overlay: disallow overlayfs as upperdir

Using overlayfs dir as upperdir to mount another
overlayfs should fail.

CC: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Xiong Zhou <xzhou@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

tests/overlay/022

@@ -0,0 +1,82 @@
+#! /bin/bash
+# FS QA Test 022
+#
+# Regression test for kernel commit:
+#     76bc8e2 ovl: disallow overlayfs as upperdir
+#
+# This reproducer was originally written by
+#     Miklos Szeredi <mszeredi@redhat.com>
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2017 Red Hat Inc. All Rights Reserved.
+#
+# 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.
+#
+# This program is distributed in the hope that it would 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, write the Free Software Foundation,
+# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#-----------------------------------------------------------------------
+#
+
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	cd /
+	$UMOUNT_PROG $tmp/mnt > /dev/null 2>&1
+	rm -rf $tmp
+	rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs overlay
+_supported_os Linux
+_require_scratch
+
+# Remove all files from previous tests
+_scratch_mkfs
+
+upperdir=$SCRATCH_DEV/$OVERLAY_UPPER_DIR
+mkdir -p $upperdir/upper
+mkdir -p $upperdir/work
+# mount overlay with dirs in upper
+_scratch_mount
+
+mkdir -p $tmp/{lower,mnt}
+# mount overlay using upper from another overlay upper
+# should fail
+_overlay_mount_dirs $tmp/lower $SCRATCH_MNT/upper \
+  $SCRATCH_MNT/work overlay $tmp/mnt > /dev/null 2>&1
+if [ $? -ne 0 ] ; then
+	echo "Silence is golden"
+else
+	echo "Test Fail"
+	echo "Overlay upperdir can't be another overlay upperdir"
+fi
+
+# success, all done
+status=0
+exit

tests/overlay/022.out

@@ -0,0 +1,2 @@
+QA output created by 022
+Silence is golden

tests/overlay/group

@@ -24,3 +24,4 @@
 019 auto stress
 020 auto quick copyup perms
 021 auto quick copyup
+022 auto quick