tracing/selftests: Add ownership modification tests for eventfs

As there were bugs found with the ownership of eventfs dynamic file
creation. Add a test to test it.

It will remount tracefs with a different gid and check the ownership of
the eventfs directory, as well as the system and event directories. It
will also check the event file directories.

It then does a chgrp on each of these as well to see if they all get
updated as expected.

Then it remounts the tracefs file system back to the original group and
makes sure that all the updated files and directories were reset back to
the original ownership.

It does the same for instances that change the ownership of he instance
directory.

Note, because the uid is not reset by a remount, it is tested for every
file by switching it to a new owner and then back again.
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/ftrace/test.d/00basic/test_ownership.tc

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test file and directory owership changes for eventfs
+
+original_group=`stat -c "%g" .`
+original_owner=`stat -c "%u" .`
+
+mount_point=`stat -c '%m' .`
+mount_options=`mount | grep "$mount_point" | sed -e 's/.*(\(.*\)).*/\1/'`
+
+# find another owner and group that is not the original
+other_group=`tac /etc/group | grep -v ":$original_group:" | head -1 | cut -d: -f3`
+other_owner=`tac /etc/passwd | grep -v ":$original_owner:" | head -1 | cut -d: -f3`
+
+# Remove any group ownership already
+new_options=`echo "$mount_options" | sed -e "s/gid=[0-9]*/gid=$other_group/"`
+
+if [ "$new_options" = "$mount_options" ]; then
+	new_options="$mount_options,gid=$other_group"
+	mount_options="$mount_options,gid=$original_group"
+fi
+
+canary="events/timer events/timer/timer_cancel events/timer/timer_cancel/format"
+
+test() {
+	file=$1
+	test_group=$2
+
+	owner=`stat -c "%u" $file`
+	group=`stat -c "%g" $file`
+
+	echo "testing $file $owner=$original_owner and $group=$test_group"
+	if [ $owner -ne $original_owner ]; then
+		exit_fail
+	fi
+	if [ $group -ne $test_group ]; then
+		exit_fail
+	fi
+
+	# Note, the remount does not update ownership so test going to and from owner
+	echo "test owner $file to $other_owner"
+	chown $other_owner $file
+	owner=`stat -c "%u" $file`
+	if [ $owner -ne $other_owner ]; then
+		exit_fail
+	fi
+
+	chown $original_owner $file
+	owner=`stat -c "%u" $file`
+	if [ $owner -ne $original_owner ]; then
+		exit_fail
+	fi
+
+}
+
+run_tests() {
+	for d in "." "events" "events/sched" "events/sched/sched_switch" "events/sched/sched_switch/enable" $canary; do
+		test "$d" $other_group
+	done
+
+	chgrp $original_group events
+	test "events" $original_group
+	for d in "." "events/sched" "events/sched/sched_switch" "events/sched/sched_switch/enable" $canary; do
+		test "$d" $other_group
+	done
+
+	chgrp $original_group events/sched
+	test "events/sched" $original_group
+	for d in "." "events/sched/sched_switch" "events/sched/sched_switch/enable" $canary; do
+		test "$d" $other_group
+	done
+
+	chgrp $original_group events/sched/sched_switch
+	test "events/sched/sched_switch" $original_group
+	for d in "." "events/sched/sched_switch/enable" $canary; do
+		test "$d" $other_group
+	done
+
+	chgrp $original_group events/sched/sched_switch/enable
+	test "events/sched/sched_switch/enable" $original_group
+	for d in "." $canary; do
+		test "$d" $other_group
+	done
+}
+
+mount -o remount,"$new_options" .
+
+run_tests
+
+mount -o remount,"$mount_options" .
+
+for d in "." "events" "events/sched" "events/sched/sched_switch" "events/sched/sched_switch/enable" $canary; do
+	test "$d" $original_group
+done
+
+# check instances as well
+
+chgrp $other_group instances
+
+instance="$(mktemp -u test-XXXXXX)"
+
+mkdir instances/$instance
+
+cd instances/$instance
+
+run_tests
+
+cd ../..
+
+rmdir instances/$instance
+
+chgrp $original_group instances
+
+exit 0