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

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Date:   Wed, 31 Aug 2022 17:25:15 -0400
From:   Steve Grubb <sgrubb@...hat.com>
To:     Paul Moore <paul@...l-moore.com>,
        Richard Guy Briggs <rgb@...hat.com>
Cc:     Linux-Audit Mailing List <linux-audit@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, Eric Paris <eparis@...isplace.org>,
        Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.com>
Subject: Re: [PATCH v4 3/4] fanotify,audit: Allow audit to use the full permission event response

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.

-Steev