Date: Fri, 26 Jun 1998 16:37:38 -0400 (EDT) From: andrewr <andrewr@slack.net> To: Nate Lawson <nate@almond.elite.net> Cc: Pierre.Beyssac@hsc.fr, fenner@parc.xerox.com, nate@elite.net, julian@whistle.com, freebsd-bugs@FreeBSD.ORG, freebsd-net@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG Subject: Re: sendto()/raw sockets and now spoofing Message-ID: <Pine.NEB.3.96.980626163608.25430B-100000@brooklyn.slack.net> In-Reply-To: <199806262018.NAA08152@almond.elite.net>
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I agree with nate on this, and is why I stopped in the middle of my
coding. I only coded the dumb ip_src checker, and I stopped there. I
thought to my self "Uhm, who would be spoofing the packets?? Root, most
likely.. 'doh'" And I stopped.
Andrew
*****************************************
AWR XNS, Inc.
<andrewr@slack.net>
"Drink beer, it will save your life."
On Fri, 26 Jun 1998, Nate Lawson wrote:
> >On Fri, 26 Jun 1998, Pierre Beyssac wrote:
> >> On Fri, Jun 26, 1998 at 09:38:33AM -0400, andrewr wrote:
> >> > Speaking of IP_HDRINCL, after reading raw_ip.c and noticing the protection
> >> > against spoofing (can't use IP_HDRINCL in certain situations), I started
> >> > thinking about actually comparing the user dsupplied ip->ip_src with the
> >>
> >> Are you sure you're talking about FreeBSD here ? SunOS 4 has such
> >> a protection (it checks that the source address belongs to one of
> >> the interfaces, or so it seems) but I've successfully spoofed
> >> packets on FreeBSD without any problem using IP_HDRINCL.
> >>
> >> Anyway, such a protection can easily bypassed by sending raw
> >> link-level packets through bpf (or probably /dev/nit in the case
> >> of SunOS, although I've never tried this).
> >
> >I too have spoofed packets under FreeBSD, I am just noting somethings that
> >might want to be changed.
>
> The whole point of IP_HDRINCL is to allow the (privileged) user to supply
> their own IP header. There should be no code to prevent spoofing because it
> is quite necessary to be able to write arbitrary parts of the IP header.
> A DHCP server is a perfect example of a program that must "spoof" its source
> address.
>
> How far do you start to go with this crusade? Do you then go on and verify
> ip_id is appropriate? What about making sure ip_p isn't equal to ANY of the
> known protocols since they are accessible through the ordinary sockets
> interface?
>
> If you put the checks in sendto(), I'll be forced to use BPF for my tools. If
> you put the checks in BPF too, I'll be forced to include an LKM that patches
> your BPF which ...
>
> An operating system provides a layer of abstraction from the hardware that
> provides protection -- you have this understanding right. But when a properly
> authenticated and privileged user (root in this case) uses an OS mechanism,
> IP_HDRINCL, to circumvent these checks, that user takes responsibility for the
> behavior of his code by explicitly forgoing the normal OS checks. This is the
> part you were missing.
>
> -Nate
>
>
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