From 131c23d02733c547975844226c1fe0dd4c87211c Mon Sep 17 00:00:00 2001
From: Alex Morcos <morcos@chaincode.com>
Date: Thu, 17 Sep 2015 17:43:34 -0400
Subject: [PATCH] Fix locking in GetTransaction.

GetTransaction needs to lock cs_main until ReadBlockFromDisk completes, the data inside CBlockIndex's can change since pruning.  This lock was held by all calls to GetTransaction except rest_tx.
---
 src/main.cpp | 74 +++++++++++++++++++++++++---------------------------
 1 file changed, 36 insertions(+), 38 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index 27278b977..0b5b52b49 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -954,47 +954,45 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
 bool GetTransaction(const uint256 &hash, CTransaction &txOut, uint256 &hashBlock, bool fAllowSlow)
 {
     CBlockIndex *pindexSlow = NULL;
+
+    LOCK(cs_main);
+
+    if (mempool.lookup(hash, txOut))
     {
-        LOCK(cs_main);
+        return true;
+    }
+
+    if (fTxIndex) {
+        CDiskTxPos postx;
+        if (pblocktree->ReadTxIndex(hash, postx)) {
+            CAutoFile file(OpenBlockFile(postx, true), SER_DISK, CLIENT_VERSION);
+            if (file.IsNull())
+                return error("%s: OpenBlockFile failed", __func__);
+            CBlockHeader header;
+            try {
+                file >> header;
+                fseek(file.Get(), postx.nTxOffset, SEEK_CUR);
+                file >> txOut;
+            } catch (const std::exception& e) {
+                return error("%s: Deserialize or I/O error - %s", __func__, e.what());
+            }
+            hashBlock = header.GetHash();
+            if (txOut.GetHash() != hash)
+                return error("%s: txid mismatch", __func__);
+            return true;
+        }
+    }
+
+    if (fAllowSlow) { // use coin database to locate block that contains transaction, and scan it
+        int nHeight = -1;
         {
-            if (mempool.lookup(hash, txOut))
-            {
-                return true;
-            }
-        }
-
-        if (fTxIndex) {
-            CDiskTxPos postx;
-            if (pblocktree->ReadTxIndex(hash, postx)) {
-                CAutoFile file(OpenBlockFile(postx, true), SER_DISK, CLIENT_VERSION);
-                if (file.IsNull())
-                    return error("%s: OpenBlockFile failed", __func__);
-                CBlockHeader header;
-                try {
-                    file >> header;
-                    fseek(file.Get(), postx.nTxOffset, SEEK_CUR);
-                    file >> txOut;
-                } catch (const std::exception& e) {
-                    return error("%s: Deserialize or I/O error - %s", __func__, e.what());
-                }
-                hashBlock = header.GetHash();
-                if (txOut.GetHash() != hash)
-                    return error("%s: txid mismatch", __func__);
-                return true;
-            }
-        }
-
-        if (fAllowSlow) { // use coin database to locate block that contains transaction, and scan it
-            int nHeight = -1;
-            {
-                CCoinsViewCache &view = *pcoinsTip;
-                const CCoins* coins = view.AccessCoins(hash);
-                if (coins)
-                    nHeight = coins->nHeight;
-            }
-            if (nHeight > 0)
-                pindexSlow = chainActive[nHeight];
+            CCoinsViewCache &view = *pcoinsTip;
+            const CCoins* coins = view.AccessCoins(hash);
+            if (coins)
+                nHeight = coins->nHeight;
         }
+        if (nHeight > 0)
+            pindexSlow = chainActive[nHeight];
     }
 
     if (pindexSlow) {