On Tue, Jun 09, 2020 at 09:06:27AM -0700, Andrei Vagin wrote: > On Tue, Jun 09, 2020 at 09:44:22AM +0200, Christian Brauner wrote: > > 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. > > Why do you think so bad about me;). I don't suggest to remove or Andrei, nothing could be further from me than to think bad about you! You've done way too much excellent work. ;) > 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: > > > > * 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)). Christian
