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Document how the syncer resists memory DoS

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teor 2021-03-11 11:29:21 +10:00 committed by Deirdre Connolly
parent c6358b157c
commit d494af1e90
1 changed files with 15 additions and 0 deletions
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15
zebrad/src/components/sync.rs
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@ -40,6 +40,21 @@ const BLOCK_DOWNLOAD_RETRY_LIMIT: usize = 2;
///
/// Set to two checkpoint intervals, so that we're sure that the lookahead
/// limit always contains at least one complete checkpoint.
///
/// ## Security
///
/// If a malicious node is chosen for an ObtainTips or ExtendTips request, it can
/// provide up to 500 malicious block hashes. These block hashes will be
/// distributed across all available peers. Assuming there are around 50 connected
/// peers, the malicious node will receive approximately 10 of those block requests.
///
/// Malicious deserialized blocks can take up a large amount of RAM, see
/// [`super::inbound::downloads::MAX_INBOUND_CONCURRENCY`] and #1880 for details.
/// So we want to keep the lookahead limit reasonably small.
///
/// Once these malicious blocks start failing validation, the syncer will cancel all
/// the pending download and verify tasks, drop all the blocks, and start a new
/// ObtainTips with a new set of peers.
const MIN_LOOKAHEAD_LIMIT: usize = zebra_consensus::MAX_CHECKPOINT_HEIGHT_GAP * 2;
/// Controls how long we wait for a tips response to return.