ext4_empty_dir in fs/ext4/namei.c in the Linux kernel through 5.3.12 allows a NULL pointer dereference because ext4_read_dirblock(inode,0,DIRENT_HTREE) can be zero.
https://github.com/bobfuzzer/CVE/tree/master/CVE-2019-19037
https://lists.debian.org/debian-lts-announce/2020/03/msg00001.html