On Wed, Sep 22, 2021, at 5:25 AM, Christian Brauner wrote: > On Mon, Sep 20, 2021 at 11:36:47AM -0700, Andy Lutomirski wrote: >> On Mon, Sep 20, 2021 at 11:16 AM Luis Chamberlain <mcgrof@xxxxxxxxxx> wrote: >> > >> > On Mon, Sep 20, 2021 at 04:51:19PM +0200, Thomas Weißschuh wrote: >> >> > > > Do you mean it literally invokes /sbin/modprobe? If so, hooking this >> > > > at /sbin/modprobe and calling out to the container manager seems like >> > > > a decent solution. >> > > >> > > Yes it does. Thanks for the idea, I'll see how this works out. >> > >> > Would documentation guiding you in that way have helped? If so >> > I welcome a patch that does just that. >> >> If someone wants to make this classy, we should probably have the >> container counterpart of a standardized paravirt interface. There >> should be a way for a container to, in a runtime-agnostic way, issue >> requests to its manager, and requesting a module by (name, Linux >> kernel version for which that name makes sense) seems like an >> excellent use of such an interface. > > I always thought of this in two ways we currently do this: > > 1. Caller transparent container manager requests. > This is the seccomp notifier where we transparently handle syscalls > including intercepting init_module() where we parse out the module to > be loaded from the syscall args of the container and if it is > allow-listed load it for the container otherwise continue the syscall > letting it fail or failing directly through seccomp return value. Specific problems here include aliases and dependencies. My modules.alias file, for example, has: alias net-pf-16-proto-16-family-wireguard wireguard If I do modprobe net-pf-16-proto-16-family-wireguard, modprobe parses some files in /lib/modules/`uname -r` and issues init_module() asking for 'wireguard'. So hooking init_module() is at the wrong layer -- for that to work, the container's /sbin/modprobe needs to already have figured out that the desired module is wireguard and have a .ko for it. > > 2. A process in the container explicitly calling out to the container > manager. > One example how this happens is systemd-nspawn via dbus messages > between systemd in the container and systemd outside the container to > e.g. allocate a new terminal in the container (kinda insecure but > that's another issue) or other stuff. > > So what was your idea: would it be like a device file that could be > exposed to the container where it writes requestes to the container > manager? What would be the advantage to just standardizing a socket > protocol which is what we do for example (it doesn't do module loading > of course as we handle that differently): My idea is standardizing *something*. I think it would be nice if, for example, distros could ship a /sbin/modprobe that would do the right thing inside any compliant container runtime as well as when running outside a container. I suppose container managers could also bind-mount over /sbin/modprobe, but that's more intrusive.
