of code to future proof it in previous
versions that were questioned as necessary so they were removed...

> paul-moore.com

- 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