Fix a use-after-free problem in initialization (#1920)

Don't store the result of c_str().

Luckily, this only affects logging, though it could crash or leak
sensitive data to the log in rare cases.

src/init.cpp

@@ -440,7 +440,7 @@ bool AppInit2()
 
     // ********************************************************* Step 4: application initialization: dir lock, daemonize, pidfile, debug log
 
-    const char* pszDataDir = GetDataDir().string().c_str();
+    std::string strDataDir = GetDataDir().string();
 
     // Make sure only a single Bitcoin process is using the data directory.
     boost::filesystem::path pathLockFile = GetDataDir() / ".lock";
@@ -448,7 +448,7 @@ bool AppInit2()
     if (file) fclose(file);
     static boost::interprocess::file_lock lock(pathLockFile.string().c_str());
     if (!lock.try_lock())
-        return InitError(strprintf(_("Cannot obtain a lock on data directory %s.  Bitcoin is probably already running."), pszDataDir));
+        return InitError(strprintf(_("Cannot obtain a lock on data directory %s.  Bitcoin is probably already running."), strDataDir.c_str()));
 
 #if !defined(WIN32) && !defined(QT_GUI)
     if (fDaemon)
@@ -480,7 +480,7 @@ bool AppInit2()
     if (!fLogTimestamps)
         printf("Startup time: %s\n", DateTimeStrFormat("%x %H:%M:%S", GetTime()).c_str());
     printf("Default data directory %s\n", GetDefaultDataDir().string().c_str());
-    printf("Used data directory %s\n", pszDataDir);
+    printf("Used data directory %s\n", strDataDir.c_str());
     std::ostringstream strErrors;
 
     if (fDaemon)
@@ -496,7 +496,7 @@ bool AppInit2()
     {
         string msg = strprintf(_("Error initializing database environment %s!"
                                  " To recover, BACKUP THAT DIRECTORY, then remove"
-                                 " everything from it except for wallet.dat."), pszDataDir);
+                                 " everything from it except for wallet.dat."), strDataDir.c_str());
         return InitError(msg);
     }
 
@@ -515,7 +515,7 @@ bool AppInit2()
             string msg = strprintf(_("Warning: wallet.dat corrupt, data salvaged!"
                                      " Original wallet.dat saved as wallet.{timestamp}.bak in %s; if"
                                      " your balance or transactions are incorrect you should"
-                                     " restore from a backup."), pszDataDir);
+                                     " restore from a backup."), strDataDir.c_str());
             uiInterface.ThreadSafeMessageBox(msg, _("Bitcoin"), CClientUIInterface::OK | CClientUIInterface::ICON_EXCLAMATION | CClientUIInterface::MODAL);
         }
         if (r == CDBEnv::RECOVER_FAIL)
@@ -634,7 +634,7 @@ bool AppInit2()
     {
         string msg = strprintf(_("Error initializing database environment %s!"
                                  " To recover, BACKUP THAT DIRECTORY, then remove"
-                                 " everything from it except for wallet.dat."), pszDataDir);
+                                 " everything from it except for wallet.dat."), strDataDir.c_str());
         return InitError(msg);
     }