Shulou(Shulou.com)06/03 Report--

In this issue, the editor will bring you about how to write the testtcp.ko module code generated in Linux. The article is rich in content and analyzes and describes for you from a professional point of view. I hope you can get something after reading this article.

Generate the testtcp.ko module and add it to the kernel.

After adding the module, each packet sent by the machine, if it is TCP protocol and the source port is 81, will be changed to RST packet.

I. Code

1.1Files: testtcp_main.c

# include # include unsigned int hook_mark1 (unsigned int hooknum, struct sk_buff * skb, const struct net_device * in, const struct net_device * out, int (* okfn) (struct sk_buff *)) {struct iphdr * iph; struct tcphdr * tcph; struct sk_buff * sk = skb; u16 src_port,dst_port; u16 datalen Iph = ip_hdr (sk); tcph = (struct udphdr*) ((utenint8roomt*) iph + (iph- > ihl source); dst_port = ntohs (tcph- > dest); if (src_port = = 81 | dst_port = 81) printk ("" src_port:%d, dst_port:%d, protocol:%d, rst:%d\ n ", src_port, dst_port, iph- > protocol, tcph- > rst) If (iph- > protocol = = 6 & & src_port = = 81) {printk (""-- 000---src_port:%d, dst_port:%d, protocol:%d, rst:%d\ n ", src_port, dst_port, iph- > protocol, tcph- > rst); tcph- > rst = 1; iph- > check = 0; iph- > check = ip_fast_csum ((unsigned char*) iph, iph- > ihl) Datalen = ntohs (iph- > tot_len)-(iph- > ihl check = 0; tcph- > check = csum_tcpudp_magic (iph- > saddr, iph- > daddr, datalen, iph- > protocol, csum_partial ((unsigned char*) tcph, datalen, 0); skb- > ip_summed = CHECKSUM_NONE; return NF_ACCEPT;} return NF_ACCEPT } static struct nf_hook_ops nfho_marker1;static int init_marker (void) {nfho_marker1.hook=hook_mark1; nfho_marker1.hooknum=NF_INET_LOCAL_OUT; nfho_marker1.pf=PF_INET; nfho_marker1.priority=NF_IP_PRI_LAST; nf_register_hook (& nfho_marker1); return 0;} static void exit_marker (void) {nf_unregister_hook (& nfho_marker1);} module_init (init_marker) Module_exit (exit_marker)

1.2 File Makefile:

Obj-m: = testtcp.o

Testtcp-objs: = testtcp_main.o

KERNELDIR = / lib/modules/$ (shell uname-r) / build

PWD: = $(shell pwd)

Default:

$(MAKE)-C $(KERNELDIR) masking $(PWD) modules

Clean:

$(MAKE)-C / lib/modules/$ (shell uname-r) / build PWD $(PWD) clean

Install:

Cp inerdns.ko.. /

Note:

1. The testtcp.o of the first line cannot be duplicated with the testtcp_main.o of the second line.

two。 The testtcp.o of the first line must be the same as the testtcp-objs prefix of the second line.

3. The content of the next line of "default:", "clean:", "install:" must be preceded by the tab key.

Compile and add modules to the kernel

2.1 compilation

Execute make to compile the code and produce the module testtcp.ko.

2.2 add modules to the kernel

Lsmod looks at the linux kernel module.

Insmod testtcp.ko adds the testtcp.ko module to the kernel.

(rmmod testtcp removes testtcp.ko modules from the kernel.)

Third, the function of the test module

3.1 Test code

You can modify it by referring to the following article code: http://blog.csdn.net/guowenyan001/article/details/11742621

3.2 access URL under linux

Curl 192.168.9.200:81

3.3 grab the bag and check

Use tcpdump to grab packets to see if the relevant packets have been modified to RST packets.

IV. matters needing attention

The kernel module code may cause the system to crash and need to be restarted, so it is best to test the kernel code on the test machine.

The above is the editor for you to share the Linux generated testtcp.ko module code how to write, if you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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