[gtk/ebassi/secure-buffer: 4/5] Add a secure GtkEntryBuffer

[Emmanuele Bassi <ebassi src gnome org>]

commit b2b6a0a02b874fd0362e06b01e32ed6edbf045f3
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Fri Sep 4 12:51:58 2020 +0100

    Add a secure GtkEntryBuffer
    
    We have a widget for password and passphrase entries, but we have no way
    to handle the data securely. This is usually performed by a separate
    GtkEntryBuffer—for instance, the one in GCR. While we have API for
    setting a new entry buffer on GtkText, we don't have API for
    GtkPasswordEntry, though, so the options are:
    
     - expose additional API for GtkPasswordEntry to allow setting a secure
       text buffer on the internal GtkText widget
     - provide a secure text buffer out of the box
    
    Given that an insecure-by-default GtkPasswordEntry is basically
    pointless, might as well have a secure buffer built in.
    
    We don't really need to make the password entry buffer public out of the
    box, but we can re-evaluate at a later date.
    
    Fixes: #2403

 gtk/gtkpasswordentrybuffer.c        | 196 ++++++++++++++++++++++++++++++++++++
 gtk/gtkpasswordentrybufferprivate.h |  33 ++++++
 gtk/meson.build                     |   1 +
 3 files changed, 230 insertions(+)
---
diff --git a/gtk/gtkpasswordentrybuffer.c b/gtk/gtkpasswordentrybuffer.c
new file mode 100644
index 0000000000..05844d2fc5
--- /dev/null
+++ b/gtk/gtkpasswordentrybuffer.c
@@ -0,0 +1,196 @@
+/* gtkpasswordentrybuffer.c: Entry buffer with secure allocation 
+ *
+   Copyright 2009  Stefan Walter
+ * Copyright 2020  GNOME Foundation
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "gtkpasswordentrybufferprivate.h"
+
+#include "gtksecurememoryprivate.h"
+
+#include <string.h>
+
+/* Initial size of buffer, in bytes */
+#define MIN_SIZE 16
+
+struct _GtkPasswordEntryBuffer
+{
+  GtkEntryBuffer parent_instance;
+
+  char *text;
+  gsize text_size;
+  gsize text_bytes;
+  guint text_chars;
+};
+
+G_DEFINE_TYPE (GtkPasswordEntryBuffer, gtk_password_entry_buffer, GTK_TYPE_ENTRY_BUFFER)
+
+static const char *
+gtk_password_entry_buffer_real_get_text (GtkEntryBuffer *buffer,
+                                       gsize *n_bytes)
+{
+  GtkPasswordEntryBuffer *self = GTK_PASSWORD_ENTRY_BUFFER (buffer);
+
+  if (n_bytes != NULL)
+    *n_bytes = self->text_bytes;
+
+  if (!self->text)
+    return "";
+
+  return self->text;
+}
+
+static guint
+gtk_password_entry_buffer_real_get_length (GtkEntryBuffer *buffer)
+{
+  GtkPasswordEntryBuffer *self = GTK_PASSWORD_ENTRY_BUFFER (buffer);
+  return self->text_chars;
+}
+
+static guint
+gtk_password_entry_buffer_real_insert_text (GtkEntryBuffer *buffer,
+                                            guint           position,
+                                            const char     *chars,
+                                            guint           n_chars)
+{
+  GtkPasswordEntryBuffer *self = GTK_PASSWORD_ENTRY_BUFFER (buffer);
+
+  gsize n_bytes = g_utf8_offset_to_pointer (chars, n_chars) - chars;
+
+  /* Need more memory */
+  if (n_bytes + self->text_bytes + 1 > self->text_size)
+    {
+      /* Calculate our new buffer size */
+      while (n_bytes + self->text_bytes + 1 > self->text_size)
+        {
+          if (self->text_size == 0)
+            {
+              self->text_size = MIN_SIZE;
+            }
+          else
+            {
+              if (2 * self->text_size < GTK_ENTRY_BUFFER_MAX_SIZE)
+                {
+                  self->text_size *= 2;
+                }
+              else
+                {
+                  self->text_size = GTK_ENTRY_BUFFER_MAX_SIZE;
+                  if (n_bytes > self->text_size - self->text_bytes - 1)
+                    {
+                      n_bytes = self->text_size - self->text_bytes - 1;
+                      n_bytes = g_utf8_find_prev_char (chars, chars + n_bytes + 1) - chars;
+                      n_chars = g_utf8_strlen (chars, n_bytes);
+                    }
+                  break;
+                }
+            }
+        }
+
+      self->text = gtk_secure_realloc (self->text, self->text_size);
+    }
+
+  /* Actual text insertion */
+  gsize at = g_utf8_offset_to_pointer (self->text, position) - self->text;
+  memmove (self->text + at + n_bytes, self->text + at, self->text_bytes - at);
+  memcpy (self->text + at, chars, n_bytes);
+
+  /* Book keeping */
+  self->text_bytes += n_bytes;
+  self->text_chars += n_chars;
+  self->text[self->text_bytes] = '\0';
+
+  gtk_entry_buffer_emit_inserted_text (buffer, position, chars, n_chars);
+
+  return n_chars;
+}
+
+static guint
+gtk_password_entry_buffer_real_delete_text (GtkEntryBuffer *buffer,
+                                            guint           position,
+                                            guint           n_chars)
+{
+  GtkPasswordEntryBuffer *self = GTK_PASSWORD_ENTRY_BUFFER (buffer);
+
+  if (position > self->text_chars)
+    position = self->text_chars;
+  if (position + n_chars > self->text_chars)
+    n_chars = self->text_chars - position;
+
+  if (n_chars > 0)
+    {
+      gsize start = g_utf8_offset_to_pointer (self->text, position) - self->text;
+      gsize end = g_utf8_offset_to_pointer (self->text, position + n_chars) - self->text;
+
+      memmove (self->text + start, self->text + end, self->text_bytes + 1 - end);
+      self->text_chars -= n_chars;
+      self->text_bytes -= (end - start);
+
+      gtk_entry_buffer_emit_deleted_text (buffer, position, n_chars);
+    }
+
+  return n_chars;
+}
+
+static void
+gtk_password_entry_buffer_finalize (GObject *gobject)
+{
+  GtkPasswordEntryBuffer *self = GTK_PASSWORD_ENTRY_BUFFER (gobject);
+
+  g_clear_pointer (&self->text, gtk_secure_free);
+
+  self->text_bytes = 0;
+  self->text_size = 0;
+  self->text_chars = 0;
+
+  G_OBJECT_CLASS (gtk_password_entry_buffer_parent_class)->finalize (gobject);
+}
+
+static void
+gtk_password_entry_buffer_class_init (GtkPasswordEntryBufferClass *klass)
+{
+  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
+  GtkEntryBufferClass *buffer_class = GTK_ENTRY_BUFFER_CLASS (klass);
+
+  gobject_class->finalize = gtk_password_entry_buffer_finalize;
+
+  buffer_class->get_text = gtk_password_entry_buffer_real_get_text;
+  buffer_class->get_length = gtk_password_entry_buffer_real_get_length;
+  buffer_class->insert_text = gtk_password_entry_buffer_real_insert_text;
+  buffer_class->delete_text = gtk_password_entry_buffer_real_delete_text;
+}
+
+static void
+gtk_password_entry_buffer_init (GtkPasswordEntryBuffer *self)
+{
+}
+
+/*< private >
+ * gtk_password_entry_buffer_new:
+ *
+ * Creates a new #GtkEntryBuffer using secure memory allocations.
+ *
+ * Returns: (transfer full): the newly created instance
+ */
+GtkEntryBuffer *
+gtk_password_entry_buffer_new (void)
+{
+  return g_object_new (GTK_TYPE_PASSWORD_ENTRY_BUFFER, NULL);
+}
diff --git a/gtk/gtkpasswordentrybufferprivate.h b/gtk/gtkpasswordentrybufferprivate.h
new file mode 100644
index 0000000000..2f6f1da2cd
--- /dev/null
+++ b/gtk/gtkpasswordentrybufferprivate.h
@@ -0,0 +1,33 @@
+/* gtkpasswordentrybufferprivate.h: Entry buffer using secure allocation
+ *
+ * Copyright 2020  GNOME Foundation
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <gtk/gtkentrybuffer.h>
+
+G_BEGIN_DECLS
+
+#define GTK_TYPE_PASSWORD_ENTRY_BUFFER (gtk_password_entry_buffer_get_type())
+
+G_DECLARE_FINAL_TYPE (GtkPasswordEntryBuffer, gtk_password_entry_buffer, GTK, PASSWORD_ENTRY_BUFFER, 
GtkEntryBuffer)
+
+GtkEntryBuffer *        gtk_password_entry_buffer_new   (void);
+
+G_END_DECLS
diff --git a/gtk/meson.build b/gtk/meson.build
index c644ac9696..eed4dd734b 100644
--- a/gtk/meson.build
+++ b/gtk/meson.build
@@ -121,6 +121,7 @@ gtk_private_sources = files([
   'gtkmenutrackeritem.c',
   'gtkpango.c',
   'gskpango.c',
+  'gtkpasswordentrybuffer.c',
   'gtkpathbar.c',
   'gtkplacessidebar.c',
   'gtkplacesview.c',