Merge pull request #1953 from gmaxwell/createnewblock-race

Fixes a race condition in CreateNewBlock and a future null deref on testnet.

src/main.cpp

@@ -1558,7 +1558,8 @@ bool CBlock::ConnectBlock(CBlockIndex* pindex, CCoinsViewCache &view, bool fJust
     // Now that the whole chain is irreversibly beyond that time it is applied to all blocks except the
     // two in the chain that violate it. This prevents exploiting the issue against nodes in their
     // initial block download.
-    bool fEnforceBIP30 = !((pindex->nHeight==91842 && pindex->GetBlockHash() == uint256("0x00000000000a4d0a398161ffc163c503763b1f4360639393e0e4c8e300e0caec")) ||
+    bool fEnforceBIP30 = (!pindex->phashBlock) || // Enforce on CreateNewBlock invocations which don't have a hash.
+                          !((pindex->nHeight==91842 && pindex->GetBlockHash() == uint256("0x00000000000a4d0a398161ffc163c503763b1f4360639393e0e4c8e300e0caec")) ||
                            (pindex->nHeight==91880 && pindex->GetBlockHash() == uint256("0x00000000000743f190a18c5577a3c2d2a1f610ae9601ac046a38084ccb7cd721")));
     if (fEnforceBIP30) {
         for (unsigned int i=0; i<vtx.size(); i++) {
@@ -3751,7 +3752,6 @@ public:
 
 CBlock* CreateNewBlock(CReserveKey& reservekey)
 {
-    CBlockIndex* pindexPrev = pindexBest;
 
     // Create new block
     auto_ptr<CBlock> pblock(new CBlock());
@@ -3796,6 +3796,7 @@ CBlock* CreateNewBlock(CReserveKey& reservekey)
     int64 nFees = 0;
     {
         LOCK2(cs_main, mempool.cs);
+        CBlockIndex* pindexPrev = pindexBest;
         CCoinsViewCache view(*pcoinsTip, true);
 
         // Priority order to process transactions