再次见识了内核的伟大,大半年不碰,忘记的一干二净!!!写netfilter,netlink不得不提的就是九贱和duanjigang了...
Linux 用户态与内核态的交互——netlink 篇
netlink socket 编程之 why & how
%3D1%26amp%3Bfilter%3Ddigest 有了上面两篇文章加kernel source基本上你可以干许多事了...
环境:
centos5.2 2.6.18
作用:
./user -i 禁止ping
./user -d ipaddr 禁止指定ip的tcp连接
iptables+netfilter这一套以前一直是限于理论层面,今天就自己实践了下.
我这里只是写我写程序的过程中遇到的问题,一些概念上的东东,上面两位大师已经写得很好了,我就不班门弄斧了.
struct sock* netlink_kernel_create(int unit, unsigned int groups,
void (*input)(struct sock *sk, int len),
struct module *module)
why&how那篇是:
struct sock * netlink_kernel_create(int unit, void (*input)(struct sock *sk, int len));
取数据我这里传的是结构体
nlh = (struct nlmsghdr*)skb->data;
icmp_off = ((OWN *)NLMSG_DATA(nlh))->icmp_off;
drop_ip = ((OWN *)NLMSG_DATA(nlh))->drop_ip;
netlink主要就是create和取数据那个地方,我这里是看kernel source追寻到了,不同的版本可能不一样.
nfho.hook = hook_func;
nfho.hooknum = NF_IP_LOCAL_IN;
nfho.pf = PF_INET;
nfho.priority = NF_IP_PRI_FIRST;
nf_register_hook(&nfho);
想挂多个hook的话可以
也可以
nf_register_hooks(opts, ARRAY_SIZE(opts));
取头,可以去ip.h tcp.h等去找
好了废话了这么多,上代码了
内核态程序
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include "hook.h"
static struct nf_hook_ops nfho;
struct sock *nl_sk = NULL;
EXPORT_SYMBOL_GPL(nl_sk);
static int icmp_off = 0;
static unsigned int drop_ip = 0;
void input (struct sock* sk, int len)
{
struct sk_buff* skb = NULL;
struct nlmsghdr* nlh = NULL;
printk("net_link: data is ready to read.\n");
while((skb = skb_dequeue(&sk->sk_receive_queue))!=NULL)
{
nlh = (struct nlmsghdr*)skb->data;
icmp_off = ((OWN *)NLMSG_DATA(nlh))->icmp_off;
drop_ip = ((OWN *)NLMSG_DATA(nlh))->drop_ip;
}
return;
}
static int test_netlink(void) {
nl_sk = netlink_kernel_create(NETLINK_TEST, 0, input, THIS_MODULE);
if (!nl_sk) {
printk(KERN_ERR "net_link: Cannot create netlink socket.\n");
return -EIO;
}
printk("net_link: create socket ok.\n");
return 0;
}
unsigned int hook_func(unsigned int hooknum,
struct sk_buff **skb,
const struct net_device *in,
const struct net_device *out,
int (*okfn)(struct sk_buff *))
{
struct sk_buff *sb = *skb;
struct iphdr *iph ;
iph = ip_hdr(sb);
switch(iph->protocol)
{
case IPPROTO_ICMP:{
struct icmphdr _icmph;
struct icmphdr* ich;
ich = skb_header_pointer(sb, iph->ihl*4, sizeof(_icmph), &_icmph);
printk("icmp type %u\n", ich->type);
if(icmp_off == 1)
{
printk("now we drop icmp from %d.%d.%d.%d\n", NIPQUAD(iph->saddr));
return NF_DROP;
}
break;
}
case IPPROTO_TCP:{
struct tcphdr* th = NULL;
struct tcphdr _tcph;
th = skb_header_pointer(sb, iph->ihl*4, sizeof(_tcph), &_tcph);
if(th == NULL)
{
printk("get tcp header error\n");
return NF_DROP;
}
//unsigned int sip = ntohs(th->source);
printk("saddr:%d.%d.%d.%d,sport:%u\n", NIPQUAD(iph->saddr),ntohs(th->source));
printk("daddr:%d.%d.%d.%d,dport:%u\n", NIPQUAD(iph->daddr),ntohs(th->dest));
if(iph->saddr ==drop_ip)
{
printk("now we drop tcp from %d.%d.%d.%d\n", NIPQUAD(iph->saddr));
return NF_DROP;
}
break;
}
default:
break;
}
return NF_ACCEPT;
}
static int __init hook_init()
{
printk("insmod hook test!\n");
test_netlink();
nfho.hook = hook_func;
nfho.hooknum = NF_IP_LOCAL_IN;
nfho.pf = PF_INET;
nfho.priority = NF_IP_PRI_FIRST;
nf_register_hook(&nfho);
return 0;
}
static void __exit hook_exit()
{
printk("rmmod hook test!\n");
nf_unregister_hook(&nfho);
if (nl_sk != NULL){
sock_release(nl_sk->sk_socket);
}
}
module_init(hook_init);
module_exit(hook_exit);
用户态:
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include "hook.h"
#define MAX_PAYLOAD 1024 /* maximum payload size*/
struct sockaddr_nl src_addr, dest_addr;
struct nlmsghdr *nlh = NULL;
struct iovec iov;
int sock_fd;
struct msghdr msg;
struct option longopts[] =
{
{"icmp",no_argument, NULL, 'i'},
{"help",no_argument, NULL, 'h'},
{"drop",required_argument, NULL, 'd'},
{0,0,0,0}
};
void print_help(char* str)
{
fprintf(stderr,"%s --icmp(-i)\n",str);
fprintf(stderr,"%s --drop(-d)\n",str);
fprintf(stderr,"eg:\n%s -i -d 202.114.85.105\n",str);
}
void init_own(OWN** own)
{
*own = (OWN*)malloc(sizeof(OWN));
(*own)->icmp_off = 0;
(*own)->drop_ip = 0;
}
int main(int argc, char* argv[])
{
int c;
OWN* own = NULL;
init_own(&own);
while((c=getopt_long(argc, argv, "hid:", longopts, NULL))!=-1)
{
switch(c)
{
case 'i':
{
own->icmp_off = 1;
break;
}
case 'd':
{
own->drop_ip = inet_addr(optarg);
break;
}
case 'h':
{
print_help(argv[0]);
return -1;
}
default:
break;
}
}
sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_TEST);
memset(&msg, 0, sizeof(msg));
memset(&src_addr, 0, sizeof(src_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid(); /* self pid */
src_addr.nl_groups = 0; /* not in mcast groups */
bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr));
memset(&dest_addr, 0, sizeof(dest_addr));
dest_addr.nl_family = AF_NETLINK;
dest_addr.nl_pid = 0; /* For Linux Kernel */
dest_addr.nl_groups = 0; /* unicast */
nlh=(struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_PAYLOAD));
/* Fill the netlink message header */
nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);
nlh->nlmsg_pid = getpid(); /* self pid */
nlh->nlmsg_flags = 0;
/* Fill in the netlink message payload */
printf("%d, %d\n", own->icmp_off, own->drop_ip);
memcpy(NLMSG_DATA(nlh),own ,sizeof(OWN));
iov.iov_base = (void *)nlh;
iov.iov_len = nlh->nlmsg_len;
msg.msg_name = (void *)&dest_addr;
msg.msg_namelen = sizeof(dest_addr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
printf(" Sending message. ...\n");
sendmsg(sock_fd, &msg, 0);
close(sock_fd);
free(own);
return 0;
} Makefile 头文件
hook.h
#define NETLINK_TEST 21
typedef struct my
{
int icmp_off;
unsigned int drop_ip;
}OWN;
makefile:
obj-m += hook.o
KDIR := /lib/modules/$(shell uname -r)/build
all:
make -C $(KDIR) M=$(shell pwd) modules
gcc -Wall -o user user.c
clean:
make -C $(KDIR) M=$(shell pwd) clean
rm -f *odule* user
usage:
1.make
2. insmod hook.ko (建议tail -f /var/log/messages查看是否success尤其是netlink create是否成功)
3.默认你是可以ping, 和tcp得(我实验室只有两台机子A 202.114.85.105)
4. ./user -i -d 202.114.85.105 (A机不能ping和ftp B)
5../user (取消限制了,可以ping和ftp B)
再次试验成功上传代码:
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