On Wed, Jun 10, 2020 at 08:41:29AM -0700, Casey Schaufler wrote:

On 6/10/2020 12:59 AM, Andrei Vagin wrote:

quoted

On Tue, Jun 09, 2020 at 06:14:27PM +0200, Christian Brauner wrote:

quoted

On Tue, Jun 09, 2020 at 09:06:27AM -0700, Andrei Vagin wrote:

quoted

On Tue, Jun 09, 2020 at 09:44:22AM +0200, Christian Brauner wrote:

quoted

On Mon, Jun 08, 2020 at 08:42:21PM -0700, Andrei Vagin wrote:

...

quoted

quoted

quoted

quoted

PTRACE_O_SUSPEND_SECCOMP is needed for C/R and it is protected by
CAP_SYS_ADMIN too.

This is currently capable(CAP_SYS_ADMIN) (init_ns capable) why is it
safe to allow unprivileged users to suspend security policies? That
sounds like a bad idea.

...

quoted

quoted

I don't suggest to remove or
downgrade this capability check. The patch allows all c/r related
operations if the current has CAP_CHECKPOINT_RESTORE.

So in this case the check:
     if (!capable(CAP_SYS_ADMIN))
             return -EPERM;

will be converted in:
     if (!capable(CAP_SYS_ADMIN) && !capable(CAP_CHECKPOINT_RESTORE))
             return -EPERM;

Yeah, I got that but what's the goal here? Isn't it that you want to
make it safe to install the criu binary with the CAP_CHECKPOINT_RESTORE
fscap set so that unprivileged users can restore their own processes
without creating a new user namespace or am I missing something? The
use-cases in the cover-letter make it sound like that's what this is
leading up to:

quoted

quoted

quoted

quoted

* Checkpoint/Restore in an HPC environment in combination with a resource
  manager distributing jobs where users are always running as non-root.
  There is a desire to provide a way to checkpoint and restore long running
  jobs.
* Container migration as non-root
* We have been in contact with JVM developers who are integrating
  CRIU into a Java VM to decrease the startup time. These checkpoint/restore
  applications are not meant to be running with CAP_SYS_ADMIN.

But maybe I'm just misunderstanding crucial bits (likely (TM)).

I think you understand this right. The goal is to make it possible to
use C/R functionality for unprivileged processes.

Y'all keep saying "unprivileged processes" when you mean
"processes with less than root privilege". A process with
CAP_CHECKPOINT_RESTORE *is* a privileged process. It would

That was me being imprecise. What I mean is "unprivileged user"
not "unprivileged process". It makes me a little uneasy that an
unprivileged _user_ can call the criu binary with the
CAP_CHECKPOINT_RESTORE fscap set and suspend seccomp of a process (Which
is what my original question here was about). Maybe this is paranoia but
shouldn't suspending _security_ mechanisms be kept either under
CAP_SYS_ADMIN or CAP_MAC_ADMIN?

Christian