Hi On Tue, Jul 21, 2015 at 1:37 PM, Florian Weimer <fwei...@redhat.com> wrote: > We have quite a zoo of services which listen on localhost, on a fixed > TCP port, for use by local clients. The canonical example is PostgreSQL > on 5432/TCP, for the benefit of Java clients (which cannot use the UNIX > domain socket). This has the obvious issue that if a local attacker > crashes the service, they can impersonate it by binding to the same port. > > Does socket activation reliably prevent such impersonation attacks? Or > is there race, say during systemd configuration reloading or service > restarts, where systemd temporarily does not listen to that port?
This "race" *does* exist with socket activation. The sockets may be re-created if the unit transitions between states (like restart). However, this is only triggered by actions on the socket-unit, not the actually activated unit. A crash of the activated service will thus not trigger state-changes on the socket-unit. Furthermore, we do not treat "occupying a resource" as security mechanism. If an attacker has access to bind such a port, we do not place restrictions to prevent that. Instead, you should place LSM restrictions to prevent this. And please note, the actual activated unit usually does *not* have rights to bind the socket. This is done by pid1. So an attacker would require rights of PID1 for such an attack. Thanks David _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel