linux-kernel - Re: [PATCH 1/2] integrity: Add errno field in audit message

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Date:   Tue, 16 Jun 2020 15:53:40 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Steve Grubb <sgrubb@...hat.com>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
Cc:     Paul Moore <paul@...l-moore.com>, rgb@...hat.com,
        linux-integrity@...r.kernel.org, linux-audit@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] integrity: Add errno field in audit message

On Tue, 2020-06-16 at 11:55 -0400, Steve Grubb wrote:
> On Tuesday, June 16, 2020 11:43:31 AM EDT Lakshmi Ramasubramanian wrote:
> > On 6/16/20 8:29 AM, Steve Grubb wrote:
> > >>>>> The idea is a good idea, but you're assuming that "result" is always
> > >>>>> errno.  That was probably true originally, but isn't now.  For
> > >>>>> example, ima_appraise_measurement() calls xattr_verify(), which
> > >>>>> compares the security.ima hash with the calculated file hash.  On
> > >>>>> failure, it returns the result of memcmp().  Each and every code path
> > >>>>> will need to be checked.
> > >>>> 
> > >>>> Good catch Mimi.
> > >>>> 
> > >>>> Instead of "errno" should we just use "result" and log the value given
> > >>>> in the result parameter?
> > >>> 
> > >>> That would likely collide with another field of the same name which is
> > >>> the
> > >>> operation's results. If it really is errno, the name is fine. It's
> > >>> generic
> > >>> enough that it can be reused on other events if that mattered.
> > >> 
> > >> Steve, what is the historical reason why we have both "res" and
> > >> "result" for indicating a boolean success/fail?  I'm just curious how
> > >> we ended up this way, and who may still be using "result".
> > > 
> > > I think its pam and some other user space things did this. But because of
> > > mixed machines in datacenters supporting multiple versions of OS, we have
> > > to leave result alone. It has to be 0,1 or success/fail. We cannot use
> > > it for errno.
> > 
> > As Mimi had pointed out, since the value passed in result parameter is
> > not always an error code, "errno" is not an appropriate name.
> > 
> > Can we add a new field, say, "op_result" to report the result of the
> > specified operation?
> 
> Sure. But since it is errno sometimes, how would we know when to translate 
> it?

Perhaps the solution is not to imply "res" is "errno", but pass it as
a separate "errno" field.  Then only include "errno" in the audit
message when it isn't zero.  This assumes that some audit messages for
the same audit number include errno, while others do not.

With this solution, the existing integrity_audit_msg() could become a
wrapper for the new function.

Mimi