netfilter内核态与用户态 通信 之 sockopt

用户态与内核态交互通信的方法不止一种，sockopt是比较方便的一个，写法也简单.
缺点就是使用 copy_from_user()/copy_to_user()完成内核和用户的通信， 效率其实不高， 多用在传递控制 选项 信息，不适合做大量的数据传输

用户态函数：
发送：int setsockopt ( int sockfd, int proto, int cmd, void *data, int datelen);
接收：int getsockopt(int sockfd, int proto, int cmd, void *data, int datalen)
第一个参数是socket描述符；
第二个参数proto是sock协议，IP RAW的就用SOL_SOCKET/SOL_IP等，TCP/UDP socket的可用SOL_SOCKET/SOL_IP/SOL_TCP/SOL_UDP等，即高层的socket是都可以使用低层socket的命令字 的，IPPROTO_IP；
第三个参数cmd是操作命令字，由自己定义；
第四个参数是数据缓冲区起始位置指针，set操作时是将缓冲区数据写入内核，get的时候是将内核中的数 据读入该缓冲区；
第五个参数数据长度

内核态函数
注册：nf_register_sockopt(struct nf_sockopt_ops *sockops)
解除：nf_unregister_sockopt(struct nf_sockopt_ops *sockops)

结构体 nf_sockopt_ops test_sockops

struct nf_sockopt_ops {
    struct list_head list;

    u_int8_t pf; // 协议族

    /* Non-inclusive ranges: use 0/0/NULL to never get called. */
    int set_optmin;// 定义最小set命令字
    int set_optmax;// 定义最大set命令字
    int (*set)(struct sock *sk, int optval, void __user *user, unsigned int len);// 定义set处理函数
#ifdef CONFIG_COMPAT
    int (*compat_set)(struct sock *sk, int optval,
            void __user *user, unsigned int len);
#endif
    int get_optmin;// 定义最小get命令字
    int get_optmax;// 定义最大get命令字
    int (*get)(struct sock *sk, int optval, void __user *user, int *len);// 定义get处理函数
#ifdef CONFIG_COMPAT
    int (*compat_get)(struct sock *sk, int optval,
            void __user *user, int *len);
#endif
    /* Use the module struct to lock set/get code in place */
    struct module *owner;
};

其中命令字不能和内核已有的重复，宜大不宜小。命令字很重要，是用来做标识符的。而且用户态和内核态要定义的相同，

系统调用如下：sockt==》sock_common_setsockopt==》sk->sk_prot->setsockopt==》ip_setsockopt（tcp为例）

　　　　==>do_ip_setsockopt

　　　　==> nf_setsockopt==>nf_sockopt

int ip_setsockopt(struct sock *sk, int level,
        int optname, char __user *optval, unsigned int optlen)
{
    int err;

    if (level != SOL_IP)
        return -ENOPROTOOPT;

    err = do_ip_setsockopt(sk, level, optname, optval, optlen);
#ifdef CONFIG_NETFILTER
    /* we need to exclude all possible ENOPROTOOPTs except default case */
    if (err == -ENOPROTOOPT && optname != IP_HDRINCL &&
            optname != IP_IPSEC_POLICY &&
            optname != IP_XFRM_POLICY &&
            !ip_mroute_opt(optname)) {
        lock_sock(sk);
        err = nf_setsockopt(sk, PF_INET, optname, optval, optlen);
        release_sock(sk);
    }
#endif
    return

 err;
}

/* Call get/setsockopt() */
static int nf_sockopt(struct sock *sk, u_int8_t pf, int val,
              char __user *opt, int *len, int get)
{
    struct nf_sockopt_ops *ops;
    int ret;

    ops = nf_sockopt_find(sk, pf, val, get);
    if (IS_ERR(ops))
        return PTR_ERR(ops);

    if (get)
        ret = ops->get(sk, val, opt, len);
    else
        ret = ops->set(sk, val, opt, *len);

    module_put(ops->owner);
    return ret;
}

int nf_setsockopt(struct sock *sk, u_int8_t pf, int val, char __user *opt,
          unsigned int len)
{
    return nf_sockopt(sk, pf, val, opt, &len, 0);
}

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/netfilter_ipv4.h>
#include <linux/init.h>
#include <asm/uaccess.h> 

#define SOCKET_OPS_BASE          128
#define SOCKET_OPS_SET       (SOCKET_OPS_BASE)
#define SOCKET_OPS_GET      (SOCKET_OPS_BASE)
#define SOCKET_OPS_MAX       (SOCKET_OPS_BASE + 1)

#define KMSG          "--------kernel---------"
#define KMSG_LEN      sizeof("--------kernel---------")

MODULE_LICENSE("GPL");
MODULE_AUTHOR("SiasJack");/*作者*/
MODULE_DESCRIPTION("sockopt module,simple module");//描述
MODULE_VERSION("1.0");//版本号

static int recv_msg(struct sock *sk, int cmd, void __user *user, unsigned int len)
{
    int ret = 0;
    printk(KERN_INFO "sockopt: recv_msg()\n"); 

    if (cmd == SOCKET_OPS_SET)
    {
        char umsg[64];
        int len = sizeof(char)*64;
        memset(umsg, 0, len);
        ret = copy_from_user(umsg, user, len);
        printk("recv_msg: umsg = %s. ret = %d\n", umsg, ret);
    }
    return 0;
} 

static int send_msg(struct sock *sk, int cmd, void __user *user, int *len)
{
    int ret = 0;
    printk(KERN_INFO "sockopt: send_msg()\n");
    if (cmd == SOCKET_OPS_GET)
    {
        ret = copy_to_user(user, KMSG, KMSG_LEN);
        printk("send_msg: umsg = %s. ret = %d. success\n", KMSG, ret);
    }
    return 0;

}

static struct nf_sockopt_ops test_sockops =
{
    .pf = PF_INET,
    .set_optmin = SOCKET_OPS_SET,
    .set_optmax = SOCKET_OPS_MAX,
    .set = recv_msg,
    .get_optmin = SOCKET_OPS_GET,
    .get_optmax = SOCKET_OPS_MAX,
    .get = send_msg,
    .owner = THIS_MODULE,
};

static int __init init_sockopt(void)
{
    printk(KERN_INFO "sockopt: init_sockopt()\n");
    return nf_register_sockopt(&test_sockops);
}

static void __exit exit_sockopt(void)
{
    printk(KERN_INFO "sockopt: fini_sockopt()\n");
    nf_unregister_sockopt(&test_sockops);
}

module_init(init_sockopt);

#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <linux/in.h>
#include <string.h>
#include <errno.h> 

#define SOCKET_OPS_BASE      128
#define SOCKET_OPS_SET       (SOCKET_OPS_BASE)
#define SOCKET_OPS_GET      (SOCKET_OPS_BASE)
#define SOCKET_OPS_MAX       (SOCKET_OPS_BASE + 1) 

#define UMSG      "----------user------------"
#define UMSG_LEN  sizeof("----------user------------") 

char kmsg[64]; 

int main(void)
{
    int sockfd;
    int len;
    int ret; 

    sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
    if(sockfd < 0)
    {
        printf("can not create a socket\n");
        return -1;
    }   

    /*call function recv_msg()*/
    ret = setsockopt(sockfd, IPPROTO_IP, SOCKET_OPS_SET, UMSG, UMSG_LEN);
    printf("setsockopt: ret = %d. msg = %s\n", ret, UMSG);
    len = sizeof(char)*64; 

    /*call function send_msg()*/
    ret = getsockopt(sockfd, IPPROTO_IP, SOCKET_OPS_GET, kmsg, &len);
    printf("getsockopt: ret = %d. msg = %s\n", ret, kmsg);
    if (ret != 0)
    {
        printf("getsockopt error: errno = %d, errstr = %s\n", errno, strerror(errno));
    }   

    close(sockfd);
    return 0;
}

https://blog.csdn.net/jk110333/article/details/8642261  来自转载