Ad-Hoc Wireless connection fails on Ubuntu with NetworkManager on Atheros wireless device

For some time now I experience problems with my Atherios Wireless NIC in combination with NetworkManager. For quite some time now, it’s possible for me to connect to a normal Wireless Access Point. Now I have an iPhone and want to use PDANet to connect a Laptop to the Internet using the iPhone 3G fast Internet capabilities. PDANet requires an Ad-Hoc wirless connection with the iPhone and works very similar to IP Masquarading(NAT).

With NetworkManager (which uses WPA supplicant) it’s not possible to do so. NetorkManager tries to connect to the selected Ad-Hoc network, but fails.  Analizing logfiles, I concluded that this is because the mode change from “Managed” to “Ad-Hoc” does not work. WPA supplicant is instructed by NetworkManager to do so (using DBus communication).

Ubuntu 8.10 and 8.04 both have compiled WPA Supplicant with a limited set of drivers. 8.10 was compiled with:

• wext = Linux wireless extensions (generic)
• atmel = ATMEL AT76C5XXx (USB, PCMCIA)
• wired = wpa_supplicant wired Ethernet driver

NetworkManager instructs (at least for my card) to use the wext (Linux Wireless Extensions) driver to communicate with the hardware.  Using iwconfig manualy (part wext) give an error:

root@jvz:~# iwconfig ath0 mode Managed
Error for wireless request “Set Mode” (8B06) :
SET failed on device ath0 ; Invalid argument

So it’s not strange for WPA Supplicant to fail to change the mode. ath_pci is the driver I’m using for my Atheros wireless card. See WifiDocs on ubuntu documentation for some more info on this driver.

Following the MadWifi UserDocs changing the mode of and MadWifi based card the following commands should be used:

wlanconfig ath0 destroy
wlanconfig ath0 create wlandev wifi0 wlanmode adhoc

Possible Solutions:

1. Use ath5k new MadWifi driver, but I have tested it and the link stability was not good, but it works out of the box with NetworkManager
2. Recompile WPA Supplicant to support the madwifi driver extensions and patch NetworkManager to use madfiwi instead of wext as commandline parameter for WPA Supplicant – not my favorite option!
3. Create a sudo script which stops NetworkManager and issue the above madwifi wlanconfig command from the script and connect manualy

I choose to use the third option. Here is my adhoc.sh bash sudo script:

#!/bin/sh
 
if [ "$1" != "sudo" ]; then {
    exec sudo "$0" sudo "$1"
} fi
 
function reload() {
	/etc/init.d/NetworkManager stop
	ifconfig ath0 down
	rmmod ath_pci
	modprobe ath_pci
	wlanconfig ath0 destroy
	wlanconfig ath0 create wlandev wifi0 wlanmode adhoc
	sleep 2
	iwconfig ath0 key s:11111
	iwconfig ath0 essid J3G
	iwconfig
	sleep 10
}
 
function dhcp() {
	dhclient ath0
}
 
function mail () {
   netstat -pan 2>/dev/null| grep ":25" | grep "tcpW" | grep LISTEN | grep ssh | awk '{print $7}' | sed 's!/ssh!!' 
      | while read pid; do
  		echo killing ssh: $pid
   		sudo kill -9 $pid
        done
   echo -n "Starting SMTP tunnel...."
   ssh -N -f -L 25:mailserver:25 user@domain.tld
   echo "done"
}
 
function stop() {
	ifconfig ath0 down
	rmmod ath_pci
	modprobe ath_pci
	/etc/init.d/NetworkManager start
}
 
if [ "$2" == "mail" ]; then
	mail
 	exit 0
elif [ "$2" == "all" ]; then
	reload
   	dhcp
	mail
elif [ "$2" == "dhcp" ]; then
        dhcp
elif [ "$2" == "stop" ]; then
 	stop
else
	echo "usage: $0 all|dhcp|mail|stop"
        exit 1
fi