[BUG]: wlan0 control interface in wpa_supplicant and networkmanager

[joshschmelzle]

What happened?

wpa_supplicant and networkmanager had control interfaces for wlan0 which was preventing monitor mode from capturing OTA frames.

Relevant log output

Linux wlanpi-a4c 6.12.11-v8-wlanpi+ #1 SMP PREEMPT Mon Jan 27 13:43:30 UTC 2025 aarch64
Welcome to WLAN Pi OS!

* This device is for educational, lab, or testing use ONLY.
* Permanent installs, continuous transmission, & commercial use are PROHIBITED.
* NO WARRANTY, express or implied.
* You are solely responsible for complying with all laws and for the consequences of any use. 

By using this device, you agree to these terms.

Last login: Wed Jan 29 23:09:13 CST 2025 from 10.42.0.10 on pts/0
wlanpi@wlanpi-a4c:~$ ps aux | grep -E 'NetworkManager|wpa_supplicant'
root         466  0.3  1.0 262584 18936 ?        Ssl  00:15   0:00 /usr/sbin/NetworkManager --no-daemon
root         470  0.0  0.5  17540 10992 ?        Ss   00:15   0:00 /sbin/wpa_supplicant -u -s -O DIR=/run/wpa_supplicant GROUP=netdev
wlanpi       953  0.0  0.1   6228  1992 ttyAMA3  S+   00:19   0:00 grep --color=auto -E NetworkManager|wpa_supplicant

How often does this bug happen?

Every time

What version are you using?

Latest

Self Service

• I would be willing to fix this bug myself.

Guidelines and Policies

• I have read the contributing guidelines and agree to follow the code of conduct and contribution policies.

[joshschmelzle]

Another way to confirm this problem is setup a monitor interface like so:

sudo iw dev mon0 del 2>/dev/null
sudo ip link set wlan0 down
sudo iw phy phy0 interface add mon0 type monitor
sudo ip link set mon0 up
sudo ip link set wlan0 up

Open a second terminal or pane in tmux:

sudo tcpdump -i mon0 -n

Wait a few moments just to make sure you have no data coming in.

Trigger a scan on wlan0 from the first terminal/pane:

sudo iw dev wlan0 scan ssid ""

You will see probe responses and beacons come through from the scan.

If you are patient enough (1-2 minutes) and wlan0 is an active control interface, eventually you'll probably see automatic probe responses and beacons during the next scan interval.