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

On Wed, Jun 03, 2020 at 06:23:26PM +0200, Adrian Reber wrote:

quoted

This patch introduces CAP_CHECKPOINT_RESTORE, a new capability facilitating
checkpoint/restore for non-root users.

Over the last years, The CRIU (Checkpoint/Restore In Userspace) team has been
asked numerous times if it is possible to checkpoint/restore a process as
non-root. The answer usually was: 'almost'.

The main blocker to restore a process as non-root was to control the PID of the
restored process. This feature available via the clone3 system call, or via
/proc/sys/kernel/ns_last_pid is unfortunately guarded by CAP_SYS_ADMIN.

In the past two years, requests for non-root checkpoint/restore have increased
due to the following use cases:
* 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.

...

quoted

The introduced capability allows to:
* Control PIDs when the current user is CAP_CHECKPOINT_RESTORE capable
  for the corresponding PID namespace via ns_last_pid/clone3.
* Open files in /proc/pid/map_files when the current user is
  CAP_CHECKPOINT_RESTORE capable in the root namespace, useful for recovering
  files that are unreachable via the file system such as deleted files, or memfd
  files.

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.

	if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) {
		if (!IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) ||
		    !IS_ENABLED(CONFIG_SECCOMP))
			return -EINVAL;

		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;

		if (seccomp_mode(&current->seccomp) != SECCOMP_MODE_DISABLED ||
		    current->ptrace & PT_SUSPEND_SECCOMP)
			return -EPERM;
	}

Christian