gstrfuncs: Add internal g_memdup2() function

This will replace the existing `g_memdup()` function for use within
GLib. It has an unavoidable security flaw of taking its `byte_size`
argument as a `guint` rather than as a `gsize`. Most callers will
expect it to be a `gsize`, and may pass in large values which could
silently be truncated, resulting in an undersize allocation compared
to what the caller expects.

This could lead to a classic buffer overflow vulnerability for many
callers of `g_memdup()`.

`g_memdup2()`, in comparison, takes its `byte_size` as a `gsize`.

Spotted by Kevin Backhouse of GHSL.

In GLib 2.68, `g_memdup2()` will be a new public API. In this version
for backport to older stable releases, it’s a new `static inline` API
in a private header, so that use of `g_memdup()` within GLib can be
fixed without adding a new API in a stable release series.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Helps: CVE-2021-27219
Helps: GHSL-2021-045
Helps: #2319
(cherry picked from commit 5e5f75a77e)

docs/reference/glib/meson.build

@@ -20,6 +20,7 @@ if get_option('gtk_doc')
     'gprintfint.h',
     'gmirroringtable.h',
     'gscripttable.h',
+    'gstrfuncsprivate.h',
     'glib-mirroring-tab',
     'gnulib',
     'pcre',

glib/gstrfuncsprivate.h

@@ -0,0 +1,55 @@
+/* GLIB - Library of useful routines for C programming
+ * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
+ *
+ * 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 <glib.h>
+#include <string.h>
+
+/*
+ * g_memdup2:
+ * @mem: (nullable): the memory to copy.
+ * @byte_size: the number of bytes to copy.
+ *
+ * Allocates @byte_size bytes of memory, and copies @byte_size bytes into it
+ * from @mem. If @mem is %NULL it returns %NULL.
+ *
+ * This replaces g_memdup(), which was prone to integer overflows when
+ * converting the argument from a #gsize to a #guint.
+ *
+ * This static inline version is a backport of the new public API from
+ * GLib 2.68, kept internal to GLib for backport to older stable releases.
+ * See https://gitlab.gnome.org/GNOME/glib/-/issues/2319.
+ *
+ * Returns: (nullable): a pointer to the newly-allocated copy of the memory,
+ *    or %NULL if @mem is %NULL.
+ * Since: 2.68
+ */
+static inline gpointer
+g_memdup2 (gconstpointer mem,
+           gsize         byte_size)
+{
+  gpointer new_mem;
+
+  if (mem && byte_size != 0)
+    {
+      new_mem = g_malloc (byte_size);
+      memcpy (new_mem, mem, byte_size);
+    }
+  else
+    new_mem = NULL;
+
+  return new_mem;
+}

glib/meson.build

@@ -167,6 +167,7 @@ glib_sources = files(
   'gslist.c',
   'gstdio.c',
   'gstrfuncs.c',
+  'gstrfuncsprivate.h',
   'gstring.c',
   'gstringchunk.c',
   'gtestutils.c',

glib/tests/strfuncs.c

@@ -32,6 +32,8 @@
 #include <string.h>
 #include "glib.h"
 
+#include "gstrfuncsprivate.h"
+
 #if defined (_MSC_VER) && (_MSC_VER <= 1800)
 #define isnan(x) _isnan(x)
 
@@ -199,6 +201,26 @@ test_is_to_digit (void)
   #undef TEST_DIGIT
 }
 
+/* Testing g_memdup2() function with various positive and negative cases */
+static void
+test_memdup2 (void)
+{
+  gchar *str_dup = NULL;
+  const gchar *str = "The quick brown fox jumps over the lazy dog";
+
+  /* Testing negative cases */
+  g_assert_null (g_memdup2 (NULL, 1024));
+  g_assert_null (g_memdup2 (str, 0));
+  g_assert_null (g_memdup2 (NULL, 0));
+
+  /* Testing normal usage cases */
+  str_dup = g_memdup2 (str, strlen (str) + 1);
+  g_assert_nonnull (str_dup);
+  g_assert_cmpstr (str, ==, str_dup);
+
+  g_free (str_dup);
+}
+
 static void
 test_strdup (void)
 {
@@ -1726,6 +1748,7 @@ main (int   argc,
   g_test_init (&argc, &argv, NULL);
 
   g_test_add_func ("/strfuncs/test-is-to-digit", test_is_to_digit);
+  g_test_add_func ("/strfuncs/memdup2", test_memdup2);
   g_test_add_func ("/strfuncs/strdup", test_strdup);
   g_test_add_func ("/strfuncs/strndup", test_strndup);
   g_test_add_func ("/strfuncs/strdup-printf", test_strdup_printf);