OpenBSD 3.2 Kthread Madness

OPENBSD 3.2 - \3.2\sys\kern\kern_kthread.c

Ohk, here is the function:

int
kthread_create(void (*func)(void *), void *arg,
    struct proc **newpp, const char *fmt, ...) <---- where the data is
{
        struct proc *p2; <--------- New proc struct
        register_t rv[2];
        int error;
        va_list ap;

        /*
         * First, create the new process. Share the memory, file
         * descriptors and don't leave the exit status around for the
         * parent to wait for.
         */
        error = fork1(&proc0, 0,
            FORK_SHAREVM|FORK_NOZOMBIE|FORK_SIGHAND, NULL, 0, func, arg,
rv);
        if (error)
                return (error);

        p2 = pfind(rv[0]);

        /*
         * Mark it as a system process and not a candidate for
         * swapping.
         */
        p2->p_flag |= P_INMEM | P_SYSTEM; /* XXX */

        /* Name it as specified. */
        va_start(ap, fmt);
        vsprintf(p2->p_comm, fmt, ap); <--- HELLO!
        va_end(ap);

        /* All done! */
        if (newpp != NULL)
                *newpp = p2;
        return (0);
}

some notes:
- proc.h defines p_comm for a size of MAXCOMLEN+1
- MAXCOMLEN is defined in param.h as 16.
- This gives use 17 bytes to overflow.

but how? you wont be able to do it from user-land (i presume) and the only
way i can imagine this being done is via a LKM. but then i realise that
you need root to do anything associated with lkm's. so the chances of
actually exploiting it, comes down to modifying a call in init_main.c and
watvhing your system not power up!

for patch wise..is there a vslprintf i can stick in there?
 - nd

-- 
http://felinemenace.org/~nd