linux-kernel - How do I read kernel audit messages using NETLINK

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Date:   Tue, 8 Dec 2020 14:10:06 +0000
From:   "Bhat, Jayalakshmi Manjunath" <jayalakshmi.bhat@...com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>
Subject: How do I read kernel audit messages using NETLINK_AUDIT in user space

Hi All,

I am trying to read kernel audit messages specially generated by XFRM in user space. I wrote Netlink client stub to read the audit message as below. But the call recvfrom gets blocked indefinite.
Can any one tell me what am I doing wrong?

Regards,
Jayalakshmi

#include <sys/socket.h>
#include <linux/netlink.h>
#include <stdio.h>
#include <malloc.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main() 
{
  int fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_AUDIT);

  if (fd < 0) {
    printf("Socket creation failed. try again\n");
  }
  else
  {
	struct sockaddr_nl src_addr;
	struct sockaddr_nl dest_addr;
	struct iovec iov;
	struct msghdr msg;
	struct nlmsghdr *nlh =(struct nlmsghdr *) malloc(NLMSG_SPACE(1024));
	
	memset(nlh, 0, NLMSG_SPACE(1024));
	memset(&iov, 0, sizeof(iov));

	nlh->nlmsg_len   = NLMSG_SPACE(1024);
	nlh->nlmsg_pid   = getpid();
	nlh->nlmsg_flags = 0;

	src_addr.nl_family  = AF_NETLINK;
	src_addr.nl_pid     = getpid();
	src_addr.nl_groups  = 0;

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

	iov.iov_base = (void *)nlh;  
	iov.iov_len = nlh->nlmsg_len;  

	msg.msg_name = (void *)&src_addr;
	msg.msg_namelen = sizeof(src_addr);
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
  
    recvfrom(fd, &msg,sizeof(msg),0,(struct sockaddr *) &dest_addr,sizeof(dest_addr));
    printf("Received message: %s\n", (char *)NLMSG_DATA(nlh));
    close(fd);
}