Re: Nmap labeled ethernet address problem

I looked into it a few days ago and came to a fairly similar conclusion,
but wasn't confident enough in it to say anything to the mailing list.
But, everything I found agreed with what Kris said. I also noticed that
if you set an interface alias to something that doesn't start with
"ifname:" the ifconfig tool completely pukes. So, I think it's either a
problem with the "ip" tool, or whoever's architecting the networking API
in linux not specifying clearly what aliases should look like.

Benson

On Tue, Apr 29, 2008 at 09:27:21PM -0500, Kris Katterjohn wrote:
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> Hey Fyodor,
>
> Fyodor wrote:
> > Nmap seems to quit when it encounters labeled ethernet addresses on
> > Linux.
> <snip>
> >> # ip addr add 1.1.1.1/32 dev eth0 label eth0vip
> >> # ip addr list dev eth0
> >> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
> >> link/ether 00:12:79:de:38:13 brd ff:ff:ff:ff:ff:ff
> >> inet 192.34.35.49/28 brd 192.34.35.63 scope global eth0
> >> inet 1.1.1.1/32 scope global eth0vip
> >> inet6 fe80::212:79ff:fede:3813/64 scope link
> >> valid_lft forever preferred_lft forever
> >> # nmap -sP -PI 192.34.35.1-5
> >>
> >> Starting Nmap 4.60 ( http://nmap.org ) at 2008-04-17 17:33 MDT
> >> Failed to determine the netmask of eth0vip!: No such device (19)
> >>
>
> I've been looking into this. It looks like "labels" are the same as the
> older "aliases", which are traditionally either the same name as the
> interface (as on BSD) or prefixed with the interface name and a colon
> (as on Solaris). Linux seems to support both.
>
> Nmap already knows about the colon notation:
>
> Strncpy(mydevs[numifaces].devname, ifr->ifr_name, [...]);
> /* devname isn't allowed to have alias qualification */
> if ((p = strchr(mydevs[numifaces].devname, ':')))
> *p = '\0';
>
> I confirmed that using a label of "eth0:0" works as expected.
>
> After devname stuff, the netmask stuff is done:
>
> Strncpy(tmpifr.ifr_name, ifr->ifr_name, sizeof(tmpifr.ifr_name));
> memcpy(&(tmpifr.ifr_addr), sin, [...]);
> rc = ioctl(sd, SIOCGIFNETMASK, &tmpifr);
>
> But notice that ifr->ifr_name is used rather than devname, so the
> SIOCGIFNETMASK apparently works for aliases and labels *if* they're in
> the right format.
>
> The ip manpage on my system says this about labels:
>
> "Each address may be tagged with a label string. In order to preserve
> compatibility with Linux-2.0 net aliases, this string must coincide with
> the name of the device or must be prefixed with the device name followed
> by colon."
>
> So it seems that Nmap isn't at fault, but rather the user for selecting
> the improper label and ip for not producing an error or warning.
>
> So given this, I'm not sure what should be done about it :)
>
> > Cheers,
> > -F
> >
>
> Thanks,
> Kris Katterjohn
>
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