If a device is referenced in fstab, invoke mount/umount as the calling user

Signed-off-by: David Zeuthen <davidz@redhat.com>

12 files changed, 352 insertions, 46 deletions

diff --git a/data/org.freedesktop.UDisks2.xml b/data/org.freedesktop.UDisks2.xml
index 476e605..3d3514b 100644
--- a/data/org.freedesktop.UDisks2.xml
+++ b/data/org.freedesktop.UDisks2.xml
@@ -393,7 +393,7 @@
         @options: Options - known options (in addition to <link linkend="udisks-std-options">standard options</link>) includes <parameter>fstype</parameter> (of type 's') and <parameter>options</parameter> (of type 's').
         @mount_path: The filesystem path where the device was mounted.
 
-        Mount the filesystem.
+        Mount a filesystem on the device.
 
         The directory the device will be mounted in is determined by
         looking at data related to the device (such the filesystem
@@ -420,6 +420,19 @@
         <citerefentry><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry>
         command. Note that the mount options are validated - only a
         small subset per filesystem type is allowed.
+
+        If the device in question is referenced in a system-wide
+        configuration file (such as the
+        <citerefentry><refentrytitle>/etc/fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        file)
+        then the
+        <citerefentry><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+        command is called directly as the calling user and no clean-up
+        is performed when the device is removed. Additionally, the
+        given <parameter>options</parameter> and
+        <parameter>fstype</parameter> options are not used as they are
+        instead read from the system-wide configuration file in
+        question.
     -->
     <method name="Mount">
       <arg name="options" direction="in" type="a{sv}"/>
@@ -434,6 +447,14 @@
 
         If the filesystem is busy, this operation fails unless the
         option <parameter>force</parameter> is given.
+
+        If the device in question is referenced in a system-wide
+        configuration file (such as the
+        <citerefentry><refentrytitle>/etc/fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        file)
+        then the
+        <citerefentry><refentrytitle>umount</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+        command is called directly as the calling user.
     -->
     <method name="Unmount">
       <arg name="options" direction="in" type="a{sv}"/>
diff --git a/src/tests/test.c b/src/tests/test.c
index eda10a0..0964e12 100644
--- a/src/tests/test.c
+++ b/src/tests/test.c
@@ -69,7 +69,7 @@ test_spawned_job_successful (void)
 {
   UDisksSpawnedJob *job;
 
-  job = udisks_spawned_job_new ("/bin/true", NULL, NULL);
+  job = udisks_spawned_job_new ("/bin/true", NULL, getuid (), NULL);
   _g_assert_signal_received (job, "completed", G_CALLBACK (on_completed_expect_success), NULL);
   g_object_unref (job);
 }
@@ -81,7 +81,7 @@ test_spawned_job_failure (void)
 {
   UDisksSpawnedJob *job;
 
-  job = udisks_spawned_job_new ("/bin/false", NULL, NULL);
+  job = udisks_spawned_job_new ("/bin/false", NULL, getuid (), NULL);
   _g_assert_signal_received (job, "completed", G_CALLBACK (on_completed_expect_failure),
                              "Command-line `/bin/false' exited with non-zero exit status 1: ");
   g_object_unref (job);
@@ -94,7 +94,7 @@ test_spawned_job_missing_program (void)
 {
   UDisksSpawnedJob *job;
 
-  job = udisks_spawned_job_new ("/path/to/unknown/file", NULL, NULL);
+  job = udisks_spawned_job_new ("/path/to/unknown/file", NULL, getuid (), NULL);
   _g_assert_signal_received (job, "completed", G_CALLBACK (on_completed_expect_failure),
                              "Error spawning command-line `/path/to/unknown/file': Failed to execute child process \"/path/to/unknown/file\" (No such file or directory) (g-exec-error-quark, 8)");
   g_object_unref (job);
@@ -110,7 +110,7 @@ test_spawned_job_cancelled_at_start (void)
 
   cancellable = g_cancellable_new ();
   g_cancellable_cancel (cancellable);
-  job = udisks_spawned_job_new ("/bin/true", NULL, cancellable);
+  job = udisks_spawned_job_new ("/bin/true", NULL, getuid (), cancellable);
   _g_assert_signal_received (job, "completed", G_CALLBACK (on_completed_expect_failure),
                              "Operation was cancelled (g-io-error-quark, 19)");
   g_object_unref (job);
@@ -135,7 +135,7 @@ test_spawned_job_cancelled_midway (void)
   GCancellable *cancellable;
 
   cancellable = g_cancellable_new ();
-  job = udisks_spawned_job_new ("/bin/sleep 0.5", NULL, cancellable);
+  job = udisks_spawned_job_new ("/bin/sleep 0.5", NULL, getuid (), cancellable);
   g_timeout_add (10, on_timeout, cancellable); /* 10 msec */
   g_main_loop_run (loop);
   _g_assert_signal_received (job, "completed", G_CALLBACK (on_completed_expect_failure),
@@ -167,7 +167,7 @@ test_spawned_job_override_signal_handler (void)
   UDisksSpawnedJob *job;
   gboolean handler_ran;
 
-  job = udisks_spawned_job_new ("/path/to/unknown/file", NULL, NULL /* GCancellable */);
+  job = udisks_spawned_job_new ("/path/to/unknown/file", NULL, getuid (), NULL /* GCancellable */);
   handler_ran = FALSE;
   g_signal_connect (job, "spawned-job-completed", G_CALLBACK (on_spawned_job_completed), &handler_ran);
   _g_assert_signal_received (job, "completed", G_CALLBACK (on_completed_expect_failure),
@@ -183,7 +183,7 @@ test_spawned_job_premature_termination (void)
 {
   UDisksSpawnedJob *job;
 
-  job = udisks_spawned_job_new ("/bin/sleep 1000", NULL, NULL /* GCancellable */);
+  job = udisks_spawned_job_new ("/bin/sleep 1000", NULL, getuid (), NULL /* GCancellable */);
   g_object_unref (job);
 }
 
@@ -214,7 +214,7 @@ test_spawned_job_read_stdout (void)
   gchar *s;
 
   s = g_strdup_printf (UDISKS_TEST_DIR "/udisks-test-helper 0");
-  job = udisks_spawned_job_new (s, NULL, NULL);
+  job = udisks_spawned_job_new (s, NULL, getuid (), NULL);
   _g_assert_signal_received (job, "spawned-job-completed", G_CALLBACK (read_stdout_on_spawned_job_completed), NULL);
   g_object_unref (job);
   g_free (s);
@@ -247,7 +247,7 @@ test_spawned_job_read_stderr (void)
   gchar *s;
 
   s = g_strdup_printf (UDISKS_TEST_DIR "/udisks-test-helper 1");
-  job = udisks_spawned_job_new (s, NULL, NULL);
+  job = udisks_spawned_job_new (s, NULL, getuid (), NULL);
   _g_assert_signal_received (job, "spawned-job-completed", G_CALLBACK (read_stderr_on_spawned_job_completed), NULL);
   g_object_unref (job);
   g_free (s);
@@ -278,14 +278,14 @@ test_spawned_job_exit_status (void)
   gchar *s;
 
   s = g_strdup_printf (UDISKS_TEST_DIR "/udisks-test-helper 2");
-  job = udisks_spawned_job_new (s, NULL, NULL);
+  job = udisks_spawned_job_new (s, NULL, getuid (), NULL);
   _g_assert_signal_received (job, "spawned-job-completed", G_CALLBACK (exit_status_on_spawned_job_completed),
                              GINT_TO_POINTER (1));
   g_object_unref (job);
   g_free (s);
 
   s = g_strdup_printf (UDISKS_TEST_DIR "/udisks-test-helper 3");
-  job = udisks_spawned_job_new (s, NULL, NULL);
+  job = udisks_spawned_job_new (s, NULL, getuid (), NULL);
   _g_assert_signal_received (job, "spawned-job-completed", G_CALLBACK (exit_status_on_spawned_job_completed),
                              GINT_TO_POINTER (2));
   g_object_unref (job);
@@ -301,7 +301,7 @@ test_spawned_job_abnormal_termination (void)
   gchar *s;
 
   s = g_strdup_printf (UDISKS_TEST_DIR "/udisks-test-helper 4");
-  job = udisks_spawned_job_new (s, NULL, NULL);
+  job = udisks_spawned_job_new (s, NULL, getuid (), NULL);
   _g_assert_signal_received (job, "completed", G_CALLBACK (on_completed_expect_failure),
                              "Command-line `./udisks-test-helper 4' was signaled with signal SIGSEGV (11): "
                              "OK, deliberately causing a segfault\n");
@@ -309,7 +309,7 @@ test_spawned_job_abnormal_termination (void)
   g_free (s);
 
   s = g_strdup_printf (UDISKS_TEST_DIR "/udisks-test-helper 5");
-  job = udisks_spawned_job_new (s, NULL, NULL);
+  job = udisks_spawned_job_new (s, NULL, getuid (), NULL);
   _g_assert_signal_received (job, "completed", G_CALLBACK (on_completed_expect_failure),
                              "Command-line `./udisks-test-helper 5' was signaled with signal SIGABRT (6): "
                              "OK, deliberately abort()'ing\n");
@@ -350,7 +350,7 @@ test_spawned_job_binary_output (void)
   gchar *s;
 
   s = g_strdup_printf (UDISKS_TEST_DIR "/udisks-test-helper 6");
-  job = udisks_spawned_job_new (s, NULL, NULL);
+  job = udisks_spawned_job_new (s, NULL, getuid (), NULL);
   _g_assert_signal_received (job, "spawned-job-completed", G_CALLBACK (binary_output_on_spawned_job_completed), NULL);
   g_object_unref (job);
   g_free (s);
@@ -381,7 +381,7 @@ test_spawned_job_input_string (void)
   gchar *s;
 
   s = g_strdup_printf (UDISKS_TEST_DIR "/udisks-test-helper 7");
-  job = udisks_spawned_job_new (s, "foobar", NULL);
+  job = udisks_spawned_job_new (s, "foobar", getuid (), NULL);
   _g_assert_signal_received (job, "spawned-job-completed", G_CALLBACK (input_string_on_spawned_job_completed), NULL);
   g_object_unref (job);
   g_free (s);
diff --git a/src/udiskscleanup.c b/src/udiskscleanup.c
index 6747f08..2ecce6d 100644
--- a/src/udiskscleanup.c
+++ b/src/udiskscleanup.c
@@ -604,6 +604,7 @@ udisks_cleanup_check_mounted_fs_entry (UDisksCleanup  *cleanup,
           /* right now -l is the only way to "force unmount" file systems... */
           if (!udisks_daemon_launch_spawned_job_sync (cleanup->daemon,
                                                       NULL,  /* GCancellable */
+                                                      0, /* uid_t run_as */
                                                       &error_message,
                                                       NULL,  /* input_string */
                                                       "umount -l \"%s\"",
@@ -1248,6 +1249,7 @@ udisks_cleanup_check_unlocked_luks_entry (UDisksCleanup  *cleanup,
           escaped_device_file = g_strescape (device_file_cleartext, NULL);
           if (!udisks_daemon_launch_spawned_job_sync (cleanup->daemon,
                                                       NULL,  /* GCancellable */
+                                                      0, /* uid_t run_as */
                                                       &error_message,
                                                       NULL,  /* input_string */
                                                       "cryptsetup luksClose \"%s\"",
@@ -1916,6 +1918,7 @@ udisks_cleanup_check_loop_entry (UDisksCleanup  *cleanup,
           escaped_loop_device_file = g_strescape (loop_device, NULL);
           if (!udisks_daemon_launch_spawned_job_sync (cleanup->daemon,
                                                       NULL,  /* GCancellable */
+                                                      0, /* uid_t run_as */
                                                       &error_message,
                                                       NULL,  /* input_string */
                                                       "losetup -d \"%s\"",
diff --git a/src/udiskscleanup.h b/src/udiskscleanup.h
index 0fe710a..e29b432 100644
--- a/src/udiskscleanup.h
+++ b/src/udiskscleanup.h
@@ -92,9 +92,9 @@ gboolean         udisks_cleanup_has_loop      (UDisksCleanup   *cleanup,
                                                uid_t           *out_uid,
                                                GError         **error);
 gboolean         udisks_cleanup_ignore_loop   (UDisksCleanup   *cleanup,
-                                               const gchar     *device);
+                                               const gchar     *device_file);
 void             udisks_cleanup_unignore_loop (UDisksCleanup   *cleanup,
-                                               const gchar     *device);
+                                               const gchar     *device_file);
 
 G_END_DECLS
 
diff --git a/src/udisksdaemon.c b/src/udisksdaemon.c
index 0ecbc79..2b048e0 100644
--- a/src/udisksdaemon.c
+++ b/src/udisksdaemon.c
@@ -545,6 +545,7 @@ udisks_daemon_launch_threaded_job  (UDisksDaemon    *daemon,
  * udisks_daemon_launch_spawned_job:
  * @daemon: A #UDisksDaemon.
  * @cancellable: A #GCancellable or %NULL.
+ * @run_as: The #uid_t to run the command as.
  * @input_string: A string to write to stdin of the spawned program or %NULL.
  * @command_line_format: printf()-style format for the command line to spawn.
  * @...: Arguments for @command_line_format.
@@ -564,6 +565,7 @@ udisks_daemon_launch_threaded_job  (UDisksDaemon    *daemon,
 UDisksBaseJob *
 udisks_daemon_launch_spawned_job (UDisksDaemon    *daemon,
                                   GCancellable    *cancellable,
+                                  uid_t            run_as,
                                   const gchar     *input_string,
                                   const gchar     *command_line_format,
                                   ...)
@@ -581,7 +583,7 @@ udisks_daemon_launch_spawned_job (UDisksDaemon    *daemon,
   va_start (var_args, command_line_format);
   command_line = g_strdup_vprintf (command_line_format, var_args);
   va_end (var_args);
-  job = udisks_spawned_job_new (command_line, input_string, cancellable);
+  job = udisks_spawned_job_new (command_line, input_string, run_as, cancellable);
   g_free (command_line);
 
   /* TODO: protect job_id by a mutex */
@@ -625,6 +627,7 @@ spawned_job_sync_on_job_completed (UDisksJob    *job,
  * udisks_daemon_launch_spawned_job_sync:
  * @daemon: A #UDisksDaemon.
  * @cancellable: A #GCancellable or %NULL.
+ * @run_as: The #uid_t to run the command as.
  * @input_string: A string to write to stdin of the spawned program or %NULL.
  * @out_message: Return location for the @message parameter of the #UDisksJob::completed signal.
  * @command_line_format: printf()-style format for the command line to spawn.
@@ -638,6 +641,7 @@ spawned_job_sync_on_job_completed (UDisksJob    *job,
 gboolean
 udisks_daemon_launch_spawned_job_sync (UDisksDaemon    *daemon,
                                        GCancellable    *cancellable,
+                                       uid_t            run_as,
                                        gchar          **out_message,
                                        const gchar     *input_string,
                                        const gchar     *command_line_format,
@@ -663,6 +667,7 @@ udisks_daemon_launch_spawned_job_sync (UDisksDaemon    *daemon,
   va_end (var_args);
   job = udisks_daemon_launch_spawned_job (daemon,
                                           cancellable,
+                                          run_as,
                                           input_string,
                                           "%s",
                                           command_line);
diff --git a/src/udisksdaemon.h b/src/udisksdaemon.h
index 4939c8b..305b79a 100644
--- a/src/udisksdaemon.h
+++ b/src/udisksdaemon.h
@@ -70,15 +70,17 @@ UDisksBaseJob            *udisks_daemon_launch_simple_job     (UDisksDaemon    *
                                                                GCancellable    *cancellable);
 UDisksBaseJob            *udisks_daemon_launch_spawned_job    (UDisksDaemon    *daemon,
                                                                GCancellable    *cancellable,
+                                                               uid_t            run_as,
                                                                const gchar     *input_string,
                                                                const gchar     *command_line_format,
-                                                               ...) G_GNUC_PRINTF (4, 5);
+                                                               ...) G_GNUC_PRINTF (5, 6);
 gboolean                  udisks_daemon_launch_spawned_job_sync (UDisksDaemon    *daemon,
                                                                  GCancellable    *cancellable,
+                                                                 uid_t            run_as,
                                                                  gchar          **out_message,
                                                                  const gchar     *input_string,
                                                                  const gchar     *command_line_format,
-                                                                 ...) G_GNUC_PRINTF (5, 6);
+                                                                 ...) G_GNUC_PRINTF (6, 7);
 UDisksBaseJob            *udisks_daemon_launch_threaded_job   (UDisksDaemon    *daemon,
                                                                UDisksThreadedJobFunc job_func,
                                                                gpointer         user_data,
diff --git a/src/udiskslinuxencrypted.c b/src/udiskslinuxencrypted.c
index 41c4edd..aa631da 100644
--- a/src/udiskslinuxencrypted.c
+++ b/src/udiskslinuxencrypted.c
@@ -222,6 +222,7 @@ handle_unlock (UDisksEncrypted        *encrypted,
   /* TODO: support a 'readonly' option */
   if (!udisks_daemon_launch_spawned_job_sync (daemon,
                                               NULL,  /* GCancellable */
+                                              0, /* uid_t run_as */
                                               &error_message,
                                               passphrase,  /* input_string */
                                               "cryptsetup luksOpen \"%s\" \"%s\"",
@@ -429,6 +430,7 @@ handle_lock (UDisksEncrypted        *encrypted,
 
   if (!udisks_daemon_launch_spawned_job_sync (daemon,
                                               NULL,  /* GCancellable */
+                                              0, /* uid_t run_as */
                                               &error_message,
                                               NULL,  /* input_string */
                                               "cryptsetup luksClose \"%s\"",
diff --git a/src/udiskslinuxfilesystem.c b/src/udiskslinuxfilesystem.c
index 553bd6a..c54178b 100644
--- a/src/udiskslinuxfilesystem.c
+++ b/src/udiskslinuxfilesystem.c
@@ -26,6 +26,8 @@
 #include <grp.h>
 #include <string.h>
 #include <stdlib.h>
+#include <stdio.h>
+#include <mntent.h>
 
 #include <glib/gstdio.h>
 
@@ -647,6 +649,105 @@ calculate_mount_point (UDisksBlockDevice         *block,
 
 /* ---------------------------------------------------------------------------------------------------- */
 
+static gboolean
+is_in_fstab (UDisksBlockDevice  *block,
+             const gchar        *fstab_path,
+             gchar             **out_mount_point)
+{
+  gboolean ret;
+  FILE *f;
+  char buf[8192];
+  struct mntent mbuf;
+  struct mntent *m;
+
+  ret = FALSE;
+  f = fopen (fstab_path, "r");
+  if (f == NULL)
+    {
+      udisks_warning ("Error opening fstab file %s: %m", fstab_path);
+      goto out;
+    }
+
+  while ((m = getmntent_r (f, &mbuf, buf, sizeof (buf))) != NULL && !ret)
+    {
+      gchar *device;
+      struct stat sb;
+
+      device = NULL;
+      if (g_str_has_prefix (m->mnt_fsname, "UUID="))
+        {
+          device = g_strdup_printf ("/dev/disk/by-uuid/%s", m->mnt_fsname + 5);
+        }
+      else if (g_str_has_prefix (m->mnt_fsname, "LABEL="))
+        {
+          device = g_strdup_printf ("/dev/disk/by-label/%s", m->mnt_fsname + 6);
+        }
+      else if (g_str_has_prefix (m->mnt_fsname, "/dev"))
+        {
+          device = g_strdup (m->mnt_fsname);
+        }
+      else
+        {
+          /* ignore non-device entries */
+          goto continue_loop;
+        }
+
+      if (stat (device, &sb) != 0)
+        {
+          udisks_debug ("Error statting %s (for entry %s): %m", device, m->mnt_fsname);
+          goto continue_loop;
+        }
+      if (!S_ISBLK (sb.st_mode))
+        {
+          udisks_debug ("Device %s (for entry %s) is not a block device", device, m->mnt_fsname);
+          goto continue_loop;
+        }
+
+      /* udisks_debug ("device %d:%d for entry %s", major (sb.st_rdev), minor (sb.st_rdev), m->mnt_fsname); */
+
+      if (makedev (udisks_block_device_get_major (block),
+                   udisks_block_device_get_minor (block)) == sb.st_rdev)
+        {
+          ret = TRUE;
+          if (out_mount_point != NULL)
+            *out_mount_point = g_strdup (m->mnt_dir);
+        }
+
+    continue_loop:
+      g_free (device);
+    }
+
+ out:
+  if (f != NULL)
+    fclose (f);
+  return ret;
+}
+
+/* returns TRUE if, and only if, device is referenced in e.g. /etc/fstab
+ *
+ * TODO: check all files in /etc/fstab.d (it's a non-standard Linux extension)
+ * TODO: check if systemd has a specific "unit" for the device
+ */
+static gboolean
+is_system_managed (UDisksBlockDevice  *block,
+                   gchar             **out_mount_point)
+{
+  gboolean ret;
+
+  ret = TRUE;
+
+  /* First, check /etc/fstab */
+  if (is_in_fstab (block, "/etc/fstab", out_mount_point))
+    goto out;
+
+  ret = FALSE;
+
+ out:
+  return ret;
+}
+
+/* ---------------------------------------------------------------------------------------------------- */
+
 /* runs in thread dedicated to handling @invocation */
 static gboolean
 handle_mount (UDisksFilesystem       *filesystem,
@@ -669,6 +770,7 @@ handle_mount (UDisksFilesystem       *filesystem,
   gchar *error_message;
   GError *error;
   const gchar *action_id;
+  gboolean system_managed;
 
   object = NULL;
   error_message = NULL;
@@ -678,16 +780,18 @@ handle_mount (UDisksFilesystem       *filesystem,
   escaped_fs_type_to_use = NULL;
   escaped_mount_options_to_use = NULL;
   escaped_mount_point_to_use = NULL;
+  system_managed = FALSE;
 
   object = UDISKS_OBJECT (g_dbus_interface_get_object (G_DBUS_INTERFACE (filesystem)));
   block = udisks_object_peek_block_device (object);
   daemon = udisks_linux_block_get_daemon (UDISKS_LINUX_BLOCK (object));
   cleanup = udisks_daemon_get_cleanup (daemon);
 
-  /* TODO: check if mount point is managed by e.g. /etc/fstab or
-   *       similar - if so, use that instead of managing mount points
-   *       in /media
-   */
+  /* check if mount point is managed by e.g. /etc/fstab or similar */
+  if (is_system_managed (block, &mount_point_to_use))
+    {
+      system_managed = TRUE;
+    }
 
   /* First, fail if the device is already mounted */
   existing_mount_points = udisks_filesystem_get_mount_points (filesystem);
@@ -712,7 +816,45 @@ handle_mount (UDisksFilesystem       *filesystem,
       goto out;
     }
 
-  /* Them fail if the device is not mountable - we actually allow mounting
+  error = NULL;
+  if (!udisks_daemon_util_get_caller_uid_sync (daemon, invocation, NULL /* GCancellable */, &caller_uid, &error))
+    {
+      g_dbus_method_invocation_return_gerror (invocation, error);
+      g_error_free (error);
+      goto out;
+    }
+
+  /* if system-managed (e.g. referenced in /etc/fstab or similar), just
+   * run mount(8) as the calling user
+   */
+  if (system_managed)
+    {
+      escaped_mount_point_to_use   = g_strescape (mount_point_to_use, NULL);
+      if (!udisks_daemon_launch_spawned_job_sync (daemon,
+                                                  NULL,  /* GCancellable */
+                                                  caller_uid, /* uid_t run_as */
+                                                  &error_message,
+                                                  NULL,  /* input_string */
+                                                  "mount \"%s\"",
+                                                  escaped_mount_point_to_use))
+        {
+          g_dbus_method_invocation_return_error (invocation,
+                                                 UDISKS_ERROR,
+                                                 UDISKS_ERROR_FAILED,
+                                                 "Error mounting system-managed device %s: %s",
+                                                 udisks_block_device_get_device (block),
+                                                 error_message);
+          goto out;
+        }
+      udisks_notice ("Mounted %s (system) at %s on behalf of uid %d",
+                     udisks_block_device_get_device (block),
+                     mount_point_to_use,
+                     caller_uid);
+      udisks_filesystem_complete_mount (filesystem, invocation, mount_point_to_use);
+      goto out;
+    }
+
+  /* Then fail if the device is not mountable - we actually allow mounting
    * devices that are not probed since since it could be that we just
    * don't have the data in the udev database but the device has a
    * filesystem *anyway*...
@@ -736,15 +878,6 @@ handle_mount (UDisksFilesystem       *filesystem,
       goto out;
     }
 
-  /* we need the uid of the caller to check mount options */
-  error = NULL;
-  if (!udisks_daemon_util_get_caller_uid_sync (daemon, invocation, NULL /* GCancellable */, &caller_uid, &error))
-    {
-      g_dbus_method_invocation_return_gerror (invocation, error);
-      g_error_free (error);
-      goto out;
-    }
-
   /* calculate filesystem type (guaranteed to be valid UTF-8) */
   error = NULL;
   fs_type_to_use = calculate_fs_type (block,
@@ -825,6 +958,7 @@ handle_mount (UDisksFilesystem       *filesystem,
   /* run mount(8) */
   if (!udisks_daemon_launch_spawned_job_sync (daemon,
                                               NULL,  /* GCancellable */
+                                              0, /* uid_t run_as */
                                               &error_message,
                                               NULL,  /* input_string */
                                               "mount -t \"%s\" -o \"%s\" \"%s\" \"%s\"",
@@ -905,6 +1039,7 @@ handle_unmount (UDisksFilesystem       *filesystem,
   const gchar *const *mount_points;
   gboolean opt_force;
   gboolean rc;
+  gboolean system_managed;
 
   mount_point = NULL;
   escaped_mount_point = NULL;
@@ -915,6 +1050,7 @@ handle_unmount (UDisksFilesystem       *filesystem,
   block = udisks_object_peek_block_device (object);
   daemon = udisks_linux_block_get_daemon (UDISKS_LINUX_BLOCK (object));
   cleanup = udisks_daemon_get_cleanup (daemon);
+  system_managed = FALSE;
 
   if (options != NULL)
     {
@@ -936,6 +1072,65 @@ handle_unmount (UDisksFilesystem       *filesystem,
     }
 
   error = NULL;
+  if (!udisks_daemon_util_get_caller_uid_sync (daemon, invocation, NULL, &caller_uid, &error))
+    {
+      g_dbus_method_invocation_return_gerror (invocation, error);
+      g_error_free (error);
+      goto out;
+    }
+
+  /* check if mount point is managed by e.g. /etc/fstab or similar */
+  if (is_system_managed (block, &mount_point))
+    {
+      system_managed = TRUE;
+    }
+
+  /* if system-managed (e.g. referenced in /etc/fstab or similar), just
+   * run mount(8) as the calling user
+   */
+  if (system_managed)
+    {
+      escaped_mount_point = g_strescape (mount_point, NULL);
+      /* right now -l is the only way to "force unmount" file systems... */
+      if (opt_force)
+        {
+          rc = udisks_daemon_launch_spawned_job_sync (daemon,
+                                                      NULL,  /* GCancellable */
+                                                      caller_uid, /* uid_t run_as */
+                                                      &error_message,
+                                                      NULL,  /* input_string */
+                                                      "umount -l \"%s\"",
+                                                      escaped_mount_point);
+        }
+      else
+        {
+          rc = udisks_daemon_launch_spawned_job_sync (daemon,
+                                                      NULL,  /* GCancellable */
+                                                      caller_uid, /* uid_t run_as */
+                                                      &error_message,
+                                                      NULL,  /* input_string */
+                                                      "umount \"%s\"",
+                                                      escaped_mount_point);
+        }
+      if (!rc)
+        {
+          g_dbus_method_invocation_return_error (invocation,
+                                                 UDISKS_ERROR,
+                                                 UDISKS_ERROR_FAILED,
+                                                 "Error unmounting system-managed device %s: %s",
+                                                 udisks_block_device_get_device (block),
+                                                 error_message);
+          goto out;
+        }
+      udisks_notice ("Unmounted %s (system) from %s on behalf of uid %d",
+                     udisks_block_device_get_device (block),
+                     mount_point,
+                     caller_uid);
+      udisks_filesystem_complete_unmount (filesystem, invocation);
+      goto out;
+    }
+
+  error = NULL;
   mount_point = udisks_cleanup_find_mounted_fs (cleanup,
                                                 makedev (udisks_block_device_get_major (block), udisks_block_device_get_minor (block)),
                                                 &mounted_by_uid,
@@ -965,14 +1160,6 @@ handle_unmount (UDisksFilesystem       *filesystem,
 
   /* TODO: allow unmounting stuff not in the mounted-fs file? */
 
-  error = NULL;
-  if (!udisks_daemon_util_get_caller_uid_sync (daemon, invocation, NULL, &caller_uid, &error))
-    {
-      g_dbus_method_invocation_return_gerror (invocation, error);
-      g_error_free (error);
-      goto out;
-    }
-
   if (caller_uid != 0 && (caller_uid != mounted_by_uid))
     {
       if (!udisks_daemon_util_check_authorization_sync (daemon,
@@ -1002,6 +1189,7 @@ handle_unmount (UDisksFilesystem       *filesystem,
       /* right now -l is the only way to "force unmount" file systems... */
       rc = udisks_daemon_launch_spawned_job_sync (daemon,
                                                   NULL,  /* GCancellable */
+                                                  0, /* uid_t run_as */
                                                   &error_message,
                                                   NULL,  /* input_string */
                                                   "umount -l \"%s\"",
@@ -1011,6 +1199,7 @@ handle_unmount (UDisksFilesystem       *filesystem,
     {
       rc = udisks_daemon_launch_spawned_job_sync (daemon,
                                                   NULL,  /* GCancellable */
+                                                  0, /* uid_t run_as */
                                                   &error_message,
                                                   NULL,  /* input_string */
                                                   "umount \"%s\"",
@@ -1192,6 +1381,7 @@ handle_set_label (UDisksFilesystem       *filesystem,
   escaped_label = g_shell_quote (label);
   job = udisks_daemon_launch_spawned_job (daemon,
                                           NULL, /* cancellable */
+                                          0, /* uid_t run_as */
                                           NULL, /* input_string */
                                           "e2label %s %s",
                                           udisks_block_device_get_device (block),
diff --git a/src/udiskslinuxloop.c b/src/udiskslinuxloop.c
index 57150df..27f243b 100644
--- a/src/udiskslinuxloop.c
+++ b/src/udiskslinuxloop.c
@@ -179,6 +179,7 @@ handle_delete (UDisksLoop             *loop,
 
   if (!udisks_daemon_launch_spawned_job_sync (daemon,
                                               NULL,  /* GCancellable */
+                                              0, /* uid_t run_as */
                                               &error_message,
                                               NULL,  /* input_string */
                                               "losetup -d \"%s\"",
diff --git a/src/udiskslinuxswapspace.c b/src/udiskslinuxswapspace.c
index 5cf5e97..43bda2f 100644
--- a/src/udiskslinuxswapspace.c
+++ b/src/udiskslinuxswapspace.c
@@ -142,6 +142,7 @@ handle_start (UDisksSwapspace        *swapspace,
 
   job = udisks_daemon_launch_spawned_job (daemon,
                                           NULL, /* cancellable */
+                                          0, /* uid_t run_as */
                                           NULL, /* input_string */
                                           "swapon %s",
                                           udisks_block_device_get_device (block));
@@ -202,6 +203,7 @@ handle_stop (UDisksSwapspace        *swapspace,
 
   job = udisks_daemon_launch_spawned_job (daemon,
                                           NULL, /* cancellable */
+                                          0, /* uid_t run_as */
                                           NULL, /* input_string */
                                           "swapoff %s",
                                           udisks_block_device_get_device (block));
diff --git a/src/udisksspawnedjob.c b/src/udisksspawnedjob.c
index a3b612d..a790cd0 100644
--- a/src/udisksspawnedjob.c
+++ b/src/udisksspawnedjob.c
@@ -24,6 +24,10 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <string.h>
+#include <unistd.h>
+#include <pwd.h>
+#include <grp.h>
+#include <stdlib.h>
 
 #include "udisksbasejob.h"
 #include "udisksspawnedjob.h"
@@ -56,6 +60,7 @@ struct _UDisksSpawnedJob
   GMainContext *main_context;
 
   gchar *input_string;
+  uid_t run_as;
   const gchar *input_string_cursor;
 
   GPid child_pid;
@@ -93,7 +98,8 @@ enum
 {
   PROP_0,
   PROP_COMMAND_LINE,
-  PROP_INPUT_STRING
+  PROP_INPUT_STRING,
+  PROP_RUN_AS
 };
 
 enum
@@ -178,6 +184,10 @@ udisks_spawned_job_set_property (GObject      *object,
       job->input_string = g_value_dup_string (value);
       break;
 
+    case PROP_RUN_AS:
+      job->run_as = g_value_get_uint (value);
+      break;
+
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -348,6 +358,57 @@ child_watch_cb (GPid     pid,
   g_object_unref (job);
 }
 
+#include <stdio.h>
+
+/* careful, this is in the fork()'ed child so all utility threads etc are not available */
+static void
+child_setup (gpointer user_data)
+{
+  UDisksSpawnedJob *job = UDISKS_SPAWNED_JOB (user_data);
+  struct passwd *pw;
+
+  if (job->run_as == getuid ())
+    goto out;
+
+  pw = getpwuid (job->run_as);
+  if (pw == NULL)
+   {
+     g_printerr ("No password record for uid %d: %m\n", (gint) job->run_as);
+     abort ();
+   }
+
+  /* become the user...
+   *
+   * TODO: this might need to involve running the whole PAM 'session'
+   * stack as done by e.g. pkexec(1) and various login managers
+   * otherwise things like the SELinux context might not be entirely
+   * right. What we really need is some library function to
+   * impersonate a pid or uid. What a mess.
+   */
+  if (setgroups (0, NULL) != 0)
+    {
+      g_printerr ("Error resetting groups: %m\n");
+      abort ();
+    }
+  if (initgroups (pw->pw_name, pw->pw_gid) != 0)
+    {
+      g_printerr ("Error initializing groups for uid %d: %m\n", (gint) job->run_as);
+      abort ();
+    }
+  if (setregid (pw->pw_gid, pw->pw_gid) != 0)
+    {
+      g_printerr ("Error setting real+effective gid for uid %d: %m\n", (gint) job->run_as);
+      abort ();
+    }
+  if (setreuid (pw->pw_uid, pw->pw_uid) != 0)
+    {
+      g_printerr ("Error setting real+effective uid for uid %d: %m\n", (gint) job->run_as);
+      abort ();
+    }
+
+ out:
+  ;
+}
 
 static void
 udisks_spawned_job_constructed (GObject *object)
@@ -397,8 +458,8 @@ udisks_spawned_job_constructed (GObject *object)
                                  child_argv,
                                  NULL, /* envp */
                                  G_SPAWN_SEARCH_PATH | G_SPAWN_DO_NOT_REAP_CHILD,
-                                 NULL, /* child_setup */
-                                 NULL, /* child_setup's user_data */
+                                 child_setup, /* child_setup */
+                                 job, /* child_setup's user_data */
                                  &(job->child_pid),
                                  job->input_string != NULL ? &(job->child_stdin_fd) : NULL,
                                  &(job->child_stdout_fd),
@@ -504,6 +565,21 @@ udisks_spawned_job_class_init (UDisksSpawnedJobClass *klass)
                                                         G_PARAM_STATIC_STRINGS));
 
   /**
+   * UDisksSpawnedJob:run-as:
+   *
+   * The #uid_t to run the program as.
+   */
+  g_object_class_install_property (gobject_class,
+                                   PROP_RUN_AS,
+                                   g_param_spec_uint ("run-as",
+                                                      "Run As",
+                                                      "The uid_t to run the program as",
+                                                      0, G_MAXUINT, 0,
+                                                      G_PARAM_WRITABLE |
+                                                      G_PARAM_CONSTRUCT_ONLY |
+                                                      G_PARAM_STATIC_STRINGS));
+
+  /**
    * UDisksSpawnedJob::spawned-job-completed:
    * @job: The #UDisksSpawnedJob emitting the signal.
    * @error: %NULL if running the whole command line succeeded, otherwise a #GError that is set.
@@ -552,6 +628,7 @@ udisks_spawned_job_class_init (UDisksSpawnedJobClass *klass)
  * udisks_spawned_job_new:
  * @command_line: The command line to run.
  * @input_string: A string to write to stdin of the spawned program or %NULL.
+ * @run_as: The #uid_t to run the program as.
  * @cancellable: A #GCancellable or %NULL.
  *
  * Creates a new #UDisksSpawnedJob instance.
@@ -565,6 +642,7 @@ udisks_spawned_job_class_init (UDisksSpawnedJobClass *klass)
 UDisksSpawnedJob *
 udisks_spawned_job_new (const gchar  *command_line,
                         const gchar  *input_string,
+                        uid_t         run_as,
                         GCancellable *cancellable)
 {
   g_return_val_if_fail (command_line != NULL, NULL);
@@ -572,6 +650,7 @@ udisks_spawned_job_new (const gchar  *command_line,
   return UDISKS_SPAWNED_JOB (g_object_new (UDISKS_TYPE_SPAWNED_JOB,
                                            "command-line", command_line,
                                            "input-string", input_string,
+                                           "run-as", run_as,
                                            "cancellable", cancellable,
                                            NULL));
 }
diff --git a/src/udisksspawnedjob.h b/src/udisksspawnedjob.h
index ad62418..547ee26 100644
--- a/src/udisksspawnedjob.h
+++ b/src/udisksspawnedjob.h
@@ -32,6 +32,7 @@ G_BEGIN_DECLS
 GType              udisks_spawned_job_get_type         (void) G_GNUC_CONST;
 UDisksSpawnedJob  *udisks_spawned_job_new              (const gchar  *command_line,
                                                         const gchar  *input_string,
+                                                        uid_t         run_as,
                                                         GCancellable *cancellable);
 const gchar       *udisks_spawned_job_get_command_line (UDisksSpawnedJob *job);