802.11 monitor mode changes coming

[Paul B. Mahol]

On 5/25/09, Paul B. Mahol <onemda at gmail.com> wrote:
> On 5/18/09, Sam Leffler <sam at errno.com> wrote:
>> The patch here:
>>
>> http://people.freebsd.org/~sam/monitor-20090518.patch
>>
>> has significant changes to monitor mode operation.  Most importantly it
>> replaces DLT_IEEE802_11 support in net80211 by DLT_IEEE802_11_RADIO and
>> removes the latter from the underlying device.  The upshot is that you
>> can no longer do:
>>
>> tcpdump -i ath0
>>
>> instead you will now need a wlanX ifnet; e.g.
>>
>> ifconfig wlan create wlandev ath0 wlanmode monitor channel 6 up
>> tcpdump -i wlan0 -y IEEE802_11_RADIO
>>
>> This addresses the longstanding issue that applications like kismet that
>> want radiotap data needed to open two ifnets, one to receive data and
>> one to do channel changes.  My main concern is whether losing
>> DLT_IEEE802_11 support will affect any apps.  Those that depend on it
>> should be easy to change; you just request a different DLT and strip the
>> radiotap header from tap'd frames (or similar).
>>
>> In sweeping the drivers to do these changes I've made radiotap support
>> more consistent and improved some drivers.  Drivers not tested so far:
>> malo, ipw, wpi, and upgt.  I tested iwi and it appears broken in that no
>> frames are rx'd but I'm not sure I'll look at it before 8.0.
>>
>> I plan to commit these changes by the end of the week.
>
> It makes ndisulator panic, following stupid patch fix it for me:
>
> --- /sys/net80211/ieee80211_radiotap.c  2009-05-25 12:14:29.000000000 +0000
> +++ ieee80211_radiotap.c        2009-05-25 12:13:59.000000000 +0000
> @@ -102,6 +102,8 @@
>         struct ieee80211com *ic = vap->iv_ic;
>         struct ieee80211_radiotap_header *th = ic->ic_th;
>
> +       if (th == NULL)
> +               return;
>         KASSERT(th != NULL, ("no radiotap setup"));
>
>         /* radiotap DLT for raw 802.11 frames */

Unfortunately this one makes system panic on detach somewhere in bpf code,
so correct way to fix this is to use radiotap code only and only if device
have monitor cap.


-- 
Paul