An issue was discovered in the Linux kernel through 4.17.10. There is a use-after-free in try_merge_free_space() when mounting a crafted btrfs image, because of a lack of chunk type flag checks in btrfs_check_chunk_valid in fs/btrfs/volumes.c.
https://bugzilla.kernel.org/show_bug.cgi?id=199839
https://lists.debian.org/debian-lts-announce/2019/03/msg00017.html
https://lists.debian.org/debian-lts-announce/2020/06/msg00011.html
https://lists.debian.org/debian-lts-announce/2020/06/msg00013.html
https://patchwork.kernel.org/patch/10503099/
https://usn.ubuntu.com/3932-1/
https://usn.ubuntu.com/3932-2/