A lack of CPU resource in the Linux kernel tracing module functionality in versions prior to 5.14-rc3 was found in the way user uses trace ring buffer in a specific way. Only privileged local users (with CAP_SYS_ADMIN capability) could use this flaw to starve the resources causing denial of service.
https://www.debian.org/security/2021/dsa-4978
https://lists.debian.org/debian-lts-announce/2021/12/msg00012.html
https://lists.debian.org/debian-lts-announce/2021/10/msg00010.html