Firewall rule

• Firewall rules defines what kind of Internet traffic is allowed or blocked
• Firewall Rules examine the control information in individual packets.
• These rules either block or allow the packets based on rules that are defined on the device or in code

Categories

•  4 categories of rules

1. 1. raw - To route raw packets
   2. mangle - QoS configuration
   3. nat - routing for IPv4 LAN , ipv6
   4. filter - filtering internal packets before forward

How it is handled in RDKB 

• 10_firewall exe is responsible for firewall events and it registers for sysevent callback with service name as firewall.
• Handler script is firewall_log_handle.sh.
• If any firewall event occurs sysevent is triggered with firewall-restart event name.
• On firewall-restart event service_start() method gets called.
• Ip4table and Ip6table rules are prepared by reading data from shared memory, written into /tmp/.ipt and /tmp/.ipt_v6 files respectively.
• Iptable rules are restored using these files.

Steps to persist the new rules

• If to replace all the rules with your set of rules

1. Create a script and place it under ./meta-rdk-broadband/recipes-ccsp/util/utopia

2. Add and install in utopia.bb file

   SRC_URI += "file://iptables.sh" install -m 755 ${WORKDIR}/iptables.sh ${D}${sysconfdir}

3. In firewall.c file , create your function to invoke the script instead of service_start(); in main()

   static int new_firewall() { system("sh /etc/iptables.sh"); return 0; }

• To have new rules on top of existing rules

1. Install your script under /etc 

2. Invoke your script from firewall_log_handle.sh file 

   /fss/gw/usr/bin/GenFWLog -c /fss/gw/usr/bin/firewall $* /etc/fw_iptables.sh   /fss/gw/usr/bin/GenFWLog -gc

3. In script , the rules has to be cleared/flushed before adding . During firewall restarts , if the rules are not cleared before adding , the same rules will be listed multiple times in "iptables -L / -S" .

• Manual adding of firewall rules on board

1. Place all your new rules in a script under /nvram

2. In firewall_log_handle.sh file , add a condition as below

   if [ -f /nvram/<file>.sh ] then   . /nvram/<file>.sh fi

3. Suppose , if  any script already running with few set of ip rules (from source code ) which is invoked in firewall_log_handle.sh file , follow the below steps

4. copy the existing script from /<original-path>  to /nvram

5. The changes (adding new rules manually) should be done in the script under /nvram

6. In firewall_log_handle.sh file , add the condition as 

   if [ -f /nvram/<file>.sh ] then   . /nvram/<file>.sh else   . /<original-path>/<file>.sh fi

7. Once the complete verification is done , the script file from /nvram has to be deleted .

Limitations

1. We should not add/remove the rules directly in firewall.c file since it is common to all other boards
2. We can do by enabling DISTRO_FEATURE . But again we should be knowing the exact rules to remove/add . This should not affect the basic functionalities like board bring up , components bring up , routing packets, etc.,