Merge pull request #17 from moneromooo-monero/blockchain

db_lmdb: catch attempt to remove block from an empty blockchain
db_lmdb: do not give the group database write permissions

src/cryptonote_core/BlockchainDB_impl/db_lmdb.cpp

@@ -207,6 +207,9 @@ void BlockchainLMDB::remove_block()
   LOG_PRINT_L3("BlockchainLMDB::" << __func__);
   check_open();
 
+  if (m_height == 0)
+    throw0(BLOCK_DNE ("Attempting to remove block from an empty blockchain"));
+
   MDB_val_copy<uint64_t> k(m_height - 1);
   MDB_val h;
   if (mdb_get(*m_write_txn, m_block_hashes, &k, &h))
@@ -527,7 +530,7 @@ void BlockchainLMDB::open(const std::string& filename)
   size_t mapsize = 1LL << 34;
   if (auto result = mdb_env_set_mapsize(m_env, mapsize))
     throw0(DB_ERROR(std::string("Failed to set max memory map size: ").append(mdb_strerror(result)).c_str()));
-  if (auto result = mdb_env_open(m_env, filename.c_str(), 0, 0664))
+  if (auto result = mdb_env_open(m_env, filename.c_str(), 0, 0644))
     throw0(DB_ERROR(std::string("Failed to open lmdb environment: ").append(mdb_strerror(result)).c_str()));
 
   // get a read/write MDB_txn