Re: [B.A.T.M.A.N.] [PATCH] batctl: add raw wifi packet decapsulation support

Andrew Lunn
2011-01-28T17:24:16Z

On Thu, Jan 27, 2011 at 01:27:57PM +0100, Marek Lindner wrote:
>
> Hi,
>
> > > + shost = wifi_hdr->addr2;
> > > + if (fc & IEEE80211_FCTL_FROMDS)
> > > + shost = wifi_hdr->addr3;
> > > + else if (fc & IEEE80211_FCTL_TODS)
> > > + shost = wifi_hdr->addr4;
> > > +
> > > + dhost = wifi_hdr->addr1;
> > > + if (fc & IEEE80211_FCTL_TODS)
> > > + dhost = wifi_hdr->addr3;
> >
> > What would happen if you happened to pick up a WDS packet? Four
> > addresses in the packet. Do we see sensible addresses?
>
> we should - that is what addr4 is used for but I did not test it. Let me know
> if it does not work for you.
>
>
> > > +
> > > + hdr_len = 24;
> > > + if ((fc & IEEE80211_FCTL_FROMDS) && (fc & IEEE80211_FCTL_TODS))
> > > + hdr_len = 30;
> >
> > Again, WDS? We are now a few bytes out when decoding the rest of the
> > packet.

OK. Sorry. I'm wrong.

What confused me is time spent debugging WDS in madwifi. It has macros
similar to what you have:

#define IEEE80211_FC1_DIR_NODS 0x00 /* STA->STA */
#define IEEE80211_FC1_DIR_TODS 0x01 /* STA->AP */
#define IEEE80211_FC1_DIR_FROMDS 0x02 /* AP ->STA */
#define IEEE80211_FC1_DIR_DSTODS 0x03 /* AP ->AP */

So i was expecting to see something like DSTODS. However the madwifi
macros are for the complete DIR field, where as you are looking at
individual bits. So

(fc & IEEE80211_FCTL_FROMDS) && (fc & IEEE80211_FCTL_TODS)

is equivalent to the madwifi IEEE80211_FC1_DIR_DSTODS.

So you header length calculation looks O.K.

Andrew