NetBSD Problem Report #48390

From apb@cequrux.com  Wed Nov 20 20:19:09 2013
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Date: Wed, 20 Nov 2013 00:54:04 +0000 (UTC)
From: apb@cequrux.com
To: gnats-bugs@NetBSD.org
Subject: wifi signal strength always reported as zero
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>Number:         48390
>Category:       kern
>Synopsis:       wifi signal strength always reported as zero
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Nov 20 20:20:01 +0000 2013
>Last-Modified:  Wed Nov 20 22:45:00 +0000 2013
>Originator:     Alan Barrett
>Release:        NetBSD 6.99.25
>Organization:
Not much
>Environment:
System: NetBSD 6.99.25
Architecture: i386
Machine: i386
>Description:
        When there are multiple wifi access points with the same
        SSID, wpa_supplicant makes no attempt to use the one with the
        best signal/noise ratio.  Instead, it seems to use any access
        point, in some arbitrary order of preference.  Sending the
        "reassociate" command via wpa_cli makes it try another access
        point, and if this is repeated often enough then wpa_supplicant
        may eventually choose the desired access point.

	I am classifying this as a kernel bug, because the underlying
	problem seems to be that the signal strength is always reported as
	zero, so it's unreasonable to expect wpa_supplicant to make a
	good choice.

	In case it matters, the hardware is probed as follows:

	athn0 at pci2 dev 0 function 0: Atheros AR9285
	athn0: rev 2 (1T1R), ROM rev 14, address b4:xx:xx:xx:xx:xx
	athn0: interrupting at ioapic0 pin 16
	athn0: 11b rates: 1Mbps 2Mbps 5.5Mbps 11Mbps
	athn0: 11g rates: 1Mbps 2Mbps 5.5Mbps 11Mbps 6Mbps 9Mbps 12Mbps 18Mbps 24Mbps 36Mbps 48Mbps 54Mbps

>How-To-Repeat:
	Go to a place that has many access points on the same SSID.

	Run wpa_supplicant:

	$ /usr/sbin/wpa_supplicant -B -i athn0 -c /etc/wpa_supplicant.conf \
		-ddtf/var/log/wpa_supplicant.debug

        A wifi monitor running on an Android phone reports that one of
        the access points has a much higher signal strength than all the
        others, but wpa_supplicant doesn't know this, as can be seen
        through wpa_cli.

        Run wpa_cli, and observe that all access points have signal
        strength 0:

	$ wpa_cli
	Selected interface 'athn0'
	Interactive mode
	> scan_results
	21:24:21.057: bssid / frequency / signal level / flags / ssid
	f8:xx:xx:xx:xx:f6       2432    0       [ESS]   XXXX
	f8:xx:xx:xx:xx:a7       2417    0       [ESS]   XXXX
	f8:xx:xx:xx:xx:d3       2437    0       [ESS]   XXXX
	f8:xx:xx:xx:xx:86       2417    0       [ESS]   XXXX
	f8:xx:xx:xx:xx:23       2447    0       [ESS]   XXXX
	f8:xx:xx:xx:xx:83       2432    0       [ESS]   XXXX
	f8:xx:xx:xx:xx:64       2412    0       [ESS]   XXXX
	> status
	[...] bssid=f8:xx:xx:xx:xx:f6
	[...]
	> reassociate
	[...] OK
	[...] CTRL-EVENT-DISCONNECTED bssid=f8:xx:xx:xx:xx:f6 reason=0
	[...] CTRL-EVENT-SCAN-RESULTS
	[...] Trying to associate with f8:xx:xx:xx:xx:f6 [...]
	[...] Associated with f8:1a:67:ec:cf:f6
	[...] CTRL-EVENT-CONNECTED - Connection to f8:xx:xx:xx:xx:f6 [...]

	(Notice that it disconnected and re-associated with the same
	access point.)

	> reassociate
	[...] OK
	[...] CTRL-EVENT-DISCONNECTED bssid=f8:xx:xx:xx:xx:f6 reason=0
	[...] CTRL-EVENT-SCAN-RESULTS
	[...] Trying to associate with f8:xx:xx:xx:xx:83 [...]
	[...] Associated with f8:1a:67:ec:cf:83
	[...] CTRL-EVENT-CONNECTED - Connection to f8:xx:xx:xx:xx:83 [...]

        (This time, it re-associated with a different acecss point.
        Repeat until it eventually chooses an access point with a usable
        signal strength.)

>Fix:
        Make the device driver report the signal strength to
        wpa_supplicant.  (I assume, but have not checked, that
        wpa_supplicant will then sue that information to choose the
        access point with the best signal.)

        Workaround: manually issue "reassociate" commands to wpa_cli
        as many times as necessary to make wpa_supplicant choose the
        "right" acecss point.

>Audit-Trail:
From: Leonardo Taccari <iamleot@gmail.com>
To: gnats-bugs@NetBSD.org
Cc: 
Subject: Re: kern/48390: wifi signal strength always reported as zero
Date: Wed, 20 Nov 2013 23:44:23 +0100

 Hello Alan and all the NetBSD community,

 On Wed, Nov 20, 2013 at 08:20:01PM +0000, apb@cequrux.com wrote:
 > 	I am classifying this as a kernel bug, because the underlying
 > 	problem seems to be that the signal strength is always reported as
 > 	zero, so it's unreasonable to expect wpa_supplicant to make a
 > 	good choice.
 > 
 > 	In case it matters, the hardware is probed as follows:
 > 
 > 	athn0 at pci2 dev 0 function 0: Atheros AR9285
 > 	athn0: rev 2 (1T1R), ROM rev 14, address b4:xx:xx:xx:xx:xx
 > 	athn0: interrupting at ioapic0 pin 16
 > 	athn0: 11b rates: 1Mbps 2Mbps 5.5Mbps 11Mbps
 > 	athn0: 11g rates: 1Mbps 2Mbps 5.5Mbps 11Mbps 6Mbps 9Mbps 12Mbps 18Mbps 24Mbps 36Mbps 48Mbps 54Mbps
 I can confirm that too with (I'm running NetBSD/i386 6.1.2):

  ath0 at pci3 dev 0 function 0: Atheros 5424/2424
  ath0: interrupting at ioapic0 pin 18
  ath0: 11b rates: 1Mbps 2Mbps 5.5Mbps 11Mbps
  ath0: 11g rates: 1Mbps 2Mbps 5.5Mbps 11Mbps 6Mbps 9Mbps 12Mbps 18Mbps 24Mbps 36Mbps 48Mbps 54Mbps
  ath0: mac 14.2 phy 7.0 radio 10.2

 e.g.:

  $ wpa_cli scan_res
  Selected interface 'ath0'
  23:34:47.593: bssid / frequency / signal level / flags / ssid
  XX:XX:XX:XX:XX:XX       2412    0       [WPA2-PSK-CCMP][ESS]      XXX1
  XX:XX:XX:XX:XX:XX       2412    0       [WPA2-PSK-TKIP+CCMP][ESS] XXX0
  XX:XX:XX:XX:XX:XX       2412    0       [WPA-PSK-TKIP][ESS]       XXX2

 However, with:

  # ifconfig ath0 list scan
  SSID                              BSSID              CHAN RATE  S:N     INT CAPS
  XXX0                              XX:XX:XX:XX:XX:XX    1   54M   7:0    100 EP   RSN WME
  XXX1                              XX:XX:XX:XX:XX:XX    1   54M   1:0    100 EP   RSN WME

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