On Wed, Jan 18, 2023 at 1:34 PM Steve Grubb <sgrubb@xxxxxxxxxx> wrote:
>
> Hello Richard,
>
> I built a new kernel and tested this with old and new user space. It is
> working as advertised. The only thing I'm wondering about is why we have 3F
> as the default value when no additional info was sent? Would it be better to
> just make it 0?
...
> On Tuesday, January 17, 2023 4:14:07 PM EST Richard Guy Briggs wrote:
> > 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;
> > + }
(I'm working under the assumption that the "fan_info=3F" in the record
above is what Steve was referring to in his comment.)
I vaguely recall Richard commenting on this in the past, although
maybe not ... my thought is that the "3F" is simply the hex encoded
"?" character in ASCII ('man 7 ascii' is your friend). I suppose the
question is what to do in the FAN_RESPONSE_INFO_NONE case.
Historically when we had a missing field we would follow the "field=?"
pattern, but I don't recall doing that for a field which was
potentially hex encoded, is there an existing case where we use "?"
for a field that is hex encoded? If so, we can swap out the "3F" for
a more obvious "?".
However, another option might be to simply output the current
AUDIT_FANOTIFY record format in the FAN_RESPONSE_INFO_NONE case, e.g.
only "resp=%u". This is a little against the usual guidance of
"fields should not disappear from a record", but considering that
userspace will always need to support the original resp-only format
for compatibility reasons this may be an option.
--
paul-moore.com
