On 04/18, Christian Brauner wrote: > > On Thu, Apr 18, 2019 at 03:12:07PM +0200, Oleg Nesterov wrote: > > Should we allow CLONE_THREAD | CLONE_PIDFD ? > > I think so, yes. I have thought about this. OK, I won't insist. But let me explain why did I ask. > Yes, due to CLONE_FILES | > CLONE_VM you'd necessarily hand the pidfd to the child but threads are > no security boundary in the first place. No, no, I am not not worried about security. CLONE_PARENT | CLONE_PIDFD looks more problematic to me, but I see nothing dangerous security-wise.. I agree that CLONE_THREAD | CLONE_PIDFD may be usefule, but I am not sure we should allow this from the very begining, until we have a "real" use-case. IIUC, we are going to make it pollable soon. OK, but proc_tgid_base_poll() (which should be turned into pidfd_poll) simply can't work if pid_task() is not a group leader. poll(pidfd) will hang forever if pidfd was created by CLONE_THREAD | CLONE_PIDFD. Sure, we can (should?) improve pidfd_poll() but this will need more nasty changes in the core kernel code. Do we really need/want this? Right now it is not clear to me. Instead, we can simply disallow CLONE_THREAD|CLONE_PIDFD until we decide that yes, we want to poll sub-threads. But again, I am fine with CLONE_THREAD | CLONE_PIDFD. Oleg.
