Netlink socket problem

[Mikado]

Hi,

I write a kernel module and a userspace client. They use netlink sockets to communicate with each
other. The source codes are attached below. Inserting the module is ok but when I ran the client,
my kernel crashed after the client received first message from the module. Is there anything wrong
in my codes?

Thank you.

=== nltest.c - kernel module ===
#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_VFW 18
#define VFW_GROUP 0
#define MSG_SIZE NLMSG_SPACE(1024)

static struct sock *nl_sk = NULL;

static void nltest_rcv(struct sock *sk, int len)
{
        struct sk_buff *nl_skb;
        struct nlmsghdr *nl_hdr;
        int pid;

        while ((nl_skb = skb_dequeue(&sk->sk_receive_queue)) != NULL) {
                nl_hdr = (struct nlmsghdr *)nl_skb->data;
                pid = nl_hdr->nlmsg_pid;
                printk(KERN_ALERT "nltest: message from user (pid = %d) = %s\n", pid, (char
*)NLMSG_DATA(nl_hdr));
                nl_skb = alloc_skb(MSG_SIZE, in_interrupt() ? GFP_ATOMIC : GFP_KERNEL);
                skb_put(nl_skb, MSG_SIZE);
                nl_hdr = (struct nlmsghdr *)nl_skb->data;
                nl_hdr->nlmsg_len = MSG_SIZE;
                nl_hdr->nlmsg_pid = pid;
                nl_hdr->nlmsg_flags = 0;
                strcpy(NLMSG_DATA(nl_hdr), "hello user abcd1234");
                NETLINK_CB(nl_skb).pid = 0;
                NETLINK_CB(nl_skb).dst_pid = pid;
                NETLINK_CB(nl_skb).dst_group = VFW_GROUP;
                netlink_unicast(nl_sk, nl_skb, pid, 0);
                kfree_skb(nl_skb);
        }
}

static int __init nltest_init(void)
{
        printk(KERN_ALERT "nltest: init\n");

        nl_sk = netlink_kernel_create(NETLINK_VFW, VFW_GROUP, nltest_rcv, THIS_MODULE);
        if (!nl_sk) {
                printk(KERN_ALERT "nltest: netlink_kernel_create() failed\n");
                return -1;
        }

        return 0;
}

static void __exit nltest_exit(void)
{
        printk(KERN_ALERT "nltest: exit\n");

        sock_release(nl_sk->sk_socket);

        return;
}

module_init(nltest_init);
module_exit(nltest_exit);

MODULE_DESCRIPTION("Netlink Test");
MODULE_LICENSE("GPL");

=== nlclient.c - userspace client ===
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <asm/types.h>
#include <linux/netlink.h>

#define NETLINK_VFW 18
#define VFW_GROUP 0
#define MSG_SIZE NLMSG_SPACE(1024)

int main(void)
{
        int nl_sd;
        struct sockaddr_nl src_addr;
        struct nlmsghdr *nl_hdr;
        unsigned char buf[MSG_SIZE];
        int ret;

        memset(&src_addr, 0, sizeof(struct sockaddr_nl));
        memset(buf, 0, MSG_SIZE);

        nl_sd = socket(PF_NETLINK, SOCK_RAW, NETLINK_VFW);

        src_addr.nl_family = AF_NETLINK;
        src_addr.nl_pid = getpid();
        src_addr.nl_groups = VFW_GROUP;

        bind(nl_sd, (struct sockaddr *)&src_addr, sizeof(struct sockaddr));

        nl_hdr = (struct nlmsghdr *)buf;
        nl_hdr->nlmsg_len = MSG_SIZE;
        nl_hdr->nlmsg_pid = getpid();
        nl_hdr->nlmsg_flags = 0;
        strcpy(NLMSG_DATA(nl_hdr), "hello kernel");

        ret = send(nl_sd, buf, MSG_SIZE, 0);
        printf("send ret = %d\n", ret);
        if (ret == -1)
                return ret;

        while (1) {
                ret = recv(nl_sd, buf, MSG_SIZE, 0);
                printf("message from kernel = %s\n", (char *)NLMSG_DATA(nl_hdr));
        }

        return 0;
}

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Attachment: nltest.c
Description: 938020532-nltest.c

Attachment: nlclient.c
Description: 3903798118-nlclient.c