Bug#684291: aircrack-ng: Negative signal levels with drivers based on mac80211

[Paul Menzel]

Package: aircrack-ng
Version: 1:1.1-5
Severity: normal

Dear Debian folks,


trying Aircrack-ng on a Debian Eee PC 701 4G with the following WLAN device

01:00.0 Ethernet controller: Atheros Communications Inc. AR242x / AR542x Wireless Network Adapter (PCI-Express) (rev 01)

and the following module

$ sudo modinfo ath5k
filename: /lib/modules/3.2.0-3-686-pae/kernel/drivers/net/wireless/ath/ath5k/ath5k.ko
license: Dual BSD/GPL
description: Support for 5xxx series of Atheros 802.11 wireless LAN cards.
author: Nick Kossifidis
author: Jiri Slaby
alias: pci:v0000168Cd0000001Dsv*sd*bc*sc*i*
alias: pci:v0000168Cd0000001Csv*sd*bc*sc*i*
alias: pci:v0000168Cd0000001Bsv*sd*bc*sc*i*
alias: pci:v0000168Cd0000001Asv*sd*bc*sc*i*
alias: pci:v0000168Cd00000019sv*sd*bc*sc*i*
alias: pci:v0000168Cd00000018sv*sd*bc*sc*i*
alias: pci:v0000168Cd00000017sv*sd*bc*sc*i*
alias: pci:v0000168Cd00000016sv*sd*bc*sc*i*
alias: pci:v0000168Cd00000015sv*sd*bc*sc*i*
alias: pci:v0000168Cd00000014sv*sd*bc*sc*i*
alias: pci:v0000168Cd00001014sv*sd*bc*sc*i*
alias: pci:v000010B7d00000013sv*sd*bc*sc*i*
alias: pci:v0000A727d00000013sv*sd*bc*sc*i*
alias: pci:v0000168Cd00000013sv*sd*bc*sc*i*
alias: pci:v0000168Cd00000012sv*sd*bc*sc*i*
alias: pci:v0000168Cd00000011sv*sd*bc*sc*i*
alias: pci:v0000168Cd00000007sv*sd*bc*sc*i*
alias: pci:v0000168Cd00000207sv*sd*bc*sc*i*
depends: mac80211,cfg80211,ath
intree: Y
vermagic: 3.2.0-3-686-pae SMP mod_unload modversions 686
parm: nohwcrypt:Disable hardware encryption. (bool)
parm: all_channels:Expose all channels the device can use. (bool)
parm: fastchanswitch:Enable fast channel switching for AR2413/AR5413 radios. (bool)

`airodump-ng` show negative signal levels (PWR) [1].

This seems to be a know problem with drivers based on the new mac80211
stack [2]. It is written in the Wiki that aircrack-ng v1.0-rc2 fixes
this issue which does not seem to be the case though.


Thanks,

Paul


[1] http://www.aircrack-ng.org/doku.php?id=airodump-ng#what_s_the_meaning_of_the_fields_displayed_by_airodump-ng
[2] http://www.aircrack-ng.org/doku.php?id=mac80211#power_readings_are_way_off

-- System Information:
Debian Release: wheezy/sid
APT prefers unstable
APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: i386 (i686)

Kernel: Linux 3.2.0-3-686-pae (SMP w/1 CPU core)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages aircrack-ng depends on:
ii iw 3.4-1
ii libc6 2.13-13
ii libgcrypt11 1.4.6-8
ii libsqlite3-0 3.7.7-2
ii wireless-tools 30~pre9-8
ii zlib1g 1:1.2.7.dfsg-13

Versions of packages aircrack-ng recommends:
ii wget 1.13.4-3

aircrack-ng suggests no packages.

-- no debconf information

[Paul Menzel]

Control: reopen -1
Control: retitle -1 manual page of airodump-ng incorrectly describes PWR value
Control: found -1 1:1.0-rc2-1


Dear Carlos,


thank you for your quick response.


Am Mittwoch, den 08.08.2012, 16:04 +0200 schrieb Carlos Alberto Lopez Perez:

> On 08/08/12 15:38, Paul Menzel wrote:
> > Package: aircrack-ng
> > Version: 1:1.1-5
> > Severity: normal

> > trying Aircrack-ng on a Debian Eee PC 701 4G with the following WLAN device
> >
> > 01:00.0 Ethernet controller: Atheros Communications Inc. AR242x / AR542x Wireless Network Adapter (PCI-Express) (rev 01)
> >
> > and the following module
> >
> > $ sudo modinfo ath5k
> > filename: /lib/modules/3.2.0-3-686-pae/kernel/drivers/net/wireless/ath/ath5k/ath5k.ko

[…]

> > `airodump-ng` show negative signal levels (PWR) [1].
>

> The values shown are measured on dBm, which is almost always a negative
> number.
>
> You can find on wikipedia http://en.wikipedia.org/wiki/DBm a table
> relating dBm with power.

>
> > This seems to be a know problem with drivers based on the new mac80211
> > stack [2]. It is written in the Wiki that aircrack-ng v1.0-rc2 fixes
> > this issue which does not seem to be the case though.
>

> Please read that link with attention.
>
> The issue was that before v1.0-rc2 airodump-ng was reporting the PWR
> values in the range 150~250 because it got confused with negative numbers.
>
> After v1.0-rc2 airodump-ng correctly reports the values in dBm, that are
> almost always negative numbers.

Thank you for the clarification. I was confused because the Wiki and the
manual page of airodump-ng still describe that value incorrectly then.

> I am closing this bug, since there is no bug. Airodump-ng is doing the
> right thing: reporting the power values on dBm.

I am reopening this report and retitling it to describe the error in the
manual page.


Thanks,

Paul

[Carlos Alberto Lopez Perez]

On 08/08/12 16:13, Paul Menzel wrote:
>> I am closing this bug, since there is no bug. Airodump-ng is doing the
>> > right thing: reporting the power values on dBm.
> I am reopening this report and retitling it to describe the error in the
> manual page.

Could you be more explicit?

Which error on the manpage? I don't see any error on it

man airodump-ng(8)

PWR Signal level reported by the card. Its signification depends on the driver, but as the signal gets higher you get closer to the AP or the station.
If the BSSID PWR is -1, then the driver doesn't support signal level reporting. If the PWR is -1 for a limited number of stations then this is for
a packet which came from the AP to the client but the client transmissions are out of range for your card. Meaning you are hearing only 1/2 of the
communication. If all clients have PWR as -1 then the driver doesn't support signal level reporting.


Where there is any error on this? Is true that if the signal
level is -1 the driver don't support signal level reporting,
as also is true that the signal level can be only positive
(for example with madwifi) as also can be always almost negative
(mac80211 drivers reporting in dBm)