In the AppleTalk subsystem in the Linux kernel before 5.1, there is a potential NULL pointer dereference because register_snap_client may return NULL. This will lead to denial of service in net/appletalk/aarp.c and net/appletalk/ddp.c, as demonstrated by unregister_snap_client, aka CID-9804501fa122.
lists.opensuse.org/opensuse-security-announce/2019-12/msg00029.html
packetstormsecurity.com/files/155890/Slackware-Security-Advisory-Slackware-14.2-kernel-Updates.html
cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.1
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9804501fa1228048857910a6bf23e085aade37cc
lists.debian.org/debian-lts-announce/2020/01/msg00013.html
lists.debian.org/debian-lts-announce/2020/03/msg00001.html
seclists.org/bugtraq/2020/Jan/10
security.netapp.com/advisory/ntap-20200103-0001/
usn.ubuntu.com/4254-1/
usn.ubuntu.com/4254-2/
usn.ubuntu.com/4258-1/
usn.ubuntu.com/4287-1/
usn.ubuntu.com/4287-2/