linux-kernel - Re: [PATCH v5 3/3] fanotify,audit: Allow audit to use the full permission event response

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Message-ID: <CAHC9VhQ6Nn2DuO-w3OtMj3rrtPp+X5ULYpZW8wLTakK9sMrs0g@mail.gmail.com>
Date:   Thu, 22 Dec 2022 16:16:58 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     Jan Kara <jack@...e.cz>, linux-api@...r.kernel.org,
        Amir Goldstein <amir73il@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        linux-fsdevel@...r.kernel.org, Eric Paris <eparis@...isplace.org>
Subject: Re: [PATCH v5 3/3] fanotify,audit: Allow audit to use the full
 permission event response

On Thu, Dec 22, 2022 at 3:42 PM Richard Guy Briggs <rgb@...hat.com> wrote:
> On 2022-12-20 18:31, Paul Moore wrote:
> > On Mon, Dec 12, 2022 at 9:06 AM Richard Guy Briggs <rgb@...hat.com> 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@...l-moore.com>.
> > >
> > > 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@...hat.com>
> > > Link: https://lore.kernel.org/r/3075502.aeNJFYEL58@x2
> > > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> > > ---
> > >  fs/notify/fanotify/fanotify.c |  3 ++-
> > >  include/linux/audit.h         |  9 +++++----
> > >  kernel/auditsc.c              | 25 ++++++++++++++++++++++---
> > >  3 files changed, 29 insertions(+), 8 deletions(-)
> >
> > ...
> >
> > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > > index d1fb821de104..8d523066d81f 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"
> > >
> > > @@ -2877,10 +2878,28 @@ 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);
> > > +       struct audit_context *ctx = audit_context();
> > > +       struct audit_buffer *ab;
> > > +       char numbuf[12];
> > > +
> > > +       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);
> >
> > The fan_info, subj_trust, and obj_trust constant values used here are
> > awfully magic-numbery and not the usual sentinel values one might
> > expect for a "none" operation, e.g. zeros/INT_MAX/etc. I believe a
> > comment here explaining the values would be a good idea.
>
> Ack.  I'll add a comment.  I would have preferred zero for default of
> unset, but Steve requested 0/1/2 no/yes/unknown.

Yeah, if they were zeros I don't think we would need to comment on
them as zeros for unset/unknown/invalid is rather common, 2 ... not so
much.

-- 
paul-moore.com