Avoid masking of difficulty adjustment errors by checkpoints

sipa · sipa · commit 85c82b50d1a8 · 2017-08-10T15:39:36.000-07:00
Currently difficulty adjustment violations are not reported for
chains that branch off before the last checkpoint. Change this
by moving the checkpoint check after the difficulty check.
diff --git a/src/validation.cpp b/src/validation.cpp
@@ -2830,22 +2830,6 @@ bool CheckBlock(const CBlock& block, CValidationState& state, const Consensus::P
     return true;
 }
 
-static bool CheckIndexAgainstCheckpoint(const CBlockIndex* pindexPrev, CValidationState& state, const CChainParams& chainparams, const uint256& hash)
-{
-    if (*pindexPrev->phashBlock == chainparams.GetConsensus().hashGenesisBlock)
-        return true;
-
-    int nHeight = pindexPrev->nHeight+1;
-    // Don't accept any forks from the main chain prior to last checkpoint.
-    // GetLastCheckpoint finds the last checkpoint in MapCheckpoints that's in our
-    // MapBlockIndex.
-    CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint(chainparams.Checkpoints());
-    if (pcheckpoint && nHeight < pcheckpoint->nHeight)
-        return state.DoS(100, error("%s: forked chain older than last checkpoint (height %d)", __func__, nHeight), REJECT_CHECKPOINT, "bad-fork-prior-to-checkpoint");
-
-    return true;
-}
-
 bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params)
 {
     LOCK(cs_main);
@@ -2911,14 +2895,26 @@ std::vector<unsigned char> GenerateCoinbaseCommitment(CBlock& block, const CBloc
 /** Context-dependent validity checks.
  *  By "context", we mean only the previous block headers, but not the UTXO
  *  set; UTXO-related validity checks are done in ConnectBlock(). */
-static bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationState& state, const Consensus::Params& consensusParams, const CBlockIndex* pindexPrev, int64_t nAdjustedTime)
+static bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationState& state, const CChainParams& params, const CBlockIndex* pindexPrev, int64_t nAdjustedTime)
 {
     assert(pindexPrev != NULL);
     const int nHeight = pindexPrev->nHeight + 1;
+
     // Check proof of work
+    const Consensus::Params& consensusParams = params.GetConsensus();
     if (block.nBits != GetNextWorkRequired(pindexPrev, &block, consensusParams))
         return state.DoS(100, false, REJECT_INVALID, "bad-diffbits", false, "incorrect proof of work");
 
+    // Check against checkpoints
+    if (fCheckpointsEnabled) {
+        // Don't accept any forks from the main chain prior to last checkpoint.
+        // GetLastCheckpoint finds the last checkpoint in MapCheckpoints that's in our
+        // MapBlockIndex.
+        CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint(params.Checkpoints());
+        if (pcheckpoint && nHeight < pcheckpoint->nHeight)
+            return state.DoS(100, error("%s: forked chain older than last checkpoint (height %d)", __func__, nHeight), REJECT_CHECKPOINT, "bad-fork-prior-to-checkpoint");
+    }
+
     // Check timestamp against prev
     if (block.GetBlockTime() <= pindexPrev->GetMedianTimePast())
         return state.Invalid(false, REJECT_INVALID, "time-too-old", "block's timestamp is too early");
@@ -3049,12 +3045,7 @@ static bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state
         pindexPrev = (*mi).second;
         if (pindexPrev->nStatus & BLOCK_FAILED_MASK)
             return state.DoS(100, error("%s: prev block invalid", __func__), REJECT_INVALID, "bad-prevblk");
-
-        assert(pindexPrev);
-        if (fCheckpointsEnabled && !CheckIndexAgainstCheckpoint(pindexPrev, state, chainparams, hash))
-            return error("%s: CheckIndexAgainstCheckpoint(): %s", __func__, state.GetRejectReason().c_str());
-
-        if (!ContextualCheckBlockHeader(block, state, chainparams.GetConsensus(), pindexPrev, GetAdjustedTime()))
+        if (!ContextualCheckBlockHeader(block, state, chainparams, pindexPrev, GetAdjustedTime()))
             return error("%s: Consensus::ContextualCheckBlockHeader: %s, %s", __func__, hash.ToString(), FormatStateMessage(state));
     }
     if (pindex == NULL)
@@ -3203,16 +3194,13 @@ bool TestBlockValidity(CValidationState& state, const CChainParams& chainparams,
 {
     AssertLockHeld(cs_main);
     assert(pindexPrev && pindexPrev == chainActive.Tip());
-    if (fCheckpointsEnabled && !CheckIndexAgainstCheckpoint(pindexPrev, state, chainparams, block.GetHash()))
-        return error("%s: CheckIndexAgainstCheckpoint(): %s", __func__, state.GetRejectReason().c_str());
-
     CCoinsViewCache viewNew(pcoinsTip);
     CBlockIndex indexDummy(block);
     indexDummy.pprev = pindexPrev;
     indexDummy.nHeight = pindexPrev->nHeight + 1;
 
     // NOTE: CheckBlockHeader is called by CheckBlock
-    if (!ContextualCheckBlockHeader(block, state, chainparams.GetConsensus(), pindexPrev, GetAdjustedTime()))
+    if (!ContextualCheckBlockHeader(block, state, chainparams, pindexPrev, GetAdjustedTime()))
         return error("%s: Consensus::ContextualCheckBlockHeader: %s", __func__, FormatStateMessage(state));
     if (!CheckBlock(block, state, chainparams.GetConsensus(), fCheckPOW, fCheckMerkleRoot))
         return error("%s: Consensus::CheckBlock: %s", __func__, FormatStateMessage(state));
