core, eth/downloader: fix resetting below freezer threshold #23949
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rjl493456442
approved these changes
Nov 22, 2021
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This PR fixes two bugs that can be used by a malicious node to try and push a newly joining node into a bad state (with properly mined - thus costly - blocks).
ancestor + 1instead ofancestor, ending up with 1 header too many in the freezer to import on top.blockchain.SetHeadwhere we had a heuristic that ifhead == current blockthen we assumed it's a startup check, not a real "set the damn head" call. This lead to leaving some dangling data in the freezer and the downloader being unable to pile blocks on top.These issue are only relevant during initial snap sync where the data is pushed directly into the freezer. After initial sync the freezer is delayed by 90K blocks and there's also a cap on the max reorg depth.