Linux Firewall

Implementation of a simple Linux Firewall using Netfilter for packet manipulation. The source code is licensed under MIT license (see LICENSE) and you should use it (insert builded kernel module) ONLY at your OWN RISK.

User space application

Command line application that communicates with a given kernel module. The possible command line arguments are following:

• argument -a RULE
• add specific rule to the filtering logic
• RULE: NUMBER ACTION PROTOCOL FROM address TO address src dst, where address is IP or ANY, src is optional (SRCPORT NUMBER) and dst is optional destination port (DSTPORT NUMBER).
• argument -f FILTER-FILE
• add all rules defined in the file FILTER-FILE to the filtering logic
• argument -d RULE-ID
• delete rule from the filtering logic
• RULE-ID is a rule identificator
• argument -p
• print list of rules defined in the module

Kernel module

Implementation of the kernel modul for Linux in version compatible with kernel version 3.13.

Provided files

The repository contains files

• pdsfw.c - kernel module
• pdscli.c - user space application
• lexer.l - lexical analyzer (flex) input
• parser.y - parser (bison) input
• Makefile

Using the make command it is possible to build user space application and kernel module. The kernel module can be loaded using command insmod pdsfw.ko (at your own risk !!!) and removed using command rmmod pdsfw. In case of unexpected problems (eg. failure due to lack of memory, ...), the state is written in log file which can be displayed using command dmesg.

References

• How to Write a Linux Firewall
• Course: Data Communications, Computer Networks and Protocols