On Wed, Oct 10, 2018 at 05:39:57PM +0200, Christian Brauner wrote:

On Wed, Oct 10, 2018 at 05:33:43PM +0200, Jann Horn wrote:

quoted

On Wed, Oct 10, 2018 at 5:32 PM Paul Moore [off-list ref] wrote:

quoted

On Tue, Oct 9, 2018 at 9:36 AM Jann Horn [off-list ref] wrote:

quoted

+cc selinux people explicitly, since they probably have opinions on this

I just spent about twenty minutes working my way through this thread,
and digging through the containers archive trying to get a good
understanding of what you guys are trying to do, and I'm not quite
sure I understand it all.  However, from what I have seen, this
approach looks very ptrace-y to me (I imagine to others as well based
on the comments) and because of this I think ensuring the usual ptrace
access controls are evaluated, including the ptrace LSM hooks, is the
right thing to do.

Basically the problem is that this new ptrace() API does something
that doesn't just influence the target task, but also every other task
that has the same seccomp filter. So the classic ptrace check doesn't
work here.

Just to throw this into the mix: then maybe ptrace() isn't the right
interface and we should just go with the native seccomp() approach for
now.

Please no :).

I don't buy your arguments that 3-syscalls vs. one is better. If I'm
doing this setup with a new container, I have to do
clone(CLONE_FILES), do this seccomp thing, so that my parent can pick
it up again, then do another clone without CLONE_FILES, because in the
general case I don't want to share my fd table with the container,
wait on the middle task for errors, etc. So we're still doing a bunch
of setup, and it feels more awkward than ptrace, with at least as many
syscalls, and it only works for your children.

I don't mind leaving capable(CAP_SYS_ADMIN) for the ptrace() part,
though. So if that's ok, then I think we can agree :)

Tycho