CLONE_NEWUSER|CLONE_FS root exploit

Hi,

Seems like CLONE_NEWUSER|CLONE_FS might be a forbidden
combination.
During evaluating the new user namespace thingie, it turned out
that its trivially exploitable to get a (real) uid 0,
as demonstrated here:

http://stealth.openwall.net/xSports/clown-newuser.c

The trick is to setup a chroot in your CLONE_NEWUSER,
but also affecting the parent, which is running
in the init_user_ns, but with the chroot shared.
Then its trivial to get a rootshell from that.

Tested on a openSUSE12.1 with a custom build 3.8.2 (x86_64).

I hope I didnt make anything wrong, mixing up the UIDs,
or disabled important checks during kernel build on my test
system. ;)

regards,
Sebastian

-- 

~ perl self.pl
~ $_='print"\$_=\47$_\47;eval"';eval
~ krahmer-l3A5Bk7waGM@public.gmane.org - SuSE Security Team