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

On 2022-12-20 18:31, Paul Moore wrote:
> On Mon, Dec 12, 2022 at 9:06 AM Richard Guy Briggs <[email protected]> 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 <[email protected]>.
> >
> > 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 <[email protected]>
> > Link: https://lore.kernel.org/r/3075502.aeNJFYEL58@x2
> > Signed-off-by: Richard Guy Briggs <[email protected]>
> > ---
> >  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.

> > +               return;
> > +       }
> > +       ab = audit_log_start(ctx, GFP_KERNEL, AUDIT_FANOTIFY);
> > +       if (ab) {
> > +               audit_log_format(ab, "resp=%u fan_type=%u fan_info=",
> > +                                response, friar->hdr.type);
> > +               snprintf(numbuf, sizeof(numbuf), "%u", friar->rule_number);
> > +               audit_log_n_hex(ab, numbuf, sizeof(numbuf));
> 
> It looks like the kernel's printf format string parsing supports %X so
> why not just use that for now, we can always complicate it later if
> needed.  It would probably also remove the need for the @ab, @numbuf,
> and @ctx variables.  For example:
> 
> audit_log(audit_context(), GFP_KERNEL, AUDIT_FANOTIFY,
>   "resp=%u fan_type=%u fan_info=%X subj_trust=%u obj_trust=%u",
>   response, friar->hdr.type, friar->rule_number,
>   friar->subj_trust, friar->obj_trust);
> 
> Am I missing something?

No, I am.  Thank you, that's much cleaner.

> > +               audit_log_format(ab, " subj_trust=%u obj_trust=%u",
> > +                                friar->subj_trust, friar->obj_trust);
> > +               audit_log_end(ab);
> > +       }
> >  }
> >
> >  void __audit_tk_injoffset(struct timespec64 offset)
> > --
> > 2.27.0
> 
> -- 
> paul-moore.com
> 
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> 

- RGB

--
Richard Guy Briggs <[email protected]>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
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