[gparted] Stop copying password into insecure memory when getting entry (#795617)

[Curtis Gedak <gedakc src gnome org>]

commit 3d49fdc2e44f01ba3fcdc6a1c9ab0c1ee2067450
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Thu Mar 22 17:12:45 2018 +0000

    Stop copying password into insecure memory when getting entry (#795617)
    
    The underlying C coded Gtk Entry widget is careful to zero memory after
    use, allowing the widget to be safely used for password entry [1].
    However the C++ method Gtk::Entry::get_text() just takes the underlying
    C string from the Gtk Entry widget and copies it when constructing a
    Glib::ustring for the return value [2].
    
    So directly use the Gtk/C API to get the C string instead.
    
    [1] https://git.gnome.org/browse/gtk+/tree/gtk/gtkentrybuffer.c?h=3.22.28#n92
        See function trash_area() which zeros memory and its use in
        gtk_entry_buffer_normal_insert_text(),
        gtk_entry_buffer_normal_delete_text() and
        gtk_entry_buffer_finalize().
    
    [2] https://git.gnome.org/browse/gtkmm/tree/gtk/src/entry.hg?h=3.22.2#n104
        _WRAP_METHOD(Glib::ustring get_text() const, gtk_entry_get_text)
    
        https://git.gnome.org/browse/glibmm/tree/docs/internal/using_gmmproc.txt?h=2.46.1#n53
        _WRAP_METHOD(Glib::ustring METHOD const, FUNC) is processed to:
            Glib::ustring METHOD() const
            {
                return Glib::convert_const_gchar_ptr_to_ustring(
                    FUNC(const_cast<GtkEntry*>(gobj())));
            }
    
        https://git.gnome.org/browse/glibmm/tree/glib/glibmm/utility.h?h=2.46.1#n82
            Glib::ustring convert_const_gchar_ptr_to_ustring(const char* str)
            {
                return (str) ? Glib::ustring(str) : Glib::ustring();
            }
    
        So Gtk::Entry::get_text() calls Glib::ustring() constructor which
        copies the C string to create the Glib::ustring object returned.
    
    Bug 795617 - Implement opening and closing of LUKS mappings

 include/DialogPasswordEntry.h |    3 +--
 src/DialogPasswordEntry.cc    |    8 ++++++--
 src/Win_GParted.cc            |    2 +-
 3 files changed, 8 insertions(+), 5 deletions(-)
---
diff --git a/include/DialogPasswordEntry.h b/include/DialogPasswordEntry.h
index c351c26..367913d 100644
--- a/include/DialogPasswordEntry.h
+++ b/include/DialogPasswordEntry.h
@@ -20,7 +20,6 @@
 #include "Partition.h"
 
 #include <gtkmm/dialog.h>
-#include <glibmm/ustring.h>
 #include <gtkmm/entry.h>
 
 namespace GParted
@@ -31,7 +30,7 @@ class DialogPasswordEntry : public Gtk::Dialog
 public:
        DialogPasswordEntry( const Partition & partition );
        ~DialogPasswordEntry();
-       Glib::ustring get_password();
+       const char * get_password();
 
 private:
        Gtk::Entry *entry;
diff --git a/src/DialogPasswordEntry.cc b/src/DialogPasswordEntry.cc
index e772c4e..73f8839 100644
--- a/src/DialogPasswordEntry.cc
+++ b/src/DialogPasswordEntry.cc
@@ -20,6 +20,7 @@
 #include <glibmm/ustring.h>
 #include <gtkmm/box.h>
 #include <gtkmm/stock.h>
+#include <gtk/gtkentry.h>
 
 namespace GParted
 {
@@ -68,9 +69,12 @@ DialogPasswordEntry::~DialogPasswordEntry()
 {
 }
 
-Glib::ustring DialogPasswordEntry::get_password()
+const char * DialogPasswordEntry::get_password()
 {
-       return Glib::ustring( entry->get_text() );
+       // Avoid using the gtkmm C++ entry->get_text() because that constructs a
+       // Glib::ustring, copying the password from the underlying C GtkEntry object into
+       // an unsecured malloced chunk of memory.
+       return (const char *)gtk_entry_get_text( GTK_ENTRY( entry->gobj() ) );
 }
 
 } //GParted
diff --git a/src/Win_GParted.cc b/src/Win_GParted.cc
index 3e32a7c..273a950 100644
--- a/src/Win_GParted.cc
+++ b/src/Win_GParted.cc
@@ -2563,7 +2563,7 @@ void Win_GParted::toggle_crypt_busy_state()
                                        return;
 
                                success = open_encrypted_partition( *selected_partition_ptr,
-                                                                   dialog.get_password().c_str(),
+                                                                   dialog.get_password(),
                                                                    error_msg );
                        } while ( ! success );
                }