Questions :
- How to work kernel code?
- How to write C code on the kernel?
- How to building and install the kernel on old version linux?
- How to release the linux kernel?
- How to fixes bugs on kernel trees?
I going to write sample C kernel code the answer all question of the linux kernel and you learning write your own code on linux kernel and build it,
1- Downloading repo linux-4.8.0-netfilter_icmp :
root@raminfp ~# cd /tmp/
root@raminfp /tmp#
root@raminfp /tmp# git clone https://github.com/raminfp/linux-4.8.0-netfilter_icmp
2- We added sample module netfilter_icmp in the linux kernel:
root@raminfp /tmp/linux-4.8.0# ls
arch/ COPYING debian.master/ firmware/ ipc/ lib/ net/ samples/ sound/ usr/
block/ CREDITS Documentation/ fs/ Kbuild MAINTAINERS README scripts/ spl/ virt/
build/ crypto/ drivers/ include/ Kconfig Makefile README.md security/ tools/ zfs/
certs/ debian/ dropped.txt init/ kernel/ mm/ REPORTING-BUGS snapcraft.yaml ubuntu/
root@raminfp /tmp/linux-4.8.0# cd net/netfilter_icmp/
root@raminfp /tmp/linux-4.8.0/netfilter_icmp#
root@raminfp /tmp/linux-4.8.0/netfilter_icmp# ls
Kconfig Makefile netfilter_icmp.c
root@raminfp /tmp/linux-4.8.0/netfilter_icmp#
we see netfilter_icmp.c here when you build and install this kernel you are unable to connect to ping google.com, with this code able to drop icmp packet on RING 0,
we see Kconfig file for configuration menuconfig and define Makefile for compile object,
- back to
netdirectory,
root@raminfp /tmp/linux-4.8.0/net# pwd
/tmp/linux-4.8.0/net
root@raminfp /tmp/linux-4.8.0/net# ls
6lowpan/ ax25/ ceph/ dns_resolver/ ipv6/ key/ mac802154/ netlabel/ phonet/ sched/ tipc/ xfrm/
802/ batman-adv/ compat.c dsa/ ipx/ l2tp/ Makefile netlink/ qrtr/ sctp/ unix/
8021q/ bluetooth/ core/ ethernet/ irda/ l3mdev/ mpls/ netrom/ rds/ socket.c vmw_vsock/
9p/ bridge/ dcb/ hsr/ iucv/ lapb/ ncsi/ nfc/ rfkill/ sunrpc/ wimax/
appletalk/ caif/ dccp/ ieee802154/ kcm/ llc/ netfilter/ openvswitch/ rose/ switchdev/ wireless/
atm/ can/ decnet/ ipv4/ Kconfig mac80211/ netfilter_icmp/ packet/ rxrpc/ sysctl_net.c x25/
we see all source directory net, now we need config file Makefile and Kconfig,
Now we should define function name of file header netfilter_icmp.c
root@raminfp /tmp/linux-4.8.0/include# cd net/
root@raminfp /tmp/linux-4.8.0/include//net# ls
6lowpan.h cls_cgroup.h flow_dissector.h inetpeer.h llc.h net_ratelimit.h sock.h
9p/ codel.h flow.h inet_sock.h llc_if.h netrom.h sock_reuseport.h
act_api.h codel_impl.h fou.h inet_timewait_sock.h llc_pdu.h nexthop.h Space.h
addrconf.h codel_qdisc.h fq.h ip6_checksum.h llc_s_ac.h nfc/ stp.h
af_ieee802154.h compat.h fq_impl.h ip6_fib.h llc_sap.h nl802154.h switchdev.h
af_rxrpc.h datalink.h garp.h ip6_route.h llc_s_ev.h p8022.h tc_act/
af_unix.h dcbevent.h genetlink.h ip6_tunnel.h llc_s_st.h phonet/ tcp.h
af_vsock.h dcbnl.h geneve.h ipcomp.h lwtunnel.h ping.h tcp_states.h
ah.h devlink.h gen_stats.h ipconfig.h mac80211.h pkt_cls.h timewait_sock.h
arp.h dn_dev.h gre.h ip_fib.h mac802154.h pkt_sched.h transp_v6.h
atmclip.h dn_fib.h gro_cells.h ip.h mip6.h protocol.h tso.h
ax25.h dn.h gtp.h ip_tunnels.h mld.h psnap.h udp.h
ax88796.h dn_neigh.h gue.h ipv6.h mpls.h raw.h udplite.h
bluetooth/ dn_nsp.h hwbm.h ip_vs.h mpls_iptunnel.h rawv6.h udp_tunnel.h
bond_3ad.h dn_route.h icmp.h ipx.h mrp.h red.h vsock_addr.h
bond_alb.h dsa.h ieee80211_radiotap.h irda/ ncsi.h regulatory.h vxlan.h
bonding.h dsfield.h ieee802154_netdev.h iucv/ ndisc.h request_sock.h wext.h
bond_options.h dst_cache.h if_inet6.h iw_handler.h neighbour.h rose.h wimax.h
busy_poll.h dst.h ila.h kcm.h netevent.h route.h x25device.h
caif/ dst_metadata.h inet6_connection_sock.h l3mdev.h netfilter/ rtnetlink.h x25.h
calipso.h dst_ops.h inet6_hashtables.h lapb.h netfilter_icmp/ sch_generic.h xfrm.h
cfg80211.h esp.h inet_common.h lib80211.h netlabel.h scm.h
cfg80211-wext.h ethoc.h inet_connection_sock.h llc_c_ac.h netlink.h sctp/
cfg802154.h fib_rules.h inet_ecn.h llc_c_ev.h net_namespace.h secure_seq.h
checksum.h firewire.h inet_frag.h llc_conn.h netns/ slhc_vj.h
cipso_ipv4.h flowcache.h inet_hashtables.h llc_c_st.h netprio_cgroup.h snmp.h
root@raminfp /tmp/linux-4.8.0/include/net# cd netfilter_icmp/
root@raminfp /tmp/linux-4.8.0/include/net/netfilter_icmp# ls
netfilter_icmp.h
it's done,now we should define this function name from file header netfilter_icmp on main.c file linux,
Go to :
root@raminfp /tmp/linux-4.8.0# cd init/
root@raminfp /tmp/linux-4.8.0/init# ls
calibrate.c do_mounts.h do_mounts_md.c initramfs.c Kconfig Makefile version.c
do_mounts.c do_mounts_initrd.c do_mounts_rd.c init_task.c main.c noinitramfs.c
we declare header file init/main.c and call function header file here
Building linux kernel :
make menuconfig
Help NETFILTER ICMP
Now we build kernel code on the linux kernel you find binary package of build here
build and install kernel package :
root@raminfp /tmp# cd linux-4.8.0/
root@raminfp /tmp/linux-4.8.0# ls
arch/ COPYING debian.master/ firmware/ ipc/ lib/ net/ samples/ sound/ usr/
block/ CREDITS Documentation/ fs/ Kbuild MAINTAINERS README scripts/ spl/ virt/
build/ crypto/ drivers/ include/ Kconfig Makefile README.md security/ tools/ zfs/
certs/ debian/ dropped.txt init/ kernel/ mm/ REPORTING-BUGS snapcraft.yaml ubuntu/
root@raminfp /tmp/linux-4.8.0# cd build/
root@raminfp /tmp/linux-4.8.0/build# ls
linux-headers-4.8.17-netfilter-icmp_05-mar-2017_amd64.deb linux-image-4.8.17-netfilter-icmp_05-mar-2017_amd64.deb
root@raminfp /tmp/linux-4.8.0/build# dpkg --install linux-headers-4.8.17-netfilter-icmp_05-mar-2017_amd64.deb
root@raminfp /tmp/linux-4.8.0/build# dpkg --install linux-image-4.8.17-netfilter-icmp_05-mar-2017_amd64.deb
root@raminfp /tmp/linux-4.8.0/build# reboot
Go to advance options of ubuntu :
now we see 4.8.17-netfilter_icmp this is we kernel,
We have on own kernel now what heppen of my code , please see image, we see kernel release and access to google.com,this means any drop packet ICMP,
now echo 1 > /proc/netfilter_proc_a we see /proc/netfilter_proc_a is true this means drop ICMP packet,
