[Pkg-bitcoin-commits] [bitcoin] 87/126: Add comment explaining forced processing of compact blocks

[Jonas Smedegaard]

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js pushed a commit to annotated tag debian/0.15.1_dfsg-1
in repository bitcoin.

commit ffb6ea4e5ebfe109e9771aab058bdd4d2f6468a8
Author: Suhas Daftuar <sdaftuar at chaincode.com>
Date:   Thu Oct 19 20:52:30 2017 -0400

    Add comment explaining forced processing of compact blocks
    
    Github-Pull: #11458
    Rebased-From: 01b52cedd42f50a93b40981c91af7c12de6e45ce
---
 src/net_processing.cpp | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 5f117de..5b97509 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -2144,7 +2144,16 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
                 mapBlockSource.emplace(pblock->GetHash(), std::make_pair(pfrom->GetId(), false));
             }
             bool fNewBlock = false;
-            ProcessNewBlock(chainparams, pblock, true, &fNewBlock);
+            // Setting fForceProcessing to true means that we bypass some of
+            // our anti-DoS protections in AcceptBlock, which filters
+            // unrequested blocks that might be trying to waste our resources
+            // (eg disk space). Because we only try to reconstruct blocks when
+            // we're close to caught up (via the CanDirectFetch() requirement
+            // above, combined with the behavior of not requesting blocks until
+            // we have a chain with at least nMinimumChainWork), and we ignore
+            // compact blocks with less work than our tip, it is safe to treat
+            // reconstructed compact blocks as having been requested.
+            ProcessNewBlock(chainparams, pblock, /*fForceProcessing=*/true, &fNewBlock);
             if (fNewBlock) {
                 pfrom->nLastBlockTime = GetTime();
             } else {
@@ -2224,7 +2233,11 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
             bool fNewBlock = false;
             // Since we requested this block (it was in mapBlocksInFlight), force it to be processed,
             // even if it would not be a candidate for new tip (missing previous block, chain not long enough, etc)
-            ProcessNewBlock(chainparams, pblock, true, &fNewBlock);
+            // This bypasses some anti-DoS logic in AcceptBlock (eg to prevent
+            // disk-space attacks), but this should be safe due to the
+            // protections in the compact block handler -- see related comment
+            // in compact block optimistic reconstruction handling.
+            ProcessNewBlock(chainparams, pblock, /*fForceProcessing=*/true, &fNewBlock);
             if (fNewBlock) {
                 pfrom->nLastBlockTime = GetTime();
             } else {

-- 
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