Re: OpenBSD 2.9,2.8 local root compromise

[Jason R Thorpe <thorpej () zembu com>]

On Thu, Jun 14, 2001 at 07:09:31PM +0200, Przemyslaw Frasunek wrote:

> On Thu, Jun 14, 2001 at 05:14:46PM +0300, Georgi Guninski wrote:
> > OpenBSD 2.9,2.8
> > Have not tested on other OSes but they may be vulnerable
>
> FreeBSD 4.3-STABLE isn't vulnerable. Looks like it's dropping set[ug]id
> privileges before allowing detach.

Uh, the fundamental problem is that there's a chance to PT_ATTACH to
such a process before the P_SUGID bit is set in the proc.  This can
happen when, e.g. the ucred structure is copied (there is a potentially
blocking malloc() call in that path).

A cursory glance shows several places where the FreeBSD kernel has
code like:

        /* sanity check */
        /* blocking call */
        /* change user/group ID */
        /* set P_SUGID */

During the /* blocking call */, another process can sneak in and PT_ATTACH
the process that is about to become sugid.

-- 
        -- Jason R. Thorpe <thorpej () zembu com>