invoke_ns3.c

#define _GNU_SOURCE
#include <sys/wait.h>
#include <sys/mount.h>
#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
#include <unistd.h>
#include <string.h>


// Define size of space for stack used by child process
#define STACK_SIZE (64 * 1024)

struct arguments {
    int  verbose;
    int  flags;
    char *hostname;
    char **command;
};


// Function to print command usage
static void usage(char *prog)
{
    fprintf(stderr, "\nUsage: %s [options] [cmd [arg...]]\n", prog);
    fprintf(stderr, "Options can be:\n");
    fprintf(stderr, "    -h           display this help message\n");
    fprintf(stderr, "    -v           display verbose messages\n");
    fprintf(stderr, "    -p           new PID namespace\n");
    fprintf(stderr, "    -m           new MNT namespace\n");
    fprintf(stderr, "    -u hostname  new UTS namespace with associated hostname\n");
}


// Function passed to the clone system call
int childFunction(void *child_args)
{
    struct arguments *args = child_args;

    if (args->verbose)
        printf(" Child: PID of child is %d\n", getpid());

    // Mount new proc instance in new mount namespace if and only if
    // the child exists in both a new PID and MNT namespace
    if ((args->flags & CLONE_NEWPID) && (args->flags & CLONE_NEWNS)) {
        if (mount("none", "/proc", "", MS_REC|MS_PRIVATE, NULL) == -1)
            perror(" Child: childFunction: mount");
        if (mount("proc", "/proc", "proc", 0, NULL) == -1)
            perror(" Child: childFunction: mount");
    }

    // Set new hostname in UTS namespace if applicable
    if (args->flags & CLONE_NEWUTS)
        if (sethostname(args->hostname, strlen(args->hostname)) == -1)
            perror(" Child: childFunction: sethostname");

    // Execute command if given
    if (args->command != NULL) {
        if (clearenv() != 0)
            fprintf(stderr, " Child: childFunction: couldn't clear environment\n");
        if (args->verbose)
            printf(" Child: executing command %s ...\n", args->command[0]);
        execvp(args->command[0], &args->command[0]);
    }
    else
        exit(EXIT_SUCCESS);

    perror(" Child: childFunction: execvp");
    exit(EXIT_FAILURE);
}



int main(int argc, char *argv[])
{
    char             *child_stack;
    int              i;
    int              option;
    int              flags = 0;
    pid_t            child;
    struct arguments args;

    args.verbose = 0;
    args.flags = 0;
    args.hostname = NULL;
    args.command = NULL;

    // Parse command line options and construct arguments
    // to be passed to childFunction
    while ((option = getopt(argc, argv, "+hvpmu:")) != -1) {
        switch (option) {
            case 'u':
                flags |= CLONE_NEWUTS;
                args.hostname = malloc(sizeof(char) * (strlen(optarg) + 1));
                strcpy(args.hostname, optarg);
                break;
            case 'm':
                flags |= CLONE_NEWNS;
                break;
            case 'p':
                flags |= CLONE_NEWPID;
                break;
            case 'v':
                args.verbose = 1;
                break;
            case 'h':
                usage(argv[0]);
                exit(EXIT_SUCCESS);
            default:
                usage(argv[0]);
                exit(EXIT_FAILURE);
        }
    }

    // childFunc needs to know which namespaces have been created
    args.flags = flags;

    // Assemble command to be executed in namespace
    if(optind != argc) {
        args.command = malloc(sizeof(char *) * (argc - optind + 1));
        for (i = optind; i < argc; i++) {
            args.command[i - optind] = malloc(strlen(argv[i]) + 1);
            strcpy(args.command[i - optind], argv[i]);
        }
        args.command[argc - optind] = NULL;
    }

    if (args.verbose)
        printf("Parent: PID of parent is %d\n", getpid());

    // Allocate heap for child's stack
    child_stack = malloc(STACK_SIZE);
    if (child_stack == NULL) {
        perror("Parent: main: malloc");
        exit(EXIT_FAILURE);
    }

    // Clone child process
    child = clone(childFunction, child_stack + STACK_SIZE, flags | SIGCHLD, &args);
    if (child == -1) {
        perror("Parent: main: clone");
        exit(EXIT_FAILURE);
    }

    if (args.verbose)
        printf("Parent: PID of child is %d\n", child);

    // Wait for child to finish
    if (waitpid(child, NULL, 0) == -1) {
        perror("Parent: main: waitpid");
        exit(EXIT_FAILURE);
    }

    if (args.verbose)
        printf("Parent: %s - Finishing up\n", argv[0]);

    exit(EXIT_SUCCESS);
}