0c85dc30e6b628f7538a67776c7eefcb84ef4f82 p2p: Don't use timestamps from inbound peers (Martin Zumsande)
Pull request description:
`GetAdjustedTime()` (used e.g. in validation and addrman) returns a time with an offset that is influenced by timestamps that our peers have sent us in their version message.
Currently, timestamps from all peers are used for this.
However, I think that it would make sense to ignore the timedata samples from inbound peers, making it much harder for others to influence the Adjusted Time in a targeted way.
With the extra feeler connections (every 2 minutes on average) and extra block-relay-only connections (every 5 minutes on average) there are also now plenty of opportunities to gather a meaningful number of timedata samples from outbound peers.
There are some measures in place to prevent abuse: the `-maxtimeadjustment` parameter with a default of 70 minutes, warnings in cases of large deviations, only using the first 200 samples ([explanation](383d350bd5/src/timedata.cpp (L57-L72))), but I think that only using samples from outbound connections in the first place would be an additional safety measure that would make sense.
See also issue #4521 for further context and links: There have been several discussions in the past about replacing or abolishing the existing timedata system.
ACKs for top commit:
jnewbery:
Concept and code review ACK 0c85dc30e6b628f7538a67776c7eefcb84ef4f82
naumenkogs:
ACK 0c85dc30e6b628f7538a67776c7eefcb84ef4f82
vasild:
ACK 0c85dc30e6b628f7538a67776c7eefcb84ef4f82
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