/usr/src/xtables-addons-2.6/extensions/pknock/pknlusr.c is in xtables-addons-dkms 2.6-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 | #include <sys/socket.h>
#include <unistd.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <linux/netlink.h>
#include <linux/connector.h>
#include "xt_pknock.h"
#define GROUP 1
static struct sockaddr_nl src_addr, dest_addr;
static int sock_fd;
static unsigned char *buf;
static struct xt_pknock_nl_msg *nlmsg;
int main(void)
{
socklen_t addrlen;
int status;
int group = GROUP;
int buf_size;
const char *ip;
char ipbuf[48];
sock_fd = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
if (sock_fd == -1) {
perror("socket()");
return 1;
}
memset(&src_addr, 0, sizeof(src_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid();
src_addr.nl_groups = group;
status = bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr));
if (status == -1) {
close(sock_fd);
perror("bind()");
return 1;
}
memset(&dest_addr, 0, sizeof(dest_addr));
dest_addr.nl_family = AF_NETLINK;
dest_addr.nl_pid = 0;
dest_addr.nl_groups = group;
buf_size = sizeof(struct xt_pknock_nl_msg) + sizeof(struct cn_msg) + sizeof(struct nlmsghdr);
buf = malloc(buf_size);
if (!buf) {
perror("malloc()");
return 1;
}
addrlen = sizeof(dest_addr);
while(1) {
memset(buf, 0, buf_size);
status = recvfrom(sock_fd, buf, buf_size, 0, (struct sockaddr *)&dest_addr, &addrlen);
if (status <= 0) {
perror("recvfrom()");
return 1;
}
nlmsg = (struct xt_pknock_nl_msg *) (buf + sizeof(struct cn_msg) + sizeof(struct nlmsghdr));
ip = inet_ntop(AF_INET, &nlmsg->peer_ip, ipbuf, sizeof(ipbuf));
printf("rule_name: %s - ip %s\n", nlmsg->rule_name, ip);
}
close(sock_fd);
free(buf);
return 0;
}
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