Netlink 套接字创建 returns NULL

Question

我一直在尝试在内核模块和进程之间实现一个非常简单的网络链接通信。但似乎我坚持在内核模块上创建 netlink 套接字。正如我从内核 3.6 及更高版本了解到的那样，netlink_kernel_create 签名是：

static inline struct sock * netlink_kernel_create(struct net *net, int unit, struct netlink_kernel_cfg *cfg)

我的内核是 3.13，因此这是我正在使用的声明。但它总是 returns NULL。

代码如下：

#define NETLINK_LISTEN 17 

struct netlink_kernel_cfg cfg = {
        .input = recieved_message,
};
/* create netlink socket */
netlink = netlink_kernel_create(&init_net, NETLINK_LISTEN , &cfg);

if (!netlink)
{
    << always gets here >> 
    return -1;
} 
else 
{
    return 0;
}

我的OS信息：

uname -a
Linux Mint 3.13.0-37-generic #64-Ubuntu SMP Mon Sep 22 21:28:38 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

Answer 1

我从 : How to use netlink socket to communicate with a kernel module?

如果你像这样初始化组：

struct netlink_kernel_cfg cfg = {
   .groups  = 1,
   .input = hello_nl_recv_msg,
};

然后它在 3.13 内核中也能正常工作:

这段代码对我有用：
内核space:

#include <linux/module.h>
#include <net/sock.h>
#include <linux/netlink.h>
#include <linux/skbuff.h>
#include <net/net_namespace.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");
}

struct netlink_kernel_cfg cfg = {
   .groups  = 1,
   .input = hello_nl_recv_msg,
};

static int __init hello_init(void)
{

    printk("Entering: %s\n", __FUNCTION__);
    nl_sk = netlink_kernel_create(&init_net, NETLINK_USER, &cfg);

    // 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);

MODULE_LICENSE("GPL");

用户Space：

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#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;

    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));
    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);
}

先插入内核模块，然后运行用户 space 可执行文件。

Answer 2

放大MAX_LINKS，在kerel中包含改变 MAX_LINKS

Netlink 套接字创建 returns NULL

Netlink socket creation returns NULL

c

sockets

kernel

linux-kernel

netlink