foo.c

/* This file is licensed under the GPL v2 (http://www.gnu.org/licenses/gpl2.txt) (some parts was originally borrowed from proc events example)

pmon.c

code highlighted with GNU source-highlight 3.1
*/

#define _XOPEN_SOURCE 700
#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/connector.h>
#include <linux/cn_proc.h>
#include <signal.h>
#include <errno.h>
#include <stdbool.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>

int get_exe_for_pid(pid_t pid, char *buf, size_t bufsize) {
    char path[32];
    sprintf(path, "/proc/%d/exe", pid);
    return readlink(path, buf, bufsize);
}
/*
* connect to netlink
* returns netlink socket, or -1 on error
*/
static int nl_connect()
{
    int rc;
    int nl_sock;
    struct sockaddr_nl sa_nl;

    nl_sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
    if (nl_sock == -1)
    {
        perror("socket");
        return -1;
    }

    sa_nl.nl_family = AF_NETLINK;
    sa_nl.nl_groups = CN_IDX_PROC;
    sa_nl.nl_pid = getpid();

    rc = bind(nl_sock, (struct sockaddr *)&sa_nl, sizeof(sa_nl));
    if (rc == -1)
    {
        perror("bind");
        close(nl_sock);
        return -1;
    }

    return nl_sock;
}

/*
* subscribe on proc events (process notifications)
*/
static int set_proc_ev_listen(int nl_sock, bool enable)
{
    int rc;
    struct __attribute__((aligned(NLMSG_ALIGNTO)))
    {
        struct nlmsghdr nl_hdr;
        struct __attribute__((__packed__))
        {
            struct cn_msg cn_msg;
            enum proc_cn_mcast_op cn_mcast;
        };
    } nlcn_msg;

    memset(&nlcn_msg, 0, sizeof(nlcn_msg));
    nlcn_msg.nl_hdr.nlmsg_len = sizeof(nlcn_msg);
    nlcn_msg.nl_hdr.nlmsg_pid = getpid();
    nlcn_msg.nl_hdr.nlmsg_type = NLMSG_DONE;

    nlcn_msg.cn_msg.id.idx = CN_IDX_PROC;
    nlcn_msg.cn_msg.id.val = CN_VAL_PROC;
    nlcn_msg.cn_msg.len = sizeof(enum proc_cn_mcast_op);

    nlcn_msg.cn_mcast = enable ? PROC_CN_MCAST_LISTEN : PROC_CN_MCAST_IGNORE;

    rc = send(nl_sock, &nlcn_msg, sizeof(nlcn_msg), 0);
    if (rc == -1)
    {
        perror("netlink send");
        return -1;
    }

    return 0;
}

/*
* handle a single process event
*/
static volatile bool need_exit = false;
static int handle_proc_ev(int nl_sock)
{
    int rc;
    struct __attribute__((aligned(NLMSG_ALIGNTO)))
    {
        struct nlmsghdr nl_hdr;
        struct __attribute__((__packed__))
        {
            struct cn_msg cn_msg;
            struct proc_event proc_ev;
        };
    } nlcn_msg;

    while (!need_exit)
    {
        rc = recv(nl_sock, &nlcn_msg, sizeof(nlcn_msg), 0);
        if (rc == 0)
        {
            /* shutdown? */
            return 0;
        }
        else if (rc == -1)
        {
            if (errno == EINTR)
                continue;
            perror("netlink recv");
            return -1;
        }
        int pid;
        switch (nlcn_msg.proc_ev.what)
        {
        case PROC_EVENT_NONE:
            printf("set mcast listen ok\n");
            break;
        case PROC_EVENT_FORK:
            printf("fork: parent tid=%d pid=%d -> child tid=%d pid=%d\n",
                   nlcn_msg.proc_ev.event_data.fork.parent_pid,
                   nlcn_msg.proc_ev.event_data.fork.parent_tgid,
                   nlcn_msg.proc_ev.event_data.fork.child_pid,
                   nlcn_msg.proc_ev.event_data.fork.child_tgid);
            break;
        case PROC_EVENT_EXEC:
            pid = nlcn_msg.proc_ev.event_data.exec.process_pid;

            printf("exec: tid=%d pid=%d\n",
                   nlcn_msg.proc_ev.event_data.exec.process_pid,
                   nlcn_msg.proc_ev.event_data.exec.process_tgid);
            char buf[256];
            get_exe_for_pid(pid, buf, sizeof(buf));
            printf("exec: process path=%s\n", buf);          
            sprintf(buf, "/proc/%d/cmdline", pid);
            int fd = open(buf, O_RDONLY);
            read(fd, buf, sizeof(buf));
           
            printf("exec: cmdline = %s\n", buf);
            close(fd);
            break;
        case PROC_EVENT_UID:
            printf("uid change: tid=%d pid=%d from %d to %d\n",
                   nlcn_msg.proc_ev.event_data.id.process_pid,
                   nlcn_msg.proc_ev.event_data.id.process_tgid,
                   nlcn_msg.proc_ev.event_data.id.r.ruid,
                   nlcn_msg.proc_ev.event_data.id.e.euid);
            break;
        case PROC_EVENT_GID:
            printf("gid change: tid=%d pid=%d from %d to %d\n",
                   nlcn_msg.proc_ev.event_data.id.process_pid,
                   nlcn_msg.proc_ev.event_data.id.process_tgid,
                   nlcn_msg.proc_ev.event_data.id.r.rgid,
                   nlcn_msg.proc_ev.event_data.id.e.egid);
            break;
        case PROC_EVENT_EXIT:
            printf("exit: tid=%d pid=%d exit_code=%d\n",
                   nlcn_msg.proc_ev.event_data.exit.process_pid,
                   nlcn_msg.proc_ev.event_data.exit.process_tgid,
                   nlcn_msg.proc_ev.event_data.exit.exit_code);
            break;
        default:
            printf("unhandled proc event\n");
            break;
        }
    }

    return 0;
}

static void on_sigint(int unused)
{
    need_exit = true;
}

int main(int argc, const char *argv[])
{
    int nl_sock;
    int rc = EXIT_SUCCESS;

    signal(SIGINT, &on_sigint);
    siginterrupt(SIGINT, true);

    nl_sock = nl_connect();
    if (nl_sock == -1)
        exit(EXIT_FAILURE);

    rc = set_proc_ev_listen(nl_sock, true);
    if (rc == -1)
    {
        rc = EXIT_FAILURE;
        goto out;
    }

    rc = handle_proc_ev(nl_sock);
    if (rc == -1)
    {
        rc = EXIT_FAILURE;
        goto out;
    }

    set_proc_ev_listen(nl_sock, false);

out:
    close(nl_sock);
    exit(rc);
}