Commits on Oct 25, 2022

1. Allow nodes to overshoot final htlc amount and expiry …

   When nodes receive HTLCs, they verify that the contents of those HTLCs
   match the intructions that the sender provided in the onion. It is
   important to ensure that intermediate nodes and final nodes have similar
   requirements, otherwise a malicious intermediate node could easily probe
   whether the next node is the final recipient or not.
   
   Unfortunately, the requirements for intermediate nodes were more lenient
   than the requirements for final nodes. Intermediate nodes allowed overpaying
   and increasing the CLTV expiry, whereas final nodes required a perfect
   equality between the HTLC values and the onion values.
   
   This provided a trivial way of probing: when relaying an HTLC, nodes could
   relay 1 msat more than what the onion instructed (or increase the outgoing
   expiry by 1). If the next node was an intermediate node, they would accept
   this HTLC, but if the next node was the recipient, they would reject it.
   
   We update those requirements to fix this probing attack vector.
   
   See lightning/bolts#1032

   

   t-bast committed Oct 25, 2022
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