From c933a929f07421ec747cebb24d5e620fc2b97037 Mon Sep 17 00:00:00 2001
From: David Zeuthen <davidz@redhat.com>
Date: Tue, 15 Mar 2011 13:20:44 +0000
Subject: Bug 32232 – CVE-2010-4661: Arbitrary kernel module load

Validate what is passed to the mount(8) command. In particular, only
allow either well-known filesystems, filesystems already loaded or
filesystem explicitly allowed by the administrator via the
/etc/filesystems file.

See https://bugs.freedesktop.org/show_bug.cgi?id=32232 for details.

Signed-off-by: David Zeuthen <davidz@redhat.com>
---
diff --git a/src/device.c b/src/device.c
index 21d9530..d6595b8 100644
--- a/src/device.c
+++ b/src/device.c
@@ -5891,6 +5891,27 @@ static const FSMountOptions fs_mount_options[] =
     { "udf", udf_defaults, udf_allow, udf_allow_uid_self, udf_allow_gid_self },
   };
 
+static const gchar *well_known_filesystems[] =
+{
+  "btrfs",
+  "ext2",
+  "ext3",
+  "ext4",
+  "udf",
+  "iso9660",
+  "xfs",
+  "jfs",
+  "nilfs",
+  "reiserfs",
+  "reiser4",
+  "msdos",
+  "umsdos",
+  "vfat",
+  "exfat"
+  "ntfs",
+  NULL,
+};
+
 /* ------------------------------------------------ */
 
 static int num_fs_mount_options = sizeof(fs_mount_options) / sizeof(FSMountOptions);
@@ -6225,6 +6246,86 @@ filesystem_mount_completed_cb (DBusGMethodInvocation *context,
     }
 }
 
+static gboolean
+is_in_filesystem_file (const gchar *filesystems_file,
+                       const gchar *fstype)
+{
+  gchar *filesystems;
+  GError *error;
+  gboolean ret;
+  gchar **lines;
+  guint n;
+
+  ret = FALSE;
+  filesystems = NULL;
+  lines = NULL;
+
+  error = NULL;
+  if (!g_file_get_contents (filesystems_file,
+                            &filesystems,
+                            NULL, /* gsize *out_length */
+                            &error))
+    {
+      g_warning ("Error reading /etc/filesystems: %s (%s %d)",
+                 error->message,
+                 g_quark_to_string (error->domain),
+                 error->code);
+      g_error_free (error);
+      goto out;
+    }
+
+  lines = g_strsplit (filesystems, "\n", -1);
+  for (n = 0; lines != NULL && lines[n] != NULL && !ret; n++)
+    {
+      gchar **tokens;
+      gint num_tokens;
+      g_strdelimit (lines[n], " \t", ' ');
+      g_strstrip (lines[n]);
+      tokens = g_strsplit (lines[n], " ", -1);
+      num_tokens = g_strv_length (tokens);
+      if (num_tokens == 1 && g_strcmp0 (tokens[0], fstype) == 0)
+        {
+          ret = TRUE;
+        }
+      g_strfreev (tokens);
+    }
+
+ out:
+  g_strfreev (lines);
+  g_free (filesystems);
+  return ret;
+}
+
+static gboolean
+is_well_known_filesystem (const gchar *fstype)
+{
+  gboolean ret;
+  guint n;
+
+  ret = FALSE;
+  for (n = 0; well_known_filesystems[n] != NULL; n++)
+    {
+      if (g_strcmp0 (well_known_filesystems[n], fstype) == 0)
+        {
+          ret = TRUE;
+          goto out;
+        }
+    }
+ out:
+  return ret;
+}
+
+/* this is not a very efficient implementation but it's very rarely
+ * called so no real point in optimizing it...
+ */
+static gboolean
+is_allowed_filesystem (const gchar *fstype)
+{
+  return is_well_known_filesystem (fstype) ||
+    is_in_filesystem_file ("/proc/filesystems", fstype) ||
+    is_in_filesystem_file ("/etc/filesystems", fstype);
+}
+
 static void
 device_filesystem_mount_authorized_cb (Daemon *daemon,
                                        Device *device,
@@ -6255,6 +6356,35 @@ device_filesystem_mount_authorized_cb (Daemon *daemon,
   remove_dir_on_unmount = FALSE;
   error = NULL;
 
+  /* If the user requests the filesystem type, error out unless the
+   * filesystem type is
+   *
+   * - well-known [1]; or
+   * - in the /etc/filesystems file; or
+   * - in the /proc/filesystems file
+   *
+   * We do this because mount(8) on Linux allows loading any arbitrary
+   * kernel module (when invoked as root) by passing something appropriate
+   * to the -t option. So we have to validate whatever we pass.
+   *
+   * See https://bugs.freedesktop.org/show_bug.cgi?id=32232 for more
+   * details.
+   *
+   * [1] : since /etc/filesystems may be horribly out of date and not
+   *       contain e.g. ext4
+   */
+  if (filesystem_type != NULL && strlen (filesystem_type) > 0 &&
+      g_strcmp0 (filesystem_type, "auto") != 0)
+    {
+      if (!is_allowed_filesystem (filesystem_type))
+        {
+          throw_error (context, ERROR_FAILED,
+                       "Requested filesystem type is neither well-known nor "
+                       "in /proc/filesystems nor in /etc/filesystems");
+          goto out;
+        }
+    }
+
   daemon_local_get_uid (device->priv->daemon, &caller_uid, context);
 
   if (device->priv->id_usage == NULL || strcmp (device->priv->id_usage, "filesystem") != 0)
--
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