通过netlink实现内核模块和应用层通信

skb常用操作函数，比较容易弄混

skb_put : skb->tail += len, skb->len += len
skb_pull: skb->data += len, skb->len -= len
skb_push: skb->data -= len, skb->len += len

内核版本Linux2.6.38，编译环境gcc 4.4.4，CentOS6.0

内核模块代码：

/*
* author: [email protected]
* date : 2011-10-29
*/
#include <linux/module.h>
#include <linux/netlink.h>
#include <linux/sched.h>
#include <net/sock.h>
#include <linux/proc_fs.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/icmp.h>
#include <linux/udp.h>
#define NETLINK_TEST 30
/* 调试信息 */
#define LOGMSG(fmt, arg...) \
do{ \
printk("[func:%s,line:%d]: "fmt, __FUNCTION__, __LINE__, ##arg); \
}while(0)
/* 错误信息 */
#define LOGERR(fmt, arg...) \
do{ \
printk("[func:%s,line:%d]: "fmt, __FUNCTION__, __LINE__, ##arg); \
}while(0)
/* 断言 */
#define ASSERT(expr) \
if (unlikely(!(expr))) { \
printk("Assertion failed! %s,%s,%s,line=%d\n", \
#expr, __FILE__, __func__, __LINE__); \
}
/* 消息最大值 */
#define MAX_MSG_LEN 1024
enum{
NLMSG_TYPE_NONE = 0,
NLMSG_TYPE_SETPID, /* 设置PID */
NLMSG_TYPE_KERNEL, /* 消息来自内核 */
NLMSG_TYPE_APP, /* 消息来自应用层 */
};
struct nlmsg{
int type; /* 消息类型 */
int len; /* 消息长度，包括头部 */
char msg[MAX_MSG_LEN]; /* 消息正文 */
};
/* netlink socket */
static struct sock *g_nl_sk = NULL;
static int g_nlpid = -1; /* 应用层接收程序PID */
/*
* 发送整个从ip头开始的skb数据到应用层
*
* param[in]: sk, skb发送目的socket
* param[in]: skb, 待发送的skb
* return -1, 失败; 0, 成功
* */
int nl_sendskb(struct sock *sk, struct sk_buff *skb)
{
struct iphdr *iph = NULL;
struct nlmsghdr *nlh = NULL;
struct sk_buff *nl_skb = NULL;
int skb_len = 0;
ASSERT(skb != NULL);
ASSERT(sk != NULL);
if(g_nlpid < 0)
return 0;
iph = ip_hdr(skb);
skb_len = iph->tot_len;
/* NLMSG_SPACE: sizeof(struct nlmsghdr) + len按4字节对齐 */
nl_skb = alloc_skb(NLMSG_SPACE(skb_len), GFP_ATOMIC);
if(!nl_skb)
{
LOGERR("nl_skb == NULL, failed!\n");
return -1;
}
/*
* static inline struct nlmsghdr *nlmsg_put(struct sk_buff *skb, u32 pid, u32 seq,
* int type, int payload, int flags);
* 设置skb->tail指针指向skb->data + sizeof(struct nlmsghdr) + payload
* skb->len = sizeof(struct nlmsghdr) + payload
*/
nlh = nlmsg_put(nl_skb, 0, 0, 0, NLMSG_SPACE(skb_len) - sizeof(struct nlmsghdr), 0);
NETLINK_CB(nl_skb).pid = 0; /* 0代表数据来自内核 */
memcpy(NLMSG_DATA(nlh), (char *)iph, htons(iph->tot_len));
/* 将数据发送给进程号22345的进程 */
return netlink_unicast(sk, nl_skb, g_nlpid , MSG_DONTWAIT);
}
/*
* 发送字符串到应用层
*
* param[in]: sk, 数据发往的socket
* param[in]: pmsg, 待发送字符串
* param[in]: msglen, 待发送字符串长度
*
* return: -1, 失败; 0, 成功
* */
int nl_sendmsg(struct sock *sk, struct nlmsg *pmsg)
{
struct nlmsghdr *nlh = NULL;
struct sk_buff *nl_skb = NULL;
int msglen = pmsg->len;
ASSERT(pmsg != NULL);
ASSERT(sk != NULL);
if(g_nlpid < 0)
return 0;
nl_skb = alloc_skb(NLMSG_SPACE(msglen), GFP_ATOMIC);
if(!nl_skb)
{
LOGERR("nl_skb == NULL, msglen = %d, failed!\n", msglen);
return -1;
}
nlh = nlmsg_put(nl_skb, 0, 0, 0,
NLMSG_SPACE(msglen) - NLMSG_HDRLEN, 0);
NETLINK_CB(nl_skb).pid = 0;
memcpy(NLMSG_DATA(nlh), pmsg, msglen);
return netlink_unicast(sk, nl_skb, g_nlpid , MSG_DONTWAIT);
}
/*
* 从应用层接收数据, netlink_kernel_create注册的回调
* param[in]: skb, 包含netlink数据的skb
*
* skb常用操作函数
* skb_put : skb->tail += len, skb->len += len
* skb_pull: skb->data += len, skb->len -= len
* skb_push: skb->data -= len, skb->len += len
*/
static void nl_recvmsg(struct sk_buff *skb)
{
struct nlmsg *pmsg = NULL;
struct nlmsghdr *nlh = NULL;
uint32_t rlen = 0;
while(skb->len >= NLMSG_SPACE(0))
{
nlh = nlmsg_hdr(skb);
if(nlh->nlmsg_len < sizeof(*nlh) || skb->len < nlh->nlmsg_len)
return;
rlen = NLMSG_ALIGN(nlh->nlmsg_len);
if(rlen > skb->len)
rlen = skb->len;
pmsg = (struct nlmsg*)NLMSG_DATA(nlh);
switch(pmsg->type)
{
case NLMSG_TYPE_SETPID:
g_nlpid = nlh->nlmsg_pid;
LOGMSG("pid: %d\n", g_nlpid);
LOGMSG("msg: %s\n", pmsg->msg);
break;
case NLMSG_TYPE_KERNEL:
break;
case NLMSG_TYPE_APP:
break;
}
/* 获取下一条netlink消息 */
skb_pull(skb, rlen);
}
}
/*
* netfilter PRE_ROUTING钩子
* */
unsigned int pre_routing_hook(unsigned int hooknum,
struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
int (*okfn)(struct sk_buff *))
{
char *psend = "msg for kernel";
struct nlmsg msg;
int ret = 0;
msg.type = NLMSG_TYPE_KERNEL;
msg.len = strlen(psend) + offsetof(struct nlmsg, msg) + 1;
memcpy(msg.msg, psend, msg.len);
//ret = nl_sendskb(g_nl_sk, skb);
ret = nl_sendmsg(g_nl_sk, &msg);
//LOGMSG("ok\n");
return NF_ACCEPT;
}
static struct nf_hook_ops local_in_ops __read_mostly = {
.hook = pre_routing_hook,
.owner = THIS_MODULE,
.pf = PF_INET,
.hooknum = NF_INET_PRE_ROUTING,
.priority = NF_IP_PRI_FIRST
};
static int __init nl_init(void)
{
int ret = 0;
/*
* struct sock *netlink_kernel_create(struct net *net, int unit, unsigned int groups,
* void (*input)(struct sk_buff *skb),
* struct mutex *cb_mutex, struct module *module)
*/
g_nl_sk = netlink_kernel_create(&init_net, NETLINK_TEST, 0, nl_recvmsg, NULL, THIS_MODULE);
if (!g_nl_sk) {
LOGERR("Fail to create netlink socket.\n");
return -1;
}
ret = nf_register_hook(&local_in_ops);
if(ret < 0)
{
LOGMSG("nf_register_hook failed!\n");
goto sock_release;
}
LOGMSG("ok!\n");
return 0;
sock_release:
if(g_nl_sk)
sock_release(g_nl_sk->sk_socket);
return -1;
}
static void __exit nl_exit(void)
{
synchronize_sched();
if(g_nl_sk)
sock_release(g_nl_sk->sk_socket);
nf_unregister_hook(&local_in_ops);
LOGMSG("ok!\n");
}
module_init(nl_init);
module_exit(nl_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("[email protected]");

通过netlink实现内核模块和应用层通信

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