df: report correct device in presence of eclipsed mounts

* src/df.c (last_device_for_mount): A new function to identify
the last device mounted for a mount point.
(get_disk): Use the above to discard mount entries for a device,
where a later mount entry uses a different device name than
that of the user specified device.
* tests/df/over-mount-device.sh: A new root test.
* tests/local.mk: Reference the new test.
* NEWS: Reword for all these related recent fixes.
Discussed at: http://bugs.gnu.org/16539#69

2 files changed, 58 insertions, 0 deletions

diff --git a/tests/df/over-mount-device.sh b/tests/df/over-mount-device.sh
new file mode 100755
index 000000000..a85ce8dbf
--- /dev/null
+++ b/tests/df/over-mount-device.sh
@@ -0,0 +1,57 @@
+#!/bin/sh
+# Ensure that df /dev/loop0 errors out if overmounted by another device
+
+# Copyright (C) 2014 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program 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 General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ df
+require_root_
+
+cwd=$(pwd)
+cleanup_() { cd /; umount "$cwd/mnt"; umount "$cwd/mnt"; }
+
+skip=0
+
+# Create 2 file systems
+for i in 1 2; do
+  dd if=/dev/zero of=blob$i bs=8192 count=200 > /dev/null 2>&1 \
+                                             || skip=1
+  mkfs -t ext2 -F blob$i \
+    || skip_ "failed to create ext2 file system"
+done
+
+# Mount both at the same place (eclipsing the first)
+mkdir mnt                                    || skip=1
+mount -oloop blob1 mnt                       || skip=1
+eclipsed_dev=$(df --o=source mnt | tail -n1) || skip=1
+mount -oloop blob2 mnt                       || skip=1
+
+test $skip = 1 \
+  && skip_ "insufficient mount/ext2 support"
+
+df . || skip_ "failed to lookup the device for the current dir"
+
+echo "df: cannot access '$eclipsed_dev': over-mounted by another device" > exp
+
+# We should get an error for the eclipsed device and continue
+df $eclipsed_dev . > out 2> err && fail=1
+
+# header and single entry in output
+test $(wc -l < out) = 2 || fail=1
+
+compare exp err || fail=1
+
+Exit $fail
diff --git a/tests/local.mk b/tests/local.mk
index cd7da5b2f..86050dc79 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -115,6 +115,7 @@ all_root_tests =				\
   tests/cp/sparse-fiemap.sh			\
   tests/dd/skip-seek-past-dev.sh		\
   tests/df/problematic-chars.sh			\
+  tests/df/over-mount-device.sh			\
   tests/du/bind-mount-dir-cycle.sh		\
   tests/id/setgid.sh				\
   tests/install/install-C-root.sh		\