AP reboot issue in wpa_supplicant with generic Linux wireless extensions

Morris Lin morrisl at ruckuswireless.com
Wed Jun 20 02:26:48 EDT 2007


Greetings,

	When AP reboots, supplicant may take a long time to connect to
the AP in generic Linux wireless extension mode. (when no driver is
specified in command line.)

	Environment:
		Wireless NIC: dlink AG-660
		supplicant	: wpa_supplicant 0.57
		Driver	: madwifi 0.9.3
		OS     	: Fedora 6 (2.6.18-1.2798.fc62.6.18-1.2798.fc6)
		Command	: wpa_supplicant -i ath0 -c psk.conf -dd

		psk.conf
	
//============================================================
		update_config=0
		ctrl_interface=/var/run/wpa_supplicant
		ctrl_interface_group=0
		ap_scan=1
		network={
	        disabled=0
	        scan_ssid=1
	        priority=0
	        mode=0
	        ssid="dlink-wpa2"
	        proto=WPA
	        auth_alg=OPEN
	        key_mgmt=WPA-PSK
	        pairwise=TKIP
	        group=CCMP TKIP
	        psk="tropostest"
		}
	
//============================================================




Solution:
		
	Solution 1:   Specify driver in command line		

	Command 		:wpa_supplicant -i ath0 -Dmadwifi -c
psk.conf -dd
	(the date path is different from generic wireless mode)

	Solution 2:   Code change

	
//==============================================================
void wpa_supplicant_associate(struct wpa_supplicant *wpa_s,
                              struct wpa_scan_result *bss,
                              struct wpa_ssid *ssid)
{
        u8 wpa_ie[80];
        size_t wpa_ie_len;
        int use_crypt, ret, i;
        int algs = AUTH_ALG_OPEN_SYSTEM;
        wpa_cipher cipher_pairwise, cipher_group;
        struct wpa_driver_associate_params params;
        int wep_keys_set = 0;
        struct wpa_driver_capa capa;
        int assoc_failed = 0;

        -wpa_s->reassociate = 0;  <-------remove this line
        if (bss) {
                wpa_msg(wpa_s, MSG_INFO, "Trying to associate with "
MACSTR
                        " (SSID='%s' freq=%d MHz)", MAC2STR(bss->bssid),
                        wpa_ssid_txt(bss->ssid, bss->ssid_len),
bss->freq);
                os_memset(wpa_s->bssid, 0, ETH_ALEN);
                os_memcpy(wpa_s->pending_bssid, bss->bssid, ETH_ALEN);
        } else {
                wpa_msg(wpa_s, MSG_INFO, "Trying to associate with SSID
'%s'",
                        wpa_ssid_txt(ssid->ssid, ssid->ssid_len));
                os_memset(wpa_s->pending_bssid, 0, ETH_ALEN);
        }

	
//============================================================== 
	 


Following is my understanding about this issue. 
//======================================================================
=
		
	. Supplicant have to wait for driver to send 0x8b15 event to
notify the ASSOC is done. After that, the 4 way handshake will begin.

	. When supplicant reconnect(AP reboots), supplicant will send an
SIOCGIWSCAN ioctl to issue AP SCAN which will block sta_pick_bss from
going to auth state. (coz IEEE80211_SCAN_NOPICK is set)

	.But IEEE80211_SCAN_NOPICK will be self clear when it had been
triggered in sta_pick_bss.

	. If sta_pick_bss can't go into auth state, then the 0x8b15
won't send to supplicant. 
	. wpa_supplicant_timeout will occur in every 10 seconds and will
issue SIOCGIWSCAN ioctl which will turn on  IEEE80211_SCAN_NOPICK.

	. Supplicant will have more chance to keep looping between scan
and timeout.



	. solution:

		1. If sta_pick_bss can keep running, then
IEEE80211_SCAN_NOPICK will be clear in the first match. 
		2. And suppliciant won't trigger SIOCGIWSCAN ioctl which
will set IEEE80211_SCAN_NOPICK on again.
		3. Then madwifi could have more chance to assoc with the
AP.
	
		
	. Code fix:
		1. Mark wpa_s->reassociate = 0
		2. Then supplicant will keep calling
wpa_supplicant_associate instead of let wpa_supplicant_timeout to occur
when match AP is found.
		3. SIOCGIWSCAN ioctl won't be trigger.
		4. Then madwifi could have more chance to assoc with
selecte AP.
//======================================================================
=
Please correct me if I was wrong!!








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