On Mon, Nov 19, 2018 at 1:21 PM, Christian Brauner <christian@xxxxxxxxxx> wrote: > That can be done without a loop by comparing the level counter for the > two pid namespaces. > >> >> And you can rewrite pidns_get_parent to use it. So you would instead be >> doing: >> >> if (pidns_is_descendant(proc_pid_ns, task_active_pid_ns(current))) >> return -EPERM; >> >> (Or you can just copy the 5-line loop into procfd_signal -- though I >> imagine we'll need this for all of the procfd_* APIs.) Why is any of this even necessary? Why does the child namespace we're considering even have a file descriptor to its ancestor's procfs? If it has one of these FDs, it can already *read* all sorts of information it really shouldn't be able to acquire, so the additional ability to send a signal (subject to the usual permission checks) feels like sticking a finger in a dike that's already well-perforated. IMHO, we shouldn't bother with this check. The patch would be simpler without it.
