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Category: linux

NcN 2013 CTF canada write up

In this post I will cover the second binary challenge of the No Con Name 2013 CTF driven by the Facebook security team. The binary is available here

This binary challenge is based on a i386 stripped elf file which prompts for a flag:

$ file ./howtobasic
./howtobasic: ELF 32-bit LSB executable, Intel 80386, version 1 (GNU/Linux), statically linked, for GNU/Linux 2.6.26, BuildID[sha1]=4f288f1a66ad673dc50b51c7e85635358bb11da0, stripped
$ ./howtobasic
Facebook CTF
Enter flag: asdasdasdasd
Sorry, that is not correct.
$ 

PF_RING + intel igb + snort + DAQ on debian

In this article, I’m going to resume the steps to have a full packet capture solution with snort IDS and Intel NIC’s.

This solutions is based on Luca Deri’s software PF_RING, a new type of socket to exploit the capabilities of packet capture and snort.

We will follow these steps

  1. Download and compile PF_RING
  2. Compile the PF_RING aware network driver
  3. Compile the libpcap
  4. Download and compile DAQ
  5. Compile PF_RING DAQ module
  6. Download and compile snort agains DAQ

bypassing devmem_is_allowed with kernel probes

In this article I’m going to illustrate how to read the full content of /dev/mem on linux 3.x machines. I will bypass the function devmem_is_allowed with a kernel return probe.

The kernel probes is a kernel component designed for kernel developers to debug the system internals.It can dynamically break into any kernel routine and modify the function’s behavour. This proves had been heavily since yeah by kernel developers. RedHat has build an user interface to kprobes called SystemTap
You can find kprobes’ documentation in Documentation/kprobes.txt. You should also download the article example files kprobe.tgz

Reduce BTRFS on LVM (quick recipe)

This is a quick recipe on reducing a btrfs FS inside a LMV structure.

First, the will reduce the “content”, then we will operate over the “container”.

This is the algorithm:

  1. umount /path/to/fs
  2. resize2fs /dev/mapper/vol SIZE (see man resize2fs)
  3. deactivate the volume
  4. lvreduce -L nG /dev/mapper/vol
  5. resize2fs /dev/mapper/vol nG

btrfs is actually considered “experimental”, but is included since stable kernel 3.0.0. Btrfs is the answer from the GNU/Linux community to Sun Microsystems ZFS. You will find more info on wikipedia:

http://es.wikipedia.org/wiki/Btrfs
http://es.wikipedia.org/wiki/ZFS_%28sistema_de_archivos%29