[syzbot] general protection fault in legacy_parse_param

[syzbot]

syzbot has bisected this issue to:

commit 54261af473be4c5481f6196064445d2945f2bdab
Author: KP Singh <kpsingh at google.com>
Date:   Thu Apr 30 15:52:40 2020 +0000

    security: Fix the default value of fs_context_parse_param hook

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=160c5d75300000
start commit:   77dd11439b86 Merge tag 'drm-fixes-2021-08-27' of git://ano..
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=150c5d75300000
console output: https://syzkaller.appspot.com/x/log.txt?x=110c5d75300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2fd902af77ff1e56
dashboard link: https://syzkaller.appspot.com/bug?extid=d1e3b1d92d25abf97943
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=126d084d300000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16216eb1300000

Reported-by: syzbot+d1e3b1d92d25abf97943 at syzkaller.appspotmail.com
Fixes: 54261af473be ("security: Fix the default value of fs_context_parse_param hook")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection