On Mon, Nov 19, 2018 at 01:26:22PM -0800, Daniel Colascione wrote: > 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 Because you can send file descriptors between processes and container runtimes tend to do that. > 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. We will definitely not allow signaling processes in an ancestor pid namespace! That is a security issue! I can imagine container runtimes killing their monitoring process etc. pp. Not happening, unless someone with deep expertise in signals can convince me otherwise.
