Messages in this thread | | | From | Andy Lutomirski <> | Date | Mon, 13 Aug 2012 11:10:46 -0700 | Subject | Re: linux-user-chroot 2012.2 |
| |
On Fri, Aug 10, 2012 at 1:58 PM, Colin Walters <walters@verbum.org> wrote: > Hi, > > This is the release of linux-user-chroot 2012.2. The major change now > is that it makes use of Andy's new PR_SET_NO_NEW_PRIVS. This doesn't > close any security hole I'm aware of - our previous use of the MS_NOSUID > bind mount over / should work - but, belt and suspenders as they say. > > The code: > http://git.gnome.org/browse/linux-user-chroot/commit/?id=515c714471d0b5923f6633ef44a2270b23656ee9 > > As for how linux-user-chroot and PR_SET_NO_NEW_PRIVS relate, see this > thread: > http://thread.gmane.org/gmane.linux.kernel.lsm/15339 > > Summary > ------- > > This tool allows regular (non-root) users to call chroot(2), create > Linux bind mounts, and use some Linux container features. It's > primarily intended for use by build systems.
Nifty.
One of these days, I intend to resurrect my unprivileged chroot kernel patches. My current thought is to add a new syscall weak_chroot, which should have these properties:
1. Can't be used unless no_new_privs is set or you have CAP_SYS_ADMIN. 2. Can't be used if fs->users > 1 (to avoid a trivial no_new_privs bypass). 3. Can't be used to break out of chroot jail.
The interface might be:
weak_chroot_at(int fd, const char *path, int flags)
Sets fs->weak_root to path, as seen from fd, according to flags. Works if (no_new_privs && fs->users == 1) || capable(CAP_SYS_ADMIN).
Modify chroot to change fs->weak_root and fs->root. Further modify the path walking code so that / sees weak_root instead of root and so that .. will not traverse root or weak_root.
I'm somewhat tempted to add a flag to weak_chroot_at to break out of weak_root jail to prevent people from thinking that it's a security feature. I'm not sure about that, though.
--Andy
| |