generic/692: test group ownership changefs.idmapped.group.fix.v2

When group ownership is changed a caller whose fsuid owns the inode can
change the group of the inode to any group they are a member of. When
searching through the caller's groups we failed to use the gid mapped
according to the idmapped mount otherwise we fail to change ownership.
Add a test for this.

Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: <fstests@vger.kernel.org>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
---
/* v2 */
- Zorro Lang <zlang@redhat.com>:
  - various minor fixes

- Christian Brauner (Microsoft) <brauner@kernel.org>:
  - Expand test to also cover overlayfs on top of idmapped mounts.

2 files changed, 212 insertions, 0 deletions

diff --git a/tests/generic/692 b/tests/generic/692
new file mode 100755
index 0000000000..9c982c8a96
--- /dev/null
+++ b/tests/generic/692
@@ -0,0 +1,181 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2022 Christian Brauner (Microsoft).  All Rights Reserved.
+#
+# FS QA Test 692
+#
+# Test that users can changed group ownership of a file they own to a group
+# they are a member of.
+#
+# Regression test for commit:
+#
+# 168f91289340 ("fs: account for group membership")
+#
+. ./common/preamble
+_begin_fstest auto quick perms attr idmapped mount
+
+# Override the default cleanup function.
+_cleanup()
+{
+	cd /
+	$UMOUNT_PROG $SCRATCH_MNT/target-mnt 2>/dev/null
+	$UMOUNT_PROG $SCRATCH_MNT/ovl-merge 2>/dev/null
+	$UMOUNT_PROG $SCRATCH_MNT 2>/dev/null
+	rm -r -f $tmp.*
+}
+
+# real QA test starts here
+_supported_fs ^overlay
+_require_extra_fs overlay
+_supports_filetype $SCRATCH_MNT || _notrun "overlayfs test requires d_type"
+_require_scratch
+_require_chown
+_require_idmapped_mounts
+_require_test_program "vfs/mount-idmapped"
+_require_user fsgqa2
+_require_group fsgqa2
+# Do this SECOND so that qa_user is fsgqa, and _user_do uses that account
+_require_user fsgqa
+_require_group fsgqa
+
+_scratch_mkfs >> $seqres.full
+_scratch_mount
+
+uqid=`id -u fsgqa`
+gqid=`id -g fsgqa`
+uqid2=`id -u fsgqa2`
+gqid2=`id -g fsgqa2`
+
+setup_tree()
+{
+	mkdir -p $SCRATCH_MNT/source-mnt
+	chmod 0777 $SCRATCH_MNT/source-mnt
+	touch $SCRATCH_MNT/source-mnt/file1
+	chown 65534:65534 $SCRATCH_MNT
+	chown 65534:65534 $SCRATCH_MNT/source-mnt
+	chown 65534:65535 $SCRATCH_MNT/source-mnt/file1
+
+	mkdir -p $SCRATCH_MNT/target-mnt
+	chmod 0777 $SCRATCH_MNT/target-mnt
+}
+
+# Setup an idmapped mount where uid and gid 65534 are mapped to fsgqa and uid
+# and gid 65535 are mapped to fsgqa2.
+setup_idmapped_mnt()
+{
+	$here/src/vfs/mount-idmapped \
+		--map-mount=u:65534:$uqid:1 \
+		--map-mount=g:65534:$gqid:1 \
+		--map-mount=u:65535:$uqid2:1 \
+		--map-mount=g:65535:$gqid2:1 \
+		$SCRATCH_MNT/source-mnt $SCRATCH_MNT/target-mnt
+}
+
+# We've created a layout where fsgqa owns the target file but the group of the
+# target file is owned by another group. We now test that user fsgqa can change
+# the group ownership of the file to a group they control. In this case to the
+# fsgqa group.
+change_group_ownership()
+{
+	local path="$1"
+
+	stat -c '%U:%G' $path
+	_user_do "id -u --name; id -g --name; chgrp $gqid $path"
+	stat -c '%U:%G' $path
+}
+
+reset_ownership()
+{
+	local path="$SCRATCH_MNT/source-mnt/file1"
+
+	echo ""
+	echo "reset ownership"
+	chown 65534:65534 $path
+	stat -c '%u:%g' $path
+	chown 65534:65535 $path
+	stat -c '%u:%g' $path
+}
+
+# Basic test as explained in the comment for change_group_ownership().
+run_base_test()
+{
+	echo ""
+	echo "base idmapped test"
+	change_group_ownership "$SCRATCH_MNT/target-mnt/file1"
+	reset_ownership
+}
+
+lower="$SCRATCH_MNT/target-mnt"
+upper="$SCRATCH_MNT/ovl-upper"
+work="$SCRATCH_MNT/ovl-work"
+merge="$SCRATCH_MNT/ovl-merge"
+
+# Prepare overlayfs with metacopy turned off.
+setup_overlayfs_idmapped_lower_metacopy_off()
+{
+	mkdir $upper
+	mkdir $work
+	mkdir $merge
+
+	mount -t overlay overlay -o "lowerdir=$lower,upperdir=$upper,workdir=$work,metacopy=off" $merge || _notrun "overlayfs test doesn't support idmappped layers" 
+}
+
+# Prepare overlayfs with metacopy turned on.
+setup_overlayfs_idmapped_lower_metacopy_on()
+{
+	mkdir $upper
+	mkdir $work
+	mkdir $merge
+
+	mount -t overlay overlay -o "lowerdir=$lower,upperdir=$upper,workdir=$work,metacopy=on" $merge
+}
+
+reset_overlayfs()
+{
+	rm -rf $upper
+	rm -rf $work
+	$UMOUNT_PROG $SCRATCH_MNT/ovl-merge 2>/dev/null
+	rm -rf $merge
+}
+
+# Overlayfs can be mounted on top of idmapped layers. Make sure that the basic
+# test explained in the comment for change_group_ownership() passes with
+# overlayfs mounted on top of it.
+# This tests overlayfs with metacopy turned off, i.e., changing a file copies
+# up data and metadata.
+run_overlayfs_idmapped_lower_metacopy_off()
+{
+	echo ""
+	echo "overlayfs idmapped lower metacopy off"
+	change_group_ownership "$SCRATCH_MNT/ovl-merge/file1"
+	reset_overlayfs
+	reset_ownership
+}
+
+# Overlayfs can be mounted on top of idmapped layers. Make sure that the basic
+# test explained in the comment for change_group_ownership() passes with
+# overlayfs mounted on top of it.
+# This tests overlayfs with metacopy turned on, i.e., changing a file tries to
+# only copy up metadata.
+run_overlayfs_idmapped_lower_metacopy_on()
+{
+	echo ""
+	echo "overlayfs idmapped lower metacopy on"
+	change_group_ownership "$SCRATCH_MNT/ovl-merge/file1"
+	reset_overlayfs
+	reset_ownership
+}
+
+setup_tree
+setup_idmapped_mnt
+run_base_test
+
+setup_overlayfs_idmapped_lower_metacopy_off
+run_overlayfs_idmapped_lower_metacopy_off
+
+setup_overlayfs_idmapped_lower_metacopy_on
+run_overlayfs_idmapped_lower_metacopy_on
+
+# success, all done
+status=0
+exit
diff --git a/tests/generic/692.out b/tests/generic/692.out
new file mode 100644
index 0000000000..bda8400e95
--- /dev/null
+++ b/tests/generic/692.out
@@ -0,0 +1,31 @@
+QA output created by 692
+
+base idmapped test
+fsgqa:fsgqa2
+fsgqa
+fsgqa
+fsgqa:fsgqa
+
+reset ownership
+65534:65534
+65534:65535
+
+overlayfs idmapped lower metacopy off
+fsgqa:fsgqa2
+fsgqa
+fsgqa
+fsgqa:fsgqa
+
+reset ownership
+65534:65534
+65534:65535
+
+overlayfs idmapped lower metacopy on
+fsgqa:fsgqa2
+fsgqa
+fsgqa
+fsgqa:fsgqa
+
+reset ownership
+65534:65534
+65534:65535