[wallet] Securely erase potentially sensitive keys/values

src/support/cleanse.h

@@ -8,6 +8,7 @@
 
 #include <stdlib.h>
 
+// Attempt to overwrite data in the specified memory span.
 void memory_cleanse(void *ptr, size_t len);
 
 #endif // BITCOIN_SUPPORT_CLEANSE_H

src/wallet/db.h

@@ -180,22 +180,23 @@ public:
         Dbt datValue;
         datValue.set_flags(DB_DBT_MALLOC);
         int ret = pdb->get(activeTxn, &datKey, &datValue, 0);
-        memset(datKey.get_data(), 0, datKey.get_size());
-        if (datValue.get_data() == NULL)
-            return false;
-
+        memory_cleanse(datKey.get_data(), datKey.get_size());
+        bool success = false;
+        if (datValue.get_data() != NULL) {
             // Unserialize value
             try {
                 CDataStream ssValue((char*)datValue.get_data(), (char*)datValue.get_data() + datValue.get_size(), SER_DISK, CLIENT_VERSION);
                 ssValue >> value;
+                success = true;
             } catch (const std::exception&) {
-            return false;
+                // In this case success remains 'false'
             }
 
             // Clear and free memory
-        memset(datValue.get_data(), 0, datValue.get_size());
+            memory_cleanse(datValue.get_data(), datValue.get_size());
             free(datValue.get_data());
-        return (ret == 0);
+        }
+        return ret == 0 && success;
     }
 
     template <typename K, typename T>
@@ -222,8 +223,8 @@ public:
         int ret = pdb->put(activeTxn, &datKey, &datValue, (fOverwrite ? 0 : DB_NOOVERWRITE));
 
         // Clear memory in case it was a private key
-        memset(datKey.get_data(), 0, datKey.get_size());
-        memset(datValue.get_data(), 0, datValue.get_size());
+        memory_cleanse(datKey.get_data(), datKey.get_size());
+        memory_cleanse(datValue.get_data(), datValue.get_size());
         return (ret == 0);
     }
 
@@ -245,7 +246,7 @@ public:
         int ret = pdb->del(activeTxn, &datKey, 0);
 
         // Clear memory
-        memset(datKey.get_data(), 0, datKey.get_size());
+        memory_cleanse(datKey.get_data(), datKey.get_size());
         return (ret == 0 || ret == DB_NOTFOUND);
     }
 
@@ -265,7 +266,7 @@ public:
         int ret = pdb->exists(activeTxn, &datKey, 0);
 
         // Clear memory
-        memset(datKey.get_data(), 0, datKey.get_size());
+        memory_cleanse(datKey.get_data(), datKey.get_size());
         return (ret == 0);
     }
 
@@ -308,8 +309,8 @@ public:
         ssValue.write((char*)datValue.get_data(), datValue.get_size());
 
         // Clear and free memory
-        memset(datKey.get_data(), 0, datKey.get_size());
-        memset(datValue.get_data(), 0, datValue.get_size());
+        memory_cleanse(datKey.get_data(), datKey.get_size());
+        memory_cleanse(datValue.get_data(), datValue.get_size());
         free(datKey.get_data());
         free(datValue.get_data());
         return 0;