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Merge bitcoin/bitcoin#26355: p2p: Handle IsContinuationOfLowWorkHeadersSync return value correctly when new headers sync is started

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7ad15d1100 [net processing] Handle IsContinuationOfLowWorkHeadersSync return value correctly when new headers sync is started (dergoegge)

Pull request description:

  This PR fixes a bug in the headers sync logic that enables submitting headers to a nodes block index that don't lead to a chain that surpasses our DoS limit.

  The issue is that we ignore the return value on [the first `IsContinuationOfLowWorkHeadersSync` call after a new headers sync is started](fabc031048/src/net_processing.cpp (L2553-L2568)), which leads to us passing headers to [`ProcessNewBlockHeaders`](fabc031048/src/net_processing.cpp (L2856)) when that initial `IsContinuationOfLowWorkHeadersSync` call returns `false`. One easy way (maybe the only?) to trigger this is by sending 2000 headers where the last header has a different `nBits` value than the prior headers (which fails the pre-sync logic [here](fabc031048/src/headerssync.cpp (L189))). Those 2000 headers will be passed to `ProcessNewBlockHeaders`.

  I haven't included a test here so far because we can't test this without changing the default value for `CRegTestParams::consensus.fPowAllowMinDifficultyBlocks` or doing some more involved refactoring.

ACKs for top commit:
  sipa:
    ACK 7ad15d1100
  glozow:
    ACK 7ad15d1100

Tree-SHA512: 9aabb8bf3700401e79863d0accda0befd2a83c4d469a53f97d827e51139e2f826aee08cdfbc8866b311b153f61fdac9b7aa515fcfa2a21c5e2812c2bf3c03664
This commit is contained in:
glozow 2022-10-24 15:34:27 +01:00
commit 3d0fca1288
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1 changed files with 12 additions and 4 deletions
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src/net_processing.cpp
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@ -2565,14 +2565,22 @@ bool PeerManagerImpl::TryLowWorkHeadersSync(Peer& peer, CNode& pfrom, const CBlo
// Now a HeadersSyncState object for tracking this synchronization is created,
// process the headers using it as normal.
return IsContinuationOfLowWorkHeadersSync(peer, pfrom, headers);
if (!IsContinuationOfLowWorkHeadersSync(peer, pfrom, headers)) {
// Something went wrong, reset the headers sync.
peer.m_headers_sync.reset(nullptr);
LOCK(m_headers_presync_mutex);
m_headers_presync_stats.erase(peer.m_id);
}
} else {
LogPrint(BCLog::NET, "Ignoring low-work chain (height=%u) from peer=%d\n", chain_start_header->nHeight + headers.size(), pfrom.GetId());
// Since this is a low-work headers chain, no further processing is required.
headers = {};
return true;
}
// The peer has not yet given us a chain that meets our work threshold,
// so we want to prevent further processing of the headers in any case.
headers = {};
return true;
}
return false;
}