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

On Wed, Jan 18, 2023 at 1:34 PM Steve Grubb <sgrubb(a)redhat.com&gt; 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