diff -urNp coreutils-8.22-orig/src/df.c coreutils-8.22/src/df.c

--- coreutils-8.22-orig/src/df.c	2015-07-03 15:51:44.293116375 +0200

+++ coreutils-8.22/src/df.c	2015-07-03 16:02:48.743390691 +0200

@@ -1057,6 +1057,33 @@ get_dev (char const *disk, char const *m

   free (dev_name);

 }

+/* Scan the mount list returning the _last_ device found for MOUNT.

+   NULL is returned if MOUNT not found.  The result is malloced.  */

+static char *

+last_device_for_mount (char const* mount)

+{

+  struct mount_entry const *me;

+  struct mount_entry const *le = NULL;

+

+  for (me = mount_list; me; me = me->me_next)

+    {

+      if (STREQ (me->me_mountdir, mount))

+        le = me;

+    }

+

+  if (le)

+    {

+      char *devname = le->me_devname;

+      char *canon_dev = canonicalize_file_name (devname);

+      if (canon_dev && IS_ABSOLUTE_FILE_NAME (canon_dev))

+        return canon_dev;

+      free (canon_dev);

+      return xstrdup (le->me_devname);

+    }

+  else

+    return NULL;

+}

+

 /* If DISK corresponds to a mount point, show its usage

    and return true.  Otherwise, return false.  */

 static bool

@@ -1064,27 +1091,57 @@ get_disk (char const *disk)

 {

   struct mount_entry const *me;

   struct mount_entry const *best_match = NULL;

+  bool best_match_accessible = false;

+  bool eclipsed_device = false;

   char const *file = disk;

   char *resolved = canonicalize_file_name (disk);

-  if (resolved && resolved[0] == '/')

+  if (resolved && IS_ABSOLUTE_FILE_NAME (resolved))

     disk = resolved;

   size_t best_match_len = SIZE_MAX;

   for (me = mount_list; me; me = me->me_next)

     {

-      if (STREQ (disk, me->me_devname))

+      /* TODO: Should cache canon_dev in the mount_entry struct.  */

+      char *devname = me->me_devname;

+      char *canon_dev = canonicalize_file_name (me->me_devname);

+      if (canon_dev && IS_ABSOLUTE_FILE_NAME (canon_dev))

+        devname = canon_dev;

+

+      if (STREQ (disk, devname))

         {

+          char *last_device = last_device_for_mount (me->me_mountdir);

+          eclipsed_device = last_device && ! STREQ (last_device, devname);

           size_t len = strlen (me->me_mountdir);

-          if (len < best_match_len)

+

+          if (! eclipsed_device

+              && (! best_match_accessible || len < best_match_len))

             {

-              best_match = me;

-              if (len == 1) /* Traditional root.  */

-                break;

-              else

-                best_match_len = len;

+              struct stat disk_stats;

+              bool this_match_accessible = false;

+

+              if (stat (me->me_mountdir, &disk_stats) == 0)

+                best_match_accessible = this_match_accessible = true;

+

+              if (this_match_accessible

+                  || (! best_match_accessible && len < best_match_len))

+                {

+                  best_match = me;

+                  if (len == 1) /* Traditional root.  */

+                    {

+                      free (last_device);

+                      free (canon_dev);

+                      break;

+                    }

+                  else

+                    best_match_len = len;

+                }

             }

+

+          free (last_device);

         }

+

+      free (canon_dev);

     }

   free (resolved);

@@ -1096,6 +1153,13 @@ get_disk (char const *disk)

                best_match->me_remote, NULL, false);

       return true;

     }

+  else if (eclipsed_device)

+    {

+      error (0, 0, _("cannot access %s: over-mounted by another device"),

+             quote (file));

+      exit_status = EXIT_FAILURE;

+      return true;

+    }

   return false;

 }