The ext4_xattr_check_entries function in fs/ext4/xattr.c in the Linux kernel through 4.15.15 does not properly validate xattr sizes, which causes misinterpretation of a size as an error code, and consequently allows attackers to cause a denial of service (get_acl NULL pointer dereference and system crash) via a crafted ext4 image.
https://usn.ubuntu.com/3695-2/
https://usn.ubuntu.com/3695-1/
https://bugzilla.redhat.com/show_bug.cgi?id=1560793
https://bugzilla.kernel.org/show_bug.cgi?id=199185