I recently had to setup some openSUSE Linux boxes which will be used to capture add-hoc network traffic for debugging purposes. As there will be multiple users with the need to do this, I wanted to allow the use of tcpdump by non-root users. This is fairly straight forward to accomplish using file system capabilities, but as it’s not clearly documented anywhere else here is what I came up with:

1. First install tcpdump and libcap-progs:

   zypper install tcpdump libcap-progs
   

2. Then create a dedicated group called pcap for users who should be able to run tcpdump and add your user to it:

   groupadd pcap
   usermod -a -G pcap peter
   

3. Modify the group ownership and permissions of the tcpdump binary so that only users in the pcap group can run it:

   chgrp pcap /usr/sbin/tcpdump
   chmod 750 /usr/sbin/tcpdump
   

4. Set the CAP_NET_RAW and CAP_NET_ADMIN capabilities on the tcpdump binary to allow it to run without root access (These options allow raw packet captures and network interface manipulation):

   setcap cap_net_raw,cap_net_admin=eip /usr/sbin/tcpdump
   

5. Optionally, check that the permissions are correct:

   # ls -l /usr/sbin/tcpdump
   -rwxr-x--- 1 root pcap 770776 Feb 19  2011 /usr/sbin/tcpdump
   
   # getcap /usr/sbin/tcpdump
   /usr/sbin/tcpdump = cap_net_admin,cap_net_raw+eip
   

6. Optionally, symlink the tcpdump binary to a directory that is in the path for a normal user:

   ln -s /usr/sbin/tcpdump /usr/local/bin/tcpdump
   

7. Optionally, configure the SuSEconfig permissions module so that it wont reset the file permissions next time you run it by adding the following to the bottom of /etc/permissions.local

   /usr/sbin/tcpdump             root:pcap       0750
    +capabilities cap_net_admin,cap_net_raw+eip
   

8. Inform that Linux kernel that it should enable file system capabilities at boot by adding the following option to the kernel line in /boot/grub/menu.lst:

   file_caps=1
   

9. Reboot to enable file system capabilities

Harald Welte, has written on his blog about operating an Open Source GSM network at the recent HAR2009 conference. Photographs and a description and of the setup, run under license of the Dutch regulatory authority, are provided; essentially the setup consisted of a pair of BTS’ (Base Transceiver Stations) running at 100mW transmit power each and tied to a tree. In turn these provided access to the Base Station Controller (BSC), in this case a Linux server in a tent running OpenBSC. The system authenticated users with a token sent via SMS; in total 391 users subscribed to the service and were able to use their phones as if they were on any other network. Independent researchers are increasingly examining GSM networks and equipment, Welte’s work proves that GSM is in the realm of the hackers now and that this realm of mobile networking could be set for a few surprises in the future.

I just discovered Pyrit which takes a step ahead in attacking WPA-PSK and WPA2-PSK, the protocols that protect today’s public WIFI-airspace.

Pyrit‘s implementation allows to create massive databases, pre-computing part of the WPA/WPA2-PSK authentication phase in a space-time-tradeoff. The performance gain for real-world-attacks is in the range of three orders of magnitude which urges for re-consideration of the protocol’s security. Exploiting the computational power of Many-Core- and other platforms through ATI-Stream, Nvidia CUDA, OpenCL and VIA Padlock, it is currently by far the most powerful attack against one of the world’s most used security-protocols.

I continue to be amazed by the widely varied uses that these hardware graphics accelerators can be put to!