Use Ubuntu’s “hostapd” to monitor your smartphone

I don’t like smart-phones at all. I do not like how people use them in bars and restaurants. I also don’t like that the phone is always online. Especially not since all kinds of “apps” and background processes are constant leaking information about me. Call me a fool, but I’m worried about my privacy. Since my friends nowadays refuse to send me SMS (they solely rely on WhatsApp) I was getting socially isolated (showing up at canceled events and so on). That is why I recently gave up my stubbornness and decided to buy a smartphone as well. Still everyday I am wondering what (and how) my smartphone is communicating over the Internet. To get an answer to this question I decided to investigate this.

Parts

I had the above Sitecom (WL-113) USB wifi dongle laying around that could serve as an access point for my phone so that I could peek into the communication on my PC using the excellent open source Wireshark software. This is a diagram of the infrastructure:

I am running Xubuntu 14.04 and I connected my USB dongle.

Preparation

First I ran “lsusb” to confirm the adapter was identified.

maurits@nuc:~$ lsusb
...
Bus 002 Device 024: ID 0df6:9071 Sitecom Europe B.V. WL-113 rev 1 Wireless Network USB Adapter

And yes it was. Great! Now to see what the system says about it when I connected it. Running “dmesg” showed me the driver that was loaded:

maurits@nuc:~$ dmesg
...
[20068.576242] usb 2-1.4: new high-speed USB device number 24 using ehci-pci
[20068.669492] usb 2-1.4: New USB device found, idVendor=0df6, idProduct=9071
[20068.669498] usb 2-1.4: New USB device strings: Mfr=16, Product=32, SerialNumber=0
[20068.669501] usb 2-1.4: Product: USB2.0 WLAN
[20068.669504] usb 2-1.4: Manufacturer: Sitecom
[20068.744236] usb 2-1.4: reset high-speed USB device number 24 using ehci-pci
[20068.837283] ieee80211 phy12: Selected rate control algorithm 'minstrel_ht'
[20068.837521] zd1211rw 2-1.4:1.0: phy12
[20068.855382] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready

To see whether the adapter was really there I ran “ifconfig -a” and yes it was and it was named “wlan0”:

maurits@nuc:~$ ifconfig -a
...
lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:5387 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5387 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:634228 (634.2 KB)  TX bytes:634228 (634.2 KB)

wlan0     Link encap:Ethernet  HWaddr 00:00:de:ad:be:ef
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

I did get a little curious of what the dongle would look like on the inside, so I Googled for “zydas wl-113”. I found the following image on Wireless-Forum.ch:

I also found a guy who had a Sitecom WL-113 with a Ralink 2571WF chip inside (probably not a “rev 1” model). But I am pretty sure mine has a ZyDAS 1211 as in the above picture (but I did not open it up). Before we can do “nice” things with it we need to see whether it supports “master mode“. This means that the dongle goes into a mode in which it behaves as an access point. Ubuntu has a tool called “iw” (install it with “sudo apt-get install iw”) that allows you to list the supported modes (amongst many other things) like this:

maurits@nuc:~$ iw list
Wiphy phy12
    ...
    Supported interface modes:
         * IBSS
         * managed
         * AP
         * AP/VLAN
         * monitor
         * mesh point

Bingo! Our dongle supports “AP” mode (many devices do not). You may want to try to put the adapter in master mode with the following command:

maurits@nuc:~$ iwconfig wlan0 mode master
Error for wireless request "Set Mode" (8B06) :
    SET failed on device wlan0 ; Operation not permitted.

But that fails. After reading the web a little I found that this does not mean that the dongle does not support it.

Installing “hostapd” the host access point daemon

You just need to install “hostapd” program using “sudo apt-get install hostapd”. Before you can start the hostapd application you need to take a few steps. First I had to create the “/etc/hostapd/hostapd.conf” file with the following contents:

interface=wlan0
bridge=br0
driver=nl80211
ssid=MyNetwork
hw_mode=g
channel=7
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=3
wpa_passphrase=YourPassPhrase
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

Now edit the file “/etc/default/hostapd” and uncomment the “DAEMON_CONF” line and make it:

DAEMON_CONF="/etc/hostapd/hostapd.conf"

If we want the PC to temporarily act like a router we need to enable IPv4 forwarding:

sudo sysctl -w net.ipv4.ip_forward=1

Now you can start the “hostapd” access point software with:

sudo hostapd /etc/hostapd/hostapd.conf

If all goes well it should show:

maurits@nuc:~$ sudo hostapd /etc/hostapd/hostapd.conf
Configuration file: /etc/hostapd/hostapd.conf
Using interface wlan0 with hwaddr 00:00:de:ad:be:ef and ssid "MyNetwork"
wlan0: interface state UNINITIALIZED->ENABLED
wlan0: AP-ENABLED

If it does not work you may want to run the following:

sudo nmcli nm wifi off
sudo rfkill unblock wlan

This is because network manager has detected the wlan interface and grabbed it. If you need debug output you may run:

sudo hostapd -d /etc/hostapd/hostapd.conf

If you need even more debug output you may run:

sudo hostapd -dd /etc/hostapd/hostapd.conf

If this fails with the following message:

hostapd_free_hapd_data: Interface wlan0 wasn't started

Then execute:

sudo service hostapd stop

If it says it started (using “sudo hostapd”), but you actually don’t see the Wifi network on your smartphone then reconnecting the dongle and starting all over again may help. Note that the “hostapd” service will automatically be started on next boot.

Bridging to get Internet access

Now you may want to configure a bridge between eth0 (your Internet connection) and wlan0 (your dongle access point). First we remove the IP address from eth0 using. Then we add eth0 to bridge br0 (which already contains wlan0). After that we bring the bridge up, let it do DHCP and which also adds a default route to the gateway using:

sudo ifconfig eth0 inet 0.0.0.0
sudo brctl addif br0 eth0
sudo ifconfig br0 up
sudo dhclient br0

Now you should still be able to surf the Internet while you also have a software access point running on your computer. If you want to undo the bridge configuration you may run:

sudo ifconfig br0 down
sudo brctl delif br0 wlan0
sudo brctl delif br0 eth0
sudo ifconfig br0 down
sudo dhclient eth0

Permanent configuration (persist on reboot)

The IPv4 forwarding setting can be made permanent by uncommenting the following line in “/etc/sysctl.conf”:

# Uncomment the next line to enable packet forwarding for IPv4
net.ipv4.ip_forward=1

If you want to make the bridge configuration permanent you can add the following to “/etc/network/interfaces”:

manual wlan0
manual eth0

auto br0
iface br0 inet dhcp
        bridge_ports eth0

Note that this wont work since the network manager will still grab the wlan0 and execute “rfkill”. To avoid this you can turn off the network manager completely (and permanently) with:

sudo service network-manager stop
echo "manual" | sudo tee /etc/init/network-manager.override

To re-enable the network manager simply do the opposite:

sudo rm /etc/init/network-manager.override
sudo service network-manager start

Capturing with Wifi with Wireshark

Now we can start Wireshark on the wlan0 interface using:

sudo wireshark wlan0

And we get nice output:

Using this tool I can record and analyze the communication of the apps I installed on my smartphone.

Links/sources

Figuring all the above out was not possible without the following websites:

• http://cberner.com/2013/02/03/using-hostapd-on-ubuntu-to-create-a-wifi-access-point/
• http://superuser.com/questions/520172/wired-to-wireless-bridge-in-linux
• http://superuser.com/questions/715913/configuring-wifi-access-point-on-laptop-with-hostapd
• https://bugs.launchpad.net/ubuntu/+source/wpa/+bug/1289047
• https://wiki.archlinux.org/index.php/Software_Access_Point
• http://wireless.kernel.org/en/users/Documentation/hostapd?action=show&redirect=RTFM-AP
• http://www.cyberciti.biz/faq/debian-ubuntu-linux-setting-wireless-access-point/
• https://help.ubuntu.com/community/NetworkConnectionBridge
• http://xmodulo.com/disable-network-manager-linux.html