/Firewall

Primary LanguageC

Changes

Before inserting firewall, please make below changes in the firewall code:

  1. Change it to your web server ip: static unsigned char *ip_address = "\xC0\xA8\x01\x03"

  2. Also change eth1 to the interface name by which web client is connected with firewall

Running firewall

To insert firewall module please run following command:

  1. make

  2. insmod firewall.ko

After running make you will get output like this:

root@Firewall:~# make

make -C /lib/modules/3.13.0-68-generic/build M=/root modules
make[1]: Entering directory `/usr/src/linux-headers-3.13.0-68-generic'
CC [M]  /root/firewall.o
/root/firewall.c: In function ‘init_module’:
/root/firewall.c:79:27: warning: assignment from incompatible pointer type [enabled by default]
netfilter_ops_in.hook = main_hook;
                      ^
Building modules, stage 2.
MODPOST 1 modules
LD [M]  /root/firewall.ko
make[1]: Leaving directory `/usr/src/linux-headers-3.13.0-68-generic'

  1. To check information about that module:

    root@Firewall:~# modinfo firewall.ko

    filename: /root/firewall.ko srcversion: 5E8AB462D88D98EABC598BC depends:
    vermagic: 3.13.0-68-generic SMP mod_unload modversions

To remove firewall module please run following command:

  1. rmmod firewall

Firewall Rules:

  1. Block all unsolicited ICMP packets coming in from outside except the ones going to the web-server. However,the local hosts should be able to ping outside.

  2. Block all ssh attempts from outside.

  3. Block port 80 (http) access from outside except for the web-server and test that an internal website on a local host is only accessible from inside.

System detail

  This code is tested in below linux environment:
  Ubuntu 14.04
  root@Firewall:~# uname -a
  Linux Firewall 3.13.0-68-generic #111-Ubuntu SMP Fri Nov 6 18:17:06 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux