Re: [PATCH v4 3/4] fanotify,audit: Allow audit to use the full permission event response

On Wed, Aug 31, 2022 at 7:55 PM Steve Grubb <sgrubb(a)redhat.com&gt; wrote: > On Wednesday, August 31, 2022 6:19:40 PM EDT Richard Guy Briggs wrote: > > On 2022-08-31 17:25, Steve Grubb wrote: > > > On Wednesday, August 31, 2022 5:07:25 PM EDT Richard Guy Briggs wrote: > > > > > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c > > > > > > index 433418d73584..f000fec52360 100644 > > > > > > --- a/kernel/auditsc.c > > > > > > +++ b/kernel/auditsc.c > > > > > > @@ -64,6 +64,7 @@ > > > > > > #include <uapi/linux/limits.h> > > > > > > #include <uapi/linux/netfilter/nf_tables.h> > > > > > > #include <uapi/linux/openat2.h> // struct open_how > > > > > > +#include <uapi/linux/fanotify.h> > > > > > > > > > > > > #include "audit.h" > > > > > > > > > > > > @@ -2899,10 +2900,34 @@ void __audit_log_kern_module(char *name) > > > > > > context->type = AUDIT_KERN_MODULE; > > > > > > } > > > > > > > > > > > > -void __audit_fanotify(u32 response) > > > > > > +void __audit_fanotify(u32 response, size_t len, char *buf) > > > > > > { > > > > > > - audit_log(audit_context(), GFP_KERNEL, > > > > > > - AUDIT_FANOTIFY, "resp=%u", response); > > > > > > + struct fanotify_response_info_audit_rule *friar; > > > > > > + size_t c = len; > > > > > > + char *ib = buf; > > > > > > + > > > > > > + if (!(len && buf)) { > > > > > > + audit_log(audit_context(), GFP_KERNEL, > > > > > > AUDIT_FANOTIFY, > > > > > > + "resp=%u fan_type=0 fan_info=?", > > > > > > response); > > > > > > + return; > > > > > > + } > > > > > > + while (c >= sizeof(struct fanotify_response_info_header)) { > > > > > > + friar = (struct fanotify_response_info_audit_rule > > > > > > *)buf; > > > > > > > > > > Since the only use of this at the moment is the > > > > > fanotify_response_info_rule, why not pass the > > > > > fanotify_response_info_rule struct directly into this function? We > > > > > can always change it if we need to in the future without affecting > > > > > userspace, and it would simplify the code. > > > > > > > > Steve, would it make any sense for there to be more than one > > > > FAN_RESPONSE_INFO_AUDIT_RULE header in a message? Could there be more > > > > than one rule that contributes to a notify reason? If not, would it be > > > > reasonable to return -EINVAL if there is more than one? > > > > > > I don't see a reason for sending more than one header. What is more > > > probable is the need to send additional data in that header. I was > > > thinking of maybe bit mapping it in the rule number. But I'd suggest > > > padding the struct just in case it needs expanding some day. > > > > This doesn't exactly answer my question about multiple rules > > contributing to one decision. > > I don't forsee that. > > > The need for more as yet undefined information sounds like a good reason > > to define a new header if that happens. > > It's much better to pad the struct so that the size doesn't change. > > > At this point, is it reasonable to throw an error if more than one RULE > > header appears in a message? > > It is a write syscall. I'd silently discard everything else and document that > in the man pages. But the fanotify maintainers should really weigh in on > this. > > > The way I had coded this last patchset was to allow for more than one RULE > > header and each one would get its own record in the event. > > I do not forsee a need for this. > > > How many rules total are likely to exist? > > Could be a thousand. But I already know some missing information we'd like to > return to user space in an audit event, so the bit mapping on the rule number > might happen. I'd suggest padding one u32 for future use. A better way to handle an expansion like that would be to have a length/version field at the top of the struct that could be used to determine the size and layout of the struct.