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

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

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

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

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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.

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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:

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* 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. And for me, here are
two separate tasks. The first one is how to allow unprivileged users to
use C/R from the root user namespace. This is what we discuss here.

And another one is how to allow to use C/R functionality from a non-root
user namespaces. The second task is about downgrading capable to
ns_capable for map_files and PTRACE_O_SUSPEND_SECCOMP.

Thanks,
Andrei