Similar to #14917: Client's choice of rend point can leak info about guard(s) of misconfigured hidden services with EntryNodes option

Hello !

I discovered #14917 (moved) while configuring an onion service with the EntryNodes option set. I believe (after checking the tor-0.2.9.8 source code) that a similar problem arises when the EntryNodes option is set AND the operator configures entry nodes that are part of the same family or the same /16. (let's say that the operator configures the service with 2 of its own guard nodes running in the same cloud provider, thinking this move is wise). Then this happens:

• When someone use a RDV point of the same family or the same /16 than the onion's guards, then as you said: "entry_list_is_constrained() is true, so populate_live_entry_guards() will happily return an empty list if your one choice is inappropriate, resulting in choose_random_entry_impl() returning NULL".

Is there a reason why we do not check family, /16 and user misconfiguration ? "EntryNodes fingerprint1, fingerprint1" works just fine for example. What do you think ?