overlay: Test lost immutable/append-only flags on copy-up

Chengguang Xu reported [1] that append-only flag is lost on copy-up.
I had noticed that for directories, immutable flag can also be lost
on copy up (when parent is copied up). That's an old overlayfs bug.

Fixing this requires some VFS API changes that Miklos has proposed[2]

[1] https://lore.kernel.org/linux-unionfs/20201226104618.239739-1-cgxu519@mykernel.net/
[2] https: //lore.kernel.org/linux-fsdevel/20210203124112.1182614-1-mszeredi@redhat.com/

[Eryu: referencing the thread of the pending fix]

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/overlay/075

@@ -0,0 +1,92 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2021 CTERA Networks. All Rights Reserved.
+#
+# FS QA Test No. 075
+#
+# Run the t_immutable test program for immutable/append-only files
+# and directories that exist in overlayfs lower layer.
+#
+# This test is similar and was derived from generic/079, but instead
+# of creating new files which are created in upper layer, prepare
+# the test area in lower layer before running the t_immutable test on
+# the overlayfs mount.
+#
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+timmutable=$here/src/t_immutable
+lowerdir=$OVL_BASE_SCRATCH_MNT/$OVL_LOWER
+upperdir=$OVL_BASE_SCRATCH_MNT/$OVL_UPPER
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	# -r will fail to remove test dirs, because we added subdirs
+	# we just need to remove the flags so use -R
+	$timmutable -R $upperdir/testdir &> /dev/null
+	$timmutable -R $lowerdir/testdir &> /dev/null
+	rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+_supported_fs overlay
+
+_require_chattr ia
+_require_test_program "t_immutable"
+_require_scratch
+
+_scratch_mkfs
+
+# Preparing test area files in lower dir and check chattr support of base fs
+mkdir -p $lowerdir
+mkdir -p $upperdir
+$timmutable -C $lowerdir/testdir >$tmp.out 2>&1
+if grep -q -e 'Operation not supported' -e "Inappropriate ioctl" $tmp.out; then
+	_notrun "Setting immutable/append flag not supported"
+fi
+# Remove the immutable/append-only flags and create subdirs
+$timmutable -R $lowerdir/testdir >$tmp.out 2>&1
+for dir in $lowerdir/testdir/*.d; do
+	mkdir $dir/subdir
+done
+# Restore the immutable/append-only flags
+$timmutable -C $lowerdir/testdir >$tmp.out 2>&1
+
+_scratch_mount
+
+# Test immutability of files in overlay
+echo "Before directories copy up"
+$timmutable $SCRATCH_MNT/testdir 2>&1
+
+# Trigger copy-up of immutable/append-only dirs by touching their subdirs
+# inode flags are not copied-up, so immutable/append-only flags are lost
+for dir in $SCRATCH_MNT/testdir/*.d; do
+	touch $dir/subdir
+done
+
+# Trigger copy-up of append-only files by touching them
+# inode flags are not copied-up, so append-only flags are lost
+# touch on the immutable files is expected to fail, so immutable
+# flags will not be lost
+for file in $SCRATCH_MNT/testdir/*.f; do
+	touch $file > /dev/null 2>&1
+done
+
+# immutable/append-only flags still exist on the overlay in-core inode
+# After mount cycle, flags are forever lost
+_scratch_cycle_mount
+
+# Test immutability of files in overlay after directories copy-up
+echo "After directories copy up"
+$timmutable $SCRATCH_MNT/testdir 2>&1
+
+status=$?
+exit

tests/overlay/075.out

@@ -0,0 +1,11 @@
+QA output created by 075
+Before directories copy up
+testing immutable...PASS.
+testing append-only...PASS.
+testing immutable as non-root...PASS.
+testing append-only as non-root...PASS.
+After directories copy up
+testing immutable...PASS.
+testing append-only...PASS.
+testing immutable as non-root...PASS.
+testing append-only as non-root...PASS.

tests/overlay/group

@@ -77,6 +77,7 @@
 072 auto quick copyup hardlink
 073 auto quick whiteout
 074 auto quick exportfs dangerous
+075 auto quick perms
 100 auto quick union samefs
 101 auto quick union nonsamefs
 102 auto quick union nonsamefs xino