Fix assumeutxo crash due to invalid base_blockhash

Can be reviewed with --color-moved=dimmed-zebra --color-moved-ws=ignore-all-space

Author: MarcoFalke

src/test/validation_chainstatemanager_tests.cpp

@@ -260,6 +260,11 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
             // Coins count is smaller than coins in file
             metadata.m_coins_count -= 1;
     }));
+    BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(
+        m_node, m_path_root, [](CAutoFile& auto_infile, SnapshotMetadata& metadata) {
+            // Wrong hash
+            metadata.m_base_blockhash = uint256::ZERO;
+    }));
     BOOST_REQUIRE(!CreateAndActivateUTXOSnapshot(
         m_node, m_path_root, [](CAutoFile& auto_infile, SnapshotMetadata& metadata) {
             // Wrong hash

src/validation.cpp

@@ -4815,6 +4815,26 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
 
     uint256 base_blockhash = metadata.m_base_blockhash;
 
+    CBlockIndex* snapshot_start_block = WITH_LOCK(::cs_main, return m_blockman.LookupBlockIndex(base_blockhash));
+
+    if (!snapshot_start_block) {
+        // Needed for GetUTXOStats and ExpectedAssumeutxo to determine the height and to avoid a crash when base_blockhash.IsNull()
+        LogPrintf("[snapshot] Did not find snapshot start blockheader %s\n",
+                  base_blockhash.ToString());
+        return false;
+    }
+
+    int base_height = snapshot_start_block->nHeight;
+    auto maybe_au_data = ExpectedAssumeutxo(base_height, ::Params());
+
+    if (!maybe_au_data) {
+        LogPrintf("[snapshot] assumeutxo height in snapshot metadata not recognized " /* Continued */
+                  "(%d) - refusing to load snapshot\n", base_height);
+        return false;
+    }
+
+    const AssumeutxoData& au_data = *maybe_au_data;
+
     COutPoint outpoint;
     Coin coin;
     const uint64_t coins_count = metadata.m_coins_count;
@@ -4905,15 +4925,6 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
 
     assert(coins_cache.GetBestBlock() == base_blockhash);
 
-    CBlockIndex* snapshot_start_block = WITH_LOCK(::cs_main, return m_blockman.LookupBlockIndex(base_blockhash));
-
-    if (!snapshot_start_block) {
-        // Needed for GetUTXOStats to determine the height
-        LogPrintf("[snapshot] Did not find snapshot start blockheader %s\n",
-                  base_blockhash.ToString());
-        return false;
-    }
-
     CCoinsStats stats{CoinStatsHashType::HASH_SERIALIZED};
     auto breakpoint_fnc = [] { /* TODO insert breakpoint here? */ };
 
@@ -4927,18 +4938,6 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
     }
 
     // Assert that the deserialized chainstate contents match the expected assumeutxo value.
-
-    int base_height = snapshot_start_block->nHeight;
-    auto maybe_au_data = ExpectedAssumeutxo(base_height, ::Params());
-
-    if (!maybe_au_data) {
-        LogPrintf("[snapshot] assumeutxo height in snapshot metadata not recognized " /* Continued */
-            "(%d) - refusing to load snapshot\n", base_height);
-        return false;
-    }
-
-    const AssumeutxoData& au_data = *maybe_au_data;
-
     if (AssumeutxoHash{stats.hashSerialized} != au_data.hash_serialized) {
         LogPrintf("[snapshot] bad snapshot content hash: expected %s, got %s\n",
             au_data.hash_serialized.ToString(), stats.hashSerialized.ToString());