Hello,One of my relays (guard, not exit) started to report being overloaded since once week ago for the first time in its life.
The consensus weight and advertised bandwidth are proper as per what they should be, considering the relay's configuration. More than this, they have not changed for years. So, I started to look at it more closely.
Apparently the overload is triggered at 5-6 days by flooding it with circuit creation requests. All I can see in tor.log is:
[warn] Your computer is too slow to handle this many circuit creation requests! Please consider using the MaxAdvertisedBandwidth config option or choosing a more restricted exit policy. [68382 similar message(s) suppressed in last 482700 seconds]
[warn] Your computer is too slow to handle this many circuit creation requests! Please consider using the MaxAdvertisedBandwidth config option or choosing a more restricted exit policy. [7882 similar message(s) suppressed in last 60 seconds]
This message is logged like 4-5 or 6 time as 1 minute (60 sec) difference between each warn entry.
After that, the relay is back to normal. So it feels like it is being probed or something like this. CPU usage is at 65%, RAM is at under 45%, SSD no problem, bandwidth no problem.
Metrics port says:
tor_relay_load_tcp_exhaustion_total 0
tor_relay_load_onionskins_total{type="tap",action="processed"} 52073
tor_relay_load_onionskins_total{type="tap",action="dropped"} 0
tor_relay_load_onionskins_total{type="fast",action="processed"} 0
tor_relay_load_onionskins_total{type="fast",action="dropped"} 0
tor_relay_load_onionskins_total{type="ntor",action="processed"} 8069522
tor_relay_load_onionskins_total{type="ntor",action="dropped"} 273275
So if we account the dropped ntor circuits with the processed ntor
circuits we end up with a reasonable % (it's >8 million vs <300k).
So the question here is: does the computed consensus weight of a relay change if that relay keeps sending reports to directory authorities that it is being overloaded? If yes, could this be triggered by an attacker, in order to arbitrary decrease a relay's consensus weight even when it's not really overloaded (to maybe increase the consensus weights of other malicious relays that we don't know about)?
Also, as a side note, I think that if the dropped/processed ratio is not over 15% or 20% a relay should not consider itself overloaded. Would this be a good idea?
Sending to tor-relays@ for now, if some of you think of this in any way we can open a thread about it on tor-dev@ - please let me know if I should do this.
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