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. > >> 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. --Andy _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
