Re: [PATCH v1 1/2] audit: record fanotify event regardless of presence of rules

[Paul Moore <paul@paul-moore.com>]

On Tue, May 27, 2025 at 9:10 AM Richard Guy Briggs <rgb@redhat.com> wrote:
> On 2025-04-11 14:14, Paul Moore wrote:
> > On Mar  5, 2025 Richard Guy Briggs <rgb@redhat.com> wrote:
> > >
> > > When no audit rules are in place, fanotify event results are
> > > unconditionally dropped due to an explicit check for the existence of
> > > any audit rules.  Given this is a report from another security
> > > sub-system, allow it to be recorded regardless of the existence of any
> > > audit rules.
> > >
> > > To test, install and run the fapolicyd daemon with default config.  Then
> > > as an unprivileged user, create and run a very simple binary that should
> > > be denied.  Then check for an event with
> > >     ausearch -m FANOTIFY -ts recent
> > >
> > > Link: https://issues.redhat.com/browse/RHEL-1367
> > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > > Acked-by: Jan Kara <jack@suse.cz>
> > > ---
> > >  include/linux/audit.h | 8 +-------
> > >  kernel/auditsc.c      | 2 +-
> > >  2 files changed, 2 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > > index 0050ef288ab3..d0c6f23503a1 100644
> > > --- a/include/linux/audit.h
> > > +++ b/include/linux/audit.h
> > > @@ -418,7 +418,7 @@ extern void __audit_log_capset(const struct cred *new, const struct cred *old);
> > >  extern void __audit_mmap_fd(int fd, int flags);
> > >  extern void __audit_openat2_how(struct open_how *how);
> > >  extern void __audit_log_kern_module(char *name);
> > > -extern void __audit_fanotify(u32 response, struct fanotify_response_info_audit_rule *friar);
> > > +extern void audit_fanotify(u32 response, struct fanotify_response_info_audit_rule *friar);
> > >  extern void __audit_tk_injoffset(struct timespec64 offset);
> > >  extern void __audit_ntp_log(const struct audit_ntp_data *ad);
> > >  extern void __audit_log_nfcfg(const char *name, u8 af, unsigned int nentries,
> > > @@ -525,12 +525,6 @@ static inline void audit_log_kern_module(char *name)
> > >             __audit_log_kern_module(name);
> > >  }
> > >
> > > -static inline void audit_fanotify(u32 response, struct fanotify_response_info_audit_rule *friar)
> > > -{
> > > -   if (!audit_dummy_context())
> > > -           __audit_fanotify(response, friar);
> > > -}
> >
> > It seems like we should at least have an audit_enabled() check, yes?
> > We've had people complain about audit events being generated when audit
> > is disabled, any while we don't currently have such a check in place
> > here, I believe the dummy context check is doing that for us.
> >
> >   static inline void audit_fanotify(...)
> >   {
> >     if (!audit_enabled)
> >       return;
> >     __audit_fanotify(...);
> >   }
>
> That would be consistent with other security events messages.  I was
> going through the selinux code to see what it does and I am missing it
> if selinux checks with audit_enabled().  Are selinux messages somehow
> exempt from audit_enabled()?

There are likely a number of callers in the kernel that don't have
audit_enabled() checks, some are probably bugs, others probably
intentional; I wouldn't worry too much about what one subsystem does
when deciding what to do for another.  In the case of fanotify, I
suspect the right thing to do is add an audit_enabled() check since it
is already doing an audit_dummy_context() check.  To be clear, there
may be some cases where we do an audit_dummy_context() check and doing
an audit_enabled() check would be wrong, but I don't believe that is
the case with fanotify.

-- 
paul-moore.com