Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes: > On Fri, Apr 25, 2014 at 12:37 PM, Eric W. Biederman > <ebiederm@xxxxxxxxxxxx> wrote: >> Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes: >> >>> Unless I'm missing some trick, it's currently rather painful to mount >>> a namespace /proc. You have to actually be in the pid namespace to >>> mount the correct /proc instance, and you can't unmount the old /proc >>> until you've mounted the new /proc. This means that you have to fork >>> into the new pid namespace before you can finish setting it up. >> >> Yes. You have to be inside just about all namespaces before you can >> finish setting them up. >> >> I don't know the context in which needed to be inside the pid namespace >> is a burden. > > I'm trying to sandbox myself. I unshare everything, setup up new > mounts, pivot_root, umount the old stuff, fork, and wait around for > the child to finish. > > This doesn't work: the parent can't mount the new /proc, and the child > can't either because it's too late. > > The only solution I can think of without kernel changes is to fork the > child (pid 1) before pivot_root, which makes everything more > complicated. I suppose I can unshare, fork immediately, have the > child set up all the mounts, and then wake the parent, but this is an > annoying bit of extra complexity for no obvious gain. Or perhaps just use clone and clone flags. What are you doing with the parent process? What value does it serve? >>> Would it make sense to add a mount option to procfs to request a mount >>> for pid_ns_for_children instead of task_active_pid_ns? >> >> This is about the using setns and unshare? >> >> Adding a proc amount option that takes a pid namespace file descriptor >> would be the general solution, and might be worth implementing. >> >> Getting a pid namespace file descriptors when there are no pids might be >> a challenge. > > Indeed, hence my request for a specific mode to mount /proc for > pid_ns_for_children. > > FWIW, I also tried forking, having the child mount /proc and exit, > then forking again later on. That also doesn't work -- it looks like > you can't recreate pid 1 after it does. Nope. Once pid 1 (init) is dead the pid namespace is dead. Eric _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
