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SubjectRe: [PATCH v2 1/3] capabilities: Introduce CAP_CHECKPOINT_RESTORE
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:
> > 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.
> >
> ...
> >
> > 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

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