In the Linux kernel 5.0.21, mounting a crafted btrfs filesystem image, performing some operations, and unmounting can lead to a use-after-free in btrfs_queue_work in fs/btrfs/async-thread.c.
https://usn.ubuntu.com/4414-1/
https://usn.ubuntu.com/4369-1/
https://usn.ubuntu.com/4367-1/
https://security.netapp.com/advisory/ntap-20200103-0001/
https://lists.debian.org/debian-lts-announce/2020/12/msg00015.html