syzbot suspects this bug was fixed by commit:

commit 32c72165dbd0e246e69d16a3ad348a4851afd415
Author: Kadlecsik József [off-list ref]
Date:   Sun Jan 19 21:06:49 2020 +0000

    netfilter: ipset: use bitmap infrastructure completely

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=122e7c1de00000
start commit:   d5d359b0 Merge branch 'for-linus' of git://git.kernel.org/..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=cf8e288883e40aba
dashboard link: https://syzkaller.appspot.com/bug?extid=7b6206fb525c1f5ec3f8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15909f21e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=141a1611e00000

If the result looks correct, please mark the bug fixed by replying with:

#syz fix: netfilter: ipset: use bitmap infrastructure completely

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