hide_pid.c

/* pidns_init_sleep.c

   Copyright 2013, Michael Kerrisk
   Licensed under GNU General Public License v2 or later

   A simple demonstration of PID namespaces.
*/
#define _GNU_SOURCE
#include <sched.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <sys/mount.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <signal.h>
#include <stdio.h>
#include <fcntl.h>

/* A simple error-handling function: print an error message based
   on the value in 'errno' and terminate the calling process */

#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                        } while (0)

static int              /* Start function for cloned child */
childFunc(void *arg)
{
    printf("childFunc(): PID  = %ld\n", (long) getpid());
    printf("childFunc(): PPID = %ld\n", (long) getppid());

    char *mount_point = arg;

    if (mount_point != NULL) {
        const char *opts = "hidepid=2";

        mkdir(mount_point, 0555);       /* Create directory for mount point */
        if (mount("proc", mount_point, "proc", 0, opts) == -1)
            errExit("mount");
        printf("Mounting procfs at %s, opts %s\n", mount_point, opts);
    }

    char *f, buf[1024];
    asprintf(&f, "%s/1/%s", mount_point, "cmdline");

    int fd;
    fd = open(f, O_RDONLY | O_NONBLOCK);
    if (fd < 0)
        errExit("open");

    read(fd, buf, sizeof(buf));
    printf("Content of '%s': >%s<\n", f, buf);

    printf("sleeping ...\n");

    int i = 60;
    while (i--)
        sleep(1);

    exit(0);
}

#define STACK_SIZE (1024 * 1024)

static char child_stack[STACK_SIZE];    /* Space for child's stack */

int
main(int argc, char *argv[])
{
    pid_t child_pid;

    child_pid = clone(childFunc,
                    child_stack + STACK_SIZE,   /* Points to start of downwardly growing stack */
                    CLONE_NEWPID | SIGCHLD, argv[1]);

    if (child_pid == -1)
        errExit("clone");

    printf("PID returned by clone(): %ld\n", (long) child_pid);

    if (waitpid(child_pid, NULL, 0) == -1)      /* Wait for child */
        errExit("waitpid");

    exit(EXIT_SUCCESS);
}