[syzbot] KASAN: use-after-free Read in drm_gem_object_release_handle

[syzbot]

syzbot has bisected this issue to:

commit 45d9c8dde4cd8589f9180309ec60f0da2ce486e4
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Thu Aug 12 13:14:12 2021 +0000

    drm/vgem: use shmem helpers

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=147953cbb00000
start commit:   3f667b5d4053 Merge tag 'tty-5.16-rc6' of git://git.kernel...
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=167953cbb00000
console output: https://syzkaller.appspot.com/x/log.txt?x=127953cbb00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fa556098924b78f0
dashboard link: https://syzkaller.appspot.com/bug?extid=c8ae65286134dd1b800d
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16fd41ebb00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1483c7d5b00000

Reported-by: syzbot+c8ae65286134dd1b800d at syzkaller.appspotmail.com
Fixes: 45d9c8dde4cd ("drm/vgem: use shmem helpers")

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