Re: AUDIT_NETFILTER_PKT message format

Richard Guy Briggs
2017-01-17T16:12:28Z

On 2017-01-17 08:55, Steve Grubb wrote:
> On Tuesday, January 17, 2017 12:25:51 AM EST Richard Guy Briggs wrote:
> > I'm just starting to look at the normalization of AUDIT_NETFILTER_PKT
> > event messages and it is not quite as straightforward as I had expected.
> >
> > It is being tracked here:
> > https://github.com/linux-audit/audit-kernel/issues/11
> > and refers to a previous posting from Mr. Dash Four from four years ago
> > to which there was no reply.
> >
> > The example given in the tracker above for "frag=" is fairly
> > straightforward, but digging more, there are a number of others that are
> > not quite so obvious.
> >
> > How many different combinations of fields is acceptable? Can we create
> > new message types for each one, or is there a preferred way to indicate
> > which sub-type it is other than implicit from the arguments given?
>
> That would be preferential to swinging fields in and out. But we also don't
> want to add too many new types. If two protocols look almost identical, I'd
> try to coerce them to be the same. If adding 2 new types solves the problem
> just do it. If it takes 10, then maybe we should understand why.

Ok, I'll have a go at mapping some out and see where we end up...

> > Others that are straightforward:
> > - The first "truncated=" gets pulled in with "0".
> >
> > - "mark=" gets pulled in with "0".
> >
> > Ones that are not so straightforward:
> > - "secmark" depends on a kernel config setting, so should it always be
> > present but "(none)" if that kernel feature is compiled out?
>
> If this is selinux related, I'd treat it the same way that we do subj
> everywhere else.

Ok.

> > - ARPHRD_ETHER pulls in 3 fields, I would pull them all in and set them
> > to "(none)" to indicate that type isn't present.
>
> "(none)" is for character fields that have nothing. Typically we set -1 for
> numeric fields that are unset. If numbers are expected, its going to get the
> strtol() treatment and "(none)" will cause a conversion error.

Ah, ok. I certainly don't want to break the parser, so I'll use -1 or
find another way to indicate it.

> > - audit_ip4() and audit_ip6 share "saddr=", "daddr=", proto=", but ip4
> > adds "ipid=", which would be set to "(none)" for ip6.
>
> That is numeric. -1?

Yup, 16-bit. I'll make it -1.

> -Steve
>
> > - audit_proto() pulls in "truncated=" again, then either "sport=" and
> > "dport=" OR "icmptype=" and "icmpcode=".
> >
> > If all fields are pulled in, we end up adding 10 fields beyond a
> > standard well-formed packet, and 15 beyond a truncated packet.
> >
> > Note: In the cases of "mark" and "secmark" both are unions. In the case of
> > "mark", I don't see a problem since it isn't conditionally compiled out
> > and won't be mis-interpreted. In the case of "secmark=", it could be
> > mis-interpreted as offload_fwd_mark if that field is even compiled in,
> > but that would be addressed in the compiler directive...
> >
> >
> > One last question: Does anyone have a test suite that can generate any
> > or all of these types of packets?
> >
> >
> > Thanks!
> >
> >
> > - RGB

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Kernel Security Engineering, Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635