如何使用netlink socket与内核模块通信？

Question

我正在尝试编写一个使用netlink与用户进程通信的linux内核模块.我正在使用netlink,因为我想要通信的用户程序只使用套接字进行通信,我无法改变它来添加ioctl()或任何东西.

问题是我无法弄清楚如何做到这一点.我用Google搜索,但我发现所有的例子都是老喜欢这一个,不再适用于当前的内核版本.我也看了这个问题,但这里的示例使用libnl进行套接字操作,但我想坚持使用标准套接字函数(定义sys/socket.h).那么有些人可以在这里指导我一些教程或指南或一些可以帮助我理解netlink的界面和用法的东西.我非常感谢一个工作示例,没什么特别的,只是一个非常基本的例子,说明如何建立从用户程序中的套接字到内核中的套接字的连接,然后将数据从用户进程发送到内核并从内核接收回来.

另请不要告诉我查看内核代码.我已经在做了,但这需要花费很多时间,而且我没有留下很多东西.

更新: 经过大量的试验和错误后,我有以下代码将消息从用户程序发送到内核,但是从内核到用户程序的消息即使用netlink_unicast()不起作用.它不仅没有工作,呼叫挂起系统,然后我必须重新启动机器.有人可以看看,告诉我我在做什么错.该netlink_unicast()调用在以下代码中进行了注释.它应该是内核到用户程序消息的未注释.

用户程序

#include <sys/socket.h>  
#include <linux/netlink.h>  
#define NETLINK_USER 31  
#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;  

void main()  
{  
    sock_fd=socket(PF_NETLINK, SOCK_RAW, NETLINK_USER);  
    if(sock_fd<0)  
        return -1;  

    memset(&src_addr, 0, sizeof(src_addr));  
    src_addr.nl_family = AF_NETLINK;  
    src_addr.nl_pid = getpid();  /* self pid */  
    /* interested in group 1<<0 */  
    bind(sock_fd, (struct sockaddr*)&src_addr,  
      sizeof(src_addr));  

    memset(&dest_addr, 0, sizeof(dest_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));  
    memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));  
    nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);  
    nlh->nlmsg_pid = getpid();  
    nlh->nlmsg_flags = 0;  

    strcpy(NLMSG_DATA(nlh), "Hello");  

    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 to kernel\n");  
    sendmsg(sock_fd,&msg,0);  
    printf("Waiting for message from kernel\n");  

    /* Read message from kernel */  
    recvmsg(sock_fd, &msg, 0);  
    printf(" Received message payload: %s\n",  
        NLMSG_DATA(nlh));  
    close(sock_fd);  
}

内核代码

#include <linux/module.h>  
#include <linux/kernel.h>  
#include <linux/init.h>  
#include <net/sock.h>  
#include <linux/socket.h>  
#include <linux/net.h>  
#include <asm/types.h>  
#include <linux/netlink.h>  
#include <linux/skbuff.h>  

#define NETLINK_USER 31  

struct sock *nl_sk = NULL;  

static void hello_nl_recv_msg(struct sk_buff *skb)  
{
        struct nlmsghdr *nlh;  
        int pid;  

        printk(KERN_INFO "Entering: %s\n", __FUNCTION__);  

        nlh=(struct nlmsghdr*)skb->data;  
        printk(KERN_INFO "Netlink received msg payload: %s\n",
            (char*)NLMSG_DATA(nlh));  
        pid = nlh->nlmsg_pid; /*pid of sending process */  
        NETLINK_CB(skb).dst_group = 0; /* not in mcast group */  
        NETLINK_CB(skb).pid = 0;      /* from kernel */  
        //NETLINK_CB(skb).groups = 0; /* not in mcast group */  
        //NETLINK_CB(skb).dst_pid = pid;  
        printk("About to send msg bak:\n");  
        //netlink_unicast(nl_sk,skb,pid,MSG_DONTWAIT);  

}  

static int __init hello_init(void)  
{  

        printk("Entering: %s\n",__FUNCTION__);  
        nl_sk=netlink_kernel_create(&init_net, NETLINK_USER, 0,
               hello_nl_recv_msg, NULL, THIS_MODULE);  
        if(!nl_sk)  
        {   
                printk(KERN_ALERT "Error creating socket.\n");  
                return -10;  
        }  
        return 0;  
}  

static void __exit hello_exit(void)  
{

        printk(KERN_INFO "exiting hello module\n");  
        netlink_kernel_release(nl_sk);  
}  

module_init(hello_init);  
module_exit(hello_exit);  

Answer 1

在阅读内核源代码后,我终于设法让netlink套接字为我工作.下面是Netlink套接字基础知识的示例,即打开netlink套接字,读取和写入并关闭它.

内核模块

#include <linux/module.h>
#include <net/sock.h> 
#include <linux/netlink.h>
#include <linux/skbuff.h> 
#define NETLINK_USER 31

struct sock *nl_sk = NULL;

static void hello_nl_recv_msg(struct sk_buff *skb)
{

    struct nlmsghdr *nlh;
    int pid;
    struct sk_buff *skb_out;
    int msg_size;
    char *msg = "Hello from kernel";
    int res;

    printk(KERN_INFO "Entering: %s\n", __FUNCTION__);

    msg_size = strlen(msg);

    nlh = (struct nlmsghdr *)skb->data;
    printk(KERN_INFO "Netlink received msg payload:%s\n", (char *)nlmsg_data(nlh));
    pid = nlh->nlmsg_pid; /*pid of sending process */

    skb_out = nlmsg_new(msg_size, 0);
    if (!skb_out) {
        printk(KERN_ERR "Failed to allocate new skb\n");
        return;
    }

    nlh = nlmsg_put(skb_out, 0, 0, NLMSG_DONE, msg_size, 0);
    NETLINK_CB(skb_out).dst_group = 0; /* not in mcast group */
    strncpy(nlmsg_data(nlh), msg, msg_size);

    res = nlmsg_unicast(nl_sk, skb_out, pid);
    if (res < 0)
        printk(KERN_INFO "Error while sending bak to user\n");
}

static int __init hello_init(void)
{

    printk("Entering: %s\n", __FUNCTION__);
    //nl_sk = netlink_kernel_create(&init_net, NETLINK_USER, 0, hello_nl_recv_msg, NULL, THIS_MODULE);
    struct netlink_kernel_cfg cfg = {
        .input = hello_nl_recv_msg,
    };

    nl_sk = netlink_kernel_create(&init_net, NETLINK_USER, &cfg);
    if (!nl_sk) {
        printk(KERN_ALERT "Error creating socket.\n");
        return -10;
    }

    return 0;
}

static void __exit hello_exit(void)
{

    printk(KERN_INFO "exiting hello module\n");
    netlink_kernel_release(nl_sk);
}

module_init(hello_init); module_exit(hello_exit);

MODULE_LICENSE("GPL");

用户程序

#include <linux/netlink.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

#define NETLINK_USER 31

#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;

int main()
{
    sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_USER);
    if (sock_fd < 0)
        return -1;

    memset(&src_addr, 0, sizeof(src_addr));
    src_addr.nl_family = AF_NETLINK;
    src_addr.nl_pid = getpid(); /* self pid */

    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));
    memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));
    nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);
    nlh->nlmsg_pid = getpid();
    nlh->nlmsg_flags = 0;

    strcpy(NLMSG_DATA(nlh), "Hello");

    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 to kernel\n");
    sendmsg(sock_fd, &msg, 0);
    printf("Waiting for message from kernel\n");

    /* Read message from kernel */
    recvmsg(sock_fd, &msg, 0);
    printf("Received message payload: %s\n", NLMSG_DATA(nlh));
    close(sock_fd);
}

关于魔术常量的相关主题NETLINK_USER 31:我可以在内核空间中拥有超过32个netlink套接字吗？

Answer 2

万一有人不知道如何编译,谷歌"如何编译和加载内核模块"

请参阅http://www.cyberciti.biz/tips/compiling-linux-kernel-module.html

从http://kernel.org获取要编译模块的内核源代码

或者,如果您正在运行预期的内核,只需更新标头

# apt-get install kernel-headers-$(uname -r)

例如,创建一个makefile

obj-m = hello.o
KVERSION = $(shell uname -r)
all:
        make -C /lib/modules/$(KVERSION)/build M=$(PWD) modules
clean:
        make -C /lib/modules/$(KVERSION)/build M=$(PWD) clean

制作,你会得到一堆文件.*.ko是你将加载到内核中的那个,运行

# insmod hello.ko

如果你我们lsmod检查所有加载的模块,你会找到你的,你很可能会看到:

hello       12575  0 

在我们的例子中,编译并运行用户代码:

gcc hello.c -o hello.o
./hello.o

如果一切正常,您将使用binW的代码获得以下消息:

Sending message to kernel
Waiting for message from kernel
 Received message payload: Hello from kernel

最后,使用以下命令删除模块:

# rmmod hello

Answer 3

它适用于内核3.2.对于内核3.6及更高版本,它需要对该netlink_kernel_create函数进行一些更改.

 struct netlink_kernel_cfg cfg = {
                .groups = 1,
                .input = hello_nl_recv_msg,
        };
        printk("Entering: %s\n", __FUNCTION__);
        nl_sk = netlink_kernel_create(&init_net, NETLINK_USER, &cfg);