From ef6dbe6863d92710fd2da7781e5b2aac87578751 Mon Sep 17 00:00:00 2001 From: Suhas Daftuar Date: Wed, 26 Jan 2022 18:29:56 -0500 Subject: [PATCH 1/2] Respond to getheaders if we have sufficient chainwork Previously, we would check to see if we were in IBD and ignore getheaders requests accordingly. However, the IBD criteria -- an optimization mostly targeted at behavior when we have peers serving us many blocks we need to download -- is difficult to reason about in edge-case scenarios, such as if the network were to go a long time without any blocks found and nodes getting restarted during that time. To make things simpler to reason about, just use nMinimumChainWork as our anti-DoS threshold; as long as our chain has that much work, it should be fine to respond to a peer asking for our headers (and this should allow such a peer to request blocks from us if needed). --- src/net_processing.cpp | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/src/net_processing.cpp b/src/net_processing.cpp index 273cb4fccb5..ac6b4654f17 100644 --- a/src/net_processing.cpp +++ b/src/net_processing.cpp @@ -3189,9 +3189,23 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type, return; } + if (fImporting || fReindex) { + LogPrint(BCLog::NET, "Ignoring getheaders from peer=%d while importing/reindexing\n", pfrom.GetId()); + return; + } + LOCK(cs_main); - if (m_chainman.ActiveChainstate().IsInitialBlockDownload() && !pfrom.HasPermission(NetPermissionFlags::Download)) { - LogPrint(BCLog::NET, "Ignoring getheaders from peer=%d because node is in initial block download\n", pfrom.GetId()); + + // Note that if we were to be on a chain that forks from the checkpointed + // chain, then serving those headers to a peer that has seen the + // checkpointed chain would cause that peer to disconnect us. Requiring + // that our chainwork exceed nMinimumChainWork is a protection against + // being fed a bogus chain when we started up for the first time and + // getting partitioned off the honest network for serving that chain to + // others. + if (m_chainman.ActiveTip() == nullptr || + (m_chainman.ActiveTip()->nChainWork < nMinimumChainWork && !pfrom.HasPermission(NetPermissionFlags::Download))) { + LogPrint(BCLog::NET, "Ignoring getheaders from peer=%d because active chain has too little work\n", pfrom.GetId()); return; } From a35f963edf1a14ee572abea106fb0147575e4694 Mon Sep 17 00:00:00 2001 From: Suhas Daftuar Date: Wed, 26 Jan 2022 19:18:27 -0500 Subject: [PATCH 2/2] Add test for getheaders behavior Expect responses to a getheaders iff the node has a chain with more than nMinimumChainWork --- test/functional/feature_minchainwork.py | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/test/functional/feature_minchainwork.py b/test/functional/feature_minchainwork.py index 489a729cfc7..f6432ed20eb 100755 --- a/test/functional/feature_minchainwork.py +++ b/test/functional/feature_minchainwork.py @@ -17,6 +17,7 @@ only succeeds past a given node once its nMinimumChainWork has been exceeded. import time +from test_framework.p2p import P2PInterface, msg_getheaders from test_framework.test_framework import BitcoinTestFramework from test_framework.util import assert_equal @@ -41,6 +42,9 @@ class MinimumChainWorkTest(BitcoinTestFramework): for i in range(self.num_nodes-1): self.connect_nodes(i+1, i) + # Set clock of node2 2 days ahead, to keep it in IBD during this test. + self.nodes[2].setmocktime(int(time.time()) + 48*60*60) + def run_test(self): # Start building a chain on node0. node2 shouldn't be able to sync until node1's # minchainwork is exceeded @@ -71,6 +75,15 @@ class MinimumChainWorkTest(BitcoinTestFramework): assert self.nodes[1].getbestblockhash() != self.nodes[0].getbestblockhash() assert_equal(self.nodes[2].getblockcount(), starting_blockcount) + self.log.info("Check that getheaders requests to node2 are ignored") + peer = self.nodes[2].add_p2p_connection(P2PInterface()) + msg = msg_getheaders() + msg.locator.vHave = [int(self.nodes[2].getbestblockhash(), 16)] + msg.hashstop = 0 + peer.send_and_ping(msg) + time.sleep(5) + assert "headers" not in peer.last_message + self.log.info("Generating one more block") self.generate(self.nodes[0], 1) @@ -85,5 +98,13 @@ class MinimumChainWorkTest(BitcoinTestFramework): self.sync_all() self.log.info(f"Blockcounts: {[n.getblockcount() for n in self.nodes]}") + self.log.info("Test that getheaders requests to node2 are not ignored") + peer.send_and_ping(msg) + assert "headers" in peer.last_message + + # Verify that node2 is in fact still in IBD (otherwise this test may + # not be exercising the logic we want!) + assert_equal(self.nodes[2].getblockchaininfo()['initialblockdownload'], True) + if __name__ == '__main__': MinimumChainWorkTest().main()